Bicycle Mechanics - Verticaly untrue wheel

Is it ok to race it? Laterally it is perfect.

No, you'll lose energy from the tiny up and down motion it causes and Lose The Race.

Why not try to true it? What you have is called a "hop". At the top of the "hop" the spokes are under less tension (assuming the rim is not bent), so tighten the two, four or six spokes that encompass the hop. Be careful, if you are not sure of yourself, do not attempt this. Only do 1/8 to 1/4 turn at a time, and when you're done, check the lateral trueness.

In order to do this, you need to tighten two, four or six spokes. If you only tighten one, three or five spokes, you'll throw off the trueness.

Careful: the OP didn't say whether the vertical error is up (a hop) or down (a dip, i.e. a flat spot.)

In a hop, the rim is not usually bent and can indeed often be corrected by tightening spokes in the area of the hop. If the spokes are noticeably looser at the hop than they should be, tightening just those spokes will usually do it, but it takes one-half to a full turn to see much effect in vertical movement. But if the spokes at the hop are roughly the same tension as the other spokes, then you really need to loosen spokes elsewhere around the rim to bring the wheel as a whole into roundness. This can be a challenge and is definitely not something to tackle as your introduction to wheel-building. Merely making the spokes at the hop extra tight will not work in the long run and will cause the rim to fail prematurely. A rim that started out round but is now egg-shaped has often started to fail anyway by cracking around the spoke holes.

An isolated dip/flat spot is another story. In this case the rim is nearly always bent (from hitting a pothole, say) and the sidewalls are often flared out so they interfere with the brake pads. The spokes in the area of the flat spot will be loose because the rim has been pushed permanently closer to the hub. A flat spot cannot be worked out by tightening spokes. The rim will need to be replaced. References on wheel-building and repair discuss a variety of expedients to get a badly dented rim straight enough to ride in an emergency.

I like what Peter White has to say on this subject, he puts a real world perspective on it. He mentions that even with quality rims, up to 1mm vertical deflection can sometimes be expected, and that in real world riding, you'd never feel that. Anything more than that, with a quality rim such as Mavic or Velocity, is unacceptable to him. Scroll down to the heading "how true will your wheel be?"

http://www.peterwhitecycles.com/wheels.asp

His wheels are magnificent. Utterly true vertically & laterally. Everyone who gets a wheel/sees a wheel From him raves.

thanks for replies.
the question is not how to fix it but is it ok/safe to race it?

If it's really bad, like > 5 mm, then you should fix it. If it's < 2mm then test that the spokes are nearly the same tension by plucking them, and race it if they are- the tire has more vertical bounce than that. Between those extremes, I would spend some quality time with my spoke wrench, but YMMV.

I've had a few minor hops in my wheels when hand building them that usually fall right at the weld or seam - it appears there is slightly more material on the rim in this area. I get it as close as I can them leave it alone. They have been Good for years.

thanks for replies.
the question is not how to fix it but is it ok/safe to race it?

Take it for a ride and see how it goes. If you cant feel anything then its OK. If you can feel it then maybe its not. My experience with a hop on a cheap wheel is that when just riding around it was OK, not dangerous but it did cause the wheel to wobble from side to side and it was a little unstable, particularly when riding with no hands despite it being true from side to side.

Anthony

You people do realize that wheel trueness isn't what defines a quality build. It's trueness and as even tension as possible... right?

Any moron can make a wheel hyper true at the expense of tension.

Yes, this moron recognizes that even spoke tension is more important than "hyper trueness" (whatever that is.)

To the OP:
1) If the hop or (particularly) flat spot causes the rim to catch on the brakes as I mentioned above, then I would not ride it in a peloton because your braking modulation will be jerky, especially with dual-pivot brakes that don't "follow" the wheel imperfections as well as side-pulls do.
2) If there is enough of a hop that you can feel it bouncing under you, that can't make your control any better when you are pushing yourself to your limits in cornering.
3) If the hop doesn't do either of these things but is due to uneven spoke tension, then the wheel will go progressively out of round or out of true and eventually become unrideable, but until it does, .... go for it. Other riders will nag you about it though.

You people do realize that wheel trueness isn't what defines a quality build. It's trueness and as even tension as possible... right?

Any moron can make a wheel hyper true at the expense of tension.

So your condescending statements are back again. Now you are calling us all morons? There are a lot better ways to converse without being so rude. I'm starting to see a pattern here.