_ForceD_

I just replaced my chain rings (double), chain, and cassette (7 gear). The new components are the same sizes as those I took off with the exception of the inner chainring. Instead of 52/42 combination I decided to go with a 52/38 combination. Everything is OK except when the chain is on the small ring, and small gear of the cassette, the chain rubs slightly on the inside of the large ring. I guess it's because the smaller physical size of the 38 compared to the 42 changes the angle of the chain slightly. So, I removed the rings and put very thin washers on the inside of the large ring just to move it outward. And that's enough...it doesn't rub now. Everything still fits nicely. But my concern is...is there any issue that may cause down the road?Da

justsaymint

Does your front derailer shifter have a barrell adjuster? You could either use that to put a little slack in the cable or just loosen the low limit screw a touch. But if it works it works

_ForceD_

The chain is rubbing on the inside of the large ring, not the derailleur. Adjusting the derailleur/shifter doesn't move the chain or chain ring.

Dan

BobFishell

I would be wary of stripping your chainring bolts. If they're steel, you should be OK, but I would be careful of aluminum. You could do a couple of other things. Going to a wider spindle in your BB would work, but they don't make these things in small increments. Another idea is to add a 2mm axle spacer on the drive side of the rear wheel, while removing 2mm from the non-drive side. Then you have to re-dish the wheel, of course.

As a rule, you don't ride on diagonal gears, anyway. You'll find something in the gear range you want on your big ring.

Bigbus

If the shims (washers) work, then you shouldn't have any problems down the road. Keep a check on the gear and make sure it doesn't come loose on you though. On a side note here, I hear people saying you shouldn't be cross chaining in the extreme gears anyway. Well, I disagree with that. I use all the gears on occasion and feel that if they are there, they're meant to be used and I will do whatever it takes to make sure they're all functional all the time.

HillRider

Your problem is common with two chainrings of significantly different size, particularly if the frame has short chainstays. The real solution is to not cross-chain. There is no reason to use the small-small combination as the same ratio can be found in the big chainring and one of the larger cogs.

_ForceD_

Concur with the cross chaining. Generally I try not to do it...but sometimes I do. These shims/washers just seem like the easiest way to overcome the rub. Obviously there are other ways (i.e. the rear axle driveside washer and re-dishing, wider spindle, etc.). Those just seem overly cost and/or labor intensive.

Dan

delbiker1 

The above quote is right on. Just curious, did this happen with the old chain. If not, is the new chain the same type/make as the old chain?

79pmooney

Two cautions: One - the "nut" of the chainring bolts is a sleeve that needs to extend through the inside chainring, the spindle for the crank AND it must start into the outside chainring. Adding a washer could move the chainring out so the sleeve no longer is supporting the chainring. Those little bolts are only strong enough to keep the chainrings on that sleeve. They are in no way hefty enough to prevent the chainring from sliding when you apply pressure to the chain. Those sleeves to all the work.

Second, you are increasing the risk of dropping the chain between the chainrings on a shift. If this is at the start of a hill and you push hard on the pedals, you can jam and damage both chain and chainrings. (For famous footage of jamming a chain, see Andy Schleck and the 2010(?) Tour de France.)

You can avoid the rubbing on the outer chainring by moving the entire crankset out, either with a longer BB spindle or by using a spacer for the fixed BB cup. This will make your low gear chainlines less optimal and be harder on chainlife. You can learn to live with the rub, either ignoring the sound or not using that gear. (Assuming the rub doesn't lead to chain pick-up and un-intended attempted shifts - a nuisance but rarely are there consequences beyond that nuisance. (This will slowly get better as the chain wears off the offending inside of the chainring tooth tips.) If you have the ability to "trim" the front derailleur, you can adjust the FD so the outside of the cage just rubs - a much smoother, more predictable rub than the chainring teeth and this will prevent accidental pick-up by that outside ring.

So it's a case of picking your poisons. (Or you could just go back to the bigger inside chainring. Bike will be quiet and only your legs will scream.)

I am making different but similar choices on a triple I am setting up for very rough road gravel that I will be riding with no chance to preview. Mountain climbs and I am 67 years old, I need low gears but I do not want to throw my chain on the rough stuff so I have choosen to use an FD without a deep wide cage. Chain will rub a lot on both the cage sides and the bushing on the bottom when I am in the 4 smallest cogs in back and that little inner chainring. I still have to ride it and see if it actually works. The bike is set up with a 50-38-24 X 13-28 7-speed. Different problem from yours, but again, it is about compromises. Finding a solution that does what I want with drawbacks I can live with. (In this case, I am not concerned with wear. The big ride is 6 weeks away and goes 5 days, After that I have 3 more identical derailleurs in a box! (SunTour made a lot of those AR derailleurs and they are very easy to find.)

Ben

79pmooney

Using small-small. I do it. I love to climb and I love to climb hard. When climb levels out for a brief stretch, I would much rather run small-small than "take a time out" and do a double shift, knowing I will have to do it again when the grade steepens. Yes, it cost me some money. Yes it is noisy. (But my breathing is such that I cannot hear it and other probably cannot either.) So I do my best to have bikes that can run every possible combo (in school terms) with a passing grade.

Ben

_ForceD_

Ben, good info there. Thanks. I had not considered a spacer on the driveside of the BB cartridge. I may convert to that. The washers I used really are quite thin. I had some that are about half the thickness of a credit card. Actually I thought they were going to be too thin to do what I intended. So I think the bolt/nut joint is intact.

Dan

79pmooney

You can pull off the outside chainring and look to make sure you have some shoulder showing. If too little is, go buy a set of longer crankbolts. (I'm guessing you can get them long enough for a triple using one set of bolts. Never looked for them as I have used the common 110 and 74 BCD cranksets. But I know it can be done. The old TAs did it. I put many miles on those cranksets long ago.) You might have to cut or file them. (The sleeve must be shorter than the distance of - inside of inner chainring to outside of outer chainring. If not, the bolt will not be able to squeeze everything tight as it comes up against the sleeve. Typically, the original sleeves come to roughly midway inside the outer chainring. That's why I was worried you might be spacing the chainring off the sleeve.

Ben

ThermionicScott 

Chain rub/noise in the small-small combination is expected on my bikes because I set them up to run smooth in the big-big combo.

_ForceD_

Thinking about the spacer for the BB on the drive side again... Wouldn't that cause the removable ring on the non-drive side to not seat properly? Isn't its function to act as a shim and secure the cartridge on the non-drive side?

Dan

79pmooney

You have to look at your BB. They are not all the same. Older BBs (not sealed cartridges) had a lockring on the threading of the non-drive-side cup. Sometimes there was enough thread to add a drive-side spacer, sometimes not. Some BB shells are 68 mm wide, some 70 mm. Likewise the BBs themselves.

Many cartridge BBs have non-drive-side sleeves that simply thread in until they snug up against the cartridge shell. With these, the only risk I could see is bottoming out on the threads of the BB shell. If it were close, I'd see no reason not to just file off enough of the sleeve that it threaded in far enough.

Ben