Double Chainline Rub

[Bug]

Before I go back to Wiggle and make a fool of myself, I just want to check with the experts here. On my compact double, I'm finding that on the small ring, on the smaller half of the rear cassette the chain is rubbing to an ever-increasing extent the large ring. Normally I'd expect this from the front mech, but there is no rubbing at all from there - just on the ring. I'd also expect it on a triple, or on a double big-big, small-small, but for half of the cassette to rub this way...?

I'll add that my previous non-compact double had none of these problems. I'm wondering if the disc brakes on the new bike are pushing the cassette further out than it would normally be?

 

[skwerl]

the cassette can't go anywhere. it has to sit in the limit of the dropouts. Possible the BB axle length is wrong.
I'm guessing it's a Focus cross bike?

 

[Bug]

It is indeed. And I'm stupido for not realising that obviously the cassette can't go further than the dropouts!! D'oh! I'm e-mail Wiggle. It's a lovely bike, but this chain rub is really annoying me!

 

[Bug]

Hmm... Although I've still written to Wiggle about it, it may not be as bad as thought... Sheldon's gear calculator shows that everything after the largest four sprockets on the small ring is duplicated on the big ring. I'll try on my commute home to alter my shift pattern to go s1 - s2 - s3 - s4 - b1 - b2 - etc..

It's a bit annoying to have to drop back four sprockets on the up change, and to go up four on the downchange, but I'll give it a go. I don't think I've ever 'properly' shifted, anyway, as I've always stayed on the small ring and only moved to the large on downhills.

It's interesting to note that there are only 14 unique gears on my 20-speed system too...

 

[skwerl]

It's interesting to note that there are only 14 unique gears on my 20-speed system too...

That's quite normal. You always get duplication of ratios.

I still wouldn't expect you to get chain contacting the outer ring until you get further down the cassette though. This is an issue with compacts given the smaller size of the inner ring but I don't know for sure what acceptable would be. I had a compact for a while in 2007 and I don't remember having the issues you're seeing