Chain fouling large chainring

[Stange]

Morning all, firstly, I've done a search and can't find the answer, so:

I've got a 2009 spec Trek 1.5 (the green one) with a 50/34 on the front (Tiagra front, Sora rear) and when I'm on the small front ring and the smallest 3 rear gears the chain rubs against the large ring. Is it out of alignment or something? No amount of fettling by me seems to be able to cure this.

I've put up with it until now but a super smooth Cervelo went passed me this morning as quiet as a summer breeze and my bike sounded like a concrete mixer!

Any advice appreciated!

 

[nigelnorris]

Sheldon Brown:

"Try to avoid the gears that make the chain cross over at an extreme angle. These "criss-cross" gears are bad for the chain and sprockets. Especially bad is to combine the inside (small) front sprocket with the outside (small) rear sprocket. This noisy, inefficient gear causes the chain to wear out prematurely."

Those articles about which gears to use usually have a diagram showing how thw chain crossing from big to big or small to small either fouls the chainrings or falls off into your rear wheel. But I can't remember the correct term used to describe the front to rear chain alignment so I can't find one.

 

[Stange]

I see, thanks for that, so better to use a mid range combo....it seems that I was going for the easy option!

 

[GrasB]

I had this on my road bike, thing is I have 42/54 chainrings with a 12-21 cassette. I ended up pushing the wheel over to the non-drive side so it was off-centre in the frame but allowed me to have a reasonable crossover. This involved me having to make spacers etc to get everything right again.

 

[nigelnorris]

I had this on my road bike, thing is I have 42/54 chainrings with a 12-21 cassette. I ended up pushing the wheel over to the non-drive side so it was off-centre in the frame but allowed me to have a reasonable crossover. This involved me having to make spacers etc to get everything right again.

Doesn't that just shift the problem across so that you lose combinations from the other side?

 

[peanut]

Some Shimano shifters have what is called a 'trim' feature which is supposed to help with that problem.There should be a small lever movement (1 click) that doesn't shift the chain on the chainrings but justs moves the front mech cage away from the chain to prevent rubbing.

If it has just started making the noise I would check that everything is still properly aligned and the mechs haven't had a knock.

 

[GrasB]

Doesn't that just shift the problem across so that you lose combinations from the other side?

Yeah, I spent ages getting the minimum number of unavailable gears I ended with 7 out of 8 usable gears on both chain rings. But that frame was just weird though, I ended up getting shot of it after not much time.

 

[mickle]

Stange, is it rubbing on the big ring or on the front mech?

 

[nigelnorris]

Some Shimano shifters have what is called a 'trim' feature which is supposed to help with that problem.There should be a small lever movement (1 click) that doesn't shift the chain on the chainrings but justs moves the front mech cage away from the chain to prevent rubbing.

Ohmygosh is THAT why it does that. I thought there was a problem with mine, didn't want to ask why it did it for fear of looking stupid.

 

[Stange]

Stange, is it rubbing on the big ring or on the front mech?

Morning, it rubs on the big ring, I thought it was the mech at first, but when i eventually got around to looking at it, it's definately the ring.

 

[andrew_s]

You can't adjust out of it as it's a simple matter of geometry. A straight line between the inner ring and any of the outer 3 sprockets gets close enough to the outer ring that there isn't enough clearance for the thickness of the chain. All you can do is change parts - a bigger inner or smaller outer chainring, or a longer bottom bracket axle (if you have separate).

As nigel and sheldon said, crossover gears cause premature wear. Take the noise as a reminder that you shouldn't be using those gears, and use the 52 instead. 52 and 4/5/6 will be much the same gear as 34 and 7/8/9 anyway.

 

[BorderCollieSam]

Stange,

I joined these forums specifically to post on this thread, as was scratching my head and searching the net and found your thread!

I also have the Trek 1.5 2009.

I have had nothing but trouble with this bike since day one.

I have had several broken rear spokes, replaced bottom bracket, these i was told by the palce of purchase were excluded from the warranty, however when the wheel kept breaking, and then the gears were playing up, i emailed Trek, and was told they should have been included within the warranty, so i went to another bike shop who handled my claim from thereon, and they credited me for the bottom bracket, replaced the back wheel with a brand new one, and upgraded my Shimano Tiagra rear derailier with a new 105 derailier, and repalced the cassette and chain, and still it isn't shifting properly, and i also have the chain rub.

However, my chain run occurs when i am in the 1st, 2nd, or 3rd smallest on the rear and on the middle front chainring, the chain rubs badly on the inside of the largest chainring on the front....

It sounds terrible as you say, it sounds worse than the 80's style Raleigh racer i used to own.

I may have to get back onto Trek....

 

[jimboalee]

Stange,

I joined these forums specifically to post on this thread, as was scratching my head and searching the net and found your thread!

I also have the Trek 1.5 2009.

I have had nothing but trouble with this bike since day one.

I have had several broken rear spokes, replaced bottom bracket, these i was told by the palce of purchase were excluded from the warranty, however when the wheel kept breaking, and then the gears were playing up, i emailed Trek, and was told they should have been included, they credited me for the bottom bracket, and repalced the back wheel with a new one, and upgraded my Shimano Tiagra rear derailier with a new 105 derailier, and repalced the cassette and chain, and still it isn't shifting properly, and i also have the chain rub.

However, my chain run occurs when i am in the 1st, 2nd, or 3rd smallest on the rear and on the middle front chainring, the chain rubs badly on the inside of the largest chainring on the front....

It sounds terrible as you say, it sounds worse than the 80's style Raleigh racer i used to own.

I may have to get back onto Trek....

Now, In your HONEST opinion, is that TREK a 'good' bike or something which others round here would call a "Bicycle Shaped Object"?

 

[BorderCollieSam]

Now, In your HONEST opinion, is that TREK a 'good' bike or something which others round here would call a "Bicycle Shaped Object"?

I really like the bikes appearance, i think it looks really nice, and it rides really well and is comfortable and a pleasure to ride, however i have NEVER had a bike in my 37 years that the gears have been so much of a problem on as they have been on this bike!

I also have a GT Aggressor XCR with Deore XT groupset and that bike changes gears perfectly and never misses or rubs, and thats a Tripple chainring also.

 

[Stange]

I like my Trek, it is a good bike and not a BSO, I must be quite lucky as I haven't had wheel or bracket issues ar all, is it possible that yours was a bit of a lemon (or lime given the colour!)? Or I'm just not pushing it enough, I'm going to go out the next time it isn't raining and test out my new "anti rub method" as detailed in post #2 of this thread. I shall report back......