dougdunn

I bought a used wheelset - Mavic MA40 rims and Dura Ace hubs. Front wheel was perfect, rear very warped. Bought a good set of the same rim. Took apart the old rear wheel, measured the spokes, bought new spokes and nipples. Laced the wheel up today (used Sheldon Brown's guide). The wheel looks good and is true and runs smooth. Here is what I need help with - I don't understand how to dish a rear wheel. Front wheel seems straightforward - hub and flanges are centered on the rim, but is that true for a rear wheel? For a rear wheel are the flanges also centered on the rim, or is the axle centered on the rim with the hub (flanges) offset?

It would seem to me, if the hub is offset that the spokes would need to be different lengths, but the old spokes are all the same and that is what I bought to rebuild the wheel.

Thanks for the help.

Pompiere

The rim should be centered on the axle. The right side spokes (drive side) need to be a mm or two shorter than the left side to allow for the spacing of the freewheel. It's not a big deal to have same length spokes and compensate by taking a couple extra turns on the nipple.

Here is a link to a recent thread about measuring the dish with common household items. https://www.bikeforums.net/classic-v...ring-tool.html

SurferRosa

Good work building them and following Sheldon's guide. The hard part is over. And dishing is easy. Just remember that, regardless of whether it's a front or rear wheel, the rim is always centered over the ends of the two opposing axle locknuts, not anything else. In the front, the locknuts should be equidistant with the hub flanges. So, there is no dish. But, in the rear on an externally geared bike, there is usually more space between flange and locknut on the drive-side, requiring the rim be centered (dished) more toward the right flange.

Sheldon maps out a way to make a dishing tool using two stacks of cd jewel cases (or similar, like books), a table top, and a metric ruler. Start with a wheel that is vertically and laterally true. Balance the rim on the two stacks and measure the distance between the table and end of hub locknut. Flip the wheel over and repeat with the other side. Any difference between the two measurements needs to be removed by loosening one side of spokes and tightening the other the same amount.

Ex Pres 

That is, until you fit the wheel to the frame and find out your frame's rear triangle is out just a little.

SurferRosa

Fix that while you're at it.

Salamandrine 

On vintage wheels, typically the drive side spokes are 1mm shorter. On a lot of modern wheels the theoretical difference is so little, people don't bother, and use the same length for both sides.

Anyhow, to dish the wheel, loosen all the spokes on the non drive side 1/2 turn. Then tighten all the spokes up on the drive side 1/2 turn. Use whatever method you can to check the dish. Repeat as necessary until the rim is centered between the locknuts of the hub. As you get closer, you'll want to use smaller increments on the spoke wrench. IOW loosen one side 1/4 turn, tighten the other side 1/4 turn.

That's a slightly simplified version of how to do it, but you get the idea.

If the spokes on the drive side aren't protruding past the nipple inside the rim, and there are no threads showing, you are fine even with the same length spokes. IOW, try the above before taking the wheel apart and starting over.