Mystery wheel rub

Discuss light weight issues concerning road bikes & parts.
alcatraz
Posts: 2248
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Maybe you don't clamp the rear wheel properly in its dropout.

I've often been surprised how riders neglect to really seat the wheel in the dropout. It's like they just gently lift it in there and clamp at arbitrary locations.

Then it rubs a few turns before your weight forces it in place.

Also is it possible the dropouts are too wide apart so that the hub falls inbetween somehow?

Don't you hear the rubbing?

Is your caliper bolt properly tightened?

How much chainstay clearance do you have on that side?

Is the pad holder tightly fastened? Was it ever loose? A friend rode with his vertical once. Had to tell him to stop without using his rear brake.

Check your frame for damage. "God forbid" it's flexing because of some crack somewhere.

Another idea is that the frame is crazy flexy and you're a heavy rider or something. This way when you corner the wheel deflects at the caliper so much to the right that when you brake the brakepad reaches much further down on the brake track.

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dj97223
Posts: 701
Joined: Sun Nov 06, 2005 7:27 pm

by dj97223

where do you park/store your bike? maybe the stand is rubbing the wheels
“If you save your breath I feel a man like you can manage it. And if you don't manage it, you'll die. Only slowly, very slowly, old friend.”

by Weenie


rma
Posts: 166
Joined: Mon Apr 21, 2014 9:17 pm
Location: Belo Horizonte, Brazil

by rma

Maybe something related to bike transport? Sometimes the car hot exhaust gases can damage rims if the bike is near them during transport. I have seen more than one pair of Rovals melted...

Alexandrumarian
Posts: 474
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

I have too seen the kind of guy that rides with various bits falling apart - I am not one. I check the torque on every bolt every few rides and change the chain at 2000km. I wash my bikes with baby wipes. I keep them in house in my workshop. They are well cared for. It is two different frames and three different back wheels. I install the rear wheel with chest pressure on the saddle and clamp it down very hard with solid skewers. I tried to flex the wheel, the steastays, the brakes and whatnot on the flexier carbon frame, there is no way to match the pad to the wear position.

Oh well, I'll stop with this before someone accuses me of trolling the forum. I will put a few small stickers on each wheel and keep an eye on them, see if any trend appears. Hill rides, sprints, crashes, leprechauns borrowing my bikes at night, anything.

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Valy
Posts: 231
Joined: Tue May 29, 2012 11:16 pm

by Valy

Yeah it will be interesting to see what comes out.

As a tangential example I had a creak on my bike under power in and out of saddle.

Changed/checked/lubricated/cleaned:

Pedals, BB, wheels, QRs, checked bolts for tightness, RD mount (steel frame, integrated hanger), numerous headset adjustments and 1 bearing change,

Literally ended up stripping the bike down and rebuilding.

Changed chainset.

Gone.

I suspect chainset bolts as culprits with 0.95 certainty. Other options include pedal threads or the interface of LH crank mount. (Ultegra 6700)

They were tight but not clean/greased sufficiently maybe. Or there is a compatability issue of mixing inner DA ring with outer Ultegra (B compatible up but not down as per Shimano PDF) .

Have not taken it apart, just riding with R7000 chainset. Which does not shift quite right now small to large.

Alexandrumarian
Posts: 474
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

I had the ungreased chainring thing too quite early with my road bike. It was only a couple months old but started to creak at each right foot press. Luckly i read about the bolt possibility before i got a chance to try and open up the bottom bracket.

Back on topic, I woke up with a theory. Since I am very heavy (around 95k most of the time) perhaps, on the road, under special conditions, the chain/seat stays flex enough to allow for the brake pads to reach those 5mm or so below track.

So i took the carbon frame bike, grabbed with both hands both brake and rim and squeezed them together. Since I have thin pencil seatstays and brake bridge, with a fair bit of muscle force and carbon or brake squeaking i could lower the pads down enough. But when I tried to do this on the other bike which is a more solid alu build, no way. I squuezed as hard as i could but the pads barely went down 1mm. Anyway, will add those witness stickers and keep an eye on them after each sprint or whatever.

Bluechip
Posts: 125
Joined: Thu Nov 12, 2015 2:04 am

by Bluechip

There could be flex in the system. Under hard braking the brake arms could expand and slide lower on the rims. Do you do a lot of hard braking?

PrimO
Posts: 108
Joined: Thu Nov 20, 2014 8:49 pm

by PrimO

Are you a powerful rider? Are there any rub marks on the chainstays on either bike? It looks more like wheel flex causing the rim to tough a chainstay or seat-stay.

Alexandrumarian
Posts: 474
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

Flex in the chain and seat stays under braking is the only explanation that has logic so far. I do ride steep hills often enough. The brake arms/mount themselves can't do much, they are solid metal not rubber. But the stays and bridge can flex. I already established I can do it by heavy hand force on the light carbon frame. Not on the heavier aluminium, but hand force is probably much less than a 95kg pork decelerating from 50kph...

chupster98
Posts: 17
Joined: Mon Oct 01, 2012 1:22 am

by chupster98

I'm not familiar with Campy brakes, but look for something similar to a pad wear screw, located on the inside of the pad holder - similar yo the shimano style on the photo attached.

I had a similar issue recently were I ate my rear pads on a rainy ride & noticed a similar wear mark like yours, on the exact same spot on the rim.
pad wear screw.JPG

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pdlpsher1
Posts: 2424
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

The pad wear screw is the only logical explanation. They come into contact with the rim only when braking. When not on the brakes there's no contact and no noise for the rider to notice. If it's due to chainstay flex then the OP would have heard the rubbing noise while not on the brakes.

spud
Posts: 813
Joined: Sat Feb 07, 2009 5:52 am

by spud

^ had this exact scenario on a bike 15+ years ago.

alcatraz
Posts: 2248
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Interesting. How is the wear screw supposed to work?

Is the screw only on the left side pad holder?

chupster98
Posts: 17
Joined: Mon Oct 01, 2012 1:22 am

by chupster98

To clarify - this screw is only meant to produce a warning screeching sound when the pads are almost worn, in my case I only had aprox. 2mm pad left - which is a hair less than the height of the screw head.

I didn’t notice the sound as it was raining hard. If I had continue riding it I would have completely damaged the rim.

All shimano brake pad holders (front & rears) have this screw.

I had seen this screw when cleaning the bike not really knowing it’s function, found out about it by accident.


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chupster98
Posts: 17
Joined: Mon Oct 01, 2012 1:22 am

by chupster98

Just found this photo of a campy pad holder:
Looks like it’s time to get new pads, look how much material new pads have & compare with your photo.

I’ve marked the area I think might be contacting the rim. The soft pad might be compressing under hard breaking forces & cause contact & Imagethe marks


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by Weenie


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