Crankset & BB compatibility

For discussions about bikes and equipment.
graymee
Posts: 395
Joined: 13 Jan 2007, 10:11pm
Location: Witham St Hughs, Lincoln
Contact:

Crankset & BB compatibility

Postby graymee » 16 Dec 2016, 7:15pm

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?
I'm not old and cynical, I'm realistic!

Valbrona
Posts: 2208
Joined: 7 Feb 2011, 4:49pm

Re: Crankset & BB compatibility

Postby Valbrona » 16 Dec 2016, 8:35pm

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
I should coco.

graymee
Posts: 395
Joined: 13 Jan 2007, 10:11pm
Location: Witham St Hughs, Lincoln
Contact:

Re: Crankset & BB compatibility

Postby graymee » 16 Dec 2016, 9:17pm

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.
I'm not old and cynical, I'm realistic!

User avatar
Gattonero
Posts: 3554
Joined: 31 Jan 2016, 1:35pm
Location: London
Contact:

Re: Crankset & BB compatibility

Postby Gattonero » 18 Dec 2016, 11:05am

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:
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...

graymee
Posts: 395
Joined: 13 Jan 2007, 10:11pm
Location: Witham St Hughs, Lincoln
Contact:

Re: Crankset & BB compatibility

Postby graymee » 18 Dec 2016, 3:33pm

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.
I'm not old and cynical, I'm realistic!

User avatar
Gattonero
Posts: 3554
Joined: 31 Jan 2016, 1:35pm
Location: London
Contact:

Re: Crankset & BB compatibility

Postby Gattonero » 18 Dec 2016, 4:24pm

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"
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...

graymee
Posts: 395
Joined: 13 Jan 2007, 10:11pm
Location: Witham St Hughs, Lincoln
Contact:

Re: Crankset & BB compatibility

Postby graymee » 18 Dec 2016, 6:30pm

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?
I'm not old and cynical, I'm realistic!

Brucey
Posts: 35230
Joined: 4 Jan 2012, 6:25pm

Re: Crankset & BB compatibility

Postby Brucey » 18 Dec 2016, 6:38pm

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'.

hth

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

User avatar
Gattonero
Posts: 3554
Joined: 31 Jan 2016, 1:35pm
Location: London
Contact:

Re: Crankset & BB compatibility

Postby Gattonero » 18 Dec 2016, 9:48pm

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.
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...