XC Mountain Biking Repair Lesson: Truing a mountain bike wheel with a bent rim on the trail

wheel-dish-tool

Many have us have dinged a rim and knocked it out of whack, causing it to rub like crazy again the
braking system
while on a trail in the middle of nowhere.

Truing an XC Mountain bike wheel is the art of getting the rim as straight as possible when it spins at both low and high speeds. It takes some practice and finesse to get it right, especially on the trail, where a dedicated shop truing stand is not available.

Warning: It is foolish to ride on a rim that is badly out of true, as you risk injury / death and your wheel set is expensive, so why destroy it. If you have broken multiple spokes, throw in the towel, this is not a trailside repair, and the rim is subject to folding in half on you. If only one spoke broke and if the trail is very mellow, you could ride the bike out slowly and cautiously. A rear spoke break is always a bit safer on the rider than a front wheel spoke break. The fear of face planting unexpectedly can bust you up bad or even kill you, so use common sense.

So let’s get on with our lesson…

XC Mountain Bike Trail Side Wheel Truing: Step 1

Occasionally you get off easy, and by simply locating one or more spokes that have become loose, and tightening them, the wheel is sufficient for cautious trail riding. If this is the case, tighten these loose spokes at the same tension level as the other spokes. Spin the wheel did this solve the problem?

Hint: You can apply a little bit of pressure to the center of some other tight spokes with your hand to guage an idea of how tight the other spokes are, matching the spokes you tighten to the other tighter spokes.

XC Mountain Bike Trail Side Wheel Truing: Step 2

Flip the bike upside down in the most stable position possible with the seat on the trail and the handlebars.

Generally the wheel will have at least two really bad spots, and adjusting one spot will affect the other spot(s).

Setting up a visual truing guide

Use the
braking system
as your truing guide. If you have old school v-brakes the pad will be used to gauge whether the wheel is passing to the left or the right of the pads as it is spun. If the wheel is really bad, you may have to release the V-brakes to make more room so the wheel can spin freely.

With disc brakes, the rotor passing between the calipers can be used if your rotor isn’t too bent. A rotor can be bent back into place pretty easy by applying pressure to it in the opposite direction of the bend. Pushing it slightly passed the bent position, will generally allow it to return to center, as it has some spring to it.

If it is not possible to use you the rotor and calipers due to massive wheel drag when spinning it, if you are capable you could remove the pads, and use the rotor in the caliper now as guide as you should have much more room. If you attempt to remove the pads, do not lose the little clips used to hold in the pads or any other small parts or springs used on the
braking system
.

Hint: Before you remove your pads, it may be possible to get a rough truing established so you can get the rotor to spin enough through the calipers to work it even better.

Theory

Rims might have a different amount of spokes and the patterns vary slightly but the theory remains the same. Take a look at your rim and notice the spokes on each side working in unisons to apply equal tension to the rim and maintain it in a straight position throughout its rotation. They are grouped usually in a triangular pattern. While it might seem visually like there is one spoke on one side and two on the opposite side, the pattern move to create triangles across the rim.

So let’s imagine you locate the first spot that is hitting the brakes the worst and it is pulling the rim hard to the left. You are going to want to tighten the spokes on the right side of the damage to pull the rim in the other direction.

A quality multi tool should have a spoke wrench. If not purchase a better multi tool or carry a dedicated spoke wrench with you that is high quality, compact and light.<.p>

First you must loosen the spokes at the bad spot and a little before and after it on the same side. Loosen them a quarter to half a turn depending on how tight they are. Now you can tighten the spokes on the opposite side the same amount. Get comfortable with the current spoke tension matching it as you work. Pay attention to the spokes on the opposite side making sure they are not becoming too tight and need to be loosened to avoid spoke damage, as you attempt to tighten the rim and pull it the other direction. The spokes on the opposite side are not loosened enough, you will not be able to pull the rim, so more looseing may be required.

Hint: Your spokes may not tighten in the direction you are use to looseing things and visa versa so pay close attention not to strip a spoke. Start by locating a looser spoke to get the hang of it. Also be careful that your spoke wrench fits the spoke tightly to avoid stripping it. Many times the shop, a previous owner, or even you have striped spokes and it can be a real pain to loosen them in the future. Try another riders wrench to see if they have a better one, or in a worst case situation, get out the trusty needle nose pliers if some has a set on a multi tool.

Here is where the art comes into play. When you tighten once spot / region, it will have a great affect on how other spots of the rim are affected. (See the diagram at the bottom of the page.)

After you make your first adjustment, spin the rim and see what it looks like working the next worst area or tweaking the area you just worked on. After you get the rim straighter, and bear in mind perfection is probably not an option. Verify all your spokes are tight before continuing.

I highly recommend having a friend with some experience get you going the first time, or practicing on a cheaper rim at home with your truing stand first. I had some verbal tutorage prior from a pro, and I use to watch him closely adjust my rims if they were real beat up before a ride for a couple years before I jumped into it.

He was a friend who would ride with us but he eventually moved too far, and well it was me or no one after that. I took over the job and would hook my friends up on the trail if they tweaked their rims. I wonder if now that I have moved away if they finally had to bite the bullet and go for it?

If this whole process sounds confusing, I always found it to be a bit tricky, but well within my great desire to tinker with things and I generally have good success. Like anything you do more than once, your execution time decreases as time passes on.

After the ride and repair

Either take the rim to your favorite shop for a professional truing, or put it on your stand at home and get it dialed in. If you broke spokes, replace them. If you mechanic is cool and they usually are watch him true your wheel. Just watching the process can be truly eye opening if you are a visual learner.

Click for larger image

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