Bottom bracket replacement on CGR

joncomelately

Hi folks

I have a Ribble CGR (68mm BB shell) and want to replace the GXP crankset I've got (as it keeps falling apart and the BB is rubbish).
Want to stick with a 1x set up, so looking at a GRX600 crankset. I don't think this will alter the chainline particularly, but I'm a little confused over the best BB cups to go for. Of the hollowtech II, I was looking at the Ultegra or the Deore, but I'm not clear if either of them are better suited to the shell (does Deore work better with 73mm?) or crankset and whether I'd need spacers.

I'd appreciate any advice, or ideas for alternatives that are not much more expensive. It's on a commuter which will not be lovingly treated so hardy components would be good.

Thanks in advance, happy Friday.

Munsford0

I'd suggest Ultegra because it will come with the correct size central plastic tube for a 68mm BB shell.

Deore says it's suitable for both 68 and 73, but I can't find out if it's supplied with the two different inner tubes that would require. Wiggle description suggests only one, for MTB width shells.
I do know Shimano's MTB BBs have a longer threaded portion than their road equivalents, so you cannot use an old road BB tube as it's too long.

If your BB shell has sufficient thread you could fit the Deore BB cups without any central plastic tube, but then the bearings would be more susceptible to contamination from any water making its way down the seat-tube into the BB shell. (That plastic tube with its sealing rings is there for a reason) Not a good idea I'd have thought for a commuter...

wilberforce

If a BB is stated as suitable for both 68 & 73mm shells then it is supplied with one tube and you then use the supplied spacers to fit (3 x spacers for a 68mm shell, 1 x spacer for 73mm shell).

Munsford0

I'm thinking 3 spacers would then mean the cups are too far apart for a road chainset, but maybe the GRX has a longer spindle?

Munsford0

Or is the outboard portion of the MTB cups thinner than that of the road ones, so spacers result in the same overall width?

Googling suggests GRX has a spindle that's the same as road chainsets. Seen it fitted with road BBs on 68mm shells

edward.s

My GRX 600 chainset runs in a 68mm Ultegra BB just fine.

me-109

Generally the tube only has a shoulder on one end to press against the first fixed cup. The other end is able to slot inside the second cup to whatever depth it needs.

joncomelately

Thanks all. Sounds like Ultegra cups are the most likely for minimum fuss, will go for that