Which BB length for Ritchey Logic cranks?

[d_douglas]

I am using a Ritchey Logic 110mm triple crank on my disc CX commuter with a 38t Raceface NW ring. The ring is in the middle position and a chainguard is in the outer position. I needed to buy a new BB and went with advice of experienced shop to use standard JIS 113mm, but when I installed, there is maybe 9-10mm gap between crankarm and chainstay - too much.

This would mean that the chainline would be weird as well, as I eyeballed the ring lining up with the third cog on a Campy 10spd cassette.

Aside from trial and error (which the shop is willing to let me do) is there a formula to get the right chainline for this? If a 113mm was too wide, I would think a 103mm would work (10mm narrow, split between sides means 5mm closer to chainstay for the crankarms) That said, it seems extreme to put a 103mm BB on here.

I am just buying a UN55, so nothing fancy and the shop said I waswelcome to just exchange it for another last night when I bought it, so it is more a matter of expediency, as I don't want to go to 110mm / 107mm, then 103mm if I can avoid it.

Thanks for information, if you have any!!

[donevwil]

The 110mm triples were identical to the doubles with aluminum bosses added to permit the blind holes for the third ring. The spec for the doubles called for a 108mm bb and I still run a triple as a double with a 108. How that will play with your SS chainline is a completely separate issue IMO, more a function of the hub and freewheels/cog. A road chainline is (or at least was) defined as the midpoint between the chainrings so a SS/fixed using either the inner or outer will more than likely require corresponding compensation in spindle width.

[Kontact]

Measure the chainline of the middle ring, not the crank arm clearance. The middle ring on a road triple should be 45mm from the center of the seat tube if you have a 68mm English BB shell.

It isn't going to be 103mm. It might be 113, but you won't know until you measure chainline.

[PacNW2Ford]

Yes, chainline is what’s important here. If you’re using a 135/142 rear hub, I would shoot for the old 47mm MTB chainline measured to the “middle” ring. I wouldn’t worry about the space between the arm and chainstay, 9mm is not excessive considering the Ritchey arms are likely thinner than modern arms.

[d_douglas]

This is good to know. So erring on the extreme side might be unnecessary. On my way home, I will grab a 107mm type BB and that should be adequate.

Thanks,

Darren

[Kontact]

I'll bet 107 is too small.

[gdw]

Worthless trivia...maybe. Bridgestone used a 120mm bottom bracket with that crankset on the MB1 in the early 1990's when their bikes ran 130mm hubs.

[PacNW2Ford]

Not worthless, 120mm was the standard spec for the Ritchey mountain triple. I think this resulted in the old MTB chainline of 47-48mm. This is why we think going narrower to minimize crank arm clearance is going to move the crank too far in. But, if the OP runs in the big cogs more, might not be a bad thing.

Years ago, I ran the Ritchey mountain triple on a Klein Performance as both a triple and a double with various spindles from 114 to 119.