It’s for my eldest, not me, so stiffness and durability is barely an issue. Is it possible to fit a square taper BB and cranks to a bike that currently has a standard HT2 external BB? It’s this Vitus:
https://www.wiggle.co.uk/vitus-nucleus-27-vrw-womens-mountain-bike
It’s on 170mm cranks now and she does have long legs for a 10 year old but far shorter than mine - and I’ve got 165mm cranks!
Looking at these:
If they do fit, which of the square taper BB versions is the right one?
Is it possible to fit a square taper BB and cranks to a bike that currently has a standard HT2 external BB?
Yes
If they do fit, which of the square taper BB versions is the right one?
Measure distance between inside of current crank arms and use that distance in conjunction with the table they provide. The bike spec doesn't specify the bb shell width so you'll have to measure that as well to see if you need a 68 or 73mm bb.
If you're dependent on front indexing, beware that may be affected by the changes you're making - BB length etc.
We've done exactly this on our Boardman CX - now running much lower gearing than the original cranks would allow.
Yes. I'm tempted to do it myself after having a couple of HT2 left cranks work loose...
I've just done this on my old Kona Caldera for my lad. Cheap 165 mm square taper cranks and narrow wide chainring.
I guessed at 113 mm BB and it more or less gives the same chainline with 135 mm quick release hub and 68 mm BB.
I think I use the Sheldon Brown page to help the guesswork but may have just confused myself and offered up a crank and ruler then guessed.
It works fine.
Square taper is far better than HT2 or GXP. Fit and forget. Wears out, just replace
There were some 135mm HT2 cranks on eBay a while ago, but road axle length - I took all the spacers out and just had enough clearance on a 32t snail NW ring on the eldests new Nukeproof Cub Scout
If you've got any clearance or chainline issues, be careful which square taper axle length you get. I've now got a collection of different ones, £10 a go, but heavy.
The hupp cranks are nice.
113mm for low profile cranks. I got 24mm axle direct mount cranks off alibaba
Forgot to add 155 or 165 square taper cranks with chainring were about £23 from AliExpress. They are fine. Plain black paint and no logos.
BB I used was a Sun Race from a UK supplier.
Edit: if you want 155 or smaller with non-replaceable chainrings for about £20.
Somewhere on the hup/kids racing site is a set of measurements for those cranks with different length BB axles. I used that to decide on the correct length when I bought a set.
so stiffness and durability is barely an issue
Durability is better on square taper BBs than HT2 and way better than GXP. if you notice any difference in stiffness that translates to speed in anyway then you are clearly more powerful than I am (very likely!).
It is not really much different weight wise either if that was a concern as although the BB is heaver the cranks are typically lighter.
The legendary longevity of Shimano sqaure tapers is long gone. If you can find a UN55 or higher thats near new it will serve you far better than the modern ones.
Square taper is far better than HT2
I used to say that, but it really depends on your intended usage. My HT2 BBs last a long time these days (correct installation, no jet washing; no tw&tting about with bogus frame facing nonsense), and they're much easier to install and remove with minimal tools. Once you've had to take off a square taper crank with an angle grinder your perspective changes.
Hmmm. This has prompted me to stockpile some UN55 in 73mm shell for my Middleburns before they disappear.
We have lots of wet rides and I'm sick of coming to HT2 bikes a week later to find seized bottom brackets with axles spinning on the inner sleeve. It might be light and stiff but it is an awful design where water tracks down the axle by capillary action (the "seals" on the back of the crank arms are useless).
Is there any weight limit on these "kids" cranks?
Lots of square taper bikes in the garage precisely because of past bearing issues with HT2 and no real appetite to try even bigger axles with smaller bearings. There's a weight penalty but I think it's worth it TBH.
Summer roady and nicer MTB still use HT2 though, and seem to have lasted OK they both see less abuse in bad weather and more maintenance...
I tend to go shopping on eBay for old Shimano cranks, they often seem to last well without costing the earth where some other brands tapers get chewed to death presumably by over tightening and/or fudged up landings. Spa seem to be the go to for new sprog's cranks, but I ended up DIY shortening a pair of LX which did the job nicely for my kids...
Added advantage is that you can fit nice silver cranks not the nasty black stuff.
I think I understand this now!
This is the BB to use because it’s a 73mm BB width:
There are two choices of width. I’ve measured the bike and the current chain line is 50-51mm as best I can measure. It currently has a 32t chainring which has very little clearance at the chainstay so I can’t go narrower on the chain line.
The inside of the cranks are about 145mm apart and there’s over 10mm clearance to the chainstay. From what I can work out crank clearance is not an issue with either BB width (118 or 123) but the chainring is closer.
It says 45mm chain line with 107mm BB, so the 118 will increase that to 50mm and the 123mm increase that to 53mm - correct?
Is there any weight limit on these “kids” cranks?
I'd be interested to know too... I've got 2 sets of 165mm HT2 cranks, removed from both my mini-a11y's Vitus Nucleus 26 bikes. Come on, 165mm cranks on a bike designed for 140-158cm heights?! I swapped them out on both for 150mm square taper cranks.
Anyway, I've ridden with the 165mm 'kids' cranks on my hardtail but only pootling around - I since changed to 170mm Deores for reassurance. They're unbranded but described as Samox 165mm Crank Arm, 32T, Double Chain Guard, Reduced Q Factor on Vitus' site. They feel solid to be but in reality I've no idea how strong they are, or indeed how strong a set of cranks needs to be for me and my riding.
I'm not sure that your estimated length as I think that the drive side gets longer faster than the non drive side. I can't find definitive dimensions but the closest is the tables on Sheldon Brown's site.
https://www.sheldonbrown.com/bbsize.html
Just in case you thought new non standard standards were coming confusing then try finding the correct old school parts!
Also ISO tapers are narrower than JIS which can alter the fitted position. It's all a bit brain melting and usually try it and see.
It’s for my eldest, not me, so stiffness and durability is barely an issue.
Totally go for it...though I always just cut down solid HT2** cranks (**axle)
In the wider perspective I just bent a set of SRAM something cranks square tapers on my jackflash... not even a particularly poor landing.
The kids racing ones are just rebadged Chinese specials, there's tons of them out there. I fitted Jet BMX 150mm cranks to my lads Ridley when I built it.
Just be careful on the Vitus regarding chain lines and crank clearance to the DS chainstay
I have done this on my kids bikes, works great until they get BIG.
As it happens, I have 2 BBs and 2 sets of 155mm 104bcd cranks about to go up on the classifieds if anyone is interested. Drop me a PM.