July 22, 2004

9:26 PM

Mysterious bicycle problem: When I'm on my road bike it sounds like the rear brakes are rubbing, but if I get off the bike and spin the wheel, I can see there is plenty of clearance, the wheel is true, and there's no sound. What is going on?
posted by teg to (22 comments total)

This bike is a Giant OCR 3, only a few months old. I could take it into the shop, but they're quite out of the way, so I'd prefer to fix this myself if I can.

The sound seems to occur with every revolution of the rear wheel, not just when I'm pedaling. I don't feel a major drag on the bike, but it's new so I don't have much to compare to. Things I've checked: The brake pads are well clear of the rubber of the tire. If I flip the lever to give the brakes more clearance, there is still a sound. Tire pressure is as recommended. I removed and re-seated the tube and tire in case there was something there, but they look fine.
posted by teg at 9:26 PM on July 22, 2004

I don't want to sound too obvious, but have you got off the bike, picked it up, and spun the pedals to spin the wheel and then listened/looked to see what you can hear/see? If it's a regular zzzz noise every revolution you should be able to see something rubbing *somewhere.*
posted by carter at 9:48 PM on July 22, 2004

have someone else sit on the bike, and check clearances again.
posted by notsnot at 9:49 PM on July 22, 2004

If I flip the lever to give the brakes more clearance, there is still a sound.

That makes me think it's not the brake. I'd guess the problem is with the spoke tension, the hub or the rear derailleur. I'd suggest taking it to the nearest bike shop mechanic. They'll probably be able to diagnose the problem easily once it's in their stand.
posted by letitrain at 10:00 PM on July 22, 2004

Spoke tension, bearing wear/looseness, frame torque ?

Or : even looseness at the quick-release mechanism.
posted by troutfishing at 10:12 PM on July 22, 2004

Carter, that is the source of the mystery. Notsnot, clearances still seem to be fine. Letitrain, I was hoping it was something I could fix, but I think you're probably right. Spoke tension seems OK, as far as I can tell. I tightened the quick release when I re-seated the tire. I'm thinking it's probably the hub, or specifically the bearings.
posted by teg at 10:20 PM on July 22, 2004

Sorry, just realized, teg. I need some sleep! If it's once per revolution, I'd go for the bearings, then. Maybe your weight is enough to make it start grinding. Otherwise, it *is* mysterious.
posted by carter at 10:31 PM on July 22, 2004

Thanks folks. I will try to get it into the shop ASAP.
posted by teg at 10:41 PM on July 22, 2004

IAAQBM (I am, in fact a qualified bicycle mechanic)

Look for the tire rubbing against parts of the frame and the rear brake arch. Are you sure it isn't caused by the front wheel? Sometimes noises transfer to different places on the bike.

Does it only happen when there is load (a person) on the bike? Your bike has a Shimano Sora drivetrain, shimano's lowest-end road gruppo. There is a problem that usually only occurs on older, freewheel-based drivetrain. Since `90 or so almost any bicycle you buy at a bicycle shop (an important qualification) will come with a freehub and cassete.

The problem could easily be caused by a crappy freehub, and the freehub could easily be replaced independently of the cassette.

The problem could easily also be crap in the rear hub bearings, which is easily a possibility with a low-end bike that lacks the modern convinence of cartridge bearings.

Remember, Giant is the Dell of bike production.
posted by blasdelf at 10:57 PM on July 22, 2004

Also, this reminds me of the pranks I used to pull on my freinds in the bike shop.

Bike mechanics hate it when their bikes make funny noises, so naturally, I create noises by dropping a few ball bearings down the seat tube, then repeatedly removing and replacing them after multiple rounds of Mech. v. Bike; Alternatively, I would add strips of metal in akward places that make whistling noises only while moving over 15mph.

Oh sweet Eris, goddess of discord, allow me to wreak temporarily hilarious havoc upon the lives of unsuspecting coworkers.
Here ends the prayer.
posted by blasdelf at 11:28 PM on July 22, 2004

If as blasdelf says the back hub is not a cassette, and if you just bought the bike, it's also possible they just set it up wrong. IMHO it's really hard to tell which of the little grease monkeys in the back of bike shops actually knows something, and which one is going to mash up your bike. Especially with large bike store chains. It would be kind of hard to argue but if its new and not ridden too much and you've looked after it (i.e. not left it out in the rain etc.) they possibly owe you some replacement parts. Which if it is the hub, would mean not just tweaking the cones, but giving you new bearings, as the ones on there are probably a bit worn by now. If it is the bearings, that is.

Actually, if it is the bearings, if you take the wheel off the bike, and hold one end of the axle in each hand, and then spin it, you might be able to feel bad bearings as vibration/grinding through your finger tips. The vibration will come + go in sync with the revolutions of the wheel.
posted by carter at 11:30 PM on July 22, 2004

I'd like to clarify:
I didn't mean to imply that he has a freewheel, just that his freehub body might be fucked up.

Freehubs are not meant to be rebult, but replaced.

The problem could just as easily be a crushed bearing retainer or something like that in the hub.

All of it obviously stems from the use of sub-standard, non-Italian bicycle componets.
< /righteous_indignation>
posted by blasdelf at 11:57 PM on July 22, 2004

Does it have quick release hubs? Of course it does, all bikes have since I was a kid. And do you ride with without clips or cleats, so that you push only and don't pull?

If you haven't seated the axle right in the rear forks, then the wheel can twist to the side in the fork as you push on the pedals. Make sure it's seated right (ie properly square and firm).
posted by i_am_joe's_spleen at 1:53 AM on July 23, 2004

i_am_joe's_spleen,
We've already isolated the problem to a moving part on the rear wheel; barring ghosting, or some sort of phantom problem where things are not as they appear.
posted by blasdelf at 2:02 AM on July 23, 2004

Some rims creak, and depending upon how they creak it could sound like a brake rubbing. Mavic Open Pros are known for this, for instance. They won't creak without a load on them, but will start once you sit on it and the wheel rolls.

Is the wheel in true, i.e. does it maintain the same distance from the brake pads when you spin it. If it does there is less chance of it being the wheel rubbing on something.

How did you check your spokes? The easiest way is to pluck them like a guitar string. They should all make approximately the same tone.

Before making the trek to the bike shop and as Joe's Spleen suggests, I would check that the wheel is properly seated in the rear dropouts. I doubt that this is your problem though, as usually when the wheel is not properly seated in the dropouts it rubs the brakes loaded or unloaded.
posted by caddis at 5:37 AM on July 23, 2004

sounds like the rear brakes are rubbing

If this is the case, then I can't imagine why it would have anything to do with incorrect spoke tension.

Long-distance bike diagnostics is rarely successful - there's a thousand things that might be causing your problem. Taking it to a shop is definitely your best bet.
posted by normy at 7:37 AM on July 23, 2004

If this is the case, then I can't imagine why it would have anything to do with incorrect spoke tension.

... before the first coffee of the morning, that is... of course it would... just ignore me.
posted by normy at 7:44 AM on July 23, 2004

As I've reseated the tire and the wheel, and the wheel appears to be true, and the spoke tension seems to be good, I'm going to assume it's the hub. Listening to it more carefully, I now realize the sound isn't necessarily the brake pads, but it is from somewhere on the rear wheel. (People riding beside me have heard it come from the rear wheel also.) I'll be taking it to the shop tomorrow (and riding the bus home).
posted by teg at 7:59 AM on July 23, 2004

Or rather, next Thursday as they're all booked up.
posted by teg at 8:02 AM on July 23, 2004

sorry blasdelf, i skimmed.
posted by i_am_joe's_spleen at 2:30 PM on July 23, 2004

I had a recurring creaking noise on my month old mountain bike. It only occurred when weight was on the bike and the bike was moving.

I put a tiny drop of oil in each spoke hole on the hub. That fixed it permanently.
posted by jjj606 at 8:36 AM on July 24, 2004

Update: It turned out that the noise was coming from the stupid plastic disk that is supposed to protect the spokes from the chain. The bike mechanics couldn't figure out why it was making a sound (and only when someone was on the bike), but once the guard was removed, the sound was gone. All is good now.
posted by teg at 11:44 PM on August 6, 2004