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BB sizing Q - mid 80's Trek(2 posts)

BB sizing Q - mid 80's TrekSenorPedro
Oct 22, 2003 7:34 PM
Hello all,

I have a mid 80's Trek road bike that I bought used and have done a healthy amount of upgrading to. Having put quite a few miles on this bike in the past years the B.B. decided to implode today. It feels like there is a bunch of gravel spinning around while I pedal and the spindle appears to be loose (small amount of play when grasping the pedals and rocking them)in the shell.

Definitely time for a new one, plus I have been running this older bb with Tiagra cranks and the left side taper doesn't allow for the crankarm to come inboard as far as it should, creating a screwed-up Q factor.

I am just wondering what length spindle I should get, I am fairly sure it is a 63mm shell. If it helps at all, the bike originally had Shimano Exage Sport cranks and is/was running a Tiagra double.

Thanks in advance,

re: BB sizing Q - mid 80's TrekFredrico
Oct 28, 2003 12:47 PM
BB shells on road bikes in the late Eighties were either 68mm wide, the English standard, or 70mm wide, which only the Italians spec'd. The English has reverse threads on the chainring side "fixed" cup, the Italians normal threads.

I would measure the existing bb spindle, and subtract as many mm's as possible to get the narrowest Q. The crankarms must clear the chainstays. Measure from the outside edges of the flats. Go to the LBS and get the closest or nearest larger size.

BB spindles are most frequently longer on the chainring side than on the left. Could the existing one be reversed, and is that why the left side sticks out further than the right?