Dishing

[overmind]

Over Christmas break, I had to dish a rear wheel on a Dawes 700c road bike.

The V-brakes were impossible to adjust correctly owing to the dishing anomaly.
One side was permanently rubbing.

I tightened the spokes on the drive side of the wheel by 1/4 turn. It is almost
perfectly dished now. It might need 1/8 turn more to fix completely but I will
see how it rides and monitor.

I was wondering though; How does a wheel get that far out of alignment in
the first place? Presumably, it was correctly dished when new but possibly not.

 

[Ajax Bay]

Are you sure the brake calipers were centred? Your decent LBS will have a trueing stand and for a packet of biscuits (and established trust) they might let you pop that wheel in (at a non busy time) and you can check it's centred.
Another option is to put the wheel in the wrong way round (with cassette on the left) in the rear dropouts and that will tell you whether the wheel is centred (or not).

 

[I like Skol]

It is almost
perfectly dished now.

How do you know that?

For a wheel to be correctly dished you should be able to flip it around the wrong way (so the cogs are on the wrong side) and the rim will still line up with the brakes. I.e the rim is perfectly in line with the midpoint between the axle locknuts. There are some exceptions where a wheel is intentionally dished off centre to accommodate an unusual frame alignment or for similar reasons but typically a wheel, front or rear, disc brake or rim brake, will be dished centrally.

 

[I like Skol]

Double posted while I was typing.... I also want to add that it is unlikely the wheel has gone so uniformly out of alignment with use/time. Much more likely that the hub has been serviced and a washer or spacer has been put back in the wrong place, shifting the hub towards the none drive side?

 

[overmind]

How do you know that?

For a wheel to be correctly dished you should be able to flip it around the wrong way (so the cogs are on the wrong side) and the rim will still line up with the brakes. I.e the rim is perfectly in line with the midpoint between the axle locknuts. There are some exceptions where a wheel is intentionally dished off centre to accommodate an unusual frame alignment or for similar reasons but typically a wheel, front or rear, disc brake or rim brake, will be dished centrally.

I was estimating it by eye. I looked along the top of the tyre to the centre of the frame where the traditional brake calipers would be mounted. It seemed to be off by about 1/2 cm. After dishing the wheel it is much less. Another indicator is that the V-brakes when engaged were both veering off to the right. Crappy illustration below but something like:

//

Thanks for the suggestion about the hub being put back together wrong. That is entirely probable, and possibly I did it some time ago, and I just forgot. I'll flip the wheel as well to check the dish. That is a good idea.
Thanks also @Ajax Bay.

 

[Ajax Bay]

I was estimating it by eye. . . . . It seemed to be off by about 1/2 cm.
I'll flip the wheel as well to check the dish. That is a good idea.

An eye is not useful (accurate enough) for the final assessment of 'centred': you're trying to get it to <1mm. And fractions of a centimetre? mm
A 'good idea': you're welcome.

 

[I like Skol]

Ok, something here doesn't add up, I'm sure it's just a typo but ..

You said you tightened the drive side spokes to improve the dishing/brake alignment. This would move the rim toward the drive side or R/H side.
You then said the v-brake arms were originally skewed to the right which suggests the rim was already too far to the right/driveside and actually needed to move left by tensioning the non-driveside.

 

[overmind]

It must have been the left; my mistake.

 

[Gillstay]

Doing work on new bikes before they left a good shop the first thing we had to do was check the spokes as sometimes the machine had got lucky and had a perfect wheel, but had achieved it by only tightening a few spokes. So it may have been wrong from new, and not picked up.