Will the SRAM Apex GPX bottom bracket fit the BB shell of a V1.5? I'm buying a shortened SRAM Apex crankset that requires the GPX BB for 24/22mm cranks. I currently have a Shimano SM-BB6700 BB. I was told by Mark at Bikesmith that the GPX bearing shells are narrow and conical, and would not work. He suggested Wheel MFG Threaded Road Angular Contact BB for 24/22mm cranks. It cost $129 vs $41 for GPX. The Wheel MFG site says they are a Direct Replacement for GPX BB.
SRAM APEX GPX BB
- Thread starter quinsky
- Start date
chicorider
Zen MBB Master
Mark is correct. Wheels Manufacturing bb cups are square, not tapered, and the 24/22mm bearing diameters are for SRAM GPX cranks. Shimano runs 24/24mm bearings. If it weren't for that slight difference, the two brands would be cross-compatible.
I'm just learning about bottom brackets so I'm still a bit confused. I understand that the GXP BB is for the Sram crankset with 24/22mm bearing diameters. I am planning on removing the Shimano BB and replacing it with the GXP for that reason. Are saying that the GPX BB will not fit on my bike because of the taper?
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cruzKurt
Guru
I have used standard GXP bottom bracket in both of my v20's, I don't know why it would not fit in yours also. @Robert Holler is the expert of course.
chicorider
Zen MBB Master
You have an older style of chainstay, with two bands that clamp around the bb cups. The outer shape of the bb cups needs to match the inner shape of the clamping bands. Since the bands are square, the bb cups need to be square as well so that the bands have a proper clamping surface. Wheels Manufacturing bb's have that square shape, while Sram bb's usually taper down from the inside to the outside of the bb cup. The bands would only contact the inner edges of the bb cups, which is not a lot of surface area to clamp together parts that must contend with both steering and pedaling forces.
The newer current setup, which has been around for a while, solves this issue by moving the bb clamps inward, closer to the boom. They clamp around the bb shell instead of the bb cups, meaning that you can use whatever shape bb cups you want, like any other bike.
Both my first Vendetta (a v.2 like yours) and my S30 came with this older chainstay, so I had to figure out this interface as well. One other minor issue with this older design is that you have to be careful with how much you tighten those bb clamps. You don't want them too loose, obviously, but you also don't want to tighten them enough to squeeze the bearings inside the cups, creating drag and premature bearing wear. Bb cups are not designed to have anything clamped around them, so it doesn't take much torque to start squeezing the bearings. Tighten a little, spin the crank...tighten a little more, spin the crank. Keep doing that until the crank spins a little less freely, then back the bolts up a bit at a time until the cranks spin freely once more. That's about as tight as you'll get those bolts.
The newer current setup, which has been around for a while, solves this issue by moving the bb clamps inward, closer to the boom. They clamp around the bb shell instead of the bb cups, meaning that you can use whatever shape bb cups you want, like any other bike.
Both my first Vendetta (a v.2 like yours) and my S30 came with this older chainstay, so I had to figure out this interface as well. One other minor issue with this older design is that you have to be careful with how much you tighten those bb clamps. You don't want them too loose, obviously, but you also don't want to tighten them enough to squeeze the bearings inside the cups, creating drag and premature bearing wear. Bb cups are not designed to have anything clamped around them, so it doesn't take much torque to start squeezing the bearings. Tighten a little, spin the crank...tighten a little more, spin the crank. Keep doing that until the crank spins a little less freely, then back the bolts up a bit at a time until the cranks spin freely once more. That's about as tight as you'll get those bolts.
Craig,
Thank you for that explanation. It makes sense now.
The angled bearing cups are not ideal for this, but it will work. Ideally you can source a GXP compatible BB that has flat bearing casings - I think Wheels MFG makes one.
