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I've recently learned how to bunny hop. It's definitely a lot of fun. I've repeatedly tried doing a 180 (with no success). It mostly ended up having the rear wheel lifted, the bike rotated 90 degrees and landed perpendicular to the starting point (either with the front wheel lifted or stationary).

This obviously causes a lot of stress on the rims...

And soon enough, I started feeling vibrations from the rear wheel at high speeds when not pedaling. I've inspected the rear wheel and found out that the rim is bent pretty badly, but not enough to cause noticeable drag or any anyway noticeable affect my ride.

How dangerous is it? Can it make me fall, lose control or anything like that? Can I keep it until I feel comfortable jumping (and not practice this activity on the new rim)?

Can it be fixed in a bike shop (maybe by bending it backwards?), or the only way to fix it is to replace the rim?

If I have to replace the rim, how difficult is it to move everything else (disk brakes, gears)? Do I need to 'calibrate' the rim or anything of this sort?

And generally, anything I should know before walking to the shop and ask for help so they won't rip me off?

The bike is a Specialized Pitch Pro 2010 (Enduro full suspension). I don't really know, but I assume that the rims are aluminium (by look and feel). I believe these are the original rims on on the bike, the DT Swiss 445D, 32-hole.

Mark Segal
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    Hi, and welcome to bicycles.SE. What kind of a bicycle are you talking about? Is it meant for stunts, like a BMX bike? Was it an expensive bike from a bike shop, or a cheap bike from a department store? Did you get it in good shape, or had it been abused by former owners? Is the rim chromed steel, aluminum alloy, or carbon fiber? In short, please edit your question to give us a little more information. Pictures would be helpful also. – rclocher3 Aug 03 '16 at 18:13
  • If you can feel the effect of the bend while riding, its too bent to ride safely. Normally bent rim causes bad handling while leaning into a turn. You don't generally feel them on high speed traved because the bent rim is not weighted differently. – Criggie Aug 03 '16 at 20:11
  • Another option is to try trying the wheel yourself. You need three things, a spoke key that fits your spoke nipples, some way of spinning the wheel and measuring the wobble, and plenty of patience. I simply flip the bike and use a well calibrated finger resting on the chainstay/fork that lightly touches the braking track. – Criggie Aug 03 '16 at 20:21
  • Thanks for the help! I've edited the question to add info about the bike. – Mark Segal Aug 03 '16 at 21:47
  • Moving the brake disc and casette is very easy. You need tools: cassette lock-ring tool, big wrench, chain whip. You should have these anyway, since cassettes have to be changed about once a year for a bike ridden daily. Obviously, make sure you get a wheel whose hub has the right receptacle for the bolt circle of your brake disc. You could build a new wheel with just the rim, using your existing hub (and perhaps even spokes). – Kaz Aug 03 '16 at 23:40

2 Answers2

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Riding a slightly bent rim is typically not dangerous. I've continued to ride bent rims on my bikes for many months. Eventually, it may get worse, especially if you are learning 180's or how to jump. The bend is a weak spot that can get worse if you land on it with the same side loads again. From your description, it sounds like it isn't a giant bend— you can only feel it vibrating at high speed, and it isn't bent enough to contact your frame or otherwise disrupt how your wheel rolls.

It could be dangerous if the rim is cracked at all. Usually a rim only cracks under extreme damage, or after months of riding it bent, and at that point becomes much weaker. A cracked rim could collapse under load, or especially harsh impacts like landing jumps. Inspect your rim again for cracks around the bend just to be sure.

Usually, a bike shop can fix your wheel. Most bicycle wheels consist of the rim, spokes, and a hub at the center, with a bearing and axle that connect to your frame. The spokes actually give your wheel most of its stability. It's similar to a suspension bridge, where the rim is not super strong by itself, but with tension from the spokes it becomes much stronger.

If your wheel is this type, a bike shop can "true" your wheel by tightening and loosening the spokes around the bend. They have special tools to help get your wheel back in true (straight) by making minor adjustments on the spokes throughout your wheel. Usually truing your wheel doesn't require new parts, it just requires labor, and should be under $50. Also, a good wheel true can make your wheel stronger, so you might have less problems with it in the future.

This does depend on the type of bike and wheel you have though. Cheaper rims can be harder to fix, and if its bent too badly to be trued, you may need a new wheel.

When dealing with the bike shop, simply show them your wheel and ask if it can be trued. If yes, they'll tell you a price and when they can do it. If not, you can ask them about new wheel options. Replacing just a rim with your old hub and spokes is very labor intensive, which is expensive. It sounds like your wheel should be truable. But if it is not, the shop will want to sell you a new wheel, because it simply isn't practical usually to replace just the rim.

TSchafer
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Some bent rims can be fixed, and some can't. It's hard to say how dangerous your rim is without knowing more, but at least a bent rear wheel is better than a bent front wheel, because if the front wheel failed suddenly then you would probably go over the handlebars. The bends that I'm used to are bends that make the rim wobble from side to side a little, and those usually aren't very dangerous with an aluminum alloy rim as long as there are no cracks and the rim doesn't have any dents or bulges.

The late great Sheldon Brown's web site has a page about emergency wheel repairs and another page about trueing wheels that should answer most of your questions about possibly repairing your rim. If the bend isn't too bad that's often the kind of problem that a beginner mechanic can fix, and the tools are cheap.

If the rim has to be replaced, then it can get expensive if you have to buy a wheel from a bike shop, or have a shop build you a new wheel. Sometimes you can find a cheap used bike with a wheel that will work, or a used wheel. If the bike has a freewheel or a freehub then a special tool would be needed to get the freewheel or cassette off, but the tool isn't too expensive. Of course if you have a wheel built with a new rim and your old hub, then you wouldn't have to transfer the freewheel or cassette.

Good luck.

rclocher3
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