STS and front mech problem

Im trying to fit a front mech to my GT STS but for some reason when in the smallest chainring it rubs on the bottom of the cage. If I lower it, then it doesnt rub, but them it wont shift into the biggest chainring, because it will hit the big chainring.

My only thought is the suspension shock needs to be screwed down further to raise the chainline? Ive check the distance between the bolts on the shock and compared them to a LTS DS I have and they are the same, so it cant be that.

You help is much needed?

Re: STS and front problem

there should be a chainstay angle stamped on the back of the front mech cage?

Have you set up the rear mech yet, it's not in the photos? You shouldn't be using the smallest few cogs in the inner ring anyway, so set it up so that the big ring works then adjust to make sure the four biggest sprockets work in the inner ring. When you apply pressure to the pedals it will also raise the chain height slightly. Rear shock shouldn't make a difference, I've never needed to adjust the front mech after shock changes.

I think you might need a different front mech, there are differences between top/bottom swing and also clamp location. Get the right one and your problem should be solved (imho).

ishaw":3sf6fxmw said:

I think you might need a different front mech, there are differences between top/bottom swing and also clamp location. Get the right one and your problem should be solved (imho).

Click to expand...

The front mech I'm trying to fit is an XT one, and that was fitted to a 1999 LTS-1000 DS no problem at all. The chain is slightly too long i know, so need to shorten it by a couple of links. i could seek a larger chainset I suppose.

Ah, yes, i had a similar issue with a pro~flex. it's generally down to mech vs chainset(compact vs mtb) full sus seems to amplify the problem. i was trying to mate a LX567 with 4 arm stx-rc. same issue, the cage fouled or failed to shift proper due to mounting point that was good for one ring but not the other. despite the suggested chainstay angle on the mech, i just tried two or three until all worked ok .

good luck.

Re: STS and front problem

gtRTSdh":3go0zae4 said:

there should be a chainstay angle stamped on the back of the front mech cage?

Click to expand...

What does your mech say?

The height of the front mech should be set so that when the cage passes over the big ring, it misses the top of the big ring teeth by a small ammount, I go for 1mm.

How does yours compare?

"The height of the front mech should be set so that when the cage passes over the big ring, it misses the top of the big ring teeth by a small ammount, I go for 1mm."

I think that can go quite a bit higher than even the standard 2-3mm clearance, BUT the one here looks as if a bit extreme. Will the mech drop any further?

Does the bolt on front mech cylinder fit in more than one position to alter the angle?

I had this issue when i set up my LTS. in the small ring wiht no rider onbaord the suspension is fully extended and the chain will rub even about halfway down the block.

Set the front mech so it shifts from the middle ring to big ring cleanly and clears the big ring with 1 - 2 mm of normal clearance. Trim the chain to length - big cog and big ring plus one link, you will need to do this with the suspension fully extended and also fully compressed (though the LTS/STS design does mean there is not very much change in the length)

then set the suspension so you get a half an inch to an inch of sag (at the wheel - yes its not easy to measure. it was easier as i had an air shock so settled for 10 -12 mm of sag on a 40 mm stroke)- your personal preference reference there.

It should now work and the chain should clear the cage in all but the smallest 2 or3- which you would not use in the small ring usually.