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Trail Fix : Bent Wheel

So you hit that big rock/landed badly/haven't tensioned your spokes in months - DOH! Here's how to fix it so it'll get you home and maybe, just maybe, save your wheel.

The most important thing about a spoked MTB wheel is that none of the spokes are loose.

To find out if any are loose, turn the bike upside down, grab a spoke between finger and thumb (a little to the rim side of where the spokes cross), and violently (ok very firmly) shake it. If the spoke wobbles it's way loose! If it's noisy (pinging and grating sound) it's fairly loose and definitely needs more tension.

To add tension to the spoke use a 'spokey'  to turn the nipple anti-clockwise (spokey is a round plastic spoke key which is perfect for wheel truing and weighs next to nothing, make sure you get the yellow one, the orange one is for road wheels). Yeah, look I know that seems like the wrong way, but that's because you're looking at the nipple from the wrong side of the rim to see it screwing the conventional way. With a spokey you really can feel when you're putting on too much tension. You should be able to turn it just with your finger and thumb. Stop adding tension when the spoke no longer pings and grates, as you perform the test above. If you start needing a lot of 'whole hand' leverage then the spoke is probably getting too tight. Yes I know I said a loose spoke's your worst enemy (that's because if you leave it loose the rim will get bent) but an over-tightened spoke may break. This can lead to a busted rim as well.

OK so you check your spokes are not loose regularly, but still manage to bend your wheel in to a lovely potato crisp shape, what now? The problem with a bent rim is, it adds tension to the spokes, on the side you need to tighten, to correct the bend.

This means that you'll over-tension these as soon as you try and use them to pull the rim back towards straightness. The solution is to physically bend the rim a bit straighter before you start truing. You don't usually need to do this unless your rim is so bent that it won't spin between your brake blocks at all. (if you have disks you won't need to use this method unless the tyre is catching the frame, or there is a really pronounced wobble as the wheel spins)  

If the rim will spin but catches hard on the brake blocks, you may be able to push the bulge out by applying very firm pressure to the tyre and rim when the bulge is near the frame. Then use the check above for spoke tension and don't leave any very loose spokes.

However it's usually better to take the wheel off the bike and remove the tyre and skewer. Then find a solid support, a tree stump or rock, and rest the axle against it with your knee on the bottom of the wheel at the ground. Turn the wheel till the parts of the rim which bend towards you are at the 3 and 9 0clock positions. Now put your hands one on each side in these positions and lean hard on them with straight arms. A sudden hard push should do it. If the wheel is too badly bent you can try the same trick, but standing on the high spots and bouncing up and down. You may get it straight enough to get home, but get a new rim as soon as you do. Remember to add some tension to any very loose spokes when you have done this. Then true the wheel as normal. See Trail Fix - Wheel Truing

If there are any dents in your rim these can be removed by carefully bending back in the jaws of an adjustable spanner. Be careful not to bend beyond and back again as the rim may crack. This is a trail fix if someone is carrying a cool-tool.

This is the kind of damage that results from hitting a rock at speed.

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