Rear D touching spokes Tink tink tink tink

[Nomadmax]

Last time this happened to me it was the end of the RD cable hitting the spokes.

[tctyres]

Originally Posted by redir

Is there a way to accurately measure a hangar to see if
it's bent without special tools?

The easiest thing is an old wheel with a threaded axle. If you thread the axle into the derailleur hanger, the wheel is large enough that you will see a bend.

Originally Posted by Nomadmax

Last time this happened to me it was the end of the RD cable hitting the spokes.

+1 The last two generations of Shimano rear derailleurs send the cable right into the spokes, and it is not easily predictable in the stand.

EDIT: sorry you said a different wheel, not a different bike ...

[marciero]

To be clear, the two different wheels you tried have the same size large cog?
Also, regarding spoking that was mentioned- I would be curious if the they are the same- same number of spokes, and if so are drive side pulling spokes elbow in or out and do they cross under or over the first spoke. This wont fix your problems but might explain partly why one is fouling and one is not.

[Tandem Rider]

If the pulling spokes on the rear are "heads in" they will slightly move the crossing point towards the derailleur. This is only a problem when in the cog closest to the spokes and usually when climbing hard. Check the spoke tension if they are hand builts.

[oldpotatoe]

I'd check der hanger first. Then, when in lowest gear, pushing the rear der toward the rear wheel whilst pedaling(in the stand, of course), does the Rder hit the spokes? Limit screw in if it does. If it doesn't, it's not the der hitting the spokes.

[tellyho]

Originally Posted by redir

Is there a way to accurately measure a hangar to see if it's bent without special tools?

Park's DAG might be the best bang for the buck I've had in tools. I use it so much - once you get one, you realize that all your hangers are out of alignment. This is in a stable of mostly steel, FWIW.

[elvisthehorse]

I have found the really cheap soft forged RD hangers flex a lot.
I replace those cheap ones with a wheels mfg. You can tell right away its holds the RD more laterally stiff. If that makes sense.

My cervelo had one of those cheap forged RD hangers and would ghost shift under power. Went to a Wheels MFG and problem fixed.

[redir]

Originally Posted by Mark McM

As above, just because the derailleur only contacts with one wheel and another does not rule out a bent hanger. Hangers, especially replaceable ones held on with small screws, are remarkably easy to bend.

When you say the derailleur only contacts under stress, as when climbing a steep hill, does that mean it does it primarily when standing and stomping on the pedals? If so, I'd bet it rubs when stomping on the right pedal, but not when stomping on the left pedal. When standing, we typically lean the bike away from the pedal we are stomping on. This imparts a lateral load on the wheel, and the wheel may flex laterally. When we lean the bike to the left and stomp on the right pedal, the wheel may flex to the right (toward the derailleur), and when we lean the bike the right and stomp on the left pedal, the wheel may flex to the left (away from the derailleur).

Wheel flex is determined by component material and geometry, so there isn't much to do there. But if there is free-play in the bearings, it may increase deflection under lateral load, so you'll probably want to check for play in the bearings as well.

If, after checking all other things (hanger alignment, limit screw adjustment, indexing adjustment, bearing adjustment, etc.) the derailleur still contacts that spokes, then it might just be a wheels/drivetrain incompatibility - but all is not yet lost. You may be able to get more derailleur clearance by using a larger cassette. The drive side spokes angle inward from the hub flange to the rim. So the further away from the hub (larger radius), the further the derailleur will be from the spokes. With a larger cassette, the derailleur cage will be sitting further from away from the hub, and will have more spoke clearance.

I can now confirm that it is indeed only the right side pedal. It does it sitting too though.

[David Kirk]

Can you please tell us about the rim used on the wheel that you have issues with?


dave

[Mark McM]

Originally Posted by redir

I can now confirm that it is indeed only the right side pedal. It does it sitting too though.

When seating anf pushing hard on the pedals, we often lean the bike a little to the side, and also sometimes our downstrokes aren't perfectly vertical, but angled a little inboard (both of which can put a lateral load on the wheel). I'd bet if you purposely hung your upper body off to the left side of the bike (which leans the bike to the right) when pedaling the derailleur would rub less, and if you purposely hung your upper body off the right side of the bike when pedaling the derailleur would rub less. Which would mean that the wheel is flexing into the derailleur. And if so, this could indicate either that there is more lateral flex or bearing play in this wheel, or that it flexes a normal amount but there is less static clearance available for flex, than with your other wheel. Have you checked the wheel dish? Maybe this wheel is over-dished to the right.

[redir]

Originally Posted by David Kirk

Can you please tell us about the rim used on the wheel that you have issues with?


dave

Zipp 303 tubular

[November Dave]

Originally Posted by redir

Zipp 303 tubular

Interesting that it's tubular. Tubulars don't compress rims nearly as much as clinchers. That compression results in decreased spoke tension and a slight move toward the drive side. I build clincher rears with a very slight (~.5mm) NDS-biased dish, knowing that it will center when the wheel goes on and gets inflated. Tubulars you dish in the stand to where you want them with the tire on, since they don't move. So you can rule that out for being a cause.

[rowebr]

Originally Posted by tellyho

Park's DAG might be the best bang for the buck I've had in tools. I use it so much - once you get one, you realize that all your hangers are out of alignment. This is in a stable of mostly steel, FWIW.

Chiming in to second this comment. My Park DAG has paid for itself many times over, not just on my own bikes but for friends and neighbors as well.

For the OP, now that you've hopefully narrowed the issue down to wheel flex, have you checked for lateral play in that rear hub? Hold the rim by the rear brake bridge and try to move it back and forth towards and away from a seatstay. Any looseness or knocking in that side-to-side direction?

[tellyho]

Play in the rear derailleur cage? Or the mounting bolt? I'm trying to remember which RD had more play than I thought was optimal in my past. I think is was a SRAM something. I assume a Synapse is thru axle, but just in case, a loose QR skewer could also do this.

[Lewis Moon]

From the stupid human tricks department: check to see that your "over/under" on your spoke lacing is correct and also make sure one spoke didn't get drawn the wrong way through the hub (3 heads in a row on one side)