Building a custom kids bike raises the problem of where do I get a decent pair of kids crank from.

I found a couple options for kids cranks from Spawn and Turn3. Click the link below.

Probably old news, but my search also led me to a website which suggested that adults would also benefit from using much shorter (kid sized) cranks, which is also included in the link.

Options for Kids Cranks, Should Adults use Short Cranks?

Given at 6′ with a 32″ inside leg, I use 170mm cranks on the road bike in preference to the longer cranks it came with and I think I can pedal slightly smoother & faster and get more (geared) power down then yes.

In my opinion.

Highpath used to shorten cranks. My kiddyback tandem has crank shorteners. Another option is a second drilling.

I ride 165 (track)-175(mtb). I can average over 100 rpm both of these extremes. Learn to spin.

My non scientific experience is whilst a shorter crank may be a better a lower gear for hills is far more important.

My lad has 150mm cranks on a 34:25 and a 170mm crank on a 22:32. Guess which aggravates his knees?

http://www.sjscycles.co.uk/mobile/thorn-104-64-pcd-triple-crankset-mk2-black-prod31813/

They’re expensive, but Canfield do 155mm cranks.

I think I paired them with an overly-low gear – they were ludicrously twiddly. I’m going to have another go with something a little bit taller.

🙂

I shortened some old Truvitiv cranks from 175 to 130. Used a drill press, to drill the hole. Some pedal taps (cost 20quid)were then used to tap hholes. The cranks cut very easy because they are so light/soft.

I bought Thump a 160mm crankset from Spa cycles for £40.

http://www.spacycles.co.uk/products.php?plid=m2b0s109p2000

(now sold out in 160mm)

£42 in sizes from 130-155mm, you may want to look at chainring sizes though depending on the child it’s for…

When I built a bike for our lad I bought 152 mm cranks direct from Isla bikes that have a 28tooth ring fitted. Run it 1×9.

I wish I had known that you could get them direct from Islabikes. 28t would have been good.

My almost 9 year old has the 150 Thorn cranks. My 4 year old is still using the 89mm Spawn cranks that I put on the bike when I built it when he was still 2. I have got the next size up (102mm) but I decided to keep him on the 89 for now.

short adults should probably be using short cranks, yes.

tall adults? – well it would be nice to have the option.

my 5’1″ wife has 140mm cranks, i’d need 220’s to see how awful 165’s must feel for her.

(165 is the shortest on offer from Shimano – i have no idea why)

I wish I had known that you could get them direct from Islabikes. 28t would have been good.

absolute black do a 64BCD N/W 28t

My boy uses a 30t attached to a 150mm thorn crank, and I use a 165mm XT.

http://wp.me/p4HYH0-v

We’ve also used those 160mm cranks from Spa Cycles (£20), running single ring with a 26 or 28 tooth (£10).

Once kids get a bit older and for severe off road, I’m not convinced super short is always the best option. Slightly longer gives them more leverage and also sat nearer to the ground for same amount of leg extension – it just depends if they are comfortable during the rest of the pedal rotation.

Currently short 11 year old has been on 160 for the last year and 13 year old 170 for the last 2.

5ft 6″ mrs has tried everything down to 162.5mm and prefers 175 for mtb and 170 for road. When swapping between mtbs, she has noticed 5mm crank difference (she didn’t know they were different but asked about it as one felt a bit “odd”). Persevered for a few months but definitely hated the feel of the 162.5mm.

bookmarked.

4 and 5-bolt bmx cranks come in short lengths too.

check out Billys, Winstanleys et al.

mick_r – Member

Slightly longer gives them more leverage

so does changing gear.

…and also sat nearer to the ground for same amount of leg extension

the extra saddle height from shorter cranks isn’t all bad, it can help sort out odd saddle:bar levels, and give room for a go-go-gadget seatpost.

it just depends if they are comfortable during the rest of the pedal rotation.

quite.

Suntour XCT Junior crankset is 152.5mm about ?30 delivered from Germany (via Amazon I think) good looking not too heavy. It’s a triple but I replaced the outer ring with a bash guard. Nice low gear climbing gear. Once they are 12 or so you can go 165mm which are much easier to come by.

If anyone is looking to buy some shorts cranks I have a spare set of Sinz ISIS cranks I have just taken off my son’s bike. I bought them from the US as I was struggling to find short cranks here. From memory they are 140mm long and fitted with a 34t Middleburn ring.

If you’re happy running a single ring, then I’ve found stuff on ebay for ~£20 or less eg http://www.ebay.co.uk/itm/CHAINWHEEL-SET-THUN-30-TEETH-COTTERLESS-3-PIECE-CHAIN-SET-127mm-SINGLE-RING-/181799127538?pt=LH_DefaultDomain_3&hash=item2a541289f2

mick_r – Member

Slightly longer gives them more leverage

have a read of this for why you would have smaller cranks.

crank length choice

I’ve no idea what’s best, but I can tell you that this has got 155mm cranks.

Sinz on eBay are good for the money

snallest you can got is 34t with sinz cranks

i bought these (150mm Thorn cranks from SJS cycles), for a friend’s son’s bike.

would happily buy them again.

I probably should point out that when I bought shorter cranks on ebay they were 140s for my own use. I also sometimes ride with 125, but mostly on 150. These are all on direct drive* where my speed is mostly limited by how fast I can spin and shorter cranks are easier to spin faster. Very comfortable riding with them though. 150s used off-road where I’m riding up steep hills – I’ve actually tried longer cranks and the difference in leverage isn’t that significant.

*wheel goes round at the same speed as the pedals, though the 140s are on one where I also have the option of a 50% higher gear than that.

have a read of this for why you would have smaller cranks.

crank length choice

I think all that says is nobody can agree on the correct length (including all of us) 🙂

And the day 3 bike fitters can come up with the same answer is the day I believe there is hard science behind their work. I seem to remember a Dan Jarvis article in the CTC magazine that tried exactly that experiment. Bike fit is a constantly changing factor as we age and our dimensions, strength and flexibility change.

None of the kids crank lengths I mentioned is a very far off the accepted mainstream (e.g. Islabikes Beinn 26 small 152mm and Beinn 26 large 165mm).

the extra saddle height from shorter cranks isn’t all bad, it can help sort out odd saddle:bar levels, and give room for a go-go-gadget seatpost.

Don’t need to work around a badly shaped frame in this household 🙂 In truth, my statement is only true if working around a regular frame with a fixed bb height – it makes no difference on a frame designed for a specific crank length and pedal to floor clearance.

https://picasaweb.google.com/101380098662650328614/JakeSFramebuild?authkey=Gv1sRgCKOCq7fpkOOV1gE

Nice. I’m not up to that, but looking to build up a 26er for an 8yo, so I guess I’ll be stuck with a rather higher BB than ideal.