Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at email@example.com. In this installment, find out how to adapt a GXP crank to PF30, BB30, and BBRight.
I have a GXP quarq crank that I’d like to use in a PFBB30 frame (Felt DA). It seems that there are a few options – SRAM makes an adapter that glues into the frame and there seems to be a variety of other adapters such as the Wheels Manufacturing adapters. I’m just looking for the absolute best option without having to buy a new crank. Is there any way I could get your insight on this? And if so, could you detail what exactly I’ll need (bearings, adapters, etc)? Thanks so much for the help! From: Bill
I prefer the SRAM BSA PF30 adapter because it is the most secure option available and it uses a bottom bracket (standard BSA GXP threaded cups) that was designed by SRAM to work ideally with their proprietary GXP spindle design. The thing to keep in mind is that the GXP spindle was conceived when there were only two very similar bottom bracket standards in use, BSA and Italian. The design really requires that the non-drive side bearing be completely fixed in the frame (i.e. no press-fit), as the crank is fastened to this bearing. This quirk is why SRAM is such a proponent of BB30 cranks and why they developed the PF30 standard, because GXP cranks do not adapt well to the bevy of press-fit bottom bracket standards that have materialized in recent years. While the BSA adapter does not fully allow this, it is the closest SRAM sanctioned option available.
What allows the SRAM adapter to work so well is that it utilizes an included wave washer and shims that takes up excess space between the spindle and the overall width of the frame’s bottom bracket shell, the adapter, and the plastic bearing cups (hereafter referred to as the “bottom bracket assembly”). Other adapters, such as those from Wheels Manufacturing, rely on bottom bracket assemblies being made to very tight tolerances.* If the bottom bracket assembly is out of tolerance and is too wide, then the bearings will have too much preload on them and will suffer from excess drag. If the bottom bracket assembly is too narrow, then the adapter or bearing on the non-drive side will move outboard until the crank spider bottoms out on the drive side bearing. In a worst case scenario where the bearing bores, cups, or bottom bracket shell diameters are out of tolerance, the crank will move side-to-side inside the frame rather than finding a resting place as described in the previous sentence. Of course the BSA adapter will allow a modicum of side-to-side movement, as it is relying on a wave washer which is essentially a spring after all. But most BB30 cranks rely on such a device with no rider detectable play if set up properly.
On second observation/confirmation – The Felt DA does not use a press-fit system but just standard BB30! Ahhhhh. This is so confusing. So with that said, it makes everything we’ve just talked about moot! I’m so sorry. Since it is a standard BB30, do I have any other option but to use the standard BB30 bearings and the adapter cups? And if so, again, what exactly do you recommend? Thanks and sorry again! From: Bill
In that case, you should use the new Enduro BB30 GXP adapters that we just got in. The new Enduro adapters utilize a wave washer in conjunction with a dedicated machined aluminum adapter that will press into a standard BB30 bearing to step down to the 24/22mm GXP spindle. These same Enduro adapters will work with PF30 bottom brackets as well. But I still stand by my earlier recommendation for PF30 frames because it more closely mimics the original SRAM design and places the bearings as outboard as possible for better support of the spindle. This is in spite of the fact that the BSA adaptor and standard GXP bottom bracket are slightly heavier than the Enduro option. However, if you had a PF30 frame and think you might get a BB30 frame in the near future, or just want the most versatile adapter, then I would recommend the Enduro adapter for a PF30 application because the negatives of using the Enduro adaptor on a PF30 bottom bracket are minute.
Some of our readers with BBRight frames will be interested to know that we now have GXP adaptors in stock from both Enduro and Wheels Manufacturing. You may be wondering which one I think is better? That depends on what you want. The Enduro adaptors, with their wave washer, makes for easier setup and will automatically adjust for bearing wear and take up the play that will develop. However this comes at the expense of free spinning bearings. The wave washer will slightly preload the bearings and add some bearing drag. The Wheels Manufacturing shim system lets you dial in a minimum of bearing preload, but figuring this out requires taking the cranks off and on many times during installation. Plus, this will need to be repeated when the bearings wear and play develops. So, if you are really sensitive to bearing drag and like working on your bike then the Wheels Manufacturing is the way to go. For everyone else, my pick is the Enduro kit.
*Wheels Manufacturing has addressed this issue by offering a separate shim kit for use with their BB30 & PF30 GXP adaptors.
Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.