So here's my dilemma... it seems that most new frames are shipping with BB30, and my current road bike (only bike) is standard English. I want to buy a powermeter and have pretty much settled on getting the quarq s975. I know I could get the gxp version and then use adapters to fit it to any future bike that may use BB30. But, I'd rather use a BB30 crank on a BB30 bike. I know I can use a BB30 crank on my current bike using the Rotor BSA30 BB. My question is, would the q-factor be different between using a gxp quarq vs. a bb30 quarq? I'm inclined to say no since they both use external cups. But one of the hyped advantages of BB30 is the decreased Q-factor. I understand that's because the bearings are located inside the frame, but then isn't the q-factor dependent on the spindle length? Feel like I'm missing something here and not understanding the differences completely. Any help?

I am pretty sure that the Rotor adapter you mention will not allow you to use a TRUE BB30 crankset on a non BB30 frame.


A True BB30 crank does not have a spindle long enough for an external bottom bracket.

There will be no difference in Q-factor. BB30 vs. BSA doesn't really have any relation to Q-factor contrary to what many people say on the internet. Mostly Q-factor is related to chainline and how close the manufacturer wants the crank to the chain when you are in the 53/11.

With that being said, the GXP Quarq will fit on pretty much any bike but the BB30/PF30/BBRight frames will require an adapter. Likewise, the BB30 Quarq will also fit on most frames (except for Trek) when using a RotorBSA30/Zipp Vuma BB on BSA frames.

Edit: Long story short...I'd go for the BB30 Quarq if your frame is BB30 and aren't planning on riding a Trek.

I understand that it's really only the Quarq S975 and Red cranks and the Rotor 3D+ that I could use on the BSA frame with the adapter. As I'm primarily concerned with using a powermeter between my current BSA bike and a future bike that most likely will be BB30/PF30, etc., I'm okay with that. Ideally, i'd like to have a BB30 Quarq and a GXP quarq, but seeing how hard it is to convince the wife about n+1 bikes, I think I'll have to go with one or the other.



I guess my question then is whether the GXP cranks and the BB30 cranks have a different q-factor. If the S975 BB30 is designed to fit on both a BB30 frame and a GXP frame, meaning that the spindle length is great enough to fit on the GXP frame with a RotorBSA30/Zipp Vuma BB, then when using the crank on a true BB30 frame with shims, the q-factor would still be the same. But using a true BB30 crank, which would have a shorter spindle, on a BB30 frame would result in a smaller q-factor and cannot be used on a BSA frame. Correct?

Also, I've seen a lot of people complain about BB30 bearings creaking, but I haven't heard anyone complain about GXP cranks w/ adapters in BB30 frames. Would it be smarter to just go with a GXP Quarq and use GXP->BB30 adapters in a BB30 frame? With the BSA30/Zipp Vuma, I'm not using adapters, so I'd figure that would be better in either scenario. Thoughts?

The Sram BB30 Quarq crank will not work on a BSA frame, even if you use the Vuma cups. The spindle is too short.


So that pretty much settles it for you, unless you want to buy a new frame at the moment

You could get a Rotor 3DF or 3d+ crank (both of which have 30mm spindles that are longer than a normal BB30 spindle) and use it on your current frame with the Vuma cups and have quarq install a power meter spider on it for you. It's nearly the same price as the Sram unit you're looking at. The 3dF cranks are only $400. I think the Quarq spider is $1495.

That would give you a 30mm spindle that would work on anything. But the normal Sram GXP cranks will run on anything as well.

I'm pretty sure the Sram BB30 Quarq will work on a BSA frame... at least using the RotorBSA30 cups.

http://forum.slowtwitch.com/cgi-bin/gforum.cgi?post=4230451#4230451

This is wrong. The SRAM S900/S950/S975 cranks are similar to the Rotor cranks in that they have long 30mm spindles that will fit pretty much any frame.


Spindle length doesn't really matter. It's the combination of spindle length and arm offset that affects Q factor. "True" BB30 cranks like the Red Exogram cranks do have a shorter spindle but they also have a curvier arm so the Q factor ends up being the same. This does allow for more ankle clearance however, which some people will benefit from.

I've definitely heard people complain about their GXP->BB30 adapters but I never really know if that's actually the cause. 98% of the time when people complain about creaking in the BB it's their QRs or something else totally unrelated.

The Slowtwitch post is confusing BB30 with BBright.

BBRight should work with a Rotor BB30 bottom bracket. BB30 will not.

A BBRight has an 11mm longer spindle than BB30. If you buy a BB30 Quarq, it will only fit on a BB30 frame. The axle is not long enough to work with any sort of external bearing cups or a wider bb. A BBRight Quarq should fit on both, though you will need an 11mm spacer on the BB30 frameset.

When Quarq says the crankset is BB30, that means that it is compatible with BB30, but not necessarily only BB30. The SRAM S series crankset fits on pretty much any BB standard, just like Rotor. It has an extra long 30mm spindle. BB386 puts the the bearings in the same spot as an external setup, but it uses a 30mm spindle. BBRight essentially puts the non-drive side bearing where it would be for an external cup, and the drive side where a normal BB30 bearing would be. BB30 puts the bearings inside the 68mm shell.

Long story short: If any 30mm spindle crank will fit on BB386, it will fit on BBRight. Any crank that is BBRight compatible will fit on BB30. You just need to find the right spacers for your set up.

As far as I'm aware the s975 crank arms/ spindle are long enough to use on BSA. However wouldn't it just be easier if manufacturers added an extra detail line with the precise spindle length! Too much to hope for probably!

I stand corrected. I was under the assumption the 975 was a true BB30 length spindle.

You can swap the BB30 S975 between the BB30 frame and the BSA frame with the right bottom bracket. There is a spacer on the drive side for when using BB30. The downside is there's no difference in the Q factor from a bsa crank. I used a BSA S975 with BB30 adaptors for a short time and didn't care for it. May have been mental but didn't feel quite the same under heavy power transfer.

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From my recent experience, don't event consider using a S975 GXP Quarq with enduro adaptors as they creak and clunk and just do a terrible job... BB30 is by far the only option to consider here... Can't comment on Qfactor issues tho..