Boards Bottom Bracket expert?

fat bloke

Do we have a resident BB guru on here by any chance?

I have two bikes running Sram red 10 speed. A Cervelo R5 and (any day now) a Bowman Palace R. I'm pretty sure the Cervelo takes a press fit BB30 (but I don't know for sure). I know for certain that the Bowman takes a threaded BSA BB. Both chainsets are 53:39 and I'd like to change at least one of them to either 52:36 or 50:34

I really don't know anything about the mechanics of it. Can anything be made to fit anything? Is it just a matter of having the correct BB? Or is it all very specific and only limited and specific compatibility.

Ten speed Sram stuff is thin enough on the ground so beggars can't be choosers either.

Would a Sram red GXP chainset fit either of my frames?

triggermortis

Can you not just change the chainrings? I’m not familiar with SRAM but they can’t be that different to Shimano.
You don’t even need to remove the crank, just undo the bolts and slip the rings off.
You’ll probably have to adjust your chain length and front derailleur height slightly as well.
I know for sure that not all cranks fit any BB, so if you want to go that route it may be best to remove what you have fitted and take some measurements.
I tried to fit a Shimano crank to a Boardman I have and it wouldn’t go in fully as the original crank was stepped to have a different diameter on the axle at each end.
Changing chainrings would also be cheaper

gmacww

triggermortis wrote: »

Can you not just change the chainrings?

Unfortunately not. The outer chainring (53) can be swapped out for a 52 or 50 however the assuming the 53/39 is on a standard 130BCD (which is likely for that setup for a 53/39 on a 10 speed) then a 38T is the smallest a 130BCD will take.



What year is the cervelo? Chances are it uses BBright which is Cervelo's PF30 in which case it's got a 30mm spindle (bar that runs through the BB). This will not work with the BSA threaded as they are typically set to fit a 24mm crank although I have seen them at 30mm. Now that crank on the threaded BB could work with the PF30 but you'd need to use adapters. If they are both SRAM Red though can you give me the exact model of bike and year.

Idleater

First step is to find out what the bb shell is for a frame. There are many adapter for converting larger to smaller, say bb30 to gxp. You can also buy (say) gxp bb for a bb30 shell. The opposite is generally harder to impossible (bb30 crankset in ultegra bb for example)

Spindle of the crank set is the next measurement. If you are reusing your existing one you need the diameter (24mm/30mm etc) to get the corresponding adapter for the frame/bb.

Finally the bcd of the crankset. On shimano/sram 130 bcd, the smallest size ring is 38, you need 110 bcd for smaller.

iwillhtfu

Eye Wateringly expensive but sure you're riding a cervélo and a boutique alloy frame (well if it ever ships )among many others so I'm sure you'll find a way.

Probably more engineered than the bike frame itself.

https://www.hambini.com/product/bb30-to-shimano-racing-edition-black-bottom-bracket/

For the pauper approach I'm almost retained you can do what you want with adaptors.

fat bloke

Thanks all but I'm far too ignorant of the subject to identify an answer in any of the above.

Let me simplify my question and forget the Cervelo for the minute and just talk about the Bowman, which takes a threaded BSA BB.

If I buy a Gxp sram red chainset and this BB:

https://www.bike-components.de/en/SRAM/GXP-Bottom-Bracket-p26280/

Am I sorted?

Idleater

fat bloke wrote: »

Am I sorted?

I'd be picking the

grey-black/BSA 28.46€

option

Oh, and if you want < 38 tooth chainring, you'll need to pick the 110 bcd crankset for example https://www.bike-components.de/en/SRAM/Red-GXP-Compact-11-speed-Carbon-Crankset-p47105/

fat bloke

Idleater wrote: »

I'd be picking the

grey-black/BSA 28.46€

option
[/url]

Yeah. I mean that makes sense doesn't it? GXP chainset. GXP to BSA BB.

I still don't trust it....

Plastik

Gxp uses the BSA standard for BB shells for their thread in cups, no problem there.