# Gt Stomper 20" Upgrades?



## cboyd1974 (Sep 7, 2012)

My youngest son finally moved up to our 2011 Gt Stomper. He's 8 but is only the size of a 5 year old, so fitting him for the bike is my first concern. I just ordered a 30mm stem and and started looking for lighter bars. We need some sort of trigger shifter since he has a hard time with the grip shifter. I also plan on ordering some lighter/smaller pedals for it.

I have seen quite a few Hot Rock builds, but haven't been able to find anything for the GT Stomper. Anyone have any suggestions for it?


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## bme107 (Jul 23, 2008)

We started my 8yo a year late in school and he is still pretty much one of the smallest in 2nd grade. Only average compared against the 1st graders even, which are a full 2 years younger. Sounds like we have similar situations.

He bought his 20" Stomper in the spring of last year when he was only 6. 40mm stem was a necessity and a condition of the purchase. Grip shifter was the 2nd thing to go once he was fitted on the bike.

We've added (in approx. order):
-40mm DJ stem
-SRAM SRX triggers-type shifter
-lock on grips
-Kenda small block 8 tires
-Sinz 150mm cranks
-34t ring (down from stock 36 or 38?)
-AL seatpost from my parts box
-carbon riser handlebar
-e13 chainguide
-XTR v-brakes

I don't have the exact figures here but I believe weight savings are somewhere around 3.5lbs (high 26lbs to low 23lbs). Tires were the biggest offenders at almost 1lb a piece, handlebars and seatpost the next. Everything else was pretty much a wash.


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## cboyd1974 (Sep 7, 2012)

I think they are pretty close in size. My son is in 3rd grade is about the size of the kids in Kindergarten. Even a lot them are bigger than him. 

The 40mm stem should be here by tomorrow, so we can do a test run to see how it works for him. I don't want to order lighter bars for it until I figure out how he is sitting on the bike.

Have you done any fork modifications to make it any softer. he may get a 1/2" of travel if he hits a large bump. 

Did the Sinz cranks make a big difference? Did you order a complete set or were they compatible with the stock bottom bracket? We are new to mountain biking, so I am not sure about all of the compatible parts.


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## IAmHolland (Jul 8, 2010)

my 6yo daughter has a hard time with trigger shifters still. my son uses triggers, but says twist is much easier. he was using a sram x5 i think. it's a big shifter, but it shifts easy. the downside is that the brakes are a bit more inboard.

my daughter has the scamp 20". her bike is around 20lbs now.

- 1x9 with 28T chainring and alloy chainring bolts.
- 145mm cut down cranks through bikesmith designs.
- 12-36 9 speed cassette. 
- SRAM X.5 trigger. It's tough for her to actuate to a lower gear, her thumb is not strong enough.
- SRAM X.5 rear derailleur.
- Small Block 8 tires
- Intense light tubes, filled with some slime for thorns.
- home built rear wheel with velocity aeroheat rims, tiagra hub, and alloy nipples, with more spacers added to the axle to reach 135mm.
- tektro mini v-brakes
- sette 580mm flat bar cut down to size.
- 40mm stem
- zero offset seatpost, can't remember the brand, cut down.
- odyssey jr. saddle
- n-gear bumpstop
- bbg bashguard
- wellgo m111 pedals with Ti spindle
- Ti skewers
- cut down foam grips
- light bottom bracket, can't remember the brand about 230g.


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## bme107 (Jul 23, 2008)

If that stem doesn't fit I'd suggest waiting until he grows a bit. From what I saw at home all the other proportions of the bike will probably be too big.

I haven't done anything to the fork. You're right, they only get about 1/2" of actual travel. I think I can only get about 1.25" out of it and I'm 175lb. I've read most of the threads here about forks for kids but never taken the plunge. Personally I'd swap out a light weight rigid fork than invest much in his suspension fork.

There was no weight savings in the Sinz crank and chain ring swap. I switched it so that he could get a smaller front chain ring. 34T is the smallest that fit with the bolt pattern on the cranks. On our terrain this helped out his ability to climb significantly. Top end speed is reduced but very rarely is he in a situation where he's spun-out compared to others he's riding with. More often he clears a climb and the others are pushing their bikes up.

There are 2 versions of the Sinz cranks, one square taper, one ISIS. The square taper kind will work with the stock bottom bracket and pedals. You will need a new chain ring and chain ring bolts. The stock crank setup had a plastic chain keeper bash ring type thing on it. Most likely you'll need something to serve this purpose on the new parts because kids can find a way to drop a chain if there is a light breeze blowing.


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## IAmHolland (Jul 8, 2010)

The spec, for the fork, is really only 30mm with a really heavy hit. GT's documention of 70+mm is wrong, that's for the larger SR Suntour fork for 26" tires. My daughter's fork is the M2025, IIRC, or one of the M2xxx series.

There's a mod on this forum for more travel (cutting bumpers). I did it, or part of it. I can get about 50mm, or a hair less now, when my daughter rides it.

It's a heavy fork, a rigid fork would be a good idea, but I would want to put larger tires up front to make up for the loss of some suspension. I don't know if there are any lightweight 20x2.1-2.3" tires out there, but that would actually be a good route. There might even be a carbon fork out there, if your kid is only doing normal riding and not hitting jumps.

Edit: From SR SUNTOUR Cycling

Travel
63 (50) (30)

Wheel size
26", 24", 20"

I sent GT bikes a nasty email when I got the bike, basically said they are false advertising. no response, and it persists.


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## cboyd1974 (Sep 7, 2012)

Got the neck installed. Make a quite a bit if difference for him.
I noticed the bottom bracket has a lot of resistance in it , I think it may need to be replaced. How do I determine which bottom bracket would fit?

I was trying to find a rigid for, but all I csn come up with is BMX forks. Is that what I need? All of your help has been great.


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## bme107 (Jul 23, 2008)

You'll need to find out the length of the square taper spindle. Take both crank arms off and measure unless someone can provide the figure. Also measure the bottom bracket shell width, probably 68mm. 

For the fork it is all a matter of preference where your search takes you. Get one with a similar axle to crown height, steerer diameter, and brake boss locations. BMX could work.


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