Trek MT 220 build for the boy 👦🏼

[trailstar82]

All the….small things….!
It’s getting there, the crank situation isn’t resolving itself anytime soon, so just hoping his legs can push these round for a little while. Lovely little bit of xlite bling from @markoc sets off the back end nicely.

Next jobs….Red hose for the brakes and some proper guides to keep it attached.

 

[Baulz]

Nice build! I've been working on a similar project for my son with a tiny Giant XTC bike I got pretty cheap - it also just happened to have a 1st gen set of CrossMax wheels on it for me.

What did you end up with for gearing and crank length?

 

[trailstar82]

Nice build! I've been working on a similar project for my son with a tiny Giant XTC bike I got pretty cheap - it also just happened to have a 1st gen set of CrossMax wheels on it for me.

What did you end up with for gearing and crank length?

Well, I expected that 165mm was going to be too long. I keep umming and ahhing on these in 150mm.

Thorn 104/64 PCD Triple Crankset MK2 - Black

Alloy forged crank arms BCD: 104/64mm Sand blast black finish JIS Square Taper 110mm bracket required to get a 51mm chainline on middle ring, 107mm can be used if only using a single ring in the outer position. Weight: 565g (150mm)

www.sjscycles.co.uk

I may modify some RF evolve xc cranks to around 150

Gearing at the back is m770 9sp max 32t
Deore shifter and mech
Front will likely be 30-34t

I should add that it’s not finished yet. He may hate it :-/

 

[Baulz]

Thanks for the reply!

My son is almost 9, and 4'6". The bike came with 175mm which is way too long, I was surprised that cheap 150-165mm cranks with a 104mm spider are not that plentiful.

The bike was cheap but drivetrain pretty beat, I don't mind spending some money on it and just ordered a new Deore 10Spd drivetrain to get him a wide range of gears with a single ring. Same as you I can't decide what to get for cranks, and now the pressure is on biking season has crept up on me.

 

[Madmax1993]

Halfords have a surprising number of short cranksets for their junior bikes.
Single ring square taper 165mm chainset for voodoo nzumbi 13" (article 266780) £37
Single ring square taper 150mm (I think) for voodoo sobo (article 266814) £14
Single ring 140mm chainset for Carrera abyss/saruna (article 456350) £15
There are others from 24" wheeled bikes that are 152mm triple chainsets.

 

[joglo]

Hi,
I like building bikes for the little ones and also your specific build.
Just to me, it looks a bit from the side that the length of the bomber is a bit too much.
Ideally the bottom bracket height should be lower than height of the axes (modern kids Bikes using 29er principles and have a sometimes several inches lower bottom bracket, sure, only in combination with short cranks).
With a too long fork not just height from front and bar and also a bit the bottom bracket raises, also the center of gravity goes up and back. In conjunction with often needed short stem, there isn't a lot of weight on the front anymore and a loss of traction and steering guidance.
Don't want to paint it black, but just emphasize to keep on eye on the fork length.

 

[joglo]

Front will likely be 30-34t

If you're using a bcd110 crank like older RF cranks 34t is already the smallest available chaing ring.

Gearing at the back is m770 9sp max 32t

The rear mech will very likely also serve a 11-36 9spd cassette. There is a cheap and OK-ish CS-HG400 variant I could recommend.
With that there is a bit of a better granny ring for at least a bit of steeper hills, thats quite helpful especially with a 34t front chainring.

 

[mamadirt]

That is awesome - he’s a lucky lad
I’m always a sucker for tinyness

 

[trailstar82]

If anyone knows the chap that runs Kapz you’ll know he’s had an eventful and quite incredible time helping out with the Ukrainian humanitarian crisis. Any way this is a custom stem cap from Kapz with a well known YouTubers motto which josh particularly enjoys. Still need to sort those shorter cranks out though…..

 

[trailstar82]

Shorter cranks (135mm) added courtesy of a tip off from @ishaw going to find a narrow 32t that will keep the chain on instead of the standard RaceFace on there at the moment. Chain line looks good, he (the boy) just needs to grow a few inches and he’ll be ready to shred.