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Crankset & BB compatibility

Posted: 16 Dec 2016, 7:15pm
by graymee
I bought a Boardman Mountain Bike Team 29er which has a 1v11 drive train and a PF30 bottom bracket. I want to use it for a multitude of tasks and think the 34 tooth crank leaves it a bit low geared so intended to fit 34/50. I bought a SRAM Rival 22 11 Speed Chainset - BB30 BB but it doesn't fit. The crank spindle on the Rival 22 crankset is 30 mm which is what I expected but the bottom bracket is only 24 mm. Maybe I'm expecting too much by thinking both road and MTB PF30 bottom brackets would be the same size or am I missing something?

Is there a double crankset could I fit, something like 34/48 or 34/50, or am I going to have to change the bottom bracket as well?

Re: Crankset & BB compatibility

Posted: 16 Dec 2016, 8:35pm
by Valbrona
If the BB is press-fit, it could be a PF30 shell containing a PF30>24mm adapter BB. However, more likely that your BB shell is not PF30 but is instead Shimano BB86/92 press-fit standard.

PF30 is BB shell ID 46mm
Shimano BB86/92 is BB shell ID 41mm

BB86 Shimano road 86.5x41
BB92 Shimano MTB 91.5x41

PF30 road = 68x46
PF30 MTB = 73x46

Re: Crankset & BB compatibility

Posted: 16 Dec 2016, 9:17pm
by graymee
Although the Boardman and Halfords websites say the bottom bracket is BB PF30 it has notched outer shells that you would expect on a threaded bb. I think it could be FSA Mega exo.

Re: Crankset & BB compatibility

Posted: 18 Dec 2016, 11:05am
by Gattonero
34/50 on a 29er? :shock:

Anyway, like just said above, it's pretty easy to find a BB shell size by measuring the width.
If you have external cups you can just read what's etched on them! :wink:

Re: Crankset & BB compatibility

Posted: 18 Dec 2016, 3:33pm
by graymee
As I said in my 1st post I want to use my bike for a multitude of tasks and it's undergeared for some of them. It came with a 34 tooth chainring so 34/50 lets me use the same gearing as originally fitted and also have the higher gears. I'm now certain that although the Halfords and Boardman websites say it's fitted with a PF30 bottom bracket I think I may have bought an old stock model and the bottom bracket is a Mega-exo. The markings read FSA BC1.37"x24T, all I need to do is find a suitable crankset to fit.

Re: Crankset & BB compatibility

Posted: 18 Dec 2016, 4:24pm
by Gattonero
Ok, so the BB shell is a standard BSA thread.
You can fit a multitude of cranks, including some BB30 ones that would have a longer spindle, in such case the BB cups are called "BSA30"

Re: Crankset & BB compatibility

Posted: 18 Dec 2016, 6:30pm
by graymee
My problem seems to be getting a double crankset compatible with a 73 mm MTB bottom bracket that has suitable chainring sizes. A 34 tooth small chainring is what I'm after paired with a 48 or 50 tooth large chainring or something close. I bought a road compact 34/50 crankset forgetting that road bottom brackets were narrower than MTB ones and it didn't help that I bought a PF30 crankset because the websites said my bike had one. Ideally I'd like to fit a crankset that's compatible with my 24 mm internal diameter bottom bracket (FSA, Mega exo I think) but if I necessary I'll change the bottom bracket too. Anyone got any suggestions?

Re: Crankset & BB compatibility

Posted: 18 Dec 2016, 6:38pm
by Brucey
so what you are saying is that you have a 73mm shell width BSC threaded bracket?

If so I think you will be best off getting a MTB double and fitting it with different chainrings. If you did manage to fit a 'road' chainset, (and I don't see how BTW) then you would probably find that the front mech would clout the frame before you got onto the inside chainring. As it is, you may still have troubles with the bigger chainrings hitting the chainstays, even at 'MTB chainlines'.



Re: Crankset & BB compatibility

Posted: 18 Dec 2016, 9:48pm
by Gattonero
There's lots of options for "double" mtb crank arms. And with the current 1x11 trend, some good deals can be found.
I.e. a few months ago I found some RaceFace carbon for £99 (1/3 of the RRP) complete with rings. Without chainrings, you can find cranks for less than £50; then you have to fit the rings, Specialites T.A. or Stronglight do make rings in almost any size.