Originally Posted by
bradtx
Most cartridge BBs are symmetrical and many cup and cone BBs aren't. Tread width is the distance between the L&R crank arms, sometimes referred to a Q factor. While tread width won't change, you may need to equalize the L&R spacing of the crank arms with shims on the drive side. I could've worded my previous answer better.
Brad
No worries. Discussing technical details can be difficult. I also worried that my thanks to you sounded sarcastic but it wasn't meant that way. I was just thinking ahead to the next step of figuring out what you were talking about exactly and how to proceed.
Originally Posted by
Andrew R Stewart
One factor unique to tandem BB choices is the need to have both cranks' LH rings end up pretty much the same distance from the frame (in other wards be in line with each other). So when changing out the rear Bb not only does the usual RH side need to be paid attention to but also the LH side. If the OE BB was asymmetrical then have fun finding the correct current cartridge one, for a reasonable price, that matches up. Of course there's always Phil BBs that can be had in asymmetrical and custom off sets. This also would solve any loosening up issues, what with their retaining rings being Locktighted in place. Andy
Originally Posted by
Bezalel
On a tandem stoker crankset both sides are usually made with the same casting so the BB spindle is usually symmetrical.
Andrew and Bezalel, thanks for mentioning the typical symmetry of tandem stoker BBs. I had a feeling it would be more symmetrical than a bike with chainrings only on the drive side but I really don't know how much of a factor it is for the drive side to have 3 rings and the other side to have only one. I assumed that with a standard British ISO type BB, it would just be a question of getting the old BB off and screwing in the new one.
What about any thoughts on whether to go with SKF or IRD Defiant for the tandem? I've heard these are heavier duty BBs but I just spoke with a local shop and they only carry Shimano, which the mechanic claimed wouldn't be any worse than the SKF and/or IRD Defiant but since I tour on this bike, I'd be willing to invest the extra $$$ if it will be worth it in the long run.