# Our 24" Hotrock Build - novella version / guide



## jestep (Jul 23, 2004)

So, figured I'd post our 24" build just as another example for other parents looking to lighten these miniature juggernauts. I have done so much research and testing in the past few months that I think I now know more about building 24" and other kids bikes and the best components for them than all the bikes I've ever ridden or worked on in the past 25 years combined...

Before:









After:









So, we started with a 7 speed, 2011 Specialized Hotrock 24. Got it on craigslist for just over $100 and it weighed in around 27.5 lbs. We got the hotrock to replace a raleigh 24" bike that weighed an amazing 34lbs. The raleigh needed a fair amount of work, mainly wheel stuff, and it was probably cheaper to buy the specialized than to repair the wheels. Apart from a riser bar that the previous owner installed, it was all stock.

So far, we have literally upgraded every component on the bike with the exception of the headset and BB. All parts have been either stuff that's been collecting in my garage or ebay.

As it sits now, we're just under 19 lbs, and have a substantially better ride than the stock bike. Looking back, if I wanted to spend a bit more, I'm pretty confident I could actually get this down at least 2 more pounds without a substantial amount of pain.

First thoughts, get a used bike. These things are so plentiful on craigslist, at least in my area, it would be crazy to buy a new one. $100 - $150 for a good condition used 24" bike, or $300 - $400 for the same bike new, it's a no brainer. Use the money you saved, swap out some components, and you end up with a much nicer ride for less.

Something we found through this process is that wanting to swap 1 component often requires swapping something else first on these bikes. Not hard to figure out, but just write down a progression of what you are planning on upgrading on these to make sure if it works. Example, no point swapping the shifters if you can't use a normal cassette, and no point getting a normal cassette if you can't put it on the freeehub wheel.

First swap all the basics out for light aluminum or cheap chinese carbon stuff. Ditching the post, bars, and stem, you can lose a pound right off the top and it's not going to break the bank.

Our list:
Chinese carbon riser bar
Al 60mm stem
Al 27.2 seatpost
Seat???
Allen head QR's

Carbon bar was insanely light and we cut off about 50mm on each end. It's literally probably 90 - 100g now, so light that I didn't trust it would be remotely safe for a rider. Time will tell but I tried to break this thing and couldn't get it to flex so much as a mm.

We couldn't find a cheap carbon post that was lighter than cheap Al ones on ebay, so just skipped carbon on that. If you end up buying a longer 350 - 400mm post, definitely cut it down as well.

The stem was about $6 shipped and 130g so didn't feel like trying to save a scant 20 - 30g more for a carbon one that would have costed way more.

If you are dealing with a heavy or just a bad seat, WTB volt and deva saddles are fairly short and come in ti versions. I strongly suggest watching ebay for used ones as you can often get a used ti saddle for under $30 and the same one will cost $150 - $200 new. SDG makes some good shorter ti railed saddles as well but they're way harder to find used.

Instead of normal QR skewers, you can get the allen head ones which are probably as light as ti skewers and cost about $8 - $12 for a pair. There are ti ones which are even lighter, but these were light enough for the cost.

Next is where things get more complicated and prices can get out of hand with little effort. If you're going all in on a build, I recommend wheels next because so many other components are going to be reliant on them.

Wheels

We wanted the ability to use a normal cassette and shifters so wheels were the next upgrade.

Unfortunately our frame didn't have rear disc tabs so we needed to find rim brake compatible rims. This is by no amount of exaggeration not an easy task. For disc rims, Stans makes some amazingly light 24" MTB rims, not so much for rim brake rims. Problem 2 is that BMX rims which are readily available in 24" have bazaar widths/BSD's and often have far too few or too many spokes to be used as MTB rims. We were able to find some 32 hole, WTB DX23's in 24" size, which weighed a reasonable 400g per rim. We ended up getting a good deal on some koozer hubs, but for a little more you can save some decent weight with circus monkey or some other brands. For this weight range, I feel that 24 spoke wheels would be perfect, but again, this makes finding 24" non-disc rims even more difficult.

We didn't go crazy on spokes, another area to save some weight, but prices can get completely out of hand. Our wheelset came out to about 1800g for 32 spoke 3-cross lacing. Not fly weight wheels by any means, but they're close to indestructible and much, much, lighter than the stock ones.

With better spokes on the stans with circus monkey hubs, you should be able to get under 1500g for a tubeless disc wheelset. Absolutely killer setup.

Shifters and drivetrain

We have always had major problems with grip shifters so wanted to go to thumb shifters. Problem here is that almost all of these bikes use 7 speed freewheel setups, so we're either limited to lower end 7 speed components, or have to consider changing out the wheels right out of the gate. There are decent 7 speed trigger shifters, but they're definitely at the lower end of what's available for triggers. We also picked shimano over SRAM because those rapid rise derailleurs, which are more or less unnecessary, are perfect for kids.

Next we dug into the garage parts bin and came out with a SRAM 9.0 - 9 speed cassette, a PC971 chain, and an older LX rapid rise 9 speed derailleur. We paired this to a XT M770 9 speed shifter. I will tell you, this is probably the lightest pull / smoothest shifting setup I've ever seen. Takes no effort to go up or down through the gears. It makes the M786 2 x 10 setups that I am running on my own mountain bikes feel really clunky.

For the front, we went with an ebay Spectra crank running single, w/ 32t RF SNW chainring and lightweight bashguard. Under 600g with the ring and bash guard installed. We didn't bother with the BB because the only way to save some meaningful weight is with a ti BB, and they tend to cost more than $100. Just not worth it for us.

Brakes

Most of these bikes come with unbranded tectro v or disc brakes, some have lower end shimano or avid mechs for discs. These aren't terrible brakes, but typically offer limited adjustability. You're unlikely to find huge weight savings here so good deals on better brakes would be the only way I'd recommend upgrading. As much as kids would love hydraulics, just wasn't going to work for us, so we got some Avid FR5 levers on ebay. We swapped the rear brake out for an Avid SD5. We got an Avid BB7 mech for the front (more on this to follow). Lost weight on the back and gained some on the front.

Fork

So unless you have a higher end model, the stock suntour forks on these bikes are the biggest waste of weight and performance on the bike. I'm not a heavy person, but I could barely compress the fork on the lowest setting, even when jumping on the front of the bike, same thing goes for the raleigh which had a similar fork on it. No chance this is usable for a sub 75lb child who's not even going to have their entire body weight on the fork let alone double it.

For this build, and my daughter's embarrassingly timid riding style, weight was a more important factor than usable travel, so we swapped out with a rigid fork.

Amazingly the axle to crown height on the suntour was about exactly the same as rigid 26/29" forks on ebay. So for about $60, we got an aluminum mosso fork that weighed in around 700g, down from 2300g+ for the suntour. If you have a lower axle to crown, the eXotic carbon 24" fork should be a better replacement but it's more than twice the cost of the mosso.

Word of warning on these Chinese forks, I have never seen a fork that was harder to set a crown race on in my life. No chance using a race setter and a mallet, I literally had to resort to the 3ft PVC method and it still took a good 5 - 10 minutes of slamming the fork, steerer side down on the PVC pipe, on a concrete floor, to get it to set. I'm not sure if this is typical of these forks, but I seriously thought I was going to break the fork before getting a race on it which practically fell off the suntour.

As for suspension, the older SID's with disc tabs are great forks, but we found they add about 30mm to the front height of the bike. I have 2 on other bikes I was able to test with. Seeing as how slack these are setup from the factory, we determined this would likely push the geometry past the point of reason, so stuck with rigid. Suntour does make some good and usable forks like the F1rst, but it's still over 1800g and adds about $200 to the cost of the build.

Back to the front brake, using the taller fork prevented using a rim brake on the front. At the time I found a BB7 for really cheap. I personally would prefer a decent rim brake over these mechs. They are difficult to get setup in the correct position, and personally I feel that they trade what might be considered modulation for the ability to actually stop. Let's just say you will never have a problem locking the front up and going over the bars on one of these. The TRP spyres are lighter and infinitely better mechs and if I were to build this again, no question I would go for a spyre.

Grips

Grips are going to be preferential. I usually like lock ons because they're easy to install and replace. But for small hands, we went with ESI racers edge, which are very thin 30mm, and they are light. We even cut off about an inch of each one. Just great grips, I now use ESI wrap on my commuting bike.

Juliana makes some thin lock on grips if you prefer lock ons but want thinner grips.

Pedals

Pedals are another factory heavy component. Even the resin platform pedals are heavier than they would seem to be. We got some 160g rockbros ti pedals on ebay for under $30 shipped. Seems almost pointless, but you can actually save 200 - 300g fairly easily on pedals.

There's been a number of threads about the pegs being overly sharp, and potentially dangerous, but at the very least kids are going to have a much lower chance of slipping these than normal pedals. Don't ride barefoot though.

For clipless, definitely go function over weight savings. SLX or XT pedals are often super cheap on ebay or mainstream websites. They work great, they don't break, they're not expensive, definitely the way to go IMO.

If you want dual purpose I can recommend the shimano A530's. Both the platform and the clips sides are usable. Crank brothers is coming out with the double shot this month, which looks like a good pedal, but can't comment on actual function or longevity.


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## jestep (Jul 23, 2004)

Final component list:


FrameSpecialized Hotrock 24ForkMosso Rigid AlHeadsetAhead 1 1/8Front WheelKoozer 72HD WTB DX23Rear WheelKoozer 72HD WTB DX23TubesSchwalbe 20 x 2.1 UL (SV7C)Front TireSchwalbe Rocket RonRear TireSchwalbe Rocket RonStemeBay AluminumHandlebareBay CarbonSeatposteBay AluminumSeatWTB Deva TiBrake LeaversAvid FR5GripsESI racers edgeFront BrakeAvid BB7 w/rotorRear BrakeAvid SD5CranksetSpectra 3 -> 1 w/RF 32 SNW & UL BashBottom BracketOEM 68mmx119 CassetteSRAM 9.0ChainSRAM PC971ShifterM770Rear DerailleurLX Rapid RiseFront DerailleurN/ACablesJagwirePedalsCrankBros


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## jh_on_the_cape (Jan 12, 2004)

Cool!
I just went on ebay and bought some of those pedals. thanks for the tip.
I have a Ti BB I found in my parts bin. Based on what you said I put that on Ebay! I hope I get some real $$ for it! It's an FSA. I don't think I will install it on my son's bike if it's worth that much. It's also a hassle to swap, risk of screwing something up is real for me.


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## GrayJay (May 16, 2011)

jestep said:


> I feel that 24 spoke wheels would be perfect, but again, this makes finding 24" non-disc rims even more difficult.
> 
> We didn't go crazy on spokes, another area to save some weight, but prices can get completely out of hand. Our wheelset came out to about 1800g for 32 spoke 3-cross lacing. Not fly weight wheels by any means, but they're close to indestructible and much, much, lighter than the stock ones.


nice writeup...

24" wheels for a kid rider are definitely overkill with 32 spokes. You can save spoke weight with zero cost even using 32 hole rims/hubs, just don't lace all the spokes. weight savings is usually around around 7gr per spoke/nipple.

32 hole components probably are best used as a 16 spoke wheel build but need paired spoke lacing, see 
http://forums.mtbr.com/families-rid...-wheel-build-40lb-rider-need-help-891768.html

alternately, for a 24 spoke build use all16 spokes on the rear drive side (or front disk side) counter-balanced by 8 spokes on the opposite side.

did you check the rim weight on the original stock wheels? Often the stock generic singlewall rims are lighter than the available doublewall replacement rims.


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## GSJ1973 (May 8, 2011)

jestep said:


> For this build, and my daughter's embarrassingly timid riding style, weight was a more important factor than usable travel, so we swapped out with a rigid fork.
> 
> Amazingly the axle to crown height on the suntour was about exactly the same as rigid 26/29" forks on ebay.


Great post and awesome what you have done with this build. I am curious about the fork. Can you measure the axle to crown length?


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## jestep (Jul 23, 2004)

Off the top of my head it was about 415mm, but I'll try to remember to check when I get back to the house. I believe they were ranging from about 410 to 445 when we were looking for one on ebay.


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## GSJ1973 (May 8, 2011)

jestep said:


> Off the top of my head it was about 415mm, but I'll try to remember to check when I get back to the house. I believe they were ranging from about 410 to 445 when we were looking for one on ebay.


Thanks. One of the parents in our club bought basically the same bike and wants to shed some weight. I recall the Suntour has a 410-415mm A-C. Did you go with 445mm fork? 445mm would be way too tall as replacement from stock right? That's all I am seeing on those eBay listings. Thanks again.


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## jestep (Jul 23, 2004)

GSJ1973 said:


> Thanks. One of the parents in our club bought basically the same bike and wants to shed some weight. I recall the Suntour has a 410-415mm A-C. Did you go with 445mm fork? 445mm would be way too tall as replacement from stock right? That's all I am seeing on those eBay listings. Thanks again.


I just measured and the mosso is about 412mm and the suntour is about 415mm. Hard to believe without seeing them next to each other, but the mosso is definitely slightly shorter. I think the one we got was labeled 420mm on the ebay listing. It's weird because I see ones that look exactly the same labeled 445.

I agree 445 is going to be too much. The older disc SID's that we have on other bikes are right at 445 as well.


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## jestep (Jul 23, 2004)

GrayJay said:


> nice writeup...
> 
> 24" wheels for a kid rider are definitely overkill with 32 spokes. You can save spoke weight with zero cost even using 32 hole rims/hubs, just don't lace all the spokes. weight savings is usually around around 7gr per spoke/nipple.
> 
> ...


The pair lacing would be perfect for these.

We didn't deconstruct the old rims just because we figured we'd want to piece the bike back to original some day to sell it but probably a good idea especially considering how hard it is to find 24" mtb rims.


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## PMK (Oct 12, 2004)

Cool to see this. I have been building my Granddaughters Hotrock 20. The old parts bin has been a great source for stuff. Also have found some awesome deals on used stuff.

Thanks for some insight on the grips. I was unaware they came in different diameters. I just grabbed a set off the rack, shortened them and installed them. I got chunkies, and should have gotten the racer edge version for here smaller hands. Probably be the first swap of the stuff I installed.

Was kind of cool to see the before and after weights. I did not bother with a before weight, just set a target and hope I can get there. Trying for sub 18 with a suspension fork.

Time will tell. Looks good. Ride safe.

PK


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## PMK (Oct 12, 2004)

jestep said:


> The pair lacing would be perfect for these.
> 
> We didn't deconstruct the old rims just because we figured we'd want to piece the bike back to original some day to sell it but probably a good idea especially considering how hard it is to find 24" mtb rims.


Same here. Just took all the stuff removed an put it in a box. Got a set of hubs, rims are coming and had a box of seldom used size DT 14/ 15 / 14 spokes that I will shorten and make into 14 / 15. Again, stuff seldom used or laying around.

Was hoping to have the lighter tires for the wheel install, but looks like the new Schwalbes are not available until early 2016. No plans for tubliss since the really low air pressure for a lightweight lets me almost peel a tube tire off the rim while inflated. Yes that was my unofficial test to see if tubliss was even worth the effort.

PK


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## jestep (Jul 23, 2004)

PMK said:


> Cool to see this. I have been building my Granddaughters Hotrock 20. The old parts bin has been a great source for stuff. Also have found some awesome deals on used stuff.
> 
> Thanks for some insight on the grips. I was unaware they came in different diameters. I just grabbed a set off the rack, shortened them and installed them. I got chunkies, and should have gotten the racer edge version for here smaller hands. Probably be the first swap of the stuff I installed.
> 
> ...


Yeah, we found the racers edge ones just by chance, were originally going with the chunky's. I don't think there's a huge difference in these though, at least not like going from these to lock-ons.

Also, from your other comment, is schwalbe coming out with 20" rocket rons? I really like them on the 24". We're using 20" ultralite tubes on ours, which are a huge pain to get on a 24" rim, but work well once installed assuming you can get the tire back on without pinching the tube.

We thought about going tubeless, but really just didn't want to mess with it on there. If we were doing a dedicated disc build with stans, I would probably consider it, but more trouble than it's worth for our usage.


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## PMK (Oct 12, 2004)

jestep said:


> Yeah, we found the racers edge ones just by chance, were originally going with the chunky's. I don't think there's a huge difference in these though, at least not like going from these to lock-ons.
> 
> Also, from your other comment, is schwalbe coming out with 20" rocket rons? I really like them on the 24". We're using 20" ultralite tubes on ours, which are a huge pain to get on a 24" rim, but work well once installed assuming you can get the tire back on without pinching the tube.
> 
> We thought about going tubeless, but really just didn't want to mess with it on there. If we were doing a dedicated disc build with stans, I would probably consider it, but more trouble than it's worth for our usage.


No the new tire is not a Rocket Ron, it is called a Little Joe and will replace the Mow Joe. Contacted Schwalbe to order them and was told early 2016.

For now, that's fine while I finish other bits on the bike and recover from the cost. However, there is no price to be put on the smiles.

I may do something different on the grips. Pro Taper motocross is offering kid size grips for motocross. I may modify a carbon bar to fit the small grips and leave the remainder sized for normal shifters and levers. Still thinking about it.

PK


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## nimaj (Mar 23, 2014)

Did you need to do anything special when switching the rear axle to Quick release? I am working on a hotrock 24 build and find that the quick release allows the wheel to slip out easily.


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## GrayJay (May 16, 2011)

nimaj said:


> Did you need to do anything special when switching the rear axle to Quick release? I am working on a hotrock 24 build and find that the quick release allows the wheel to slip out easily.


Put on a solid internal cam QR (like a OEM shimano QR). Aftermarket external cam QR are notoriously bad about slipping...


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## jestep (Jul 23, 2004)

We used allen head ones just so we don't risk the wheels getting easily stolen. I doubt most people would even notice them to be anything different, but would rather not lose them just in case. They seem to be very secure.


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## Genes1s (Sep 10, 2017)

Jestep,

Awesome built. I'm in the similar situation now. Tires is my first one on the list, along with light and wider handle bars, stem, and seat post. I also wanting to replace the twist shifter to lever style. 

I'm keeping the 3X7 Mech with maybe doing 2X7 instead but just removing the outer chainrings. 

I was planning to keep the front fork but you had an interesting and better solution there and wondering if your kiddo fee any different due to the geometry changed or was it unnoticeable. 

Thanks


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## jestep (Jul 23, 2004)

Genes1s said:


> Jestep,
> 
> Awesome built. I'm in the similar situation now. Tires is my first one on the list, along with light and wider handle bars, stem, and seat post. I also wanting to replace the twist shifter to lever style.
> 
> ...


The geometry change was almost negligible. It looks taller but it's actually not, which believe me is still hard to believe myself. I think if the fork was usable it have been different losing the suspension, but the height change was basically nothing, so as far as just rideability, it's effectively the same.


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## Genes1s (Sep 10, 2017)

Jestep,

I found this at Ebay and it's cheap. Would this work for going 1X10 setup and disc brake? my frame has rear disc mounting already. 
https://www.ebay.com/itm/SHIMANO-DE...044072&hash=item48b091d298:g:zbwAAOSw-xNbWhFK

https://www.ebay.com/itm/Novatec-32...485890&hash=item2ab3c4a4f3:g:xcEAAOSwh1NbLvE-

If I go to brake disc and going 1X10 and rigid fork it almost makes sense to buy a new bike espcially if I can get dealer pricing..


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