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Chain Rub normal?(14 posts)

Chain Rub normal?Mazinger
May 11, 2003 7:22 PM
From the small front and the two smallest in the rear the chain rubs on the derailleur. Is this normal? I know the "rule" about not using this combo, but it shouldn't rub..should it? The problem isn't as bad when the chain is on the large ring and on the large cogs in the rear.

I just switched from a triple to a double and I don't recall having this problem with the triple.

I think I've done all I can. I'm mechanically inclined, but I'm somewhat new to road bikes. I've put together a few mountain bikes and have had no problems with the derailleurs.
probably not the derailleurDougSloan
May 11, 2003 7:49 PM
The chain is probably rubbing the inside of the large chainring, not the derailleur. If it were the derailleur, you could trim it a little and make it stop. Yes, it's normal for a 39 chainring; a 42, with a 53, won't do it.

probably not the derailleurMazinger
May 12, 2003 4:59 AM
I can see it hit the derailleur. It's a 9 speed, if that matters.

The screw is turned all the way too.
probably not the derailleurmainframe
May 12, 2003 5:44 AM
If you find a regular need for the gear inches realized by the 39 ring in combo with your two smallest cogs, perhaps using the 53 ring with larger cogs determined to achieve about the same gear inch would be helpful and surely eliminate the FD rub.
probably not the derailleurMazinger
May 12, 2003 6:11 AM
Yes, I realise this. I can use the big ring combo, but I'm just curious if the chain rub is normal. This is my first experience with a double ring setup and I just want to be sure the bike is set up properly.
trim itDougSloan
May 12, 2003 6:24 AM
If you are in the small ring, then you can move the derailleur cage out slightly and stop the rub. Has nothing to do with limit screws. Just push slightly on the large lever, like half a click or even no click.

It also has to do with chainstay length......davet
May 12, 2003 6:42 AM
If your bike has short chainstays, the angle of departure for the chain is more acute and will, more often than not, result in chainrub. With longer chainstays, the angle of departure of the chain is less acute. Bikes with longer chainstays generally do not suffer chain rub.

Be aware cross-chaining imposes very large, unusual loads on the the chain, chainrings and cogs, that will lead to premature wear, and possible failure a long way from home.
You need to double checkKerry
May 12, 2003 4:43 PM
When you say "The screw is turned all the way" what do you mean? Upper and lower limit screws have nothing to do with this problem whether it is rubbing on the large ring or on the derailleur. As others have said, you should be able to trim away the noise if it is rubbing on the derailleur cage just by moving the derailleur a bit toward the shift to the big ring. If you know another cyclist who is knowledgeable about these things, I would take it to them. It sounds as though you don't understand what is really going on.
You need to double checkMazinger
May 12, 2003 7:38 PM
As far as trimming, I know what you mean. It just seems dumb that I have click back on the shifter again after just having shifted to that cog.

I'm just used to MTBs where you click once and that's it.

It may have nothing to do with my problem, but the limit screws do move the derailleur to the left or right.

Anyway, thanks for the help guys. Maybe I'll just take it to the shop and see if I'm doing something wrong.
normal or common?Chen2
May 12, 2003 9:53 AM
I don't think it's normal but it seems to be common. My 9-speed 53-39 Shimano has never had chain rub on the rings and has had only a slight derailleur rub when in 39/smallest cog. I've never needed to trim my front derailleur. The frame is a 56cm OCLV. If you think everything is set up correctly you could try a spacer on the bottom bracket or a different BB.
Can it be the chain?Mazinger
May 12, 2003 10:03 AM
I'm using a Sram chain (for 9spd). The setup is full Ultegra.

I looked again and besides the derailleur I also noticed the chain rubs the 52 ring when it's on the 39 and small cogs combo.

Are Shimano chains narrower?
Can it be the chain?jefajones
May 12, 2003 10:28 AM
I switched to the SRAM chain and noticed a bit more rubbing. I checked around on a few of the forums and found out someone had actually checked manuals and found the SRAM to be a tiny bit wider than Shimano (like 3mm I think ??). Therefore, my bike makes a little more drivetrain noise with SRAM.
Can it beChen2
May 12, 2003 2:21 PM
Is it possible that your 39 is on backwards? The "39" stamping should face toward the frame (left), the "53" or "52" should face to the right, on a Shimano crank set. If the "39" is facing right, that could be your problem.

It seems to me that there have been chain-line problems with Ultegra. Some folks have fixed this with spacers.
Not zackleycurlybike
May 14, 2003 4:58 AM
It is not a universal truth that all chainrings are nembered the same. Almost all inner rings have a recess for the shoulder of the chainring nut to fit into. If there is a recess(counterbore) then that is the side that is closest to the frame.