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Shimano 105 39/12 rubbing(5 posts)

Shimano 105 39/12 rubbingVelocipedio
Aug 24, 2001 2:40 PM
My GF's road bike has 105 with a 12-25 cassette. When she shifts into 39/12, the chain rubs against [I'm assuming] the big chainring. Is this normal for 105? It would seem to make the 39/12 [and, to some extent, the 39/13] unusable. Is this something that should be adjusted, or is it an idiosyncracy of 105?

[I can't remember if my old bike had this problem, but I only notice it a LITTLE bit in 39/12 on Campy Daytona...]
re: Shimano 105 39/12 rubbingCliff Oates
Aug 24, 2001 3:19 PM
You should avoid the small/small and big/big combos as the chain angle is extreme and will accelerate the wear of your drivetrain components. If it rubs when you're on the second cog, you could try putting a shim between the fixed bb cup (on the drive side) and the frame to shift the chainline over a bit.
re: Shimano 105 39/12 rubbingDrD
Aug 24, 2001 3:24 PM
It's probably rubbing the front der. cage - you are pretty much cross-chained in the small-small combination - I have an Ultegra double crankset/cassette/front der, and get quite a bit of rubbing on the der. cage if I put it in the small-small (39-12) combination - don't get any rub in the 39-13, though

I avoid the small-small and big-big combinations (though I suppose only the latter is really bad)
It's normal, or at least commonKerry Irons
Aug 25, 2001 12:27 PM
If the rub is on the derailleur cage, you can adjust it out, though that may cause other shifting problems. More likely, the chain is rubbing on the inside of the big chain ring - an extremely common situation. The only way to deal with this is with a longer BB axle or by putting spacers on the right side of the BB, and either one of these approaches will put more strain on the chain line to the large cogs. Many people say that they like having a 12t cog, simply so they can use the 13 from the 39 (same gear as a 53/18). Few people would say that they can regularly use the small/small combo.
Call me retro !Steve Bailey
Aug 26, 2001 5:10 PM
Unless they get tired of the whole nonesense in some of the current Shimano (and Campy) design(s).

I went with a Heron - Rivendell designed/Waterford built frame, as it has 42.5cm chainstays - as opposed to the typical 40's. Among the advantages is the ability to use a wider selection of ring/cog combo's that don't cause as extreme a chain angle. Or chainrub on the rings.

I also ditched the STI triple system for bar-cons that allow some real trim of the front derailer.

The system is a 26/38/52 ring setup and and a custom (you can't do this with high-end 9) - 8 speed - 12-14-15-16-17-18-19-21.

I can now use up to the 26/14 combo, the 52/18 combo and 6 of 8 cogs with the middle. 19 useful gears.

Try that with STI 9 speed systems !.

SB

>Many people say that they like having a 12t cog, simply so they can >use the 13 from the 39 (same gear as a 53/18). Few people would say >that they can regularly use the small/small combo