Have been offered a new bike for my lad, but at present it has 170mm cranks. My son is 136cm. I’m trying to find something, reasonably priced, in the 145-150mm range.

Short of going to E13 carbons (way too much!), i am struggling to find any at all. 68mm bb shell. Bike currently has dub bb but am happy to change that if need be!

Do such cranksets exist?

These?

https://www.sjscycles.co.uk/cranks/150-thorn-10464-pcd-triple-crankset-mk2-black/

They’re what’s on my (5’1″) wife’s bike with a single narrow-wide ring and have tansformed her riding.

After much looking because of similar issues you’ve mentioned I got these for my daughters bike. Does the job nicely if you’re only putting a single ring up front, I put a narrow wide ring on and all is good. Square BB though so would need to change that.

Jet BMX Square Taper Race Cranks

Thanks. They look good but am a little worried about the square taper. Should I be? (Mainly a fear of the unknown having got used to Shimano and GXP easiness over the years)

HUP Kids Cranks: Children's Short Cranksets (104bcd 4-bolt) Narrow Q-Factor

I put some of these on my daughters Ramones 20″. They are for square taper BB and have 104mm PCD so nice and easy to fit to a 68mm BB. Multiple lengths too!

a little worried about the square taper. Should I be?

If they’re fitted properly, not at all. Pro downhillers raced World Champs on them 25 years ago, they’ll be fine on a kid’s bike. Just check the spindle bolts every now and again for tightness and go and get muddy.

I’ve put that Jet BMX crank on my daughters bike, square-taper BB, narrow-wide ring off ebay. No problems.

Also have a square-taper crankset on my Cotic, good as gold.

You can get other race BMX cranks in all the kids sizes that use the two piece hollow spindle system like Shimano but they’re all at least a hundred quid more, and usually out of stock.

Another user of the Jet cranks, no problems they’re fine and have a NW chainring fitted to them. No problems with a Square taper BB.

Suntour XCR Junior cranks are 145mm and available for about 30 quid (well, were). They come with triple rings but it’s just a standard 104BCD.

Frog sell their cranks as an aftermarket item. They fit square taper BB, are alloy, low Q factor and less than £20 so not too much outlay given kids growth rate.
https://www.frogbikes.co.uk/spares/cranks-bottom-brackets/replacement-cranks

What @rossburton says, whip the rings off and fit a narrow wide. Snail ones off eBay or Amazon are only a tenner.

I’ve had 2 sets and they’re fine. You do need a square taper BB though.

Although after a quick Google, I’m not sure they exist anymore…those jet BMX ones look the same though and 3 sizes!

Another Jet Square taper cranks user and a 30t N/W ring just moved them up to his bigger bike. The only disadvantage is that they are single ring only so unlike butchering a triple you can’t leave the 22t ring on for emergencies.

I’ve got some SRAM NX cranks which I think are 155mm and use GXP BB. I’m about to take them off a bike and they may be available if that’s of any interest?

FWIW I’ve got jnr#3 on 127mm frog cranks at the mo, and she’s 131cm (or a tidge more). No way she’s ready for 140+ just yet. Don’t be too eager to jump to 150s.

Useful thread! My elder daughter’s getting a bit big for her Isla Beinn 24 (I just put fatter knobbly tyres on it to make it a rigid MTB). So it looks like these short cranks with a square taper BB will work. I’ve got most of the parts from my old 27.5 hardtail but that frame’s too big for her.

Any suggestions on 27.5 frames for a lanky almost ten year old? Tapered steerer fork and non-boost hubs but they’re Hope so convertible to most standards.

Hope do a 155mm crank now. If your kid has a big piggy bank

For sub-150mm cranks square taper is definitely the way to go. I’ve had the Thorn ones from SJS, a range of Islabike ones (they do sell them separately, but you might have to pretend to have an Islabike to put them on to avoid awkward questions), and a smattering of BMX cranks. Everything used to be square taper, worked fine and the BBs last for ever. Those Jet ones look fine. If you want something a bit nicer I’ve got LDC cranks on the youngest’s track bike which are CNC’d junior BMX cranks: https://crucialbmxshop.com/ldc-4-bolt-square-taper-cranks

Through axle options can be found, but get very expensive quickly. Cheapest option is probably Sinz (£150), which go down to 140mm https://crucialbmxshop.com/sinz-mx2-cranks

The Croder ones that Kids Racing do look great, but silly money really.

Once they get bigger note that Shimano do direct mount SLX cranks in 165mm now for about £100 (without a ring) – just put some of those on the youngest’s MTB

There’s a guy selling those sinz cranks branded as alphabike (well, some samox cranks but they’re the same crank afaik) for £35. 135mm only. Word of warning I ordered a set and they never came, but I was mid postal carnage, and I did get a refund as it was eBay. I don’t necessarily blame the vendor.

A lot of kids bikes seem to come with short Samoa cranks. No idea if they’re OEM only or not.

Yes the oem catalogue from samox is huge. These are nice examples of samox cranks

HEIR Crank

They do sell their M3J and M3J carbons aftermarket but I don’t think there’s a UK distributor

Some great options already mentioned, and some good prices.

I went with a 155mm SRAM NX (?) for my daughter which seemed OK on a Whyte 405 (came with 165mm) and transferable onto the next bike.

Some great options. Thanks everyone!

So which Sqaure taper do I want? Am looking on Merlin and they seem to come in all widths from 68-107 t0 68-127 (with 3mm increments all the way between 107 and 127)

The bike has a 135mm QR rear and is running 11 speed on a shimano freehub.

I always just cut down used non-hollow armed cranks with a standard BCD (Deore spec)
You need to buy longer than you think with the fluting at the back.

If you go the Sq Taper route get the correct UN55 and it will outlast the bike.

“So which Square taper do I want?”

It depends on the cranks you decide to go for.

The BB I used replaces a loose ball cheapo that came with the bike.

I am lucky enough to have a very helpful LBS (Owens Cycles, near Petersfield) who ‘leant’ me a couple to find out what I needed. I honestly cant remember which one I settled on but I remember it being the wider option to get the chain line correct.

We’ve had a few other kid specific bits (cranks & seat spring to mind) from frog bikes. They have a great spares website, so you just order online & IMO are cheap as chips.

I am lucky enough to have a very helpful LBS (Owens Cycles, near Petersfield) who ‘leant’ me a couple to find out what I needed. I honestly cant remember which one I settled on but I remember it being the wider option to get the chain line correct.

I am not sure quite how wide would be needed for that! Am hoping someone does!

We’ve had a few other kid specific bits (cranks & seat spring to mind) from frog bikes.

Great shout. Thank you!

The frog bike cranks, anyone know what chainring they take? I’m looking for something shorter for my daughter’s Vitus (came with 165mm!).

For most Frog cranks the chainring is built into the crank. Chainring size depends on which crank.

What length are you looking for btw?

– https://www.youtube.com/watch?v=gvuPQ-oS4gs –

Crank Shortening

For most Frog cranks the chainring is built into the crank.

Probably no good then as want to fit a narrow wide ring.

150mm which is what her previous bike had fitted or at most 155mm. That would bring it more inline with frog, Isla and the recommendations on kids racing.

Square taper

150 and 155mm

HUP Kids Cranks: Children's Short Cranksets (104bcd 4-bolt) Narrow Q-Factor

152mm

SR Suntour XCT junior, but looking out of stock..

in Dub there is Sram SX in 155mm, but need to find in stock..

or as above in the current cranks are solid, Highpath can shorten them.

I’m in Canada but pretty sure I have a new set of 152mm 24mm alloy spindle cranks. Sram DM chainring. Same as vpace/trailcraft cranks.
Includes a 32t ring and PF BB but you’d need to pickup a 68/73 threaded BB if that’s what your frame needs.
Sram DM means you have 3 chainline options with other rings..
I’d need 200cdn plus postage though.

Thanks @bearback however a bit costly by the time they have got here.

I’ve not found any of the short GXP cranks anywhere. I think for the moment I will move the cranks from the old bike (152mm).

I have come across a few more options;

Trek dialed kids cranks, come dual drilled so you move the pedal up as they get older. Surprisingly low cost as well. Two options (120/140mm and 127/152mm). I’m probably goign to get one of these to fit onto the old bike for when the younger child needs it.

https://www.trekbikes.com/gb/en_GB/equipment/cycling-components/bike-cranks-and-chainrings/city-amp-kids-bike-cranks/c/E348/

Saracen tiny kids cranks (102mm)
https://www.freewheel.co.uk/saracen-mantra-1-6-chainset-102mm-26t-rns5289

Specialized riprock crank, 152mm.

I had a similar issue in the Spring. My 11 yo son 158cm, almost 80cm inside leg, I think it was 165mm single chain ring with a BCD that will allow a 34t CR. Long story short it was impossible doing it cheap so I gave up and bought a complete Rotor VEGAST24 Crank Arm Set 165mm. Its been ace

Drilled, tapped and chopped down some old Shimano LX to 145mm for my daughter’s bike a few years ago, still going strong for her younger sister. Got the taps and a big old drill bit to go with them somewhere.

Square tape FTW on kids bikes, bearings are un-killable and it actually takes some effort to break them.

Drilled, tapped and chopped down some old Shimano LX to 145mm for my daughter’s bike a few years ago, still going strong for her younger sister.

My kid is using some still and he does brutal landings, I mean totally brutal he frequently smashes rims and breaks pedal bearings/bushes on impact) I’d break my ankles or tear tendons if I even tried …. the cranks are absolutely undamaged.

AEROZINEXEON-A1 mini CRANKSET (for kidbike)

Not a budget option

Aliexpress has Cruz cranks which are gxp and go down to 155mm apparently. HOWEVER I tried buying some this summer and they kept cancelling the order. I’ve just bought some 160mm ones and they have shipped – awaiting arrival at present. About £40 inc BB.

￡31.29 | CRUZbike MTB Mountain Bike Crankset GXP Bicycle Crank 160mm/170mm/175mm Black Aluminum Alloy with Bottom Bracket
https://a.aliexpress.com/_mLQ5hhI