Disk wheel balancing?

[FiveDaysAWeek]

Hi all,

New to disk wheels, and currently setting up my time trial bike. The disk wheel seems horribly out of balance, and spinning it up to any reasonable speed makes the bike violently shake up and down on the work stand.

The culprit seems to be the cutout around the valve which I estimate removes around 15 cubic centimeters of structural foam and of course has no disk wall on one side. The weight difference is enough to make the wheel quickly freewheel to a position where the valve is uppermost when the bike is suspended.

If this was a car wheel I'd get it balanced which would mean adding lead weights to the rim, but that seems like madness when everything else on the machine is kept as light as possible. Is this an issue most people ignore, or is it a problem specific to my wheel (which came with the second-hand bike)?

Cheers.

[FiveDaysAWeek]

OK, maybe adding weight is not madness after all. This is Zipp's take on it for spoked wheels from http://www.zipp.com/support/faq/faq.php" onclick="window.open(this.href);return false;:

"How do I balance a wheel?
Use play dough or plasticine to find the ideal weight by adding and subtracting material placed opposite to the valve hole. Do this with tire and valve extenders installed. Mix epoxy and sand, equivalent in weight to a lump of plasticine, required to balance the wheel (with a tire and valve extender) and place this opposite the valve hole through adjacent tire bed spoke holes - allowing the epoxy to settle and dry between the spoke holes on the inside of the rim."

Apparently solves the reverse problem from mine, but seems to prove the concept.

[Duck!]

When the tyre is fitted the weight of the valve will correct it to a large extent.

[toolonglegs]

Ignore it. Have you ridden the bike?. I have had bikes shake like a rodeo horse on the stand... not felt a thing when ridding them.

[FiveDaysAWeek]

Not completely confident on the extensions yet, so haven't taken the bike over 50 kph (49.7 according to Strava). No issues up to that speed, but my experience with unbalanced car wheels has been that the shuddering appears in fairly narrow speed ranges. I'd hate for that to happen going downhill at 60+ kph with my hands so far from the brakes .

[Bookervab]

If you are copying to the pool and the error is about the source disk, why are you looking at the pool disk?

[Derny Driver]

I'd hate for that to happen going downhill at 60+ kph with my hands so far from the brakes .

Never descend or corner with hands on the extensions. No control there if you hit a bump.

A bike wheel is not a car wheel. You are worrying about nothing. Every disc wheel does this. Just ride it. There will be no problem.
I have heard of people trying to use golf club weights to balance their wheels. There is no need for it.