The Suntour Junior XCT is a good option. Cheap and square taper with removable chainrings.

It’s not much cheaper than a SRAM S600 but it’s 152mm and hence can’t be shortened above 130ish (if that)

I’m assuming most kids first 24 inch they are towards the smaller end of 24 and not just about to move onto a adult XS bike… so 152mm is ridiculously long if the kid is just moving into 24er or about right if you are pretty much eeking the last out of a 24er size or XS adult size) so if you are going to the effort of changing cranks … it seems worth it to do it properly… The SRAM’s (or I got an old pair of Alivio’s for £10 + post off ebay) also have a decent square taper fit for JIS…. whereas Suntour seem neither JIS or European…. and are £33 free P&P instead of the £25 ish with P&P

When I switched to the SRAMS/Alivio’s we knocked about 5mm off the BB length over the Suntour…. (and UN55 BB’s are pretty cheap weight upgrades over stock anyway) Not only did it save quite a few grams but the square taper fits properly….

If your kid is 5′ then you can get proper cranks in NX at 155mm …

Given its disk ready why not ???

The wheel was for a Hoy Bonaloy bike which is not disk ready. He’s fairly light and the v-brakes do a good job of stopping him.

Balls – stevextc are you saying that I won’t be able to re-use the BB on the bike with that Suntour chainset? Didn’t realise there were different kinds of square taper (assumed the crank/spindle interface was standard)

I bought the Suntour XCT cranks in the amazon link above and use them with a shimano square taper BB, which fits perfectly. Great for £22. Although i then ditched the chain rings and fitted a superstar NW and bashguard (to stop the school trousers getting caught!!).

I understand that if everything is perfect we’d all have different length perfectly fitting cranks, but as most people are riding around with the wrong length cranks any way why not let the kids join the party……

Which BB ads678? (apologies if you’ve already mentioned this in the thread!)

Ta

Balls – stevextc are you saying that I won’t be able to re-use the BB on the bike with that Suntour chainset? Didn’t realise there were different kinds of square taper (assumed the crank/spindle interface was standard)

You can try it…. on the kids Cannondale the axle was too long when I replaced the Suntour with either Alivio or SRAM S600…. but both fit much better on the UN55 …

The one that came with the Cannondale was some chinese thing…. UN55’sd are only a few quid…. (£16 quid at Halfords at the moment) so it’s not the end of the world… you can get the cheaper Shimano sq taper cheaper…. but like I said… if you are going to the time/expense on everything else then it seems sensible to spend the extra few quid and do it right.

The Suntour never seemed to really “fit” the square taper…. It worked but it felt like it was not quite right when it was fitted …. and seemed a bit like it fit because the alloy is softer than the steel…. so given enough torque it seemed to go on…

http://www.halfords.com/cycling/bike-parts/gears-drivetrain-cables/shimano-bb-un55-bottom-bracket-british-thread

The wheel was for a Hoy Bonaloy bike which is not disk ready. He’s fairly light and the v-brakes do a good job of stopping him.

Ah, makes sense….

The pull of disks for me was really not about stopping power…. I just hated the squeak as soon as the wheel was 1mm out of true and also riding mainly at Swinley the mud/grit on the rims….

It was also a pain taking the wheels on and off as with the brakes adjusted so they worked the whole cable had to be undone everytime I took the wheels off… (and it soon starts getting tatty)

I just got annoyed on his 20 … so when we looked for his 24 disk brakes were top of MY list …

Now he has them he says “the other brakes don’t work” but he has just got used to the modulation on hydraulics and 1 finger braking…. but he’d never complained BEFORE he tried disk…. 😀

BB for the suntour crank is 118mm wide

Which BB ads678? (apologies if you’ve already mentioned this in the thread!)

Can’t remember the exact one as it was one out of the spares bin sorry. It was probably a UN55 though…

Shameless link to my classified ad:

Classified Ad – Blast 24 Bike Split for dads

Happy to help anyone on here with bits as required – contact details in advert.

So, chainline woes.

The original bottom bracket on my Blast was destroyed when the LBS took it off with an angle grinder so I had to resort to STW hive mind when replacing, which said 118mm square taper. I kept the original 7 speed wheel but went 1x at the front and the chainline seemed acceptable.

Yesterday I swapped the rear wheel for an Islabike Creig wheelset with a 9-speed cassette. Now the chainline appears to be too tight for the bottom gears (as far as I’m aware, the freehub got longer on the inside so the bigger gears are where there used to be empty space in 7-speeds) as the chain is trying to fall off the top of the lowest gear constantly and the straight chainline is somewhere around 6th or 7th gear.

Now I’m cursing square taper brackets as I can’t just fiddle a spacer to adjust the chainline. Before I either attempt to eyeball it, or do some dubious maths, does anyone just know what size bottom bracket I’d want to get the correct chainline with a modern cassette?

Now I’m cursing square taper brackets as I can’t just fiddle a spacer to adjust the chainline

IIRC – if you can find an old Race Face one you can do this by threading the cup in to position the BB in the required place.

had no problem with a 118BB and a 10sp cassette etc also no problems with a 113mm BB with low profile crank either.

measure the chainline and see if its 50mm

Having taken delivery of stevextc’s shortened alivio cranks, I fitted them to an ex-Mrovershoot’s 68×111 bb. And I reckon it’s about right.

Maybe it would take a few mm shorter, and just mount the ring on the outside of the crank? Is that possible?

Have had an initial try at getting the creigg wheel up tubeless too – it’s now got a tube in 😉

Yeah our creigs have tubes in too…

Okay so yes, the chainline is exactly 50mm. I guess that’s not the problem then. After a quality 30 minutes fiddling with the limits it’s mostly behaving now.

Do you know if the 7 speed cassette has a spacer so that I could change it to a 9 speed cassette without changing the hub?

Do you know if the 7 speed cassette has a spacer so that I could change it to a 9 speed cassette without changing the hub?

Assuming you’re talking about the stock blast wheels there are two types I’ve come across; the earlier bikes with the white deep section rims have a 7spd cassette – you can take one cog and spacer out of a 10 spd cassette to make a 9spd that fits, using a 10spd mech and shifter works well.
The later bikes with black rims have joytech hubs that take a 10spd cassette as standard.

I wish I’d known that when I did up my eldest daughters bike as I ended up buying wheels from superstar for that one, the one I’ve just finished for my youngest has the better wheels.

[url=https://flic.kr/p/TZ28oW]IMG_0893[/url] by mike_gee32, on Flickr

[url=https://flic.kr/p/TZ28Au]IMG_0921[/url] by mike_gee32, on Flickr

[url=https://flic.kr/p/UjTegW]IMG_0908[/url] by mike_gee32, on Flickr

It’s a 7 speed as standard with white wheels, I’m wanting to change for a 9 speed cassette, shifter and mech that I have lying around.

My Blast is earlier than the one with white rims: black rims and really bad disc brakes. 7 speed hub. Now swapped for Islabike Craig wheels.

Right off to tinker in the garage!

<img src=’https://s1.postimg.org/msvnr9dcb/IMG_0499.jpg&#8217; border=’0′ alt=’postimage’/>

Before and after!

Thanks guys, gears changed, and hydrolauc discs fitted and little man loves it!

Superstar just mailed me to say that their 24″ Crests are back in stock so if you want a proper pimp wheelset then that’s the place to go: 24″ Crest mk3 rims, Switch hubs. £290 the set and ‘wheelz’ discount code might knock more off.

First ride out on it since the upgrade, he loves it!

Looking good!

Worth all the hassle I bet?! 🙂

Not really much hassle, I had all the parts from old bikes and it took about 2 hours to sort. It was well worth it.

Ross – where did you get the Islabike wheels from?

Islabikes: I phoned up and asked for a Creig 24 wheel set.

Thanks Ross, are they much lighter than the original wheels?

I didn’t it actually weigh them! More importantly they were not covered in rust and don’t have a 7-speed hub… they’re not Stans Crest levels of light but they’re not 300 quid a pair either.

In case anyone is still reading this as they’re doing a build, another thread here has mentioned that Evans now sells the cranks that they use on the Hoy bikes:

https://www.evanscycles.com/pinnacle-hoy-bonaly-24-chainset-EV252535

What size chainring bolts did you use on the suntour cranks when you swapped to a single ring?

Swapping the cranks on my daughters 20″ Luna and going with a 32t up front.

I put a the 32t on the middle and a bash on the outside so used normal bolts. If you don’t put a bash on then you’ll need shorter bolts I expect.

Thanks Ross was it a 104 ring you used?

Yeah, Suntour XCT Jr cranks are 104BCD, so Raceface chainring and bash.

Great thread. I’m thinking a year ahead and considering starting getting together everything for a build with my son (I realise it’s utopian in my head but will end up with shouting)

These Carrera’s do seem like a really good starting point and I would aim to get it down to <11kgs. Seems like sorting the wheelsets+tyres, fork and changing it to a 1×10/11 can pretty much get there. Problem is that the costs mount so quickly – especially the wheelsets + £150 on a RST First, I don’t know if I’d be financially better off looking for a second hand Isla Creig or something!

Focusing on the wheelsets – I’m trying to search for a Alexrims MD19 supplier – seems like that’s what comes on the genesis core and weighs 390g so not too much more than the crests, might be a goer if its cheap enough. Anyone able to point me in the right direction?

I tried contacting Alex direct and had no joy what so ever – European distributor would only deal with trade.
Ended up getting a set of the Superstar Stan’s wheels in the sales.

Same story here for another set of Alex rims, so many models are trade only and you just can’t find them.

Top picks so far are Crest’s in the regular Superstar sale (assuming they actually have the stock), or Islabike Creig wheelsets (£100 for wheels, tubes, and a cassette).

The Isla ones sound like a bit of a no brainer in comparison.

Did you manage to weigh them?