bottom bracket length?

[old school pete]

I have a shimano LX chainset. What length bb do I go for? The frame is 68mm. So do I go for 110mm or 113mm?

 

[hamster]

What year? What type of BB? What type of frame?

It's a bit like posting "I've just bought a bike...is it any good?"

Give us a clue! :roll:

 

[Harryburgundy]

Personally I think you can get away with quite a bit of axle length variation.
I ran 94 XT with a 107mm no worries, probably not the 'right' length.
I would bung on what you have and see if it is any good.
Carl
To be corrected very shortly no doubt

 

[kaiser]

If you have a bottom bracket to give you a size put it on and fit cranks. Then measure from the seat tube to the middle ring. This size should be between 47.5 and 50mm(47.5 for thinner seat tubes and 50 for larger). You can then adjust your axle length to suit, by doubling the difference and adding/taking away to the axle length you have. Clear as mud I'm sure :roll:

 

[old school pete]

Square taper bb. 1994 LX, if that makes things any clearer?!! I suppose its a fit it and see type thing.

I was of the understanding that its the chainset that determines the length, as opposed to the frame....probably wrong though. I was also told that there should be approx 5mm between the frame and small chainring.

 

[Anthony]

Square taper bb. 1994 LX, if that makes things any clearer?!! I suppose its a fit it and see type thing.
I was of the understanding that its the chainset that determines the length, as opposed to the frame....probably wrong though. I was also told that there should be approx 5mm between the frame and small chainring.

It's your chainstay you need to worry about. I have a 97 XT chainset on a 68/110.5 BB (as recommended) on my 97 Kilauea and the RH crank misses the chainstay by less than 2mm, so a 68/107 would be dodgy. In theory a 68/113 would affect the chainline, but since the difference is 1.25mm per side and the chain shifts about by more than that every time you change gear I don't believe it would cause any problem at all.

Some chainsets are designed completely differently though, and that's why you need bb axles anywhere up to 127mm for some of them.

I've never used 94 LX though, so can't help on that.