Disk wheel balancing?

FiveDaysAWeek
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Joined: Wed Mar 26, 2014 7:53 pm
Location: Sydney, East

Disk wheel balancing?

Postby FiveDaysAWeek » Fri Feb 06, 2015 10:26 am

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
Posts: 120
Joined: Wed Mar 26, 2014 7:53 pm
Location: Sydney, East

Re: Disk wheel balancing?

Postby FiveDaysAWeek » Fri Feb 06, 2015 1:19 pm

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:

"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.

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Duck!
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Re: Disk wheel balancing?

Postby Duck! » Mon Apr 13, 2015 9:30 pm

When the tyre is fitted the weight of the valve will correct it to a large extent.
I had a thought, but it got run over as it crossed my mind.

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toolonglegs
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Re: Disk wheel balancing?

Postby toolonglegs » Mon Apr 13, 2015 9:35 pm

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
Posts: 120
Joined: Wed Mar 26, 2014 7:53 pm
Location: Sydney, East

Re: Disk wheel balancing?

Postby FiveDaysAWeek » Wed Apr 15, 2015 9:08 am

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 :shock: .

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