I’m building a single speed 26er mtb with an onone inbread ss frame and have just ordered a set of middleburn rs7 uno square taper cranks and wondered if I anyone knows the ideal length of the bb spindle .ivd been told around 107-113 but that the shorter the better .anyone with this set up ?

Yes, me. I think I’m using a 113mm.

Ah ok and are using the same crank? If so what bb make ? Cheers

You want 68/113

Same here, and running a Shimano UN54?? BB.

UN54 +1

Is the UN54 a set length or do I need a certain un54 to fit that frame and crank ?

Sorry screen hasn’t updated so a un54 is 113 mm correct?

You need UN54 68mm/113mm. It’s a pretty common size, your local shop should have them. (UN54s can come in different sizes, you need the 68/113 one).

The 68mm is the bottom bracket shell width, and the 113 is the axel length.

I’ve got an 853 Inbred SS, UN54 68/113, Middleburn Uno RS7.

(EDITED to put 113 instead of 133!)

113 not 133

That’s what I sad… after the edit!

http://www.middleburn.co.uk/tech_bblength.php

113mm BB will give 50mm chainline which will suit screw-on rear hubs. If you’re using a freehub with spacers it doesn’t matter as long as you don’t pick a BB so short that the chainring snags the chainstay.

I think the current Shimano BB is a UN55.

Yeh I’m using a free hub mate but would rather have a decent bit of chain stay clearance do u think I’d get away with less than that and how can I find out before buying a bb ?

how can I find out before buying a bb ?

If you have the frame already measure out 50mm from the centreline and see where that puts the chainring. Not easy to do accurately, though!

Just get the 113mm axle and you’ll definitely be fine with a 32T UNO ring. Don’t forget you need heel clearance too, so don’t go too short – my heels rub my seatstays occasionally (Inbred running WI cranks on a 113mm BB).