# Rippin Red Hotrock 20 Build



## Surfpoodi (Sep 14, 2011)

After what seems to be the normal hand wringing about lack of good options, I recently wrapped up a build on a HR 20 for my 4 year old.

We had been running a RL Pitboss for the last year or so, but the front brake was really useless, the HT angle was way to steep for trail riding, and the lack of gears was a bummer....

I got inspired by the Little Shredder bikes, and almost bought one. But in the end I decided I had too many parts in the parts bin not to tackle the project myself.

First decision was which HR 20 model to buy. We live an hour from the Specialize HQ in Morgan Hill, so there were plenty of options to choose from. In the end, I went with the newer model with a slightly longer top tube, but slacker head tube angle (and a neighbor down the street was selling it). Starting weight was around 25 lbs. Goal with modifications were: drop weight, shorten reach, better gear range, better tires.

Immediately swapped out the stem and bars with a mini 30mm, and some older CF bars I had around the house, also had to change out the seat and post to something with less stack height to get the seat down low since my little guy was only 42" tall and had an inseam just over 19".

Then I ordered a Crupi Rhythm Expert rim, and had it laced up to an old Bontrager Race Lite 28h hub I had kicking around. That let us use my old 9-speed XT rear der, 11/34 cassette, and XTR shifters. Replaced tubes and tires, getting the 1.9 Small Block 8 in wire, and some ultralight tubes. Put on Avid SD Ti brakes.

Also pulled the chain keeper off, and I'm currently using a little N-Stop device.

I didn't replace the cranks because it just didn't seem like I could get big weight savings there. The stock stuff weighs 530g, and I figured I'd be in the same place using the Sinz cranks w/chainring and bash guard.

I'm still debating if it makes sense to swap out the front wheel for a matching red one. I only can get about 250g of savings, and it will cost around $150.... which makes it pretty darn expensive, but it would look so very cool.

I tried using a Sram XO/X9 setup first, but I just couldn't get the triggers to move as easily as I wanted, so I went Shimano instead. At first I was skeptical 34 tooth in back would be necessary, but with the 36 front chainring, the 34 is a good low gear. I did block out the 11 tooth in the back, because.... well, I'm a chicken, and I get scared when he rides crazy fast.

Overall we are about $350-375 into the project, and the bike weighs about 20.5 lbs. The obvious additional weight savings now would be the front wheel, pedals, and the BB. With those three I could get another pound savings, but I'd probably nearly double the cost of the bike.

I have to say I'm convinced the slack HT angle is a good thing for his confidence to roll over things. Much better than the Pitboss. Also I think well set up V-brakes work amazingly well on the 20" wheels. Initially I had thought we would retrofit to disc brakes, but I was shocked with how easily he can skid, and how powerful the brakes felt to me when I got on the bike. I'll leave it to someone else to explain the physics.

Here is a YouTube clip from the other weekend.

July 2012 UCSC Ride - YouTube


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## SRALPH (Jun 27, 2008)

*Fork?*

Nice! That grin says it all.

I saved my daughter's 20" Hotrock for my son when I upgraded her to a 24" Trek this year. Fortunately she liked the white/teal color combo Hotrock more than the pink option so no paint or powder coat required.

Q: did you change out the fork? It looks like Little Shredder uses an 80mm White Bros fork on their builds.


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## Surfpoodi (Sep 14, 2011)

We are running the stock fork right now. I have been meaning to pull it apart to see if I can tease a bit more travel out of the thing, as he is only getting about 25mm right now.

I have put in for one of the Spinner Air's that Little Shredder has ordered, which will hopefully drop weight and help performance. I think Brian has been told he should have them in mid-Aug, which is coming up.

The White Brothers forks are killer. But I am concerned their axle to crown height would kinda mess up the bike. And they are really expensive.


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## bme107 (Jul 23, 2008)

My son has asked for better performing components this week and of course I do not want to dampen his budding interest. I picked off most of the same low hanging fruit but now I've got to make the jump to a wheel build in order to put on better rear drive train.

Do you know the weight of your rear wheel build? 20" rims have me stumped. I've looked at a handful of options and everything builds up to a negligible savings from stock. A build with those crupi only lend about a 50g savings.


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## Surfpoodi (Sep 14, 2011)

bme107 said:


> Do you know the weight of your rear wheel build? 20" rims have me stumped. I've looked at a handful of options and everything builds up to a negligible savings from stock. A build with those crupi only lend about a 50g savings.


I am pretty sure the rear wheel came in at 650g. I used a Bontrager Race Lite 28h hub, which I think weighed in around 265g. I was looking at a light 28h road hub (70g) for the front wheel, which I would guess, would come in around 450g if I built it up.

I can't remember off hand what the stock rear wheel weighed, but there was real savings between the stock wheel, stock gears, and the rear new wheel with XT 9-speed cassette. I think about 1 pound.


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## bme107 (Jul 23, 2008)

Thanks. I've got to check out 28H and probably some road hubs.


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## Surfpoodi (Sep 14, 2011)

You could also consider a 36h hub, and lace it up with every other spoke. I guess it depends on size and weight, but if pro roadies ride with 18 spokes....


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## NYrr496 (Sep 10, 2008)

A couple years ago I built my son a 20" bike and used 32 hole Velocity Aeroheats on older XT 8 speed hubs. They worked out perfectly.


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## aconsola (Feb 25, 2010)

Awesome build!
I found this thread while looking for advice on building up my sons Hotrock. So far I have done very similar changes. I swapped out the brakes for some first gen xt parallel push, gave him a carbon handlebar off my old bike, and removed the chain retention plate in favor of the n-gear jump stop.
I switched out the 6 speed gripshift for an 8speed XT rapidfire trigger shifter which he likes much better. 
All the XT goodies came off my old hardtail which I have converted into a 26" single speed rigid bmx racer.

My big question has been the rear wheel.
the frame is only 130mm, while mtb spacing is 135. I was wondering how well a road hub would do. It seems like a road hub with a bmx rim is the ticket! 
I have already ordered a used medium cage rear derailleur. The 11-34 cassette sounds ideal as it will give a little lower gearing than the stock 12-28 freewheel.
Thanks for the info.


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## Surfpoodi (Sep 14, 2011)

aconsola said:


> My big question has been the rear wheel.
> the frame is only 130mm, while mtb spacing is 135. I was wondering how well a road hub would do. It seems like a road hub with a bmx rim is the ticket!
> I have already ordered a used medium cage rear derailleur. The 11-34 cassette sounds ideal as it will give a little lower gearing than the stock 12-28 freewheel.
> Thanks for the info.


Thanks. The project has been fun.

The HR model we have is 135 spacing. At least my 135 hub fits perfectly. I believe the older models did use 130 spacing though, so your measurements could be right.

If you are dealing with 130 spacing, then yes, I think a road hub would be your best option, coupled with a light bmx rim. Make sure you get the 406 rim, I nearly got fooled into the "mini" 20 rims which are actually ISO 451.

I agree, a 34 in back is a much better low gear.

I'm running a long cage rear der right now. It hangs low, but I have the chain as tight as possible and no issues so far.

Good luck!


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## manitoumtbr (Jun 21, 2004)

I also used the Velocity aeroheat 20" rims coupled with light chinese road hubs of ebay (plenty of colors to choose from too). Dropped significant weight that way + the lower range on the cassette.


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## 95silverstallion (Aug 2, 2012)

Man, that lil dude aint messin around. I bet he has some strong legs for his age.


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## NYrr496 (Sep 10, 2008)

The hub I used on my son's bike was 135mm and the frame is 130. I asked the wheel guy at my LBS if we could doctor up the spacers on the hub to fit the frame. He said absolutely, so that's what we did.


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## Cinq (Jan 2, 2003)

Great setup! At first I wanted to go for weight-savings on my sons HR20 too but in the end, I ended up with a bulletproof setup with a Race Face bashring, Titec Hell Bent handlebars and wide Sun Ringlé Rhino Lite rims laced to 36 holes XT hubs 

Kind regards,

Clemens


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## sledz (Jun 27, 2012)

*same here !*

I picked up the same 2010 HR20 this weekend !!
going to go with twist X7 shifter/X7 medium cage der.
thx for the info on BB and cranks I was debating keeping the stock setup as well due to $$


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## thesmokingman (Jan 17, 2009)

I stuck on a sunrace 13-32t 8spd freewheel but I'm so aghast at the stock hubs, I'm seriously contemplating building a proper wheel set. The stock hubs are atrocious.


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## sledz (Jun 27, 2012)

*28H or 32H Hub reccomendation to lace to lite 20 x1.5 rim*

can anyone reccomend a 28H or 36H 9 speed rear MTB non disc hub... seems a 32H nice light 20 x 1.5 BMX wheel is tough to find...Everything I have at 135mm MTB spacing is 32H...arghhhhh... trying to go with a 1x9 SRAM x7 setup


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## thesmokingman (Jan 17, 2009)

sledz said:


> can anyone reccomend a 28H or 36H 9 speed rear MTB non disc hub... seems a 32H nice light 20 x 1.5 BMX wheel is tough to find...Everything I have at 135mm MTB spacing is 32H...arghhhhh... trying to go with a 1x9 SRAM x7 setup


36H, rear non-disc, 9spd?

Shimano Deore M590 Rear Hub, Black in Tree Fort Bikes Hubs (cat86)


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## Surfpoodi (Sep 14, 2011)

The Circus Monkey hubs on EBay are light and pretty cheap. I doubt the quality is all that, but I think they should hold up just fine for a couple of years rolling the little one along.


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## sledz (Jun 27, 2012)

*rear wheel build 32H 20" rim, hub, cassette combo*

I think I found a matchup:

Sun CR-18 20" 32h Shrader Valve Rim Black, 22.2mm width amazon: $27
with/ Shimano XT Rear Hub T780 silver 32H from chain reaction cycles: $42
Sram PG-950 9 Mountain Speed Cassette 2011 $28 - price point
or Sram PG-970 9 Mountain Speed Cassette 2011 $30 -price point

any difference between the 950 or the 970 ?

no experience with spokes and nipples any suggestions?

12 or 14 guage....

thx for all the help !

sledz


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## Surfpoodi (Sep 14, 2011)

sledz said:


> I think I found a matchup:
> 
> Sun CR-18 20" 32h Shrader Valve Rim Black, 22.2mm width amazon: $27
> with/ Shimano XT Rear Hub T780 silver 32H from chain reaction cycles: $42
> ...


The difference between the 970 and 950 cassette should be around 30-40g.

I would go with thinner spokes. We used 15g.


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## Surfpoodi (Sep 14, 2011)

As an update, we added a Spinner Air 20 fork. Clearly a higher quality fork. The ability to adjust air pressure is real helpful. It was about 0.5 lbs lighter than the stock fork, so the bike is sub 20 at this point.


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## sashae (Dec 19, 2008)

Where'd you source the fork from?


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## Surfpoodi (Sep 14, 2011)

Brian at Little Shredder hooked me up.


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## Rondo (Oct 14, 2011)

Way to bomb the DH!!! :thumbsup:


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## Surfpoodi (Sep 14, 2011)

In case you've ever wanted to get inside the head of a 4 year old mountain biker, here is a vid from a camera mounted on my boy's helmet.... Heavy on the cute factor. Turn up the volume.

GOPR0071 - YouTube


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## Boatracer (Aug 31, 2012)

What is the life expectancy of one of these 20 inch bikes with the boys that are riding them? when will you need to upgrade to the next size?
How well does the 4 year old boy fit the bike now?


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## Surfpoodi (Sep 14, 2011)

Well... We got this for our boy when he was 4.5 years old or so. He got a good summer riding it this year with a 30mm stem. I figure he will ride it next Summer with the same stem, then when he is 6, we will put a 50mm stem on it, then when he is 7, we will go with a 60 or 70mm stem and maybe riser bars. Then probably get a 24" wheel bike when he turns 8.... All subject to change if he grows crazy.

So I figure it will work for up to 4 summers of riding, if you start young enough... That is longer than I ride most of my bikes!


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## NYrr496 (Sep 10, 2008)

My son rode his 20" bike from 5 years old to 7 1/2. I just put him on a 24 and he had a big growth spurt this past summer. 
I'll stretch the 24 a little bit, but I'll probably start on a 26er for him next year.


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## Surfpoodi (Sep 14, 2011)

Time to sell the Hotrock. Hoping for $300 or make an offer?


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## ssledz (Oct 8, 2008)

*HotRock*

I would probably sell for $400 if not I may just strip the parts and use for a 24" build or part out...


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## Surfpoodi (Sep 14, 2011)

ssledz said:


> I would probably sell for $400 if not I may just strip the parts and use for a 24" build or part out...


I'd be happy to take $400, if you are offering! But $300 is a great price. Building up the super light rear wheel to take a 9-speed cassette is a $200 project alone.


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## Shepski (May 24, 2006)

Reviving an old thread... building my older boy's old HR into a new bike for my 5 year old. What spoke length would be needed for the Sun Envy rims and XT 756 hubs? I plan on using 15g.

Thanks!


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## NYrr496 (Sep 10, 2008)

Shepski said:


> Reviving an old thread... building my older boy's old HR into a new bike for my 5 year old. What spoke length would be needed for the Sun Envy rims and XT 756 hubs? I plan on using 15g.
> 
> Thanks!


I got rear nds-177, ds-175
front nds 175, ds-177. 
That's 32 spokes, 2 cross.


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## Shepski (May 24, 2006)

Thanks!

Would that be for the higher flange 6 bolt disc compatible hubs?


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## NYrr496 (Sep 10, 2008)

I ran it with XT 756 hubs just like you said.


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## Shepski (May 24, 2006)

Awesome... thank you!


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## Shepski (May 24, 2006)

Wheels built... getting bike shop to dish and true... it's almost a 9 speed.


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## NYrr496 (Sep 10, 2008)

The spoke lengths were spot on?


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## Shepski (May 24, 2006)

I laced 3 cross so used longer spokes. 185 and 186. I'll get some pics up once they are on the bike.

Cheers


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## NYrr496 (Sep 10, 2008)

Cool.


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## Shepski (May 24, 2006)

Waiting for the Spinner air fork and a pair of Schwalbe Little Joe tires and she's done for the most part. Replaced the stem and bar with a Spawn stem and narrower Fly bar. Running XT hubs(disc ready) with Envy rims and Sram X7/X5 9 speed drive train. Wanted to put on a smaller chain ring but the HR comes with a one piece crank arm/ring so will replace the chain guide and cranks later. My kid will be very happy when he comes home from Kindergarten today!

Thanks a lot to all you guys for providing the great information on hotting up a Hot Rock!

Cheers!


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## Shepski (May 24, 2006)

Finally done!


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## Crashtestdummee (Sep 14, 2015)

Looks great, nice build


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## Shepski (May 24, 2006)

Thanks! Can't wait for the snow to go and the dirt to dry!


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