BB spindle lengths

[mountainz]

I have a splined Shimano crankset that uses a 68x110mm bb. The crankset that I'm switching to takes a square taper bb.
Would the spindle length remain the same? Perhaps there's a dimensional dissimilarity between the 2 cranks and this isn't an easy question to answer.

 

[alfeng]

Not necessarily ...

There really wasn't any standard, IMO, with square tapered BBs & cranks ... that was both a good-and-bad thing.

You need to match the BB length to the Q-factor which you want to achieve ...

SOME square taper cranks use BBs whose spindle is symmetrical and some which are asymmetrical.

BTW. I presume your splined Shimano BB spindle is 109.5mm & that you therefore have an XTR crankset.

• You can replace the spider with one which uses either a "standard" 104BCD or 110BCD or (if you are good at ferreting) one which uses a 130BCD and thereby get away from the obsolete 112BCD chainring size.

BTW2. WHY are you switching to a square taper BB instead of opting for an external Hollowtech II BB?

Are you riding through conditions which are THAT WET & MUDDY or is there another reason?

 

[mountainz]

I want to switch over to a compact for some serious hill climbs. I don't have the $ for a high end crankset & bb.

 

[mountainz]

Thanks for the info. I want to maintain the same Q-factor, I'll probably take the bike down to the Bike Church co-op and dig through the bb bin and find a 68 x 110 and fit it up with the crank. Btw I tried to switch to triple crankset on a mtb years ago, but the new crankarms hit the chainstays, so I'm mindful of incompatibility problems.

 

[alfeng]

Originally Posted by mountainz .

Thanks for the info. I want to maintain the same Q-factor, I'll probably take the bike down to the Bike Church co-op and dig through the bb bin and find a 68 x 110 and fit it up with the crank. Btw I tried to switch to triple crankset on a mtb years ago, but the new crankarms hit the chainstays, so I'm mindful of incompatibility problems.

If you have a possible source of components, then you should take advantage of it.

BTW. Is the crankset for a Road bike or for a MTB?

Do you already have the crankset & are simply trying to mate it to an appropriate BB?

If not, then I think that you should be able to buy a "compact" FSA MegaExo Crankset + BB cups for under $75 on eBay. You can possibly end up paying less. You can definitely pay more, too.

 

[mountainz]

It'a road bike. I already have the compact crank and just need a bottom bracket that will fit. I've seen the FSA crankset on Ebay. The crank that's on the bike (a cool old Kestrel) is Dura Ace which I'll keep to switch back. Thanks for the info