How to True a Bent Wheel

By Dan Goldwater

“Ksh ksh ksh” goes your wheel as your ride. This is the sound of a bent rim. Bent rims are frustrating because they slow you down, but they are usually easy to fix if you know how.

Rims can get bent out of shape from hitting a big pothole, by getting twisted when you try to wedge your bike in or out of a rack and when a spoke breaks. When the bend in the rim is large enough, it will hit your brake pad every time it goes around, causing the characteristic “thwp” or “ksh” sound, and slowing you down.

Fixing a moderately bent rim yourself is easily accomplished with a spoke wrench, which comes in several sizes. Most multi-tools will have two to four sizes of spoke wrench to fit the different sizes of spokes available on the market. Pro mechanics remove a bent wheel from the bike and put it on a special truing stand, but this is not needed unless you want to get a racing bike in tip-top shape. For a regular bike, you can true it quite nicely without even removing your wheel from your bike.

Checking the rim and spokes

Flip over your bike so you can spin the wheel easily. First check if you have any broken spokes. If so, you can follow the same process to straighten out your rim, but you will want to get that spoke replaced soon. Lighten the load on your bike as much as possible if you have a long way to go with a broken spoke. Next, check that your axle is fully seated in your dropouts. If you have a quick-release wheel, it might not be. You don’t want to re-true the rim if the only problem is that the axle is not sitting straight. Same thing with your brakes – first check that they didn’t get bashed to the side or the brake cable isn’t hung up on something.

Checking the alignment

Slowly rotate your wheel while you look at the size of the gap between it and your brake pad. As the wheel turns, you will notice that in some places it is closer to the pad and in some places farther away. With a perfectly true wheel, the gap will be even all around. You don’t need it to be perfect.

Finding the problem spots

Slowly rotate to the part of the rim where it is hitting the brake pad. Here my rim is bent to the left. To fix it, I tighten the spoke opposite the bend: the spoke circled in green. Tightening this spoke pulls the rim to the right. If the bend was going in the opposite direction, I’d instead tighten the spoke circled in blue.

Tightening spokes

To tighten a spoke, place the spoke nipple into the notch in the wrench. Check that you have the right size of wrench. Turn COUNTERCLOCKWISE to TIGHTEN. If you have any doubt, first “pluck” the spoke like a guitar string to make a sound. Tighten one full turn and pluck again. If the pitch is higher you are tightening the spoke; if it’s lower, you are loosening it.

Getting it true

The ding in your rim might be a couple of inches long. Start by evenly tightening the two spokes opposite the ding by a half turn of the spoke wrench. Then recheck the gap. Repeat until the ding is mostly straightened out. If you have a larger dinged area, you might end up tightening three or four spokes opposite to it. If the nipples are corroded, put a drop of oil on them so they are easier to turn.

Finishing up

After the wheel spins freely and the gap looks reasonably even all around, go around the rim squeezing each pair of spokes. This will even out any stresses in the rim. Recheck your truing after this.

Tips

• You can also loosen the spokes opposite the ones you are tightening, which is particularly helpful if you would otherwise need to tighten by a lot of turns in one area.
• If your rim has several dings in various directions, start with the largest one.
• A less common, but fixable problem: you might get an area where the rim is farther away from the hub than the other areas. This can be improved by tightening all the spokes in that area evenly.
• Pluck spokes to gauge their relative tightness.
• If you have to tighten by more than five turns of the spoke wrench, your wheel is probably in bad shape. Rims can become too damaged to be re-trued – after enough dings, you’ll need a new one.

Want more?

You can find this article with extra photos at: instructables.com/group/momentum

Dan develops bike accessories with MonkeyLectric. Previously, he co-founded instructables.com, was a scientist at MIT and developed microchips at Intel.

dan@monkeylectric.com

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