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Old 12-13-07, 10:28 AM   #1
dwood
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Wheel Dishing

I've purchased a few wheel-related tools lately, including the Park wheel dishing gauge, and have a general question about wheel dishing.

On my existing two bike's rear wheels I can simply measure the amount of offset as set up by the factory and then duplicate it. But if you are starting from scratch with a frame, cassette and a bare rim . . . what steps do you take to determine the amount of dish required?

Are there published offsets for cassettes/wheel combinations? What about frames' specs?

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Old 12-13-07, 10:39 AM   #2
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Don, the idea is to dish the wheel so that the rim is centered between the dropouts. The easiest way to do this is to flip the wheel in the truing stand frequently as you're truing it to ensure that as you tension the spokes, the rim remains centered. I have a dishing gauge, but don't use it.

EDIT - Retro Grouch expressed it better; the rim needs to be centered between the locknuts (instead of dropouts).

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Last edited by Scooper; 12-13-07 at 11:17 AM.
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Old 12-13-07, 10:39 AM   #3
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Cassettes and frame specs don't matter. In any case, you want the rim to be centered between the hub's lock nuts. One way of doing that is to use your wheel dish gauge to check the amount of offset on both sides of the wheel. When the two sides are equal, the rim is centered between the locknuts.
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Old 12-13-07, 11:52 AM   #4
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Quote:
Originally Posted by Retro Grouch View Post
Cassettes and frame specs don't matter. In any case, you want the rim to be centered between the hub's lock nuts. One way of doing that is to use your wheel dish gauge to check the amount of offset on both sides of the wheel. When the two sides are equal, the rim is centered between the locknuts.
Retro, very true!

But if the frame rear triangle is out of alignment, the rear wheel plane might not fall in teh plane of the front triangle. Assuming teh front triangle is not twisted, the fork is aligned, and the front wheel has no dish, you might want to dish the rear wheel off to one side to make the bike ride neutrally.

from "How to align bicycles when you have a truing stand but no frame alignment tools" by Road Fan.

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Old 12-13-07, 11:56 AM   #5
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Thanks to both Scooper and Retro G.

It is clear to me now. What I was somehow missing was the concept that, regardless of the width of the cassette, that the dropouts are symetrical with respect to the centerline of the frame, therefore the wheel is always centered between the locknuts [i.e. dropouts]. I was somehow laboring under the misconception that the frame was somehow manufactured with one dropout further from the centerline to accomodate the cassette. Jeez . . . a quick inspection of my bike just now showed how ridiculous that thinking was. <g>

Thanks again to this forum!

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Old 12-13-07, 12:35 PM   #6
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...if the frame rear triangle is out of alignment, the rear wheel plane might not fall in teh plane of the front triangle. Assuming teh front triangle is not twisted, the fork is aligned, and the front wheel has no dish, you might want to dish the rear wheel off to one side to make the bike ride neutrally.
I would think the way to fix this is to have the frame aligned rather than compensate with wheel dishing.

If you have more than one wheelset (e.g. one set for training, another for competition) they'd both have to be dished to compensate for the poor frame alignment, and if you have other frames, you wouldn't be able to use the compensated wheels on them.

In other words, it's better to treat the disease rather than just the symptoms.

My $.02.
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Old 12-14-07, 03:14 AM   #7
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You can correct an offset in a steel frame fork (check with magnet) the Sheldon Brown way.
Never attempt to bend an aluminium frame, and, obviously, don't even think about bending anything made of carbon fibre.
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Old 12-14-07, 09:35 AM   #8
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Originally Posted by Road Fan View Post
Retro, very true!

But if the frame rear triangle is out of alignment, the rear wheel plane might not fall in teh plane of the front triangle. Assuming teh front triangle is not twisted, the fork is aligned, and the front wheel has no dish, you might want to dish the rear wheel off to one side to make the bike ride neutrally.

from "How to align bicycles when you have a truing stand but no frame alignment tools" by Road Fan.

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Sounds to me like screwing something up in order to compensate for something else that's also screwed up.

I can see doing something like that in an emergency but wouldn't it be better to fix or replace the frame?
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Old 12-14-07, 04:08 PM   #9
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I would think the way to fix this is to have the frame aligned rather than compensate with wheel dishing.
Yeah, don't skew the wheel to center in a mis-aligned frame. If your wheel is off to one side at the chainstays or seat-stays, you can verify that the frame is out of whack by flipping a properly-dished wheel. You'll find that the rim is still off to one side by the same amount. The wheel is fine, the frame is off and should be fixed.
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