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Chain rub on trainer

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Chain rub on trainer

Old 10-18-14, 09:35 PM
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IntelXE
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Chain rub on trainer

Does anyone's chain rub against the front derailleur cage when they're on the big chainring and the smallest sprocket? It only happens when the right pedal is going down. I suspect that the crank or BB may be flexing excessively under load.
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Old 10-19-14, 05:47 AM
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And you have tried tuning it out?
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Old 10-19-14, 05:28 PM
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The chain is centered in the front derailleur cage when I spin the pedals by hand. When I am pedalling, the chain moves over to the right and starts rubbing the inside of the cage. If I loosen the limit screw any more, the chain will fall off the big ring. The cage is as far out as it goes. I think its the crappy Shimano R565 cranks and chainrings.

Last edited by IntelXE; 10-19-14 at 05:39 PM.
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Old 10-19-14, 09:11 PM
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Originally Posted by canam73 View Post
And you have tried tuning it out?
Works with annoying family members .... Sometimes.
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Old 10-19-14, 10:12 PM
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I had this issue recently with FSA gossamer cranks - I was getting rub in the tallest gear while riding and while in the trainer. Under load the rings would flex 1-1.5mm. I was able to fix it by re-aligning the derailleur, as it was slightly toed out.

You said the derailleur was centered - did you mean aligned?
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Old 10-19-14, 10:32 PM
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Being on a trainer is a bit different than being on the road. Under normal riding conditions the bike moves under you as you pedal rocking from side to side, especially when applying power. If it didn't you'd fall over because your center of forces on the frame is offset to one side.

However trainers hold the axle steady, and unless you change your riding style materially the frame is torques side to side, applying a twisting force to the chainstays. In the early days of trainers this was an area of concern, but it turns out bikes can handle it well enough.

However it does cause added chainstay and BB flx, so it's not that the FD is moving, but that the BB is twisting and the top of the ring moves over as a result. Either live with it, or adjust trim outboard enough to cure it, though you might want to adjust back for the road.
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Old 10-20-14, 03:40 AM
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Earbuds. Turn them up.
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Old 10-20-14, 03:54 AM
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That used to be the solution offered to me whenever I had an unusual noise in the car "Turn the radio up"

Even on the road, when standing to climb I can get a bit of flex in the chainring, often enough just to need one click on the left hand lever.
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Old 10-20-14, 05:21 AM
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May I ask what kind of trainer? What type resistance system? What type crank? What size cassette. I am a bit puzzled that you have any use for the large ring at all, much less in combination with the smallest cog. On any trainer that I have any experience with that would be a level of cycling effort that only Superman could sustain. World hour record kind of effort. On a Nashbar fluid trainer with fixed resistance I train on the 39/19-39/17 combinations. Admittedly I am a wuss. But you are talking about twice that level of output approximately. Is it possible that you have an extremely low pedal cadence. On the trainer I run a rather high cadence of ~100 rpm. I'm not saying that should be right for you. But even if you were only able to maintain 80 rpm you should still have sufficient resistance on your setup to avoid the big front/small rear combo. My fixed resistance trainer provides a tad more resistance to my bikes than actual flat road riding in calm wind conditions. If yours doesn't approximate road riding resistance, maybe that is your problem, since I doubt you ride at a near constant 35 mph that the big/small combo would generate on the road.

In a similar vein think about this. If you were pedaling smooth circles (more or less), you wouldn't have the problem. Why aren't you pedaling smooth circles? Is it because you are turning a gear that is too big. Why? Are you pedaling too slowly?

The two variables you need to check out are your cadence and the resistance of your system. One or both of them is too low. If you correct that problem, the rubbing issue will also be solved. Admittedly you may be only encountering the problem during small periods of a programmed training routine when strenuous climbing or sprinting is being simulated. I understand that. Nevertheless a slightly higher cadence under those conditions may be the solution to your problem.
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Old 10-20-14, 06:12 AM
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Originally Posted by rpenmanparker View Post
May I ask what kind of trainer? What type resistance system? What type crank? What size cassette. I am a bit puzzled that you have any use for the large ring at all, much less in combination with the smallest cog. On any trainer that I have any experience with that would be a level of cycling effort that only Superman could sustain. World hour record kind of effort. On a Nashbar fluid trainer with fixed resistance I train on the 39/19-39/17 combinations. Admittedly I am a wuss. But you are talking about twice that level of output approximately. Is it possible that you have an extremely low pedal cadence. On the trainer I run a rather high cadence of ~100 rpm. I'm not saying that should be right for you. But even if you were only able to maintain 80 rpm you should still have sufficient resistance on your setup to avoid the big front/small rear combo. My fixed resistance trainer provides a tad more resistance to my bikes than actual flat road riding in calm wind conditions. If yours doesn't approximate road riding resistance, maybe that is your problem, since I doubt you ride at a near constant 35 mph that the big/small combo would generate on the road.

In a similar vein think about this. If you were pedaling smooth circles (more or less), you wouldn't have the problem. Why aren't you pedaling smooth circles? Is it because you are turning a gear that is too big. Why? Are you pedaling too slowly?

The two variables you need to check out are your cadence and the resistance of your system. One or both of them is too low. If you correct that problem, the rubbing issue will also be solved. Admittedly you may be only encountering the problem during small periods of a programmed training routine when strenuous climbing or sprinting is being simulated. I understand that. Nevertheless a slightly higher cadence under those conditions may be the solution to your problem.
Don't know about op, but myself and many others use their trainer for high resistance intervals, hill simulations and other low cadence drills. I have a Kurt Kinetic and while I spin at 39/17-14, I regularly go to the big ring and on certain workouts hit the 13-12. I don't think that is unusual for racers who do some training indoors.
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Old 10-20-14, 06:52 AM
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Originally Posted by canam73 View Post
Don't know about op, but myself and many others use their trainer for high resistance intervals, hill simulations and other low cadence drills. I have a Kurt Kinetic and while I spin at 39/17-14, I regularly go to the big ring and on certain workouts hit the 13-12. I don't think that is unusual for racers who do some training indoors.
You can see that I acknowledged that (if a bit late). I guess that is the problem. Perhaps some form exercises would help avoid the mashing and resultant rubbing, but I know it isn't easy to have good form under such strenuous conditions.
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Old 10-20-14, 10:48 AM
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Alright, I adjusted the front derailleur enough that the trim setting will no longer block the chain from falling off the chainring. Otherwise, the chainring flex causes the chain to rub. It doesn't happen on the road so I'll only use the trim on the trainer. I'm using a mag trainer with the resistance all the way up. Before getting into cycling, I used to leg press 500lbs a few times so spinning the 50x12 on my bike at 100 rpm for 5 minutes isn't impossible for me.
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Old 10-20-14, 03:05 PM
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Have you considered starting over with the FD and slanting it very slightly toward the small rear cog instead of keeping it parallel to the crank. I know that violates all the rules, but sometimes you need to improvise. It is worth a shot. You may run into problems elsewhere, but they may be easier to fix. Also are you using an 11 tooth smallest cog? If not, if your smallest cog is a 12, that would allow you to get the same gearing you have now but on the second cog instead of the first one. Keep trying. Something will work.
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Old 10-20-14, 04:39 PM
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Cassette is a 12-30. The chain rubs against the entire side of the FD cage so angling won't help. Excuse the crappy iphone pics. I think the only real solution is a new crank/chainrings.

Trim (50x12):


No trim (50x12):


Risk of chain falling off trimmed (50x30, extreme case):
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Old 10-20-14, 05:45 PM
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Originally Posted by IntelXE View Post
Cassette is a 12-30. The chain rubs against the entire side of the FD cage so angling won't help. Excuse the crappy iphone pics. I think the only real solution is a new crank/chainrings.

Trim (50x12):


No trim (50x12):


Risk of chain falling off trimmed (50x30, extreme case):
Do you keep a spare rear wheel for the trainer? You could get a used one for not much money and put a cheap cassette on it with an 11 tooth smallest cog. Then you could use the 12 tooth second cog and avoid the problem. I keep a trainer wheel like that with a used tire on it. Sweet.
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Old 10-26-14, 04:26 PM
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Update:
The 172.5mm Tiagra cranks were replaced with 175mm Ultegra cranks. The chain rub is gone, which means that the Tiagra cranks/ chainrings were not stiff enough.
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