[peterk]

I upgraded from Sora to 105 shifters. As a result, I changed from an 8 speed cassette to a 10.

When I am in the middle front ring and the largest rear cog (27 tooth), the chain wants to jump from the middle ring into the granny. I think it is caused by a chainline issue and the maybe the fact that the 10 speed chain is not as forgiving as the 8 (I'm guessing). Technically, I guess I am cross chaining, but I would like to eliminate the problem. The rear derailleur is set up perfect; no rub anywhere.

The bike is a giant OCR 3 (small). I believe it has a 68mmx113mm square taper bb. Would dropping to a 110mm fix the issue? Cranks have plenty of room to move in before it hits the chainstays.

I should also mention that I am waiting for a new set of wheels to come. Does it make sense to wait and see if any discrepancy in the new wheel (dishing??), solves the problem?

It's been fun converting things over. It's my wife's wedding anniversary gift. Pics to come when the wheels are on.

Thanks

Pete

 

[C-40]

info...

So you're using an old 8 speed crank with a 10 speed chain and expect it to all work correctly? That might be a bit optimistic. The middle ring on a triple should measure 45-47.5mm from the center of the seat tube, depending on the brand and the exact seat tube diameter. That makes the middle ring on a triple sit nearly as far to the right as the big ring on a double (47-48mm), so I treat the middle ring like a double's big ring and never use it with the largest cog. It is considered off limits cross chaining.

If the chainline is 45mm, it's not wise to move the middle ring further to the left. I check the chainline with a precision rule. Measure from the side of the seat tube, then add half the ST diameter for the best accuracy. Moving the crank a little to the left may not hurt, but be sure the little ring will clear the chainstay and the FD can move further to the left. I've seen cases where a FD's lever arm hits the seat tube, but will not go far enough to the left to avoid chainrub in the little ring and largest cog, or it may not shift the chain onto the small ring.

 

[peterk]

Thats a great point about the front derailleur's ability to move. The middle ring/largest cog is the only problem. Everything else shifts and works great. I am just concerned about my wife cross chaining and dropping the chain. She may just have to learn to pay a bit of attention. The shifting is so much nicer than with her sora. The cheap sora derailleurs are working fine. I will swap out the rear once it wears out or I find a rippin' deal on 105/ultegra.