Cranks that can be shortened ???

The kids bike is currently running cranks/BB that weigh about the same as his frame… (or not far off)

Choices seem limited
Get the right length (135mm-140mm) cranks with some weird BSD you can’t find narrow wide chainrings for

Run a heavy square taper BB and use something like the SRAM S600’s cut down (or Octalink or …)

Find a Ti Square taper BB ($$$$)

Run an external BB and find cranks that can be cut.(no fluting where the pedal hole will go and no hollow cranks)..

This is the current option but Zee cranks and the over specced spindle at 73mm weigh nearly a kg… Very slightly lighter than a UN55 BB and cut down SRAM S600’s…and SLX/XT are non starters as they have the hollow channel in the crank arms…

My 8yr old lads bike is running a set of these https://www.amazon.co.uk/d/Sports-Outdoors/Kettenradgarnitur-SR-Suntour-T20242-Z%C3%A4hne-schwarz/B0029MP3AO/ref=sr_1_2?s=cycling&ie=UTF8&qid=1490799087&sr=1-2
with a supersatr NW ring on. They’ve been down actual mountains(Les Gets and Samoens) and were fine.
Still need a square taper BB though.

I’ve done some Hussefelt cranks (ISIS BB though). From 700+ g’s to 450g (for the cranks).

I’ve got the same cranks as ads678 on my son’s bike. They come with rings which are easily removed to reveal 104BCD. Once you remove the rings, the cranks are 580g for the pair (square taper, so not including the BB).

Are square taper bbs really that heavy?

Ads678… they are still a bit long (we need 140mm max) and actually the upgraded model to the “originals” from his bike that had riveted chainrings…

stevied .. look great … have you got access to a milling tool..?
but suffers the same problem with BB weight…

The real concern over weight is for when he’s racing XC – when we are hitting the trails it doesn’t really matter. (the bike would fall apart but the cranks will be solid).. but he’s racing both older kids and kids with £2000-£3000 bikes… (on a converted frame and forks I got for £250)

I could get the actual cranks lighter if I can get access to the tooling (which should be possible) … but it still leaves a whole chunck of weight in the Zee spindle…. which you could use as a level to lift a car… so the other idea is working out if/how the spindle could be swapped for one from a SLX/XT crank…

Ah, fair enough! 🙂

i bought some deore cranks, and got a tame welder to fill the scalloped ‘back’ of the crank arms – so that there was enough metal for 18bikes to drill and tap a new thread.

(shortened to 140mm for my 5foot wife)

c’mon bike companies! we can buy all sorts of parts in all sorts of sizes, but cranks come in 175-165…?

When building my son’s bike I was surprised at the lack of decent short cranks. Even modern Deore brakes work perfectly with little hands thanks to the reach adjust but want a short/light crank? No way.

As to square taper bottom bracket weight, the UN55 I used weighs 300g. Yes, I was surprised at how heavy it is after using external BBs for an age, but with those of course the axle is part of the crank not the BB.

I can 3D print you titanium ones…won’t be cheap, through.

Are square taper bbs really that heavy?

It’s all relative I suppose but about 300g…and the cranks about 600-700g so together it adds up to about 1kg (quite a bit more than 1/10th the weight of the bike)

As a comparision: A adult sized Hope BB is 110g + 641g crank (arms, axle and 34t spiderless ring) so 250g lighter for a pretty hefty (strong) crankset

XTR BB SM-BB93 90g + XT cranks (adult sized) about 600g

Or another way to look at it… even a Zee + BB is lighter than a light crank + square taper…

300g would be a lot of replacing steel bolts with Titanium ones…. (not that I’m about to do that)

if you’re running single ring look at race bmx. kids bikes down to tiny kids, with corresponding cranks.

You can but shorter cranks but mostly odd BCD’s …SJS have a load of 5 arm options ….

Hope make them but don’t sell them (fitted to their Academy 24 bikes)

Trailcraft now sell them in 140 but back to square taper…

I’m wondering if a tame welder can’t just weld a spindle from a SLX or XT onto the Zee Cranks…. and having set about them with a miller like Stevied

I use a Tange Seiki LN 7922 with my sons thorn square taper crank. Weights about 230g cost me £25 off eBay.

You are just going to have to suck it up with the weight I’m afraid

Have you had a look at race bmx cranks, a few lightweight options at 135mm from the likes of sinz etc.

Racing bmx often offers better kit for kids than mtb.

Can you remember being a child? Did you care about how much your chainset weighed?

Thinking about this a bit…

Would it be a keeerazy idea to chop a pair of hollow arms and then press, pin and/or bolt in a solid insert that could then be drilled through and tapped to take a pedal?

I’m no mechanical engineer but my hunch is “yes”.

I’d be phoning isla / frog etc and asking if they can sell you something lightish

I am a mechanical engineer, and I have an old set of hone cranks with stripped pedal threads…

Hmmm, a plan is brewing.

Singlespeed_Shep – Member
Have you had a look at race bmx cranks, a few lightweight options at 135mm from the likes of sinz etc.

Racing bmx often offers better kit for kids than mtb.

Watch the chainring offset – BMXs are 6-8mm narrower than MTBs ie 42-44mm vs 50? (iirc) not that it probably matters hugely but it could be an issue.

The real concern over weight is for when he’s racing XC – when we are hitting the trails it doesn’t really matter.

A couple of hundred grams will make **** all difference to his times.

I shortened a set of S600’s down to 102mm(iirc), worked well with a raceface taperlock BB(250g).

I was actually thinking of cutting them then injecting epoxy (the stuff used for anchoring wall bolts)

Reading up it seems the hollow part tends to end about where you are trying to put the pedal …and the issue is the free space around the pedal hole..

I’d be phoning isla / frog etc and asking if they can sell you something lightish

Tried that with isla, maybe I’m not charming enough but they said no.

You are just going to have to suck it up with the weight I’m afraid[/quote]

I’m coming to that conclusion…

I see Isla have sourced a Token Ti/Carbon BB for the Pro Creig 24… eBay price seems to be $130 + shipping so that might be back to POAH’s suggestion… and suck it up….

I can save the same weight removing his brake rotors and that will definitely make him go faster 👿

Tried that with isla, maybe I’m not charming enough but they said no.

Ah well I’m buggered for them then…. Now what company who actually make their own 135mm cranks but don’t sell them despite their main business being selling components might be susceptible to a NE lancs rougher type of charm ???

Spawn cycles sell 127mm for US$60 + shipping, might be a bit short for what you’re after though.

E-13 cranks might be worth a look. Hope do a 30mm BB that is an improvement on the E13 jobbie too.

E-13 cranks might be worth a look.

Yep … I’ve also “looked” at RaceFace and Hope…. but the problem is you can only “look” so much on the Internet.

I know Hope make a 135mm crank (they just don’t sell it but fit to the Hope Academy lease-hire bikes) … but I can’t tell from available pictures if it is from the same die as their 165-175 cranks… I’ve seen them in the flesh (or metal) but briefly at races … but it’s hard to know if they can or can’t be cut down and if the 165 has the same flute as a 175 or if that’s part of the CNC.

(In other words does it go to within so many mm of the pedal… or is it so many mm from the axle)

Logic say’s if they made a short run of 135mm cranks (purely for their lease-hire) they would if possible use the same die and then mill down… I guess the way to tell is if they use the same die for 165 and 175…

The also have had 3 different designs over a few years so it might be that one year as a better starting point than others… I have emailed them to ask so I’ll see if they respond.

The same goes for the E13/Raceface etc. (except they don’t have a 135mm model)

SRAM NX cranks are available in 155mm length. Alternatively, give IslaBikes a call.

I’m just about to try 140mm XT M770s, have drilled 20mm hole – just where the hollow bit tapers out – the outer end probably has enough metal but not the inner side. Thought about epoxy but I am not sure, epoxy is not structural, you need at least 3 threads in the metal for full strength, might get away with it but I have been in hospital with crank/chain failure and luck not to loose (more) teeth. Local eng. firm kindly made me some 20mm ally inserts for free, another local firm ready to tig them up. Then I’ll drill the inserts and I have the RH&LH taps for pedals.

Only problem is I only have a spare drive side, I need an M770 NDS arm…..

SJS have a few options. 110bcd so you could go to 33t or 34t in NW, or they do a 4-bolt too. Square taper but Token do a reasonably light and cheap version. This is what I’ve run on my kids’ bikes in the past.

https://www.sjscycles.co.uk/cranks/thorn-double-drilled-crankset-74110-pcd-115-mm-140-mm/

https://www.sjscycles.co.uk/cranks/140-thorn-11074-pcd-triple-solo-alloy-crankset-silver/

How about Bontrager kids’ cranks?

Triton has them in 20″ or 24″ wheelsize(not sure about the former but the 24″ version is 127/152mm)

Square taper I reckon – have a look at the old miche primato bb which didn’t have lips on the cups so you can get the chainline right. like this one but its out of stock[/url]
Sealing isn’t great but you can replace the bearings easily enough should the need arise.
Then scrounge an old pair of cranks and trim them down as described above (email in profile if you want me to have a rummage, pretty sure there’s something in the shed).

@ReggieGasket and Kafakaza ….

I already have some square taper cranks at the right length … (actually 2 lots) the issue is not so much the crank weight but the BB weight… and the chainline could be better but its acceptable…

I also recently got some used Zee’s and fitted a HT-II BB and the results are dissapointing …. it’s lighter than a UN55 BB + SRAM S600’s (which is lighter than the rubbish it came with) but barely.. (80-100g)

However the Zee’s are tanks… including (and I think mostly) the axle/spindle which is made for a 220lb downhill rider… not a 50lb kid doing XC 😀 ….

The SLX-670 cranks would be lighter but the issue is the cranks are hollow… (M780 XT is I think identical except for the pedal helical inserts so it would make no odds once that bit is removed anyway….)

The HT-II is fitted with the zee at the moment … so unless I can find a compelling reason I wouldn’t go back to the square taper and SRAMS

Either way I have a selection of 104 BSD chainrings that get swapped over a fair bit according to what he’s riding… (A lot of the kids XC races seem to be a fair bit of gravel and even tarmac… and probably more suitable to a CX bike than XC so I’ll change to a say a 34T/36T up front or a 30/32T oval for our normal trail riding…)

Could be…. POAH’s Tange suggestion also looked decent… the Islabikes Token Carbon/Ti … just too much for what they are…

If you do have them and they do drop some weight I’d be interested though…

To be fair as someone said… 300g won’t make ***-all difference to his times. I think I must just enjoy cutting/drilling/tapping cranks 😀 (Everyone needs a few hobbies)

Next project is quite possibly a FS-24er….I’m looking at what can be bought cheap and the shocks upgraded (or spring to air at any rate)… but finding out AC and shock lengths seems hard work and .

Quite probably won’t be weight weenie on this… as it will be a trail bike for airtime and decending not racing XC….so the Zee’s might find a new home…

Re: square taper cranks. Shimano M900 are around 490g, and a Hope Ti BB is around 190g so that’s 680g plus cranks bolts so approx. 700gr. I imagine you could pick up both of retrobike for under £100.

spawns brood styx 140mm

Yep…. but it’s just another annoying near miss showing what SHOULD be possible….

I’m guessing the M900’s were pre-Hollow cranks but the 5 arm means I’d need to have a different set of chain-rings to the present collection (that’s swapped across 3 bikes) and the M900 possibly saves 100g over the S600’s or Alivio’s I already shortened 🙁

It’s easy to forget when you get used to External BB’s that you need to find the right length square taper as well…. (I’d manage 68/110-113) but that just means you have a lot less luck in the used market

It’s the damned combination that’s so frustratingly close… with various options scoring 2/3