Triumphrat

RumRunner

Take a screw driver and spread the pads pushing the Pistons back into the calipers. Then don't use the rear brakes problem goes away. I actually did this (not exactly intentionally though) had thrown on a new rear tire and went out to bike night, then out for lunch, then out riding with the boys up in the mountain. Stepped on the rear brake at a stop light on a hill and it went to the ground... Oh crap, then I remembered and said hmm I haven't stepped on the rear brake in two weeks

tonupdave

O.K. its got you thinking all answers are feasable then WHY are the front wheels of cars so dirty?.....I will admit tha the back rim on my 1954 Ariel gets dirty and only drum brakes so the dirt off the road seems to be the likely answer very fine black grains.

kballowe

I always thought that the rear wheel picked up all of the road dust, plus the front brake dust - and there's more rear fender area to keep the dust from readily escaping.

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SDWest

You could always convert to drums


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tommyalanson

I thought it was the chain lube spray (however slight) making the rear wheel a bit sticky, and therefore attracting the grime.

I've noticed on cars that mostly it's the front wheels that get all brake dusted-up on front-wheel drive cars. On a couple of my older bimmers, brake dust gathered on the rear drive wheels.

357Bob

I stopped my rear wheel dirt problem. I changed chain and sprocket
20,000 miles ago and I haven't lubed it. No dirt. No grease. Chain
never needs adjusting. Not lubing the chain is another story. I rarely
clean my rear wheel. Love it.

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357Bob

Olhogrider

I think Bob is jerking your chain

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goo

it there anything hot back there after you ride it?

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stevemorris7

I think that the rear brake pads may be made of a different material.I read someplace that the fronts are a sintered/harder material and rears are supposed to be organic material so that they won't grab as hard as the fronts.If this is correct it could explain the condition.

Cheshire

There's a simpler solution: it's where you're riding.
Yes, a little bit of brake dust, but mostly road grime. Cars don't get it as much because they're not riding towards the center of the lane. Most of that grime is kicked up from the "grease strip" in the road.
Perfectly normal.