A rub they can't fix
 

I am frustrated and looking for some thoughts from others with more experience and bike smarts than me. I bought a Giant carbon fiber Fastroad, put about 300 miles on it, and took it back into the shop where I purchased it for a free maintenance visit. For the first 300 miles it was great. The only adjustment I made to the bike was adding a stem riser because I'm 6'4" and wanted to experiment with riding position. I found that adjustment to work pretty well.

After I got the bike from the shop (post maintenance), it immediately began making a rubbing noise that got worse when I leaned the bike to one side. But it was pretty much there to some degree all the time. I took it back in and after having it for 2 weeks they still can't completely get rid of the noise. Their initial comments in a brainstorming discussion of sorts revolved around my size (6'4", 245), maybe the stem altered the frame dynamics somehow, and perhaps the carbon fiber frame was more prone to flexing, etc. They said it was the front rotor rubbing.

It sounds logical I suppose but I find it strange that all was great pre maintenance and the rub started on the first 100 yards after maintenance.

Does anyone have any ideas on this? Maybe Giant will exchange the bike? Or maybe I should find a new bike shop.

Any helpful comments/thoughts are greatly appreciated!

realign the brake.

Maybe in the shop's maintenance check they adjusted the brakes and now the pads are just a fraction too close to the rotors???

Dan

Nope. Zero chance.

It was fine until they serviced it, right? That's not a coincidence.

They identified the problem. That's a good start. What is their reason for not remedying it?

First locate the specific parts that are rubbing. Look for evidence on the tires, insides of fork and stays, and any other suspect areas. Sound can also be a guide, since different rubs sound different.

If you suspect the discs, remove one and six if that solves it. Then repeat with the other. Just be sure not to use the non functioning brake, and/or install a keeper between the pads.

Once you know what's rubbing, you can think about how to solve it.

BTW - you won't have to remove the front disc, just turn the wheel around.

If the brake does not rub when then wheel is spun air, there is excessive flex somewhere. A common cause of the problem is insufficient clamping force from the quick release. Try tightening it--and consider getting a skewer with an internal cam, like a Shimano. No harm in taking it to a new shop to see if they can sort it out. I'd pop in a Shimano skewer, check your hub adjustment, your caliper alignment, the rotor trueness, and that the pads are resting at a reasonable distance from the rotor. This is maybe 10-15 minutes of work. If everything checks out, it's certainly possible that the fork or hub is flexing.

I smell male bovine dung.

And yeah, despite what the disc lovers try to tell you, they still don't have the technology fully sorted. That doesn't mean you have to put up with noise but it does mean the shop has to put some effort into sorting it out.

Change your fork and hub to use an enormous 20mm thru axle instead of a QR
No more flex, no more disk rub.

If i not wrong when we cycle the wheel will compress so when you steer it might cause the wheel to bend, therefore the alignment of the wheel might not be straight enough so try adjusting it the brakes.

My previous carbon bike also have rubbing sound when i steer end up it's the brake pad rubbing

I do like disc brakes, but have to agree, 40+ years and they still can't get it right.

+1

Exactly. Unfortunately disc brakes often rub. On a mountain bike... no big deal. You're tires make more noise on the ground than the disc brake does. On a road bike? It'd drive me nuts.

I had this exact problem with one of my bikes. No noise on the stand, brakes worked great. As soon as I sat on the bike they'd make noise.

Eventually I solved it by making the QR ungodly tight, then adjusting the brake to not rub. Then just never touching the QR unless I absolutely had to.

Also, make sure the wheel is properly mounted in the dropouts. Put weight on the bike, loosen the QR, then tighten the QR. The wheel will settle to where it's supposed to.

Don't blame the shop for not being able to fix this. This problem is notoriously hard to fix, even for mechanics, especially with cheapish (aka not top of the line) discs.

If a disc brake rubs when cornering but not otherwise, there are two likely causes.

1- hub bearing play -- but it would have to be pretty obvious
2- fork flex, especially likely on CF road forks that probably aren't built stiff enough for the job.

I discount QR movement because that wouldn't move back. The issue is flex, not movement related.

That said, there shouldn't be that much flex, and a properly set up brake should have enough room to accommodate it. So, I'd carefully check the alignment of the caliper with respect to the disc. Any misalignment would use up available travel narrowing the opening, and ability to accommodate normal flex.

Check the alignment by gently applying the brake to bring the shoes in to minimum contact. Then look carefully to see if the contact is perfectly flat on both sides. Otherwise loosen and realign the brake.

Unfortunately some disc brake mounts don't allow for alignment, and if the brake isn't square, fixing it calls for careful and skilled use of a file.