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Does anyone have any idea where I can buy a 140mm LH crank arm? It seems to be a scarce part.

jimmidan
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  • Found a few on Amazon and eBay but if they fit your application is another matter https://www.amazon.co.uk/FOLDER-KIDDIES-TEETH-COTTERLESS-CHAINWHEEL/dp/B078JPTZ7F/ref=mp_s_a_1_2?c=ts&keywords=Cranksets+for+Bikes&qid=1654867921&refinements=p_89%3AHard+to+find+bike+parts&s=cycling&sr=1-2&ts_id=458358031 – Dan K Jun 10 '22 at 13:33
  • I do not know where to buy but I know that velomobiles use the short cranks regularly and the people building/selling them professionally seem to be able to buy them in several sizes. So I am sure they are available in the right parts of the market. – Willeke Jun 12 '22 at 08:35

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140 mm cranks would be most useful for children and very short adults.

Most children's bikes are spec'd to be ridden for a year or two (until the kid outgrows it), and then thrown away or passed down to the next child or neighbor. As such, there's not much incentive to provide aftermarket parts.

For fully grown adults, cranks that are 165 mm in length are, at least to me, the short end of what's "normal"/regularly available.

I'm 5'10" (178 cm), with proportionally longer legs and quite like shorter cranks. While mountain biking, I like the pedal clearance they provide over rocky/jagged terrain. However, when you start to go shorter than 165 mm or 160 mm, you have to compensate by raising your saddle. As a result, you're raising your center of mass and that degrades the stability of the bike over steep and technical terrain.

A custom frame could be designed around shorter cranks by lowering the bottom bracket.

Paul H
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  • Road bikes and mountain bikes do not cover the whole bicycle market, other parts of the market do use different components. (Not -1 but please do not be short sighted.) – Willeke Jun 12 '22 at 08:37
  • @Willeke of course they don't, but without more information from the OP, I don't think it would make sense for me to speak beyond my area of most familiarity. Two other points I'd like to bring up: If you squint, road and mountain bikes make up an overwhelming majority of bikes on the market (e.g., touring, gravel, commuter bikes fall under that umbrella) and if this was a weird situation (e.g., unicycle, fully-faired recumbent, I feel confident the OP would have brought that up. – Paul H Jun 13 '22 at 13:44
  • Question is tagged BMX so I suspect this is for a kid-sized bike. – Criggie Jun 15 '22 at 22:20