Chain rubbing with middle chainring

PaddyG68

Hi all,
I recently purchased a Cannondale CAAD8 7 Sora online from www.biker-boarder.de in Germany (my first road bike). It's a great bike but I have a minor issue with the gears. When on the middle chainring, the chain rubs on the front derailleur at higher gears. If I lossen the cable tension using the barrel adjuster, it partially solves the problem, but then it rubs on the derailleur at lower gears instead. I'm pretty much a bike maintenance novice, so what would be my next step; do I fiddle with the derailleur adjustment screws?
Many thanks.

kajjal

That's not unusual on a triple unless you spend a lot of time fiddling. The easy solution is to work out which gears you use the most in the middle chainring and set it up so those don't rub.

ElectronShepherd

Does the front shifter have a trim function? You may be able to move the left-hand lever slightly to the right and get a click, and find it moves the front derailleur enough to stop the chain rub.

PaddyG68

ElectronShepherd wrote:

Does the front shifter have a trim function? You may be able to move the left-hand lever slightly to the right and get a click, and find it moves the front derailleur enough to stop the chain rub.

That's a possibility; I do have to shift the left lever 2 clicks to drop it down to the middle chain ring. I wasn't sure why at the time, but maybe that's it.

PaddyG68

I read in another forum that newer Shimano Sora's will only trim from the small to the middle chainring, not the other way round (which is where my problem lies). Is that correct? If so, should I just loosen the cable enough to stop the rubbing on the outer plate and trim to avoid rubbing on the inner plate?

I can partially avoid it by changing up to the large chainring whilst still on the middle cogs at the rear, where circumstances allow, and then go up through the gears, and vice versa on the way down.

rafletcher

Kajjal wrote:

That's not unusual on a triple unless you spend a lot of time fiddling. The easy solution is to work out which gears you use the most in the middle chainring and set it up so those don't rub.

Well yes.. and no. What WILL happen is that with a triple you'll typically (even with trimming) only be able to use say 7 out of 10 sprockets with any one chainring. So, 1-8 on the big ring 2 - 9 on the middle and 3-10 on the small )assuming 1 is the smallest sprocket.) Only (AFAIK) SRAM with their "yawing" front mechs avoid this. It's just the way it is, and you'll just have to remember to get onto the big chainring if you want to use the higher gears.

PaddyG68

rafletcher wrote:

Kajjal wrote:

That's not unusual on a triple unless you spend a lot of time fiddling. The easy solution is to work out which gears you use the most in the middle chainring and set it up so those don't rub.

Well yes.. and no. What WILL happen is that with a triple you'll typically (even with trimming) only be able to use say 7 out of 10 sprockets with any one chainring. So, 1-8 on the big ring 2 - 9 on the middle and 3-10 on the small )assuming 1 is the smallest sprocket.) Only (AFAIK) SRAM with their "yawing" front mechs avoid this. It's just the way it is, and you'll just have to remember to get onto the big chainring if you want to use the higher gears.

If the cable barrel adjustment is tight enough to avoid rubbing on the inner plate and I follow you numbering method, I can currently only use 1-5/6 on the middle chainring without significant noise.

ElectronShepherd

The other thing to check is that the front derailleur is at the right height and more importantly is parallel to the chain when the chain is on the middle ring at the front and middle cog at the rear. It's quite common for the front derailleur to rotate around the seat tube (it only takes a small knock) - assuming it's a band-on type.

rafletcher

PaddyG68 wrote:

rafletcher wrote:

Kajjal wrote:

That's not unusual on a triple unless you spend a lot of time fiddling. The easy solution is to work out which gears you use the most in the middle chainring and set it up so those don't rub.

Well yes.. and no. What WILL happen is that with a triple you'll typically (even with trimming) only be able to use say 7 out of 10 sprockets with any one chainring. So, 1-8 on the big ring 2 - 9 on the middle and 3-10 on the small )assuming 1 is the smallest sprocket.) Only (AFAIK) SRAM with their "yawing" front mechs avoid this. It's just the way it is, and you'll just have to remember to get onto the big chainring if you want to use the higher gears.

If the cable barrel adjustment is tight enough to avoid rubbing on the inner plate and I follow you numbering method, I can currently only use 1-5/6 on the middle chainring without significant noise.

Then I'd suggest you set it up from scratch using the instructions you can download from the Shimano tech docs - I wouldn't have expected you to be able to use the smallest sprocket (11T or 12T) without rubbing whilst on the middle chainring. Similarly when in the largest chainring I'd expect rubbing on the two largest sprockets.

keef66

With my 5600 105 triple I can get it to run without any rubbing in all combinations of chainring and sprocket by using the trim function.

This is of no help to you however.

PaddyG68

Dear all, it seems that the trim function eliminates the vast majority of the rubbing; I can llive with that for now. Thanks for the input.