Bora WTO rim brake “groaning” noise — toe-in not the issue, what gives?

[Xrslug]

Hoping for some help with a braking issue on my Bora WTO rim brake wheels. Bought these used in excellent shape. Mounted and using with Campy red brake pads. Front braking is good, strong braking and just the normal “zzzzz” noise of the textured braking surface when braking.

Issue is with the rear wheel: under braking it has an obnoxiously loud honking or groaning noise from what I assume is brake pad vibration or slipping/gripping. This isn’t the the high pitched shriek that can happen when carbon rim brake wheels heat up. Toe in on the pads makes it *worse* - it is actually improved slightly by eliminating toe in on the pads. So in summary:

1. Honking noise is only from the rear wheel. Front wheel has no abnormal braking noise using a slight toe in on the pads.
2. Noise from the rear wheel is worse when the pads are toed in and better (but not eliminated) when pads are flat to the rim
3. I cleaned the braking surface with isopropyl alcohol before riding and I’m using Campy red pads
4. It’s not heat related — same noise when braking on cold wheels
5. Wheel is visually true and I feel no pulsing through the lever while braking
6. No noise under very light braking (just enough to have the pads rubbing slightly) or when braking hard enough to skid the rear tire

Any suggestions? The only thing I can think to try at this point is a reverse toe in of the pads (I guess a “heel in”). What’s throwing me off is that it’s only the rear wheel, which suggests to me that something other than the brake pad / rim interface might be causing this. Wheel alignment in the frame? Wheel slightly out of true (even though lateral trueness looks perfect visually)? On the other hand, I’ve had no issues with the alloy wheels I’ve used in this frame (which would point back to the carbon brake track / pad interface as the issue). I’ve searched for this specific problem and find nothing other than toeing in the pads, which is not solving my problem.

[rheosibal]

Have you checked to see if the caliper is tightened enough to the frame? Same thing with the pad holders to the caliper.

[Xrslug]

Originally Posted by rheosibal

Have you checked to see if the caliper is tightened enough to the frame? Same thing with the pad holders to the caliper.

Thanks for those suggestions — pad holders are definitely tight. I did tighten the caliper to the frame when I got home from my ride this morning but didn’t have time for a test ride to see if that changed anything.

[BdaGhisallo]

I've had similar issues with some rim brake wheels with aggressive brake tracks like Enve's textured tracks and Bontragers lasered tracks and the problem was down to the frame, not the wheels. I tried everything you tried and then some.

I concluded that some rim brake frames simply aren't built with stout enough seat-stays to handle the vibrations that today's stiffer calipers and rougher brake tracks produce.

My solution was to have my rim brake frames built with larger OD seat-stays and thicker walls. Problem solved.

[Xrslug]

Originally Posted by BdaGhisallo

I concluded that some rim brake frames simply aren't built with stout enough seat-stays to handle the vibrations that today's stiffer calipers and rougher brake tracks produce.

Interesting… Well, the wheels are beautiful but I have an excellent set of alloy wheels to use as well if it doesn’t work out. Still need to try a few things before I give up on them.

[oldpotatoe]

Originally Posted by BdaGhisallo

I've had similar issues with some rim brake wheels with aggressive brake tracks like Enve's textured tracks and Bontragers lasered tracks and the problem was down to the frame, not the wheels. I tried everything you tried and then some.

I concluded that some rim brake frames simply aren't built with stout enough seat-stays to handle the vibrations that today's stiffer calipers and rougher brake tracks produce.

My solution was to have my rim brake frames built with larger OD seat-stays and thicker walls. Problem solved.

I would agree with this..a possible 'solution' might be find a single pivot rear brake caliper, like one of the older Campag Skeleton SP rear brakes..make it less powerful..

[nmrt]

Before blaming the frame, I'd swap the brake pads to those made by different companies -- Black Prince, Reynolds Cryo blue, or the cork ones that Bontrager makes.

If the issue is to stop these vibrations produced by a combination of frame + wheel + pad material, I'd change the pads to see if the frequency of the vibration can be changed.

[Xrslug]

Appreciate all the suggestions. I’ve tried a set of Black Prince carbon pads before the Campy red pads arrived. Same issue, which I had hoped would be fixed by using the red pads. No luck. And I did clean the brake track when I switched pads. The Campagnolo single pivot option is interesting — may give that a shot if nothing else seems to work.

[SDRide]

I chased this type of harmonic rear wheel noise when trying Hunt carbon wheels on a steel frame. Tried toe in, out, different pad makers, different slight pad angle to take advantage of a wide braking surface. I ended up mounting the caliper ahead of the seat stay and that cured it. No toe in required anymore. I did have to drill the mounting hole. I use Ultegra 8000 brakes.
You can loosen the set screws on the caliper and try to screw in the pivot bolts to lessen the play in the pivot bushings, also maybe a wider aluminum mounting washer. I tried it all and reversing the brake was the best solution for me. The cable has to come around the front of the seat tube but barely rubs and normal protection is effective. I went back to alloy rims (Fulcrum Zero) and put the brake back to the normal position but the noise returned so I ended up switching the caliper back forever this time.

[SDRide]

I erased this double post

[Clean39T]

I’ve had this happen too. It’s a resonance thing. Only cure is to disrupt the system.. unfortunately only you can experiment with that to figure out what combination works. I think Old Potatoes recommendation on trying a different brake makes the most sense as a starting point from where you are now..

[robt57]

Originally Posted by Xrslug

Appreciate all the suggestions. I’ve tried a set of Black Prince carbon pads before the Campy red pads arrived. Same issue, which I had hoped would be fixed by using the red pads. No luck. And I did clean the brake track when I switched pads. The Campagnolo single pivot option is interesting — may give that a shot if nothing else seems to work.

Did you try the wheel on another bike? Just for elimination purposes?

[Xrslug]

Appreciate all the latest suggestions — I found a cheap(ish) Campagnolo single pivot “differential” rear caliper that I’ll give a shot. Unfortunately I don’t have another bike that would work easily to test the wheel but I may try to jury rig something to test it.

[hernium]

A possible solution might be to try a vibration reducing washer made out of a dampening material - elastomer or neoprene maybe - where the caliper mounting bolt meets the frame/fork.

[dddd]

Originally Posted by hernium

A possible solution might be to try a vibration reducing washer made out of a dampening material - elastomer or neoprene maybe - where the caliper mounting bolt meets the frame/fork.

I would avoid this approach for two reasons, first that the nut may not stay tight for long, and more importantly, that the "hub" of the pivot bolt needs to be rigid against the frame in order to prevent any cyclic bending load being applied to the center bolt itself.

I have an old Cannondale with canti's, and struggled with noisy vibrations for a long time. After much toeing and a couple of pad changes, a third different set of pads finally cured it. I thought it was cursed, especially as the seatstays on that bike look quite rigid.