jbtute

So I'm due for new BB bearings/races. I'm also looking for some different gearing. So... I figured I'd just go for a full new BB and crank set. What I'm struggling with is that BB's come in a handful of lengths on the crank spindle. I'm not sure how to measure that. It appears the distance between the inside faces of the cranks is in the range that they are sold in, but I'm not sure if that's what they are actually measuring.

Can anyone help me out on this one?

Thanks!

JohnDThompson 

Well then, what do you currently have?

Be as specific as you can...

jbtute

Current bike is a 1970ish Windsor road bike - model unknown.
The spindle now is about 140mm end to end and roughly 98mm inside face to inside face. Square taper.

The spindles I've been looking at seem to be in the 110mm range. This isn't close to either measurement.

I don't much care whether I stay square taper or one of the splined options.

reddog3

The answer is in the crank design. A lot of the early cranks were made with the spindle interface on plane with the chainring spider. If you lay it flat on the bench the spiders will touch or be very close.

On newer cranks the spindle interface stands a bit proud of the spider. Place it flat on the bench and the spider will clear by a lot more.

Try to put an old crank on a shorter BB spindle and there are clearance issues at the chainstay. That's why the spindles are so much longer. Put a newer crank on the old (long) spindle and it sticks way out the, causing a chainline issue.

You'd probably be very safe selecting the recommended spindle length for the crankset you're considering.

CACycling

Spindle length is measured end to end on the spindle excluding the threaded parts if it is a nutted spindle. As reddog3 noted, spindle length is primarily determined by the crankset.

jbtute

Ok. So if I understand this correctly, If I buy a new BB crankset combo that are sold as a package, I should be good to go? I understand there may be a +- 2mm chainline variation between options, but I think I should be ok with that.

What I shouldn't do is put a new crank on the original BB as it would end up with the chain line being way out of whack.

Many of them I see offered with two spindle lengths. like 108mm and 113mm. It seems like either would probably be OK.

Ex Pres 

Sometimes if they are showing 2 lengths the shorter one is for a double crankset, the longer for the triple version. Be sure you know what you're looking at.

zukahn1 

If it is an old Windsor be sure and check the bottom brackett type some of these where made with Italian style bottom bracketts as opposed to the english standard bottom brackets that come with most crank groups. If your not sure I would have someone at your LBS take a quick look at it before you start buying ordering parts.

jbtute

I'll make sure to double check. I actually have two bikes, but I was going to get the Windsor set up first. One is a windsor, the other is a Centurion. I have a 2000ish Trek 4300 MTB with a triple that is in good shape, so I might strip that one down first and see how it fits. I would also be able to check the BB sizing and see if it fits.

jbtute

So I bought a new BB and crank. Worked great. The key is to look at the spec sheet for the crank set. So long as the BB threads are correct, the crank is what matters NOT the bike or the original BB spindle. It's only logical that this would be the case as the BB on the bike centers the spindle. Therefore the position of the crank in relation to center line of the bike is independent of the bike design and the rear wheel should always be centered on the centerline of the bike, so the chain line is also independent of frame design, but rather solely a function of crank set, spindle length and cassette.

So the point is, the bike design has no effect on spindle length and the original spindle length is meaningless. The only important measurement from the frame is the BB thread size and pitch.

Ex Pres 

congrats