Bicycle Mechanics - Untrue Wheel Symptoms

I'm just trying to wrap my head around this. I just plain old suck at mechanics and visualizing things in space.

When braking with the front I get a very distinct feedback through the brake lever that the pads are not gripping somewhere along the rim. I can also definitely feel the bike not decelerating smoothly, as there's that spot on the rim again where the brakes just don't grip, so stopping is very jerky. Basically braking with the front wheel doesn't work so swell anymore.

So that means the rim is probably bent in just that one spot, right? I mean, the sensation would be different if, say, a third of the rim were out of true, right?

(I did check the other usual suspect, like making sure the wheel was properly seated in the fork.)

Turn your bike upside down so that it is resting on the saddle and the bars. Spin the front wheel and watch as it passes the brake pads. If it doesnt stay centered as in wobbles left and/or right then the rim is not true. Its a very easy process that can be learned in 5 minutes, lateral truing that is. You need a spoke wrench though, I bought one for $4.

Get the wheel out of the bicycle, remore tire and tube, old it by the axel and spin the wheel. If you notice any bending on the rim, so the wheel is out of true. Try to check if the rim wall is even and is bent inwards at any point.

OK, I just flipped the bike over and used the brake pads to find the out-of-true spot and adjusted it. I'll see tomorrow morning if that fixes the braking problem. I just didn't realize that a slightly untrue wheel could have such an adverse affect on braking. I mean, the brakes weren't rubbing or anything, just when I applied the brakes the pads wouldn't provide a smooth and constant grip.

SOmetimes I'm amazed at how some of the bike parts operate with pretty high precision, like a very small deviation can muck things up. Bends in the rear der are the same. It don't take much to mess it up.

I wouldn't think it would have that big an effect on V or Y brakes. But who knows.
First thing to always do is to make sure the rim is clean, thats what the symptoms sounds like, a slick spot on the rim.

First thing to always do is to make sure the rim is clean, thats what the symptoms sounds like, a slick spot on the rim.
Yea, sounds like slickness. Clean rim and pads with rubbing alcohol, 90-100$% is prefered but 70% should due the trick. Then test if problem remains note just where the spot is and mark it so you can compare it to the rest of the rim and note any differences, like texture.

Hmm, that's a good idea. I'll have to give that a try. The thing is, the problem seems to have gotten better after truing up the wheel some, so I'm assuming that's the cause.

I tried wiping down the rim but it didn't seem to make a difference. But I did notice something odd.

I flipped the bike, removed the front tire, and turned the front barrel adjuster to the point just where the brake pads start to grip the rim ever so slightly. Then with my hand I slowly rotated the wheel with the pads still engaged. Wouldn't you know there's one fairly big spot (about 1/4 the circumference) where the brake pads stopped touching the rim and the wheel just spun through? Jeeze, that would explain the shuddering I felt.

The thing I don't get though, is if this is a rim truing issue. Or if the rim walls have been squeezed together in that spot (or maybe the wheel has a factory defect). The seemingly narrower part of the wheel is near to the hole for the tube's presta valve, but I can't think that's of any significance.

The other thing that bothers me is that, with the tireless wheel in the fork, if I spin it and look down along a tangent, I can't see ANY deformities in the sidewalls of the rim. Seems like I should be able to see something if the walls are narrower in one part.

And totally by-the-way, it just got freaky dark here with lightning and it looks like Armegeddon. Just thought I'd share that.

Just ride your bike....

Since the side walls of the rim are not parallel to each other but are in a V, an increase in distance from rim to hub will produce the effect of a narrowing of the rim. Check that the wheel is true radially. If there is a hump at the narrow spot, tighten the spokes in that area and loosen the spokes 45 degrees either side.

Stress relieve the spokes.That will true it somewhat.

Dude that posting was 3 years go. WT....?????????

My rear wheel was out-of-true so I trued it. Two days later this is what happened while I was riding a double century.

http://i177.photobucket.com/albums/w210/DanteBpb/CCD014.jpg

I was desending a 10% hill and had just made a left hand corner when the wheel let go. The reason the wheel was out-of-true was it was starting to fail. Check the wheel for small cracks around every spoke nipple, I know better and didn't.

Try inspecting the sides of the rims with your fingers. Feel for concave or convex irregularities. Make certain that your pads are not engaging the tire at any point of rotation. You may also try chalking your brake pads to see visual tracks on the rims.