apache wrote:
Thanks for the info. I am leaning towards the Force 22 crankset. I am trying to minimize the Q Factor distance while maximizing the U factor clearance (another darn term to add to our cycling lexicon). One of the things that I don't understand are the aftermarket conversion BBs that have external bearings and q factor. How are these designs not increasing Q factor distance??
I have a 10 speed system on my Cervelo. Based off some reading that I've done, I am assuming that there should be no issues running a 10 speed chain on a crank designed for a 11 speed chain, right? :-)
Thanks!
G
Somebody at SRAM needs to be kicked in the head for making bottom bracket naming even more confusing. They say BB30 to refer to ANYTHING with a 30mm diameter spindle with no reference to the width of the spindle. The actual width of the crank (We could also call it Q factor here) doesn't change between BB30 or GXP. It doesn't change because the bottom bracket it goes through doesn't make the crank any more narrow or wider. The crank just is what it is as far as width, but there's several ways to attach it to a bike.
Their RED (except the Quarq RED) has a 30mm diameter spindle and a 68mm width. A true BB30 or PF30 (essentially the same thing, but one is bearings sitting in cups inside a frame and the other is bearings sitting directly in the frame) is 68mm wide on a road bike or 73mm wide on a mountain bike. CX/gravel bikes use road specs of 68mm. That means a true BB30 crank would have ~68mm of spindle showing if you had it assembled outside of a bike. GXP and BSA usually mean that you thread some bearings into a frame. The frame itself was 68mm (or 73mm for mountain bikes) and then the bearings you thread in add a little width to each side for a final number in the 86-92mm range. Your Rotor 3D+ crank assembled should show about 86.5mm of spindle. A Shimano crank spindle is also about 85.5mm, but only 24mm in diameter. Same thing with GXP. A true SRAM Red BB30 crank assembled would show ~68mm of spindle. A SRAM Force BB30 crank would show ~86.5mm of spindle when assembled.....because it's not actually a BB30, it's a BB386EVO (also called BB386 for short). Something with an 86.5mm spindle fits the 79mm wide BBRight no problem. A 68mm spindle would never fit. SRAM is really making things a pain by calling both their 68mm wide cranks and 86mm wide cranks BB30 or PF30. Sure, they'll fit a BB30 or PF30 bottom bracket with some spacers added, but so does a BB386EVO crank. BB386 is what BB30/PF30 and PF86/92
should have been
10 speed chain on 11 speed rings is just fine. Most cranks and chainrings don't have any actual different between 10 and 11 speed chainrings.
The bottom bracket has nothing to do with the crank q factor and u factor (never heard that before). It's all about the crank. Then seeing if you can fit that crank to your bike!
In theory, a BB30/PF30 crank should have a more curved crankarm to provide more ankle/heel clearance.