Apex crankset fitted, Alignment needed?

carl1983

Hi, I have just fitted an Apex gxp compact crank to my Trek 1.5 which has a 9 speed rear cassette, Tiagra gs rear derailleur and tiagra tripple shifters. I am really struggling to align the chain as I thought I had set up the front derailleur (Sram force) to shift between the 2 chainrings without to much issue but when in the smaller chainring on the front and shift to the smalller cog on the rear my chain rubs against the larger chainring on the front not the front derailleur! How do I prevent this??
The bottom bracket is a gxp and came with no spacers, I assume there is some alignment issue with the crankset though? I have heard it's ok to use a 9 speed setup with 10 speed crankset so that can't be my issue!

Monty Dog

You can't - it's a function of short chainstays, big difference in chainring sizes and a wide cassette. It's also known as cross-chaining and leads to accelerated chain wear

carl1983

Monty Dog wrote:

You can't - it's a function of short chainstays, big difference in chainring sizes and a wide cassette. It's also known as cross-chaining and leads to accelerated chain wear

Is it normal to be doing this from 3 cogs up though? as I have just descovered this is the case it's rubbing all the last 3 cogs! Also shifting up and down feels very harsh like the chain is straining or to tight but length is fine, it shifts to each gear ok just clunks loudly as it does.

paulbnix

I had a similar issue with an FSA MegaExo chainset when I replaced the BB with a Hollowtech 2.
When the chain was on the small chain ring at the front it would catch on the large chain ring when on the smallest cassette sprocket - it may of caught on the next smallest as well I can't remember.
I ended up getting 2 x 1mm spacers and placing then inboard of the HT2 cups. That sorted the problem.