# 2018 Cannondale Cujo 20" Build



## johne5ive (Mar 15, 2017)

*Build Specs and Cost- ~$600:*
Cujo 20" Plus Bike - $440 
Spawn 127mm Cranks - $65
Shimano 395 Hydro Brakes - $70
Shimano UN55 BB - $20
Stans Schrader Tubeless Valves - $16
Sram X9 10 speed - $0 (Old takeoffs)
ESI Grips - $0 (Old takeoffs)

*21.5 lbs* on the scale with pedals

I originally planned to build up a Gary Fisher 20" for my son that is real similar to a Trek Pre-caliber. I was going to do the Suntour 20" air fork, spawn tubeless wheels / tires, plus the other upgrades I did here, but a few things pushed me in this direction. The cost was nearly the same and the GF was going to be heavier, but the biggest factor was watching big sister ride a 24" Plus Specialized RipRock and roll right over roots on a few uphills that were hanging him up on the Gary Fisher. The plus tires swallowed up the roots for her at slow speed and stopped him dead in his tracks.

One thing pretty cool is the Cannondale comes with a 7speed Freehub which let me upgrade the drivetrain without swapping a hub. You can fit 9 of the cogs from a 10 speed setup and adjust the limits to work fine.

In my opinion the Shimano hydros are a no brainer upgrade and the new BB was a recommendation from the shop that I never considered about but for 20 bucks seemed like a good call. Wheels setup tubeless no problem and we are running them at 10 psi. I cut the chewed up end off my grips and put them on the kids' bike and they all like the little bit of extra cushion from the ESI's

First ride we knocked out 5 miles of trail in 45 min and he noticed immediately he could ride up things he couldn't before. Downhill he never had much issue before since the speed was there and he just bounced right over everything.


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## spartan_msu (May 8, 2008)

Cool build, my son will probably be getting one soon. I think the only change I will make off the bat is trigger shifter and tubeless. How did the wheels and tires set up?


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## johne5ive (Mar 15, 2017)

The bike shop was excited to trick this one out so they did the setup for me. He said they worked great and they were still holding 10 psi 5 days later.


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## Steelshot (Mar 13, 2016)

Does your son or daughter have any trouble riding the plus size tires uphill. I can see where the would definitely benefit downhill. I have a seven year old boy and girl and looking at either upgrading their 20” bikes they have now buying them a new 20” plus. Seems you got the weight down pretty good. They both have Haro flightline 20s and weigh about 23.5 each. I figure they could get 2 more years out of a plus size bike and if it gives them confidence it would be worth it. Nice build by the way!!


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## johne5ive (Mar 15, 2017)

I have found the plus tires improved the uphill riding for us because they were getting hung up on roots more than inability to pedal. The plus size gives a little bigger rollover and the low pressure tires seem to swallow up the bumps more than bounce back and stop them in their tracks.

That being said, we don't have mile long climbs. These are short, moderately steep 30-100ft elevation changes.

My kid is 7 yrs old riding this, but also pretty short. His sisters were on 24's or about ready at that age.


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## con50582 (Jan 20, 2018)

Looks awesome.

Do you remember what size the BB was?


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## fatchanceti (Jan 12, 2005)

Just fondled one of these in the LBS. WHY WHY WHY do they (anybody) continue to spec those horrible Shimano Revo twisters? They are tough for me to twist, never mind my 8-9 year old. The display window is also terribly small. I can see that going wrong in so many ways. 

Otherwise the bike seems really solid. No stupid boat anchor suspension fork or needlessly complicated front derailleur. Seriously tempted.


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## johne5ive (Mar 15, 2017)

Still happy with ours. I actually went back to the 110mm stock cranks. Pedal clearance is an issue with the longer 127 spawn cranks on this bike. Down to about 6-7PSI in the tires as well.


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## spartan_msu (May 8, 2008)

I picked one up for my son about a month ago. I switched out the grip shift as soon as we got home. I put an old 8 speed trigger shifter (index is the same as 7 speed)on it and he took to it right away. He loves the bike and is progressing in ability really quickly. My only complaint is that the brakes work so well I will be looking for a new back tire soon :thumbsup:


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## Tjaard (Aug 17, 2007)

Steelshot said:


> Does your son or daughter have any trouble riding the plus size tires uphill. I can see where the would definitely benefit downhill. I have a seven year old boy and girl and looking at either upgrading their 20" bikes they have now buying them a new 20" plus. Seems you got the weight down pretty good. They both have Haro flightline 20s and weigh about 23.5 each. I figure they could get 2 more years out of a plus size bike and if it gives them confidence it would be worth it. Nice build by the way!!


My girls also liked the plus tires, both up and downhill. We have the Riprock (first 20 and now 24) and both sizes the Specialized Rolller 2.8 tires set up tubeless easy. They are also quite light tires, even compared to many "normal" size tires.
You can buy the Specialize Roller 2.8 or Kendra Slant Six 2.6 aftermarket, which my friend did, and fit them on his kids regular bike.


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## Dr_UNIX (Jun 28, 2015)

fatchanceti said:


> JWHY WHY WHY do they (anybody) continue to spec those horrible Shimano Revo twisters? They are tough for me to twist, never mind my 8-9 year old.


That's funny, I find the Shimano RevoShift twisters to be quite easy to turn as did my daughter. She greatly preferred them to trigger shifters. Many 8 year olds do not have the thumb strength (or reach) to use your average Shimano 7/8 speed triggers. I find good twist shifters to be a good choice for kids' bikes.

I've found the RevoShift to be the easiest to turn of the various other offerings from SRAM, MicroShift, no-name brand, etc...





 makes a good point in that the older Shimano triggers (ie, those for 7/8 speed that would be used on kids' bikes) require you to move your index finger off the brake to up-shift. Some kids I've seen don't like not always being ready to brake if they get nervous.


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## Dr_UNIX (Jun 28, 2015)

spartan_msu said:


> I switched out the grip shift as soon as we got home. I put an old 8 speed trigger shifter ...


I'm curious, did your son try the grip shifters first and preferred trigger, or did you switched them out purely on your own preference?

I've seen many kids that preferred the twist shifters and that prevented me giving them better hand-me-down parts.


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## spartan_msu (May 8, 2008)

He tried and struggled with the grip shift at the bike shop, and on our first ride at home. He took to the trigger shifter in the first minute once it was adjusted.


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## walkingonwater (Nov 1, 2018)

Hi all, do you think the specialized 20x4 or 20x3 tires that come on specialized Fatboy 20 or on the salsa timberjack will fit on this bike? Thank you


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## mrzen (Nov 2, 2018)

My son didn't get on at all with Revoshifts.. same with a few of his friends, but he and his friends get on fine with the rapidfires we replaced them with.

I guess it's different for different children...


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## johne5ive (Mar 15, 2017)

There is the tire clearance I have with stock tires. I think the 3.0's might fit, but very doubtful on the 4.0


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## HOSSinNH (Apr 26, 2013)

Came here looking for the tire clearance info as well, thanks! Was curious if I could swap some tires over for winter/fatbiking. My daughter is so light, the 2.6's are probably just fine anyway lol. 

My daughter did not get along with the twist shift either. She had the trigger shifters down inside of the first two rides.


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## josho (Jan 28, 2008)

Thread getting a little stale but great info so far!! My almost 5 yo son has about 50 miles on his in last couple months. Just put on shimano zee 10 spd shifters and derailleur, 10spd -1 xt cassette, sram pc1071 chain and avid bb7 brake levers. Next is tubeless.


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## TimTucker (Nov 9, 2011)

Picked ours up yesterday and was up late working on it.

For those that care about numbers:

Stock bike was 22.7 lbs (although there was an extra bag of reflectors not installed that weighed 74g)

- Seatpost: 297g
- Saddle: 263g
+ Spawn Brood Pivotal saddle + 125mm seatpost: 297g

Seatpost clamp 26g

- Pedals 277g
+ Tioga Dazz Lite Pedals 238g

- Rear QR skewer 65g
+ Ti rear QR skewer 27g

- wheel reflectors 34g

Sunrace 7 speed 11-34 cassette 295g
Sunrace cassette lock ring 14g

- Spoke protector 30g

Rear rotor bolts 13g

- Rear rotor 128g
+ Ashima Ai2 clone rotor 70g

- Stock 110mm cranks w/ integrated 30t chainring 500g (335g right / 165g left)
+ Spawn 102mm cranks w/ USA made 24t chainring 431g (before I removed the bash guard and spacers - should be about 40-50g lower now)

- Stock 68 x 119mm bottom bracket 337g (includes nuts / bolts)
+ Origin8 68 x 107.5mm bottom bracket 221g
+ Crank arm bolts 29g

Stock BB felt super gritty, despite appearing to be installed correctly and having enough grease.

The 107.5mm was all I had sitting around, but seems to have good frame clearance and a good chainline as long as I remove the bash guard from the Spawn cranks. 
With the bash guard and spacers the chain looked a little too close for comfort to the tire. Debating on keeping it as-is for better q factor vs ordering something closer to stock to allow for using a guard.

Rear wheel with just tire and tube 1844g

Will post more as we do more. My son is already clamoring for levers to shift (even I find it hard to turn the grip shift) and complained he can't reach the brakes with the current reach adjustment.


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## TimTucker (Nov 9, 2011)

Some more updates:

- 75mm Stem 145g
+ 40mm Wren stem 70g

- Top cap & bolt 16g
+ Origin8 integrated cap & bolt 5g

- Bar 278g
- Junit bar 260g

- Grips 78g
+ Junit grips 71g

- Stem spacers 14g
+ FSA Polycarb spacers 5g

Headset - It's listed in the specs as "FSA, Alloy, 1-1/8" Ahead, integrated"
From inspection, the outer diameter of the headset tube is ~50mm and it looks like an FSA No. 10 (93g) -- which would mean it might be possible to swap the lower with an EC44 and put in something like the Junit 120mm fork.

Chain 276g

- Shimano Tourney 6/7 speed rear derailleur 315g
+ XT 9 speed rear derailleur 224g

Kenda Slant 6 20x2.6 Tires 600g each

- Shimano grip shifter 75g (weight not including generic cable & housing)
+ Shimano 7 speed trigger shifter (optislick cable & SP41 housing)

- Kenda 2.1-2.4 rear tube 216g
- Stock rim strip 23g
+ Tubeless schrader valve 13g
+ ~3oz Stan's Sealant 90g
+ 12mm Stan's Tape

- Kenda 2.1-2.4 front tube 224g
+ Forte 1.75-2.1 tube 126g

With a lot of fuss and effort, I tried tubeless on the rear -- leaked some sealant through the rim welds and burped some on the first trial ride. From the soap bubbles I see around the bead adding a little more this morning, I'm a little worried about whether or not this is going to hold long-term.

Went ahead and just used a lighter tube from Performance Bike for the front. In hindsight, I'd have just put in the lighter tube in the rear too if I had realized the weight difference was going to be so small.

Weights without rim strips:
Rear wheel 998g
Front wheel 785g

Hubs are listed in the specs as Forumula 7-speed freehub, disc. Looking at the Formula site, the closest looking set of QR hubs I can find are:
DC-20 Front - 100mm Cup & Cone, 274g
DC-22 Rear - 135mm Cup & Cone, 486g

Looking at the weights for those, it comes pretty close when I subtract those from the front / rear -- (512g / 511g).

Making a rough guess of 5g each * 28 spokes, that would put the rims at roughly 370g

Rims are listed in the specs as labeled as Cannondale C4 Disc double wall 29mm innner width, 28H.
They're labeled with stickers stating Shining Rims DC5.0 Disc with dimensions of 406x29. I don't see anything that matches exactly on the Shining Rims site.

That makes for another ~445g dropped in the most recent round of changes, so ~1.1kg total off stock.


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## TimTucker (Nov 9, 2011)

Min saddle height with the current 20x2.6 Kenda tires and the Spawn saddle is 20", which means that a fork upgrade is out for the time being unless we want to switch to smaller tires.

So the questions now:
- Do I try more to troubleshoot the tubeless setup in the rear or just clean it out and switch to a lighter tube?

- Do I swap out the rear hub with something lighter that supports 9/10 speed like a Novatec 712 or 792 (270g / $50-60)? or a Circus Monkey HDW2 (228g / $100)?

- If I'm going to the time / expense of swapping hubs, would it be better to just build up another wheel? The new Alienation TCS Vandal rims look interesting -- 31.2mm inner diameter / 430g might be good for wider tires.


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## TimTucker (Nov 9, 2011)

Went for a ride this weekend and he was able to get through some sections of trail that were impossible for him to get up on his 16" without towing.

Ordered some Koozer CX420 hubs and a Ti bottom bracket with the sale at Aliexpress this week - should drop close to another 320g on the hubs and 70g on the bb (partly negated by adding back a 40g bash guard and spacers).

Decided to go with 119mm spindle BB after finding that the Spawn cranks can't take a 22T cihainring without spacers.

Also ordered a cheap ec44 headset just in case we do decide to try the Junit fork once he's a little taller.


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## Tex1 (Jun 16, 2013)

Thanks Tim for listing all the weights - a big help in making decisions on what to upgrade next on my kid's Cujo!

I tried to go tubeless then I gave up: the wheels could hold pressure pretty fine after a while, but under low pressure I could make them burp just using on the tire shoulder with my fingers. No good. I guess the groove in the rim isn't deep enough, or the bead in the tire is just too loose. The tires don't really POP! loudly in position when you seat them, they just go "tick". I didn't feel safe to make him ride like that so I went back to tubes. I thought I maybe could experiment with ghetto tubes or laying the rim tape onto the grooves in the rim, but I wonder if it's really worth it.

I'm not going to upgrade from the 7 speed, since I believe that less is more for our kids. The only thing that needs upgrading is the range, but with a 11-34 cassette there's already little to improve.

I was thinking about the 127mm cranks, then I had the chance to examine another bike that had them and they are way too long - you could use the pedal as a side stand! no good. My kid is 48.5" tall and doesn't seem to need longer cranks than stock.

Deore hydraulic brakes are already on, and a titanium BB is in order. 
Next on my list are carbon seatpost and handlebar, but for some reason I can't find them in the matte UD finish he'd like.
I also got a Spinner 300 air fork, then I realized that it's about 40mm longer than the stock rigid fork: I'm looking for a way to reduce the travel, not to mess up the geometry too much.


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## chike (Aug 23, 2019)

TimTucker said:


> Decided to go with 119mm spindle BB after finding that the Spawn cranks can't take a 22T cihainring without spacers.


Thanks for posting all this extremely helpful info! Curious how the Spawn crankset works out. Spawn told me their 102mm/24T probably wouldn't work on the cujo because of the smaller cranks and chainline designed for a 16" SS. I wound up trying a Cleary 25T/102mm crankset and it seems to line up perfectly and has really helped on climbs and being comfortable standing (18" inseam). Cleary is all one-piece with riveted guards. Sounds like if you find the right spacers and BB you might be able to use those Spawn cranks w/ a 22T chainring?


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## TimTucker (Nov 9, 2011)

Tex1 said:


> Thanks Tim for listing all the weights - a big help in making decisions on what to upgrade next on my kid's Cujo!
> 
> I tried to go tubeless then I gave up: the wheels could hold pressure pretty fine after a while, but under low pressure I could make them burp just using on the tire shoulder with my fingers. No good. I guess the groove in the rim isn't deep enough, or the bead in the tire is just too loose. The tires don't really POP! loudly in position when you seat them, they just go "tick". I didn't feel safe to make him ride like that so I went back to tubes. I thought I maybe could experiment with ghetto tubes or laying the rim tape onto the grooves in the rim, but I wonder if it's really worth it.


No problem -- I figure I'm weighing this stuff anyway as I go, so I might as well post it.

A few more numbers from swapping out brakes / drivetrain:

(All weights include lever, caliper, & brake line -- no adapters or mounting screws)
- Stock front brake - 335g
- Stock rear brake - 364g

+ Tektro HD-M745 rear - 297g
+ Tektro HD-M745 front - forgot to measure this one before putting it on, should be a little lighter than rear

Was a little disappointed in the weight for the Tektros since the listed specs were 271g rear / 251g front.

- 9 speed Deore XT shifter (with indicator removed) - 120g
- Stock 7 speed chain (already reduced in size to fit 24T up front) - 265g
+ 9 speed KMC X9.93 chain (after sizing) - 227g

Also swapped out the seat clamp, since I've been needing to release a bunch to get it up on the workstand:

- Stock clamp - 26g
+ Spawn QR clamp - 47g



> I'm not going to upgrade from the 7 speed, since I believe that less is more for our kids. The only thing that needs upgrading is the range, but with a 11-34 cassette there's already little to improve.


Didn't have much choice but to upgrade him to 9 speed after swapping out the brakes (currently running 11-34T cassette with the 13T cog removed to fit) -- the 7 speed shifter I had on hand didn't have a removable gear indicator and I couldn't fit a shifter with indicator along with the new brake levers on the Junit bars.

9 speed XT also gives you 2 way action on the shifter, which means that he can use both levers with his thumb now instead of needing to reach around.



> I also got a Spinner 300 air fork, then I realized that it's about 40mm longer than the stock rigid fork: I'm looking for a way to reduce the travel, not to mess up the geometry too much.


I wouldn't worry about messing up the geometry with a larger fork as long as the standover is OK -- when I did a comparison between different bikes, the Cujo actually has significantly more bottom bracket drop than most 20" bikes.

End result is that raising up the front end actually makes it a little closer to more common geometry -- here's a mockup I did comparing how close it looks to the Vitus 20 if you jack up the front end a little:
https://forums.mtbr.com/families-riding-kids/vitus-20-just-delivered-1102729.html#post14260123

If you do swap it out, let me know how the removal of the stock fork goes -- I made a quick attempt to drop it out to take a look at the headset when I swapped the stem, but it didn't want to come out on its own. I suspect that the dust seals on the stock headset just need to be removed to get it out, but haven't taken the time to give it a closer look yet.


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## TimTucker (Nov 9, 2011)

chike said:


> Thanks for posting all this extremely helpful info! Curious how the Spawn crankset works out. Spawn told me their 102mm/24T probably wouldn't work on the cujo because of the smaller cranks and chainline designed for a 16" SS. I wound up trying a Cleary 25T/102mm crankset and it seems to line up perfectly and has really helped on climbs and being comfortable standing (18" inseam). Cleary is all one-piece with riveted guards. Sounds like if you find the right spacers and BB you might be able to use those Spawn cranks w/ a 22T chainring?


The only problem I saw with chainline so far was that the chain was rubbing on the lower derailleur jockey pulley when in the largest cog using the shorter BB spindle.

No sign of chain rub at the jockey pulley when I put on the XT derailleur, though.

In theory I could have just added an extra BB spacer to move things outboard as well.

I may just go ahead and use just the spacers with no guard to move the chainline out a little more (since the extra 5.75mm from going back to a 119mm spindle should be pretty close to the original width of guard + spacers).

I'll post updates with more measurements when the new BB comes in and I take the cranks off again.

I really do like being able to use the USA Made chainrings to have something with a profile that's actually made for 1x rather than relying on the usual "bash sandwich" that kids bikes usually resort to.


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## TimTucker (Nov 9, 2011)

Also an interesting tip that I picked up looking for ways to get the bleed a little firmer so that I could move the reach as far as possible inward without the levers bottoming out on the bars before fully engaging:

- Replace the bleed block with something a little thinner than your pads + rotors (I used a spoke wrench but have ordered another bleed block to sand down for future attempts)

- Pump the brakes so that the pistons adjust outward (the key with the spacer is to find something that's just thick enough that they don't fall out -- I went a little too far on my first attempt and had to push the piston back into place)

- Proceed with bleed as normal

- Push the pistons back into place with a piston press

End result is that the system wind up with slightly more fluid than you'd normally have, which means less lever throw needed to fully engage the calipers


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## TimTucker (Nov 9, 2011)

Some updates with the new BB:
- Measured out at 145g, so pretty a decent drop from the temporary one I had it
- Chain was rubbing on the bash guard, so that had to go
- Seemed to work well with just the Spawn cranks + 5mm spacers that were originally between the guard and chainring
- Also tried with some smaller 3mm spacers, but had troubles getting the shifting as smooth with those

For those curious, the stock bash guard was about 2mm wide.


Also got in some more tires to try Vee Crown Gem 20x2.8 & CST Fringe 20x2.8"

The Crown Gems were specced at 715g, but weighed in closer to 750g. Didn't get them mounted up to tires, but the tread looks quite a bit more aggressive than the stock Kenda Slant Six -- might try them out in the Winter. Only really ordered because there was a seller on Amazon that had a 2 pack of them for the normal price of a single tire (they've since raised the price).


CST Fringe was specced at 560g and weighed in pretty close to that, unlike the Kenda that was specced at 570g, but weighed in closer to 600g.

The overall dimension of the tire itself are pretty close to the same between the two -- the only difference in sizing comes from the knobs.

CST:
- Wider / taller side knobs
- Shorter / less aggressive center knobs (maybe lower rolling resistance with slightly lower traction?)
- More squared profile
- Overall width with knobs slightly wider

Kenda:
- Same knobs across top and sides
- More rounded profile
- Overall height with knobs slightly taller


Got in Koozer CX420 hubs and picked up spokes over the weekend, so next project is going to be to rebuild the wheels.


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## Tex1 (Jun 16, 2013)

TimTucker said:


> N
> I wouldn't worry about messing up the geometry with a larger fork as long as the standover is OK -- when I did a comparison between different bikes, the Cujo actually has significantly more bottom bracket drop than most 20" bikes.
> 
> End result is that raising up the front end actually makes it a little closer to more common geometry -- here's a mockup I did comparing how close it looks to the Vitus 20 if you jack up the front end a little:
> ...


Thanks for your thoughts. I 3D printed some spacers to fir inside the fork to shorten it - I think I'll start with the 15mm one and see how it goes from there. It'll be higher than stock anyway. I haven't fitted it yet because I'd like for my son to get familiar with the rigid one first.

I did try to remove the stock fork already, and yes, at first it didn't want to come out. A couple of hits with a rubber hammer did the trick. The thing is that there's a plastic conical washer under the spacers under the stem, and wen you tighten the top nut it is wedged between the top bearing and the steerer: this takes out all the play, but it makes it difficult to remove the fork because of the friction between the washer and the steerer.


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## TimTucker (Nov 9, 2011)

Updates from rebuilding the rear wheel last night:

Stock:
Rim (387 ERD): 388g
Hub: 449g
Spokes: 122g
Nipples: 36g
Rim strip: 23g
Total: 1018g

Rebuilt wheel:
Stock Rim: 388g
Koozer CX420 Hub: 273g (including cassette spacer)
Spokes (177mm right / 179mm left): 130g
Nipples: 33g
Stan's 12mm tape: 4g
Total: 828g

Front hub is 166g and uses same length spokes (179mm right / 177mm left), so that will be 721g when finished (spoke sizes are the same).

Weight will wind up pretty close to the Spawn's Brood TR27 wheelset with 72POE and 2mm wider rims, just not tubeless.


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## tyreless (Aug 30, 2019)

My 22T USAMade chain ring, Spawn 102mm cranks, and crank puller all arrived on my doorstep this afternoon, so I took it as a sign that I should install them as soon as the kids were off to bed.

The swap went surprisingly smoothly. I tossed the stock cranks and the Spawn's bash guard into the spare parts bin, bolted on the new ring with the Spawn 5mm spacers, and was done before I realized it.

The bike is now tucked away in the crawl space behind some boxes awaiting its birthday reveal.

I'd like to thank TimTucker for blazing this trail, his posts made it super easy to duplicate his work, and not have to fret about parts not fitting.

I'm really excited about this change. Dropping from a 30T to a 22T means that my son will have a deeper low end to tackle the steep hills around here without getting frustrated (which really kills his motivation and enjoyment of a ride). Even the small hills of the "flat" park are impassible on his Dynacraft Magna "Major Damage" single speed. We're both sick of going to the same park over and over again, and this bike will really open up some new locations.


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## Tex1 (Jun 16, 2013)

Wouldn't 22-34 be too short of a gearing to pedal? 
I see my kid being already quite slow on 32-34, I can't imagine a kid having the patience to spin a 22-34 and at the same time keeping balance. Beside, kids love speed so having a shorter tallest gear would be detrimental to their fun. Just my 2 cents.


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## TimTucker (Nov 9, 2011)

Tex1 said:


> Wouldn't 22-34 be too short of a gearing to pedal?
> I see my kid being already quite slow on 32-34, I can't imagine a kid having the patience to spin a 22-34 and at the same time keeping balance. Beside, kids love speed so having a shorter tallest gear would be detrimental to their fun. Just my 2 cents.


22/34 is the same gear ratio as 32/50, which is not unheard of on adult bikes - not super useful all the time, but for a kid it came make the difference in getting up an extended climb vs. having to hop off and walk the bike.


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## Tex1 (Jun 16, 2013)

TimTucker said:


> 22/34 is the same gear ratio as 32/50, which is not unheard of on adult bikes - not super useful all the time, but for a kid it came make the difference in getting up an extended climb vs. having to hop off and walk the bike.


True, but adult bikes have 27.5" wheels or more. We have a 20+er here. 
Anyway, we'll see how it turns out.


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## tyreless (Aug 30, 2019)

Ask me again in a month and I'll tell you how it's working out.

Before doing this conversion, I calculated the gain ratios for each gear on my bike, my son's existing bike, and various combinations on the Cujo. The gain ratio takes the gear ratio, crank length, and wheel diameter into account.









In a nutshell, swapping for a 24T shifts it down by about a tooth (so the speed you'd see in the 2nd to top gear with the stock 30T is about the same as the top gear with a 24T). Going to a 22T takes it another half gear farther.

The most important consideration for me, was comparing the gain ratio on his existing single speed with the Cujo. With the stock 30T, his current gear is between 2nd and 3rd lowest speeds, so he'd only be able to down shift one (rounding down) gear below his current cruising gear. That's just not enough low end. With a 24T, he gets 2 gears, and with a 22T he gets 3.

I'll grant you that my underlying assumption is that his current gear is his true comfort gear, but honestly I'd rather have him be able to climb hills comfortably than go faster (to my discomfort). His top speed on his current bike is 11.5 mph, running that though these factors gives a top speed of 23mph stock and 18mph with a 22T. And, I can always go back if it doesn't work.


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## Tex1 (Jun 16, 2013)

Makes sense. Great analysis right there. Looking forward to hear the test results.


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## TimTucker (Nov 9, 2011)

The other pretty simple analysis is that kids and adults rode 3x drivetrains for years based around 11-34t cassettes and a 22t small ring.

We're all over the place so far between some rides where he's spent the majority of the time in the 2 largest cogs and others where he's spent most of his time in the smallest. Still working conveying the whole idea of when he might want to shift and which direction he should shift in when he does.


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## TimTucker (Nov 9, 2011)

So after a bit more practice on the trails I could see that he wasn't shifting into the largest cog and was more limited at the high end -- so we went back to 24t again, still with the 5mm spacers.

Made a few other changes:
- Swapped saddle for Tioga D-Spyder S-Spec Pivotal (~30g lighter than the Spawn and stack height is actually slightly less)
- Rebuilt the front wheel with the new hub (166g vs. 237g for the hub, 725g for the assembled wheel + Stan's tape)
- Swapped bottle bolts for nylon (<1g vs 8g) -- we're not using them, but I'd rather not have open frame holes in case we're caught out in the rain
- Replaced zip ties for cables with small blue ties that match the frame. Not something I went out of my way to find, but we happened to be at Harbor Freight and they caught his eye:
https://www.harborfreight.com/1000-pc-nylon-cable-tie-assortment-69409.html

Luggage scale after the changes was showing ~18.7lbs.

Had a few mishaps in attempts to drop weight:
- Ordered some square taper crank bolts that were advertised on Amazon as "CNC Aluminum" -- they were magnetic and weighed about 29g for 2, so pretty obviously steel.

Those went back and I ordered some blue anodized bolts off ebay pretty much for free with a $3 off coupon. Probably won't come in before the end of the local XC race season, but that'll save another 15g.

- Stopped by Albe's to check out Tubolito tubes (only 58g each!) -- apparently the first batches of 20" Schrader tubes had issues with the valve stems separating if they got fiddled with too much. There's supposed to be an updated version coming soon, but they're not in yet.

Most important part -- he finished his first XC race on Sunday (3.5 miles)!

It started pouring rain during the race and after watching some of the kids with skinny tires sliding out on turns I was glad that he had wider tires with nice big side lugs.

He wasn't a fan of the rain, but overall he seemed to have fun.


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## Tex1 (Jun 16, 2013)

Good job Tim and to your son too!

I installed the titanium spindle BB, the titanium skewers, a carbon seat tube, and the Ashima rip-off disc brakes. I shaved off about 500g. Only missing in the roadmap now are the carbon handlebar and the Spinner fork.

I noticed two threaded bosses on the sides of the rear dropouts, 2 per side I mean. I wonder what they are for, since they can't be for a fender or a rack (too close between them and no third mounting point close to the seat tube) or for a RD guard (since they are on both sides, symmetrical).


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## tyreless (Aug 30, 2019)

I decided that my little guy would benefit from having hydraulic brakes instead of the cable driven Tektros. This will give him more stopping power, allow him to use two-finger levers for his tiny hands, and might allow him to work towards two (or one) finger braking technique someday. I'll admit that this is kind of an unnecessary mod, I'm sure that the cable brakes are just fine, but I really want this bike to give him the best possible experience. Plus, I sleep a little better at night knowing that he won't speed out of control on a downhill because his hands got tired.

I spent some time researching which brakes to get, and decided on the Shimano Acera M396, over the M315s -which use adult/full-hand levers; both were going for about $50. The levers tipped the scale on this decision, even lower end brakes will do when you only have to stop a combined weight of 60 lbs!

Install day went pretty smoothly once I figured out how to get the grips off. Honestly, it's always these little things that get me. I wrestled the sifter side off, with much effort, but I just couldn't manage the longer one on the other side. Turns out all you need to do is pull back the grip a little, put some water in, and wiggle it for a while. Or use an air compressor (which I don't have). It came off (and went back on) like magic with the water. I feel kinda dumb for fighting with them for so long. Sorry; I'm new to this!

I reused the Tektro caliper mounting hardware (which the Shimanos didn't ship with), so it was super easy. Getting the calipers trued so they didn't scrape all the time took some work, and they still scrape a little, I'll have to put the bike on a stand (another thing I don't have) to work out these quirks.

I put the handles on and reinstalled the shifter and grips, but of course the hydraulic brake line was meant for a larger bike so I ended up with quite a mess of excess line at the bars.

I ordered a brake bleed kit and some Shimano oil, along with a bag of olives and fittings. I was sure that this was where I was going to get in over my head, but actually it was really easy. Slide the nut down the hose, cut off the excess with a utility knife, pop on the new olive and hammer the new fitting into place with the handle of a screwdriver, and you're good to go! I did a simple funnel-only bubble bleed, and the brakes are nice a firm. I just did this with the brakes on the rotors, I might try the "thinner bleed block" technique if Jr. has issues with the handle reach.

Even got to work some bubbles out of my own bike while I was at it!

The bike is back in the crawl space now; not too much longer to wait!


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## TimTucker (Nov 9, 2011)

tyreless said:


> Install day went pretty smoothly once I figured out how to get the grips off. Honestly, it's always these little things that get me. I wrestled the sifter side off, with much effort, but I just couldn't manage the longer one on the other side. Turns out all you need to do is pull back the grip a little, put some water in, and wiggle it for a while. Or use an air compressor (which I don't have). It came off (and went back on) like magic with the water. I feel kinda dumb for fighting with them for so long. Sorry; I'm new to this!


Sounds like he's got a nice bike waiting for him!

Slip on grips are always a pain -- my go-to is usually something like Windex that's a little more slippery than water and I can spray down in. Once the grips are off it tends to dry up a little faster than water too.

If only more brakes / shifters came with hinged clamps so you didn't have to remove your grips!


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## J Hartman (Nov 8, 2012)

Any idea how this would compare to the cujo 20 race?


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## TimTucker (Nov 9, 2011)

J Hartman said:


> Any idea how this would compare to the cujo 20 race?


2020 (standard and race) vs the 2018/2019:
Longer frame
Shorter stem
Seat tube extends slightly higher above the frame
Short summary: likely better handling out of the box, but not as good of a fit for a shorter rider on the edge of being and to ride a 20" as putting a shorter stem on the older version.

2020 standard vs race:
Mostly just a drivetrain upgrade and different paint job. Upgrading a 2019 myself got us a nicer setup than the race at a lower overall cost, but that was at least partly from having cranks and a 9 speed drivetrain lying around.


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## fastpath (Aug 27, 2004)

Could you add some more thoughts on the CST Fringe vs the Slant six?



TimTucker said:


> Some updates with the new BB:
> - Measured out at 145g, so pretty a decent drop from the temporary one I had it
> - Chain was rubbing on the bash guard, so that had to go
> - Seemed to work well with just the Spawn cranks + 5mm spacers that were originally between the guard and chainring
> ...


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## J Hartman (Nov 8, 2012)

How old / tall is your son? Trying to compare to my son to see if that 20" is the bike I need.


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## TimTucker (Nov 9, 2011)

He's 44.5" - with the pivotal saddle he's just high enough to be able to touch the ground with his toes and walk the bike forward if he needs to.

The CST tires have worked OK - they seem to cake up with mud and he loses traction and stops if he goes through larger muddy areas, but it's hard to tell how much that's just his skill level and not riding in with enough speed vs. the tires. Once he's out, the tires seem to do a decent job of shedding the mud.

With the higher volume tires he seems to have no problems bouncing off rocks and roots as long as he isn't too tired. We rode to school the other day and had a pickup stop a little too far into the crosswalk - he didn't seem to think anything of it and just veered a little left and plowed over the curb like it wasn't even there.

Night before last we were out in the yard and he ran over a few scrap 2x4s and thought it was fun. Then again he also seemed to be amused by falling over sideways onto the grass when stopping at low speed (did it once on accident and then started repeating to show me the "cool thing he did"), so I'm not really sure we have the same idea of what fun is.


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## douglas (Nov 12, 2004)

My almost 6 y/o once in a while gets in the fall off my bike on purpose mindset #notmyideaoffun


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## tyreless (Aug 30, 2019)

My 5 year old measures 44", with a 17" inseam, I'd say he is at the low end of what's possible with this bike. He has the stock seat with the post pretty much bottomed out. He's not quite on the tips of this toes when seated on the bike, but he's close.


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## Dahedd01 (Feb 16, 2018)

Im late to the thread but its been a good read. I got my 7 year old a 24+ Cujo in april after he totalled his old bike on paths around Aviemore. Its a wonderful bike, he loves that fact its like a mini fat bike so hes like me and the weight of it is ideal for him, no cheap, heavy forks upfront..

Hes fine with the grip shift for now though id like to change it and its good to know I can swap the gears around without needing a new rear up. 10 speed would be better for him than 8.


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## tyreless (Aug 30, 2019)

The RevoShift was not working out for my son. He just doesn't have the hand strength, or maybe it's that his small hands can't reach far enough around the grip. Whatever it is, it sometimes slips under his hand, and he managed to peel off a layer of skin on this thumb (on two different occasions) while trying to force it. I ordered a Shimano SL-M310 trigger shifter to replace it.

It turns out that the new shifter doesn't fit inboard of the brakes, I guess it was never designed to be paired with the m396 brake levers. I had to mount it outboard, which looks funky, and might not be ergonomically sound. I thought about cutting off the gear position indicator, but it turns out that my son loves the way it looks. We're going to try it out this way and see how well it works out. If anyone has any good ideas about this, I'd love to hear them. At least this gave me an excuse to ditch the stock grips in favor of some bolt-on Bontragers.

I know I promised to report back on the 22T, but he's still trying to master shifting (which I hope he'll be able to do by himself now!), so I'll report back after a couple more rides.


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## weevie (Dec 2, 2011)

Hi - been following this from afar. Did you ever check out the head tube ID ? I have just bought a J Unit 20" tapered fork for peanuts in the sale and now I need a bike to fit it to with a lower 1.5 cup. I like the Cujo due to lower BB height which will help accommodate the raised front end...


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## TimTucker (Nov 9, 2011)

weevie said:


> Hi - been following this from afar. Did you ever check out the head tube ID ? I have just bought a J Unit 20" tapered fork for peanuts in the sale and now I need a bike to fit it to with a lower 1.5 cup. I like the Cujo due to lower BB height which will help accommodate the raised front end...


Could have sworn that I posted this when I took the headset off on ours the other day, but I guess I just forgot to hit post -- I took off the headset on our Cujo this week and the inner diameter of the headtube is 44mm for both top and bottom.

Plan is to put one of these on top:
https://www.jensonusa.com/Cane-Creek-Viscoset-Headset

For the bottom, I'll be putting on a tapered bottom with a crown race adapter for the stock fork so it's an easy swap later to something like the Junit.


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## weevie (Dec 2, 2011)

*Thanks*



TimTucker said:


> Could have sworn that I posted this when I took the headset off on ours the other day, but I guess I just forgot to hit post -- I took off the headset on our Cujo this week and the inner diameter of the headtube is 44mm for both top and bottom.
> 
> Plan is to put one of these on top:
> https://www.jensonusa.com/Cane-Creek-Viscoset-Headset
> ...


Thanks. I saw someone did it on a Scott Roxter on another thread with some spacers to lower travel. I got a 120mm from eBay last night for cheap which was actually the wiggle/ chain Reaction Cycles Outlet in Uk as had marks on it. They have also discounted the perfect ones on their website to £200-250 odd which is better than the £400 crazy price for a kids fork over here. Now I need a wheel to fit the thing....Another challenge .. ridiculous having tapered and boost on a lad weighing less than my lunch but it's fun to tinker. Boy doesn't give a monkeys what he rides but that's not the point now is it .... Ha.


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## weevie (Dec 2, 2011)

P.S. why are you changing the top part of headset? Will fit the tapered fork won’t it?


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## TimTucker (Nov 9, 2011)

weevie said:


> Thanks. I saw someone did it on a Scott Roxter on another thread with some spacers to lower travel. I got a 120mm from eBay last night for cheap which was actually the wiggle/ chain Reaction Cycles Outlet in Uk as had marks on it. They have also discounted the perfect ones on their website to £200-250 odd which is better than the £400 crazy price for a kids fork over here. Now I need a wheel to fit the thing....Another challenge .. ridiculous having tapered and boost on a lad weighing less than my lunch but it's fun to tinker. Boy doesn't give a monkeys what he rides but that's not the point now is it .... Ha.


I've already rebuilt the wheels on ours once -- I figure it's not too big of a deal if I need to do it again to move to a new boost hub. If I could find a better option for a lightweight 20" plus rim (>30mm inner diameter) I'd consider just leaving the old wheel as-is, but so far all the options seems to be OEM-only.

What I'm dreading a little more is doing it after we move to bigger wheel sizes -- we have a local BMX shop where I can get cheap straight gauge spokes cut to custom sizes same-day.

Once we go up to bigger sizes, I'll probably have to be a little more careful with measuring and order online.


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## weevie (Dec 2, 2011)

Anyone try the Sheldon method of using 8 of the sprockets from a 9-speed cassette or 9 of the sprockets from a 10-speed cassette to get an easier gear on the back (more than 34) rather than swapping out the 30t chainset which has decent length arms?. If it’s a 7-speed Shimano Hyperglide Freehub it should work but I see the website says it’s a formula hub - so no idea if that generic lookalikeee would hack this ghetto mod? I see the cujo race has different hubs for the 10 speed but obv they use all the sprockets....appreciate you need new rear d and shifters but they are low spec anyway


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## TimTucker (Nov 9, 2011)

For a few weeks before I rebuilt the wheelset, we ran 8 of 9 with one of the smaller cogs on a 11-34t xt 9 speed cassette removed (I think I took out the 13t).

Shifted and worked just fine with a 9 speed xt shifter.


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## weevie (Dec 2, 2011)

Cool - a sunrace 11-40 less the 13T got to be worth a go...


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## TimTucker (Nov 9, 2011)

Some findings today...

Weights for stock components:

Fork - 592g
Headset (upper) - 49g
Headset (lower) - 35g
Crown race - 13g

The difference in stack height for a EC44 tapered lower headset and a Cane Creek Viscoset upper headset is enough vs. stock that there's not enough steerer for the stem to clamp on to.

Now for the debate between where to go from here:

Pop the EC44 bottom cup out and go back to the stock lower headset
Go ahead and order a Junit fork... (which will also require getting a boost hub / rebuilding the front wheel again)
Swap the stock fork and the Suntour XCT HLO 20 Air I currently have on his 16" Yoji


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## TimTucker (Nov 9, 2011)

Started down the path of option #3, but then realized that the headtube on the Yojis (both 14" and 16") are about 120mm vs. 100mm on the Cujo.

Net result is that the Cujo fork is ~10mm too short to swap over unless I start looking for a stem with shorter stack height for the Yoji.

Also weighed the Suntour fork and it was heavier than I remembered -- spec was 1780g, but actual weight was ~1900g.

Wondering now if #1 is the better option, combined with swapping the front tire for a Vee Crown Gem 20x2.8 to slacken things up a little (~300g weight penalty from the tire + slightly bigger tube, slightly less if I give it a try with the tube I have in there).


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## weevie (Dec 2, 2011)

Will it make any noticeable difference to stock set up? You seem to have already done a great job and I’m sure his bike with current upgrades is pretty perfect.. would be for my lad even with a penchant for crashing his 16” frog bike of 12” steps. Is there an Option 4 ?- stop here and start building a 24” and hope he doesn’t want to retire from cycling before he is 7?


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## TimTucker (Nov 9, 2011)

I'm honestly not sure how much practical difference any of this will make!

I just have a really hard time leaving things as-is and at this point I have to do something, since I now have 2 bikes taken apart...

Least amount of work that results in 2 bikes getting put back together is putting the stock headset lower back on with the fork and then sticking the Suntour fork back on the 16".

Even without swapping tires, that'd still give him the updated steering dampening headset to try out. No shortage of work for myself since I have similar headsets & Ti bottom brackets sitting ready to put on the 16" and 14" Yojis.

My youngest turns 3 in March, which greatly extends the amount of time all these bikes will see use.

On the 24" front I figure I'm better off waiting another year with all the rapid changes / improvements that seem to be happening in kids bikes and components.


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## TimTucker (Nov 9, 2011)

So.. kids and their priorities -- tried explaining my overall situation to my son to get his opinion on what we should do: does he want the old fork or does he want to try a squishy fork?

His response: he wants a blue fork.

Stock fork it is for now!


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## weevie (Dec 2, 2011)

Sorry - this has probably been asked before - but could someone post the AC for the stock fork for 2019 or 2020 updates model as it’s not on the website, Just finalising geometry for a rebuild with a sus fork and this bike or one other alternative that has come up


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## TimTucker (Nov 9, 2011)

weevie said:


> Sorry - this has probably been asked before - but could someone post the AC for the stock fork for 2019 or 2020 updates model as it's not on the website, Just finalising geometry for a rebuild with a sus fork and this bike or one other alternative that has come up


I think ours (the blue 2018/2019) was ~345mm when I tried measuring. Not sure on the new model.


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## weevie (Dec 2, 2011)

thanks - there is a Trek Roscoe 20 locally for a decent price which looks like would do as a donor bike as has longer rigid fork so was thinking that could work. Weirdly wide bb though for the current crank (which has too many teeth for my local hills so would need to go) - and with the boost rear I dont know if I could sort the chainline with a replacement kids crank...


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## Strattoa (Sep 22, 2018)

@TimTucker thanks for the plethora of info in this thread, I'm just starting to tinker with a new-to-us Cujo 20 and I'm trying to follow your bread crumbs. Regarding the bottom bracket that you used, did you determine that 119mm (stock) was still the best option even with the Spawn cranks? I'm not planning on changing the cranks yet, but would like the flexibility down the road.

Also, how did the CX420 hubs treat you in the long run? Can those be used with the stock 7-speed cassette? Again, not looking to replace the drivetrain yet (my son likes the grip shift so far), but will later on.

Thanks!
Drew


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## TimTucker (Nov 9, 2011)

Strattoa said:


> @TimTucker thanks for the plethora of info in this thread, I'm just starting to tinker with a new-to-us Cujo 20 and I'm trying to follow your bread crumbs. Regarding the bottom bracket that you used, did you determine that 119mm (stock) was still the best option even with the Spawn cranks? I'm not planning on changing the cranks yet, but would like the flexibility down the road.


119 seemed OK, although we did need to drop the bash ring and just use chainring + spacers in order for the chainline to work out right & get smooth shifting across the full cassette (pushes things outward a little). In theory something like a 122mm spindle would do the same thing, but would result in a bigger q-factor.



Strattoa said:


> Also, how did the CX420 hubs treat you in the long run? Can those be used with the stock 7-speed cassette? Again, not looking to replace the drivetrain yet (my son likes the grip shift so far), but will later on.


Seemed to work well -- for a 7 speed cassette on a 10 speed hub, you'll need a spacer to put behind (I think they're ~4.5-5.0mm).


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## kbahus (Sep 11, 2005)

My son's Cujo 20 has served us well for numerous years but now is having some issues. I attempted a basic tune yesterday up to find a bottom bracket that feels like rocks rolling around a majorly bent chainring. I would like to replace the bottom bracket and either a chainring or a full crankset. The 110mm length cranks have given no fitment issues, but it looks to have some prorietary crank/chainring setup. I am sure going up in length will fit the rider ok if necessary. What are the current options for upgrading the bottom bracket and crankset? It sounds like a 68 x 119mm bottom bracket is the best and the Spawn cranks in 127mm work? I would like to knock this out in one shot and not experience any fitment/chainline issues that always pop up with projects like this.


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## TimTucker (Nov 9, 2011)

kbahus said:


> My son's Cujo 20 has served us well for numerous years but now is having some issues. I attempted a basic tune yesterday up to find a bottom bracket that feels like rocks rolling around a majorly bent chainring. I would like to replace the bottom bracket and either a chainring or a full crankset. The 110mm length cranks have given no fitment issues, but it looks to have some prorietary crank/chainring setup. I am sure going up in length will fit the rider ok if necessary. What are the current options for upgrading the bottom bracket and crankset? It sounds like a 68 x 119mm bottom bracket is the best and the Spawn cranks in 127mm work? I would like to knock this out in one shot and not experience any fitment/chainline issues that always pop up with projects like this.


The BB drop is so low on the Cujo that I'd be hesitant to recommend going up in length (especially if you're using the stock rigid fork) -- the Spawn 102mm cranks are what we used along with a Ti BB to lighten things up.

If you're going a little longer, try the Prevelo 120mm cranks -- they use a standard Shimano 24mm BB and are actually in stock:








HEIR Crank


The HEIR Direct Mount Crank offers direct mount crank versatility and performance, in crank lengths that are optimized for young riders. Features Stiff and light cold forged design. Compatible with 3-bolt direct mount chain rings. Specifications COMPONENT WEIGHT HEIR 120mm Direct Mount Crank 523...




prevelo.com





For the 24" we used the Prevelo cranks along with one of these oval chainrings:








SHARKTOOTH OVAL BB30 & GXP- CLOSEOUT


USAMade introduces the Sharktooth OVAL Series with some very unique technology. ALL ORDERS SHIP FREE! Advantages of our Oval chainrings: Our Oval chainrings maximize rider efficiency by leveraging your pedal stroke where your power is produced and reducing resistance where your power is least...




usamadeco.com





Note that even when new, the cheap BBs on our Cujos felt like they were full of rocks -- it's one part that Cannondale definitely went super cheap on.


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## kbahus (Sep 11, 2005)

Thanks for the info, any issues with the Spawn cranks and spacing? I wonder if dropping down in length will be noticable or not. I am going to have to check out the bottom bracket height when I get home and see if I can go up to 120mm or not, didn't even think about it to be honest. Those Heir cranks look pretty nice too.


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## TimTucker (Nov 9, 2011)

As mentioned a few posts above, the Spawn cranks worked well with a 119mm square taper BB but I did have to take off the bash guard to get the chainline right. Note that I also used a narrowide ring instead of the stock ring from Spawn - 64 bcd does limit your options for cheap chainrings quite a bit


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## kbahus (Sep 11, 2005)

Finally got home to take the old stuff apart. I measured the stock crank arm at 116mm or so center to center so I am thinking going to 120mm with the Heir cranks is no problem. I found a new Shimano Hollowtech II bottom bracket in my parts bucket so those should go well together. Now about this new fandangled direct mount chainring stuff (I am old school and still run 2x9 and 26" tires) what is the offset all about? Will the USA made 30T chainring be the proper offset to get things lined up? I also can't help but notice these rings are like the old Biopace chainrings, I thought that ship sailed decades ago (lol).

Does anyone happen to have a stock crankset in good condition they want to part with?


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## TimTucker (Nov 9, 2011)

kbahus said:


> Now about this new fandangled direct mount chainring stuff (I am old school and still run 2x9 and 26" tires) what is the offset all about? Will the USA made 30T chainring be the proper offset to get things lined up?


With direct mount, instead of using spacers to adjust how far inward the chainring is from the cranks you buy based on offset -- 0mm is basically like having no chainring spacers, 3mm is like adding 3mm spacers, 6mm is like adding 6mm spacers. On the 24" we did OK with the 0mm offset ring. Note that USA Made does ship their direct mount rings with adapters that would let you add 6mm of offset, but I haven't used them.

With the larger tires on the Cujos, they tend to benefit from having the chainring pushed out a bit in order to clear the tires. When I used the Spawn cranks, the main reason why I used chainring spacers at all was that I put on a 26t ring and it was small enough that the chain wouldn't clear the spider on the cranks otherwise.



kbahus said:


> I also can't help but notice these rings are like the old Biopace chainrings, I thought that ship sailed decades ago (lol).


Similar look, but the modern approach to oval rings is based on the idea that Biopace had things completely backwards.

Biopace
Biggest part of the ring is in the dead spot
Theory: it'll help you "get through" the dead spot faster

Modern oval
Smallest part of the ring is in the dead spot
Theory: the part of the pedal stroke where you have the least leverage should be easiest










Oval chainrings are not new at all: Shimano Biopace... - oval-chainrings.com


The first time oval chainrings have been introduced to the cycling market has been in the middle of the 1980s by Shimano with it`s Biopace chainrings. They name derived from „Bio“ and „Pace“ and it is intended to suggest the „naturalness“ of the pedalling stroke with Biopace chainrings...



oval-chainrings.com


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## kbahus (Sep 11, 2005)

Thanks for all of the info, very informative. I ordered the Heir cranks and a 30T USA Made ring today, I wish they had a 26T or 28T but all they had in stock was a 30T. Did you face the bottom bracket on the 24" before installing the new cranks? I will make an update when the parts show up and I get them installed.


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## TimTucker (Nov 9, 2011)

kbahus said:


> Thanks for all of the info, very informative. I ordered the Heir cranks and a 30T USA Made ring today, I wish they had a 26T or 28T but all they had in stock was a 30T. Did you face the bottom bracket on the 24" before installing the new cranks? I will make an update when the parts show up and I get them installed.


Hope it works well for your son!

The gaps in USA Made's product lineup have always seemed a little odd to me too -- i.e.: no smaller sizes for direct mount rings / no bigger sizes for 64T rings.

I've yet to find facing a BB necessary -- the tolerances have been good enough on every modern frame that I've worked with that it didn't really seem like it would do much.


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## kbahus (Sep 11, 2005)

Both parts arrived and started assembly. Definitely dissapointed with the Heir cranks so far, they didn't bother to include chainring bolts or a spindle bolt. Also, the chainline is way off. I was curious if I needed to order the 6mm offset adapter from USA Cycling in the frist place, but it looks like it would not clear the bottom bracket regardless. So in retrospect I should have just ordered the full 6mm offset kit from Heir including their chainring and bottom bracket so everything fits right and all of the parts are included. 

Tim, do you have a picture of your bottom bracket/chainline setup? I just don't see how it can be done with the USA chainring.


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## TimTucker (Nov 9, 2011)

I can take a few photos later - the 24" has a little longer chainstays, which probably gives a little more flexibility for chainline.

For the bottom bracket itself, keep in mind that you'll need 2 x 2.5mm BB spacers on the drive side and 1 on the non drive side for a 68mm BB shell.

Now that you mention, I do remember our Heir cranks didn't come with chainring bolts - I just used disc rotor bolts since they're the same thread size and almost identical length.


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## kbahus (Sep 11, 2005)

Thanks for the reply. I do have the Shimano BB installed with the spacers in the proper location. I sent Prevelo an email and got a quick and curteous reply, they also sent out a spindle bolt today and were easy to work with. I added a chainring from them to the order in hopes to get a better fitment and chainline. I will update the thread when the parts come in.


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## headshok2002 (Mar 7, 2008)

Hoping for help for my kiddo's 20" Cannondale Cujo. 

Sorry to resurrect this thread but I'm hoping to get some clarity on what offset chainring to run on a DM crankset. I'm ordering from Alibaba as they have some pretty nice cranks in 114mm which include a chainring (28T).

It's cheap enough that I can just buy 0, 3, and 6mm offsets and pick which one works best but I'd rather not waste. Well, I could donate to the LBS I guess. Still, hoping for an answer here.


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## TimTucker (Nov 9, 2011)

headshok2002 said:


> Hoping for help for my kiddo's 20" Cannondale Cujo.
> 
> Sorry to resurrect this thread but I'm hoping to get some clarity on what offset chainring to run on a DM crankset. I'm ordering from Alibaba as they have some pretty nice cranks in 114mm which include a chainring (28T).
> 
> It's cheap enough that I can just buy 0, 3, and 6mm offsets and pick which one works best but I'd rather not waste. Well, I could donate to the LBS I guess. Still, hoping for an answer here.


On our 20" I used 64bcd cranks and it took some trial & error with spacers to find what worked best.

On our 24" I used a 0mm offset ring.


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## headshok2002 (Mar 7, 2008)

TimTucker said:


> On our 20" I used 64bcd cranks and it looks some trial & error with spacers to find what worked best.
> 
> On our 24" I used a 0mm offset ring.


Thanks for this... I think I'll just buy all 3 ring options and will come back here to share whichever worked out best.


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## TimTucker (Nov 9, 2011)

headshok2002 said:


> Thanks for this... I think I'll just buy all 3 ring options and will come back here to share whichever worked out best.


For the 20", that's probably the best approach -- the shorter chainstay length makes it a lot more finicky to get dialed in & also ensure that you're not getting any chain rub on the tire.


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## headshok2002 (Mar 7, 2008)

Okay, for posterity lol

I ended up receiving these Alibaba direct mount cranks (link) and they are pretty great. If the link is dead the seller is Honry Tiancheng Technology and the product was Lightweight hollowtech CNC Kids Children Direct Mount Crank Arm 114/127/152/170mm Bicycle Parts Chainrings mtb Crankset. The seller was good with communication and they were shipped via UPS, packaged very well and arrived in perfect condition. 

They were priced really cheap at about 30 bucks and another 40 USD to ship to Canada. I ended up ordering 114mm for the Cujo and, while I was at it, got a set of 127s for whatever bike comes next. Combining shipping for both cranks made for even better value. I was honestly tempted to buy 10 - 20 of these and put them up for sale at a reasonable price as DM kiddo cranksets are priced rather absurdly IMHO. I wasn't about to spend 30-40% of what the bike cost on cranks.  

These cranks seem excellent. The price includes a direct mount narrow-wide chainring (SRAM pattern) and a bottom bracket. I did order with 3 different offsets (6, 3, and 0) and after installing them yesterday *the 6mm offset ring seemed to be what yielded the same chainline as stock.* I went with a 28t ring which will be a bit better for my kiddo I think vs. 30t stock.

So, a wee bit of weight saved, a big aesthetic improvement, and gone with the garbage bottom bracket that came with this otherwise pretty awesome bike.


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