Truing an 'out of round' wheel

Question

I am building my first wheelset. The front wheel went without a hitch - nice and true both radially and laterally.

However, the rear wheel has a pronounced (5mm) bulge over about 1/4 of it. The rest of the wheel is pretty much true. As far as I can tell, I should be tightening the spokes around the bulge area, but they're already significantly tighter than the rest of the wheel, and the bulge isn't coming out.

What should I do at this point? Is it worth loosening the spokes everywhere else so that the rest of the rim settles out? Wouldn't that bring the spoke tension to be even less even?

Thanks

Answer 1

Whenever I get stuck wheelbuilding, I loosen every spoke one turn, walk away and come back in a few hours or the next day.

The worst thing you can do is keep doing something that is not providing the results you expect. It is completely possible to overtighten spokes enough that they stretch significantly under the tension. You can even break them with a bow and arrow like result that can be slightly terrifying. ( Fortunately the spoke was pointed at the ceiling and not me when that happened. )

Part of wheelbuilding is getting a feel for how much tension the spokes will support. There is a point at which tightening them further just does no good and actually makes the wheel worse, not better. In the past when rims where just boxes made as light as possible and spokes were more burly, you'd get wonky things happening to the true to let you know when you'd gone too far. Now most rims have enough structual shape that they won't deform that way and the spokes are much lighter.

In my experience out of round truing almost always requires adjusting all 4 quarters of the wheel. ( i.e. the trough as well as the bulge. ) You can't fix it by just working on one section.

If tightening stops working, it's time to take some tension out of the entire build. Start by loosening the spokes you've been working on a half turn at least and then start loosening other spokes to achieve the affect you want. If that still doesn't work, loosen all the spokes and start over.

Answer 2

There is a way to gauge both out of round and radially at the same time of you have a Park Truing Stand. I just discovered this technique tonight actually..... It involves removing the rubber caps on the calipers first, so that they are bare metal.

Next align the tips of the calipers so that they are under the rim, instead of along the vertical walls of the rim. Because the tips make a } { shape, the very most tip provides out of round reference and the sides of the calipers provide the radial reference. Does this sound legit? Because it seems to work really well, especially if you alternate adjustments AND you can reference the other adjustment instantly.

Unless I just discovered how to properly use a truing stand. In that case, I'm an idiot. But I hope not.