One of the most visually descriptive terms for a mechanical ever, the taco occurs when a wheel is forced to move sideways rather than forward or backwards. The result is that the rim folds over on itself, despite the best efforts of the spokes, and stays in the new, bent shape.
A wheel in this condition will never be the same again. Even when it’s fixed, the wheel may prefer this new shape and “pop” back into the tacoed condition at any time. Thus, don’t be overly gentle in your repair – it’s only designed to get you home.
First, remove the wheel from the frame. This may be harder than it sounds, but be creative.
You may have to remove the tire and tube at this point. If the tube didn’t puncture, you are incredibly lucky, but the fix involves pounding the rim in ways which can hurt tires. Off is better. The same applies to the brake rotor, if you have one.
Loosen off all the spokes by two turns. Now, apply pressure to the raised areas of the rim to straighten it. “Apply pressure” may mean “Jump on” or “Hit against ground” if necessary. The aim is to make the rim as close to its original shape as possible, but without damaging the rim walls where the tire bead must sit, and without damaging the axle or hub.
Once you have the rim relatively straight in its slack-spoked condition, tighten up all the spokes again. Do this one half turn at a time all the way around (start at the valve to know where you are).
After one and a half turns (three times round the wheel), the wheel may be tending to go out of true again. Put it back in the frame, and use the brake pads or a stick held against the seat stay/fork as a guide to getting it as round and wobble free as possible. See the section on wheel truing for details.
It is very unlikely that you will return the wheel to true. Instead, just make it good enough to ride out on. If you have rim brakes, this may require you to loosen off or remove the brake pads or even the brake arms, depending on how bad the kink is.
Now, check the inside of the rim for sharp and rough edges that you may have created during your re-shaping exercise, and reinstall the tube and tire.
After inflating the tire, check that the tire tread isn’t rubbing on the frame as the wheel rotates. If it does, it will cause major frame damage very quickly. You may need to straighten the wheel further or cut some of the offending tire knobs off with a knife.
Tip: You may be unsure which way to turn the spoke nipple to “tighten” and “loosen” spokes. If so, sit down with the wheel in front of you, held vertical between your legs. Rotate the wheel until the nipple of the spoke you want to move is closest to you. Turn your spoke wrench clockwise to tighten this spoke, anticlockwise to loosen it. Remember – you are turning the nipple, not the spoke (see wheel truing for more information).