Changing crankset

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Changing crankset

Postby r11ss » Thu Jun 13, 2013 7:26 am

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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by BNA » Thu Jun 13, 2013 9:02 am

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Re: Changing crankset

Postby Duck! » Thu Jun 13, 2013 9:02 am

Yes, as GXP & BB30 are not interchangeable. Check what you currently have and replace it with the same type.
I had a thought, but it got run over as it crossed my mind.
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Re: Changing crankset

Postby tsatra93 » Thu Jun 13, 2013 11:51 am

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

Postby Purt » Thu Jun 13, 2013 11:55 am

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.
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Re: Changing crankset

Postby tsatra93 » Thu Jun 13, 2013 12:20 pm

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

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?
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Re: Changing crankset

Postby Jesmol » Thu Jun 13, 2013 12:59 pm

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.
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Re: Changing crankset

Postby avroncotton » Sun Jun 16, 2013 9:21 pm

Can't you just change the chainrings and adjust the chain accordingly.
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Re: Changing crankset

Postby find_bruce » Sun Jun 16, 2013 10:25 pm

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.
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