what width bars and cranks for kids

nathanm

Likes Bikes and Dirt
so the (most wonderful beautiful amazing) girlfriends young fella has experienced his first tasty, tasty dirt. Well more to the point clipped a tree and has given himself a scare which has impacted his riding and he now has "the fear".

Even at 9, he's too big for a 24" frame and is riding my STP which has good standover, but is too long even with a short stem. Will be sticking a straight seat post on shortly and maybe shorter cranks, which will improve things, but getting him a best fit I can on the bike, considering what it is, is going to make a huge difference.

The bars are some 700+mm wide which look just way too wide even with his hands inboard. I'm guessing young Jack is probably around 4 foot 10 or so but will probably crack the 5 foot very soon.

So long story short what set up do you run for your kids.
 

moorey

I'm full, couldn't eat another dick
Both my guys are small, but on 26 by 7yo. Quinn is now 11. She likes 680 on trail bike and 720 on DH. Her XC bike she won’t ride any more was 650. Says it feels silly now.
Crank length gets expensive for anything decent under 165. I think 165 is plenty short. Quinn runs it. Felix is on 170.
 

rockmoose

Likes Dirt
My 11 year old is running 760. He is overbiked, but surprisingly not by much, and handles everything he comes across with relative aplomb.

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Plankosaurus

Hydraulic Jack specialist
I've got some at 590 for free if you want them. Nfi what I'd do with them otherwise, not even a good length for belting ebike riders with

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The Duckmeister

Eats Squid
STP isn't really an ideal frame for a kid. Sure it has low standover, but being a trials-style bike is very low for its length to reduce the risk of crunching the rider's undercarriage in the likely event of a stack....Plus it's flippin' heavy.

Anyway, bar width is a bit complex, relating to both the shoulder width of the rider (which at 9 y.o. won't be huge, even for a tall kid), and its effect on reach; other things staying constant a big bar will pull the rider forward, exacerbating any reach constraint (it will make the bike feel longer), potentially leading to discomfort or strain in various upper body muscle groups. Condensed version, probably don't want to go more than 650mm, but depending on the kid's build even that might be a bit wide.

For crank, if he's tall enough to ride an adult-sized bike (even a low frame like the STP), 165mm will be OK, but longer may increase the potential for knee injury due to the greater range of motion on pedal cycle.

Problem with kids is they don't stay the same size for very long, so you do need to change stuff more often than you do for your own grown-up bikes.
 

moorey

I'm full, couldn't eat another dick
You know I like you @The Duckmeister, but being a pure XC bandit, and running bars around 620 last time we met, your bar preference is a but slanted :p
 

silentbutdeadly

Eats Squid
Nigh on ten year old 5 footer at my place runs a 590 mm bar on his 24" Polygon...and he's got plenty of room in it yet.

In my experience, the grow fast kids have all physical aptitude of an avalanche. So bar width is the least of your concerns.
 

The Duckmeister

Eats Squid
You know I like you @The Duckmeister, but being a pure XC bandit, and running bars around 620 last time we met, your bar preference is a but slanted :p
Hey, I've grown up to 680mm bars now! :p (but given that I'm now in my 40s and still a scrawny bugger, I'm hardly likely to grow into anything much wider....) Preference is one thing, physiology is another, and there is such a thing as too wide a bar for a given rider's build. Sure a big bar helps with stability when the going gets rough, but the rider also needs to be able to tackle tighter stuff without getting yanked off the saddle & chucked face-first in the dirt by a bar that's longer than their arm....! A 650mm bar under a young kid is proportionally much wider than the same bar with an adult rider.
 

nathanm

Likes Bikes and Dirt
STP isn't really an ideal frame for a kid. Sure it has low standover, but being a trials-style bike is very low for its length to reduce the risk of crunching the rider's undercarriage in the likely event of a stack....Plus it's flippin' heavy.

Anyway, bar width is a bit complex, relating to both the shoulder width of the rider (which at 9 y.o. won't be huge, even for a tall kid), and its effect on reach; other things staying constant a big bar will pull the rider forward, exacerbating any reach constraint (it will make the bike feel longer), potentially leading to discomfort or strain in various upper body muscle groups. Condensed version, probably don't want to go more than 650mm, but depending on the kid's build even that might be a bit wide.

For crank, if he's tall enough to ride an adult-sized bike (even a low frame like the STP), 165mm will be OK, but longer may increase the potential for knee injury due to the greater range of motion on pedal cycle.

Problem with kids is they don't stay the same size for very long, so you do need to change stuff more often than you do for your own grown-up bikes.
Yeah nah it's not, but he likes it because it's camo and I cant afford to put him on anything else ATM. He only rides maybe once a fortnight with me for 2-3km so it's a good solution if albeit temporary. His dad bought him a fluid pos he bangs around on during our off weeks.

Cranks are currently 175 so if i can get 165's and maybe 6-660mm bars and a straight seat post I'm thinking the fit will be a ton better?
 

mooboyj

Likes Dirt
My wife is ~155cm and has 590mm bars/50mm stem on an XS Giant Boulder. Also has 170mm cranks as I couldn't find any 165mm cranks at the time.

Our nephew who is also sub five foot uses her bike from time to time and finds it usable (it really is a touch large though).
 

rowdyflat

chez le médecin
Women have proportionally shorter upper bodies + , narrower shoulders ,not so strong ,so even my sturdy wife doesn't have wider than about 670.
Shorter cranks actually make gears higher ie harder so ....
 

moorey

I'm full, couldn't eat another dick
actually low body fat ,good shape + fit for her age ,never called her useless though
Sound robust. I like it. Just a physical description. What would you use instead?
‘Useless’ is a whole other value judgement :oops:
 

nathanm

Likes Bikes and Dirt
should I have added an emoji? My comments were made in jest and not an indictment, just meant it to be an amusing comment on how words can be misinterpreted in a relationship. Whatever did happen to mywifesirrational. I used to love his stories about the torture his better half put him through.
 

moorey

I'm full, couldn't eat another dick
I texted him 6 months ago checking in. I think irrational wife has run him through.
 
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