Bottom bracket spacers

Question

I'm installing a Sram GXP English-threaded bearing set in my 68mm bottom bracket. It is replacing a Shimano Ultegra-level HollowTech II bearing set. The crank set I'm installing is a Sram XX 42/28, replacing an XTR 44/32/22.

I would like to center my chainline on the big ring and reserve the small ring for climbing the steeps. The Shimano bearing set had three spacers (usually two on the DS and one on the NDS but I was reverse of that for derailleur reach reasons). The Sram bearings come with two spacers and the instructions say one on each side. The Shimano bearings have fewer threads on each cup so if I put both Sram spacers on one side I still have more threads available to insert into the BB than were available on the properly installed Shimano.

I asked Sram tech support about making the spacer adjustment (without referencing to the competitors set-up). I received the pat answer of non-liability "don't think outside the box with our products."

Considering the observations I've laid out, it seems reasonable to go ahead an use the two spacers on one side without worrying about stressing the bearing and/or bottom bracket, unless, for instance, the Sram cup material is of substantially inferior material. Any opinions?

Answer 1

If you know you are doing this and accept the risk there is not really any reason not to do it.

At the least you may get increased bearing wear. However, what I would be worried about is cracking the bottom bracket shell because you are moving the bearing and therefore the leverage point further outboard. That is going to increase the stress on the edge of the shell, even though the GXP cups are longer and have more threaded area than the Hollowtech units.