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So from what ive got from various internet sites,if a child has between a 20-24 inch inseem he should run a 160/165 crank arm.Any oppinions on this?Its kinda hard to get feedback from an 8 yo.So any help would be great.
Age means nothing. Inseam means everything. My old Dans Comp catalog shows 140mm at 20" inseam, and up 5mm for every inch longer inseam. 24" inseam at 160mm. Works for us, but, best way is have them ride other kids bikes. At good speed, say first obstacle off the gate, their body should stay centered on bike, if they are bouncing side to side, cranks usually too long. If they are forging, not smooth spin, also too long.
Crupi's crank sizing chart would agree......160mm for 24" inseam..........btw, i would like to take this moment to thank Crupi for actually giving us info freaks some good info on their website......they have sizing charts and great info on frame geometry and why it matters........

I get so tired of equipment manufacturers that don't have sizing charts on their sites. I sometimes feel they purposely withholding info (don't know why?).

Thanks Greg Swingrover
And the way you measure the inseam means some more. Dan's Comp measures all the way to the floor (see photo on their page):

Whereas, the best I can tell J&R's chart is based on pant leg:
Rollin.......very good point there........I asked around on this as well and the people I would trust most had said to measure with shoes on all the way to the ground like Dan's recommends..........

from J says "inseam" but they don't clarify it. I have seen some sights that used the term "inseam" measuring the same as Dan's is.
If you take J&R as pant (not baggy ) and Dan's as the other their recomendations come out close to the same, at least on my little one. Looks like Crupi is along Dan's lines.
I run 170's I am 4'11 ( i consider myself 5) I am 31 so age means nothing! I have my 7 y/o on 130's.
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