Bicycle Mechanics - Tuning adjustments Please Help!

I am new to the road bike thing. (was a runner but lost all the cartledge in on of my knees!)

Just bought a used trek 2300 with simano ultegra components................

trying to tune up the bike (i firmly believe to do it right do it yourself!) and having the following problems..

I have a double crankset with a 9 speed sprocket.............

When I am (forgive me I dont know the correct terms here!) on the small crank up front and either of the two lowest cranks on the back my chain rubs up against the side of the front big crankset.

My rear tire seems to be aligned correctly and I just cant figure out how to properly adjust this.

Any suggestions or tips?

No need to adjust your bike... this is called "crosschaining"... it's perfectly normal, although you don't want to do it. It tends to be more of a problem with triple chainrings, but it happens with doubles too.

The reason you want to avoid it should be obvious... it causes wear on the chain. The extreme angle on the cassette and chainring can cause damage. Unfortunately, there's nothing you can do to adjust it, you have to avoid using those gear combinations. If you experiment a little, you'll find similiar gear ratios without the crosschaining. It's important to try and keep the chain coming off the chainring and cassette reasonably straight... some angle is unavoidable in certain gear combos. But some gear combos just cause too much angle and will rub.

Is it only damaging where it's rubbing or is the cassette and cogs getting damaged as well? On my mtb my highest gear is usually not high enough for the speed I ride at, subsequently it's always almost on this gear.

I am new to the road bike thing. (was a runner but lost all the cartledge in on of my knees!)

Just bought a used trek 2300 with simano ultegra components................

trying to tune up the bike (i firmly believe to do it right do it yourself!) and having the following problems..

I have a double crankset with a 9 speed sprocket.............

When I am (forgive me I dont know the correct terms here!) on the small crank up front and either of the two lowest cranks on the back my chain rubs up against the side of the front big crankset.

My rear tire seems to be aligned correctly and I just cant figure out how to properly adjust this.

Any suggestions or tips?


This is a common problem when using Shimano 9 speed and a frame with short chain stays. The angle of the chain line causes the chain to rub the big ring. As others have mentioned it's fairly normal, BUT, you can help the situation by shimming the bottom bracket over to the right with a spacer. Go to your LBS and ask for some bottom bracket spacers. They come in different sizes so you might want to try a couple of different sizes. I've used 1.0 mm and 1.5 mm before with good results. By moving the chainrings to the right the angle to the back is improved. No guarantee but worth the effort to try.

Ed

"Is it only damaging where it's rubbing or is the cassette and cogs getting damaged as well? On my mtb my highest gear is usually not high enough for the speed I ride at, subsequently it's always almost on this gear."

While cross chaining may result in premature wear if you ride in those combos often enough, you shouldn't be worried about riding in them occasionaly if you happen to get in those combos and it's not a good time to be shifting.

Operator - Are you saying that your hardest gear combo is not enough for the speeds you ride at? If so, you aren't cross chaining...your running a big chainring/small cog combo for your hardest to pedal gear, which isn't cross chaining. Big cog/big chainring or small chainring/small cog would be cross chaining.


-Moab

Oooh.. might have missed that. Yes I am using big ring in front small in back for hardest gear. That's okay then?

Oooh.. might have missed that. Yes I am using big ring in front small in back for hardest gear. That's okay then?

Yes... Here's a quick diagram I made that should help everyone get the idea here... Of course, I'm no engineer, so this isn't to scale and the angles aren't real... But it should help demonstrate the idea here. Remember, SOME angle is ok and unavoidable, you just want to avoid using the extreme angles for long periods of time.