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Just about to change my Aeris (mk 1.5) over to Eagle GX but need to replace the XTR BB with something GXP compatible.
Sram: Never had a Sram BB before but have seen lots of bad press about them over the years.
Hope + GXP converters: Heard that it might mess with the chainline and will be fitting a basic ISCG05 chain device "just in case".
if you go Hope then notch the shims before fitting them, so you can removed them in the future, when you need to replace the bearings.
yeah i'd already spotted that minor flaw! Do you put the notch on the inside bore where the two spacers would meet in the middle of the bearing to give something for a drift to sit against?
Have a Hope BB fitted to my bronson with the GXP adapters to allow for a SRAM single ring crank. Easy to install, no premature wear of bearings etc, hasn't altered the chain line at all, have eagle X01 fitted and can back pedal in the largest ring which apparently is 'impossible'.
Had a GXP BB on the enduro for 300miles or so now, still spinning smooth. I also have a hope bb which I've just replaced the bearings on, bought in 2009, been on many bikes, covered 3000miles or so.
Sram is a third of the price once you've factored in the spacers.
Bit of an apples and oranges comparison given cost difference. I do think a lot of the online hate on GXP is due to people not realising they preload differently to HT2 type BBs and thus install them incorrectly. That said, I avoid GXP BBs as I personally don't like them. As far as I understand, the GXP also doesn't try to be as well sealed as many other BB's and the designers expect users to remove cranks and regrease bearings after a good soaking.
Contrary to above I had a Hope BB with GXP adaptor and it was nothing but trouble - premature wear of bearings and a mystery click on each rotation. I switched to SRAM BB's and have stuck with them since - perhaps I was just unlucky? Certainly installation was carried out correctly.
I've also never had to regrease bearings on my GXP BB's and I think the stepped axle is really good in that you can't over-preload the bearings.
Do you put the notch on the inside bore where the two spacers would meet in the middle of the bearing to give something for a drift to sit against?
yup.
No notch = no way to get them out.
I'm not a fan of GXP myself, as the inability to accurately assess the preload on them (i.e. only with wavy washers) is a problem. Fans say that "but there is no preload young Skywalker, as the crank snadwiches the bearing on the NDS and floats on the driveside" which is fine when the BB is new but soon wear/play creeps in and there's no way to easily/accurately adjust this out.
I've used the GXP on road and MTB in the past, including the Sram BB units (which were a bit less than okay) and the Hope BB+shims (which were just okay), and Enduro units (which were better) but I stopped using them because once they start to creak it's difficult to adjust that out. The Shimano HT method is better in this respect.