Plainsman

That’s my basic question. Building a training bike. Going to use outboard bearings, 68mm English B.B. Right now I have an old Truvative Elita compact crank. Might replace it down the road, but might go with an FSA Gossamer, Shimano Tiagra, or whatever compact double is cheapest at the time. If I install a GXP bottom bracket now, am I correct that it should work fine with an FSA or Shimano two piece crank, assuming they are road cranks with 24mm spindles? Thanks!

AeroGut

Short answer is no. The GXP that is 24 on the drive side reduces to 22 on the non drive side whereas Hollowtech stays 24. Here’s a good chart:https://wheelsmfg.com/crankset-tech

Plainsman

Ahhh, got it. Many thanks!

sch

I believe that Shimano and Truvative have different splines on their spindles as well.

FWIW FSA Mega EXO is their 24mm spindle standard for which Shimano BB tools work fine.
FSA Mega EVO is their 30mm spindle standard for which a special BB tool is needed as the outer diameter
of the bearing holder is larger. Also note that IME EVO spindles are not a slide fit into the BB, but
putting the crank in the freezer for ~30 minutes before install will shrink the spindle diameter enough
to make it a slide in fit in the BB. Otherwise a hammer is needed, and will be needed to knock the crank
out of the BB.

ksryder

Somewhat as an aside the FSA Mega Exo and Evo BBs are crap. They're super expensive for some reason but they get stiff and creaky after about 10 minutes.

It's been a minute since I messed with it but I'm thinking the Shimano Hollowtech BB was a straight swap? I ended up changing cranks so it became a non-issue.

Plainsman

Thanks all. Gotta love the bazillion standards! :-) I think I'm going to punt. I've got a deal on a decent square taper crankset, so JIS it is (this is me avoiding the problem ;-), plus I'm finding my BB shell face is less than ideal due to some sloppy TIG welding.

jimc101

As a contrast, have put in over 20,000 km over 3 Mega Exo BB's and found them to work just fine, no better/worse than an equivalent Shimano HT2 BB, have moved them over several different bikes, and used for long-distance, commuting and general riding with no issues Creaking is an issue I have never had, and isn't an issue mentioned a lot with any threaded BB's (pressfit is a whole nother matter).

Have found them to be expensive vs Shimano HT2 on the aftermarket, but all mine where OEM spec on different bikes, and the FSA chainrings generally gave up before the BB's, so that made sense then to change totally to Shimano, mainly as their chainrings are more durable.

TimothyH

Part of the problem with standards is not understanding what they refer to.

GPX, Hollowtech II and Mega Exo describe cranksets.

68 mm English AKA BSA describes the bottom bracket shell which is part of the frame.

The fact that a bottom bracket works with any given crankset does not tell us what bottom bracket shell (frame) it fits. Conversely, the fact that a bottom bracket fits 68 mm English threaded bottom bracket shells does not tell us what cranks it might work with.

The bottom bracket must match both the bottom bracket shell (frame) and the crankset.
- 68 mm English (BSA) for GPX cranks
- 68 mm English (BSA) for Hollowtech II cranks
- 68 mm English (BSA) for Mega Exo cranks
- and so forth

It doesn't help that companies like FSA use the "Mega Exo" to describe bottom brackets which work with their Mega Exo cranks but fit many different bottom bracket shell standards. Shimano and SRAM are no different.


-Tim-

jimc101

At the same time, for road bikes (which the question is about) if you are looking at threaded BB's only have 2 options, the uncommon 70mm Italian threaded BB, or the most common/pretty much universal 68mm BB, which takes all the above.

For the consumer, the BB is less relevant than the crank (and it's much harder to change a BB type of a bike than a crank), so having the name of the crank type being used to also describe the BB makes marketing sense, and makes it easier for the consumer to know what to ask for, as there is no industry compatibility between brands.

For FSA MegaExo this only fits threaded BB's, they have different names for other BB specs, and when you narrow it down to road BB's you only have the 2 options as I mention above, the same goes for Shimano, their road threaded BB's only come in 68mm English or 70mm Italian flavors. As in if you went to a LBS, and wanted a Shimano BB-R60, you could just ask for 'a Shimano HT2 BB for my Ultegra crank', and they should know which part to sell you, without seeing the bike.

For the OP, get the shell faced, and then get a Shimano HT2 crank/BB, don't mess with FSA (their chainrings don't last or shift as well as Shimano) and you will probably notice an increase in flex if you go to square taper.