Australian Cycling Forums - Bicycles Network Australia

Hi,

I would like to change my Sram red 53-39 for a 50-34. Do I need to worry about which bottom bracket (GXP/BB30) cranks to buy?

Thanks


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Yes, as GXP & BB30 are not interchangeable. Check what you currently have and replace it with the same type.

Do you need to take off the cranks to see which BB you have? Or does it say it somewhere?

Duck! wrote:Yes, as GXP & BB30 are not interchangeable. Check what you currently have and replace it with the same type.

If you have BB30 you can buy an adapter to fit GXP. Not the other way round though.

tsatra93 wrote:Do you need to take off the cranks to see which BB you have? Or does it say it somewhere?

It usually won't say on the cranks. It might say something on the BB area on the frame. Could just google your bike model.

Purt wrote:

tsatra93 wrote:Do you need to take off the cranks to see which BB you have? Or does it say it somewhere?

It usually won't say on the cranks. It might say something on the BB area on the frame. Could just google your bike model.

Problem is the bike is 2nd hand with upgraded parts... Looked at the BB area and apparently I have this in it:

http://tbsm.com.au/bike-parts/drivetrai ... cups-15381" onclick="window.open(this.href);return false;

I have no idea about bike parts....but what is that? Ceramic cups? is it the bottom bracket? or just he red things at the end?

Ummmm , they dont fit SRAM cranks (at least not GXP ones).

You could probably check roughly by measuring the Internal Diameter of the tube running through the cranks, GXP Std is a 24mm OD tube, BB30 is a 30mm OD tube. Not sure what the ID is, but would be under 20mm for the GXP version.

Can't you just change the chainrings and adjust the chain accordingly.

avroncotton wrote:Can't you just change the chainrings and adjust the chain accordingly.

Sadly no - the 53/39 will have a bolt circle diameter (bcd) of 130 mm while a 50/34 will have a bcd of 110 mm.