Bicycle Mechanics - Bottom bracket/crank question

I am rebuilding an old "favorite" frame and I am trying to put my nice Ritchey triple crank on it. I need to buy a bottom bracket.

How do I know how long an axle I need?

The bb shell is 68. The only other triple I have is a 68 x 122(122.5 or 123). What do I use for guidelines? Do I just need to clear the chainstays? Does it matter what type of crank it is?

Thanks,

Blake

Rivendell says use a 120 spindle length,or a 119 to 123. I think thay are kinda whacked because the ritchey double takes a 107, and the rule of thumb for a third ring on a double crank is to add another 10mm of spindle length. I bet a shimano un52 or 72 in a 118 would work and would be my frist try. You ought to have about a minimum of 4mm of chainstay clearance.

So you are saying I just need to clear the chain stays by 4mm. What would be the drawback to using a 120 or 122?
Just the greater Q factor? or are we talking about screwing up the chain line?

I would just hate to buy a 118 and find out it is too

Thanks

Originally posted by Bikedud
So you are saying I just need to clear the chain stays by 4mm. What would be the drawback to using a 120 or 122?
Just the greater Q factor? or are we talking about screwing up the chain line?

I would just hate to buy a 118 and find out it is too

Thanks Use what ya got.That's what I do unless I know for certain. Chainline is very seldom perfect anyway and is often biased toward the big or small cogs on purpose depending on what cogs the rider may favor. I have enough choices in the junk box that I seldom have to buy anything.Nashbar was selling the un72 for $18, so it won't sink the ship.