vol

At some point toward the end of today's ride I suddenly heard some abnormal sound whenever I applied the rear brake. It sounded as if the rear tire was rubbing the ground. After I got home I tried to find out what's wrong, but couldn't see anything very obvious, except that the middle of the rear tire (the "largest circle"=the main part in contact with the ground) has become inexplicably almost smooth, losing much more of its tread than the front tire. So when I braked the rear wheel, the wheel doesn't immediately stop as it should be, but it continued forward in horizontal motion (not rolling) and rubbing the ground (i.e. with much less friction than there should be).

FYI the tire is KENDA KOURIER, 700X38C.

What's strange is that it seems this happened suddenly today, as I didn't have the problem earlier today and never before. It's a quite new bike, only been ridden a few months on regular basis. Could it be that the wheel ran over some very coarse surface (if so I'm unaware) that destroyed the tread? How? And why only the rear wheel and not the front one? My old bike never had such problem during 5 years of use.

JanMM

"It sounded as if the rear tire was rubbing the ground."

You think maybe it was skidding, which could rub a bare spot on the tire tread? The question is why was it skidding?

Aubergine 

Assuming you have an upright bike, braking normally throws your weight onto the front wheel and unweights the rear wheel. I have on occasion lifted my rear wheel off the ground on hard braking (although I try to avoid that my shoving my ample behind off the back of the seat.) Do you think you could have lifted your rear wheel up like that?

The other issue, though, is the tire wear. I find it really hard to understand why the center tread of your rear tire would wear so much faster than the front.

FBinNY 

It sounds like your rear brakes are getting grabbier for some reason. The most common reason is a dent on the rim that won't pass between the engaged brake shoes.

The rear tire was probably worn to the pattern you see long ago, and you're just noticing it now. If the brakes are locking on rim dent, you usually end up with a worn through section 2-5" long, while the rest of the rest of the tire is less affected.

Al1943

Rear tires usually wear much faster than front tires because they carry a much greater share of the weight.

As for the rubbing sound, does it occur rhythmically with the rotation of the wheel? If so check to see if a brake pad is rubbing the tire. You do not want that. Also check for rim wobble.

Since the bike is fairly new you can probably get the dealer to make needed adjustments at no cost to you.

Be sure to pump the tires up to normal pressure on a regular basis.

dabac

Let's not forget they provide they keep pushing the bike forward too. Braking happens a lot less.

dsaul

Its completely normal for a rear tire to wear into a flat shape down the center of the tread. Front tires dry rot before they show any significant wear.

spdracr39

Because most of the weight is distributed to the rear tire it wears at a faster rate. My rear tire wears twice as fast as the front so when I replace the the rear I rotate front to back and put the new one on the front.

Andrew R Stewart 

Another aspect to tire wear, as I understand it, is the side to side force that pedaling produces. the ft tire will pivot slightly with each pedal stroke. So for every crank revolution the ft tire sees a twisting between the tire and ground, at the contact patch. Now the rear tire doesn't have anywhere near the same amount of pivoting (essentially none WRT the ft action given the wheelbase long swing). So the rear tire sees much more of a side ways only scuffing at it's contact patch. Think of using a sanding block and only twisting one's wrist during the sanding of the surface. Then change to a linier motion for the sanding and see which is more effective.

I first noticed this while learning to ride rollers many decades ago. The ft tire would stay fairly centered on the ft roller while the rear tire would move laterally by a large margin. Now on the road the friction between the tire and the ground is much higher then when rolling on a smooth metal/plastic surface (rollers) so the amount of observed tire side movement is less as well as most can't really discern where the momentary tire contact actually is as we tend to look forward most of the tile (for good reason) as well as the ground doesn't have any reference markings to track the tire's location. So only mentioning the fore/aft weight differential is far more easily accepted by the uninformed. Andy.

Shimagnolo

Agreed.
And on the large frames (eg 64cm) that I ride, the weight ratio (rear:front) can be 2:1 (I've measured it). At the opposite extreme, I measured the distribution of a very small framed bike I built for an exGF, and the distribution was perfectly equal!

I normally rotate front to back, but over the past year I did an experiment by replacing only a worn out rear tire and not touching the front tire. What was interesting was that after wearing out 2 rear tires, the front tire was keeping a round profile as it wore, as opposed to the typical flat profile a rear tire develops.

vol

Thanks everyone for your input. I'm still trying to find out (as there is nothing very obvious to be detected). Even though all of what's said about tire wear are true, it shouldn't be so bad that the new bike encounters such problem due to that, as I did with my previous bike for 5 years without such problem. It's good to know that more wear to the rear tire, even being flattened, is completely normal, though. Maybe the tire wear is not the cause. FBinNY''s post led my attention to the brake, and it seems it could be that the brake lever is too loose (very close to the handlebar grip when braking), so even though the brake pads are touching the rim, the wheel is not grabbed firmly enough, so the wheel may continue to slightly move forward, partly skidding.

stumpjumper2076

The rear tire is your drive tire it wears faster same as with cars (front wheel drive vehicles wear front tires out faster) . As far as it happening all of a sudden its like many things Its all good until it isn't .

Aubergine 

Yes, indeed, but let's go back to the opening post: "It's a quite new bike, only been ridden a few months on regular basis." That was what made me curious about the wear to the tire.

CroMo Mike 

Sounds like the brake pad has a bit of grit (from the road) or a bit of metal (from the rim) embedded in it, causing it to gall and damage the rim while braking poorly.. Continuing to ride it that way usually results in more metal (from the galling) to embed, and the problem becomes worse, possibly ruining the rim. Finding the grit and metal and picking it out of the brake pad with a knife point would be the solution - or install new pads.

Shimagnolo

I have a friend who is completely oblivious to maintenance.
He bought a new high end bike, then rode it until the rear tire blew out one day;
He had worn it right down through the belts into the tube.
And of course he had no tools or spares with him, so he had to call his wife to come get him.