Through this quick question series, we will show quick fixes and collect comments from experienced riders on specific DIY mountain bike repairs. Although most of these trail classifications are covered in our maintenance articles and videos, this is a space for long-time riders and readers of the Singletracks community to share their knowledge. Please enter your relevant experience and suggestions in the comments below. Do you have a quick question? 🤔 Email [email protection]
A mountain bike with no scratches or abnormal noises has probably not been ridden. Playing in the rocks often adds a lot of features to our equipment, and rims are no exception. Whether we neglect to check tire pressure or just ride fast on rough roads, almost everyone will end up bending aluminum rims. If you are really picking up the pace, this can happen even under higher pressure and inserts, and the dents often make it difficult to achieve a strong tubeless seal.
According to Dustin Adams of We Are One Composites, curved rims are an area where carbon fiber rims are generally superior to alloys. Carbon fiber can provide significant movement during rim impact, causing it to compress into an egg shape and rebound. The aluminum will bend to a point after which it will not return to its original desired shape. One objection is that aluminum rims can usually be repaired when they are bent, and in most cases, damaged carbon fiber rims need to be replaced. We are not here to help you decide between alloy ferrules and carbon ferrules, but to repair dented metal.
The alloy ring is likely to bend back to a shape acceptable to your tire and sealant. In the best case, only the bead hook will bend, and it can be easily pulled back to a wall high enough to secure the tire and continue rolling.
The aluminum wheels of Syncros Revelstoke 1.5 and Crankbrothers Synthesis I9 that I tested last year found dents on the rims and must be hit with a hammer. The dents are sharp enough that they press the tire bead out of its channel, preventing proper tubeless sealing. The solution in both cases was found in a few pieces of medium-hard wood, a pallet and a hammer. Consider turning off your perfectionism switch; it's time for classic good enough repairs.
Find a soft surface and place the wheel where the hub can be placed without putting too much load on the spokes. A small tray like this connected to the washing machine can keep the wheels still without scratching the rim finish. Then, any wood about the size of the dent can well offset the impact of the rock impact without creating any sharp edges in the rim. Center the stick and tap until the hook becomes quite straight again. Keeping the bead seal does not need to be perfect, it is usually sufficient to bend it back by 50%. Then, put on the wheels, put on the tires, and enjoy!
If you happen to have a bench vise with a soft clapping chin, this can also bring the edges back to a straight enough posture very well. Try not to clamp too many rims, because you may end up bending a larger part and then chase the dents around the wheel and eventually need to replace the rim.
If you only need to straighten out some things for riding or racing, and don’t care about the appearance of the finished product, please use the set of pipe pliers shown in the picture below to grasp the bead hook, and then gently tilt it in the right direction. I I like to wrap my chin in old jeans so that they don’t cut into the alloy and cause tire problems. Be careful not to bend too much, because it is easy to dent the outer ring or inner ring contour with pliers and cause new problems. If there is an impact or a cut in the pliers, the rim tape may need to be replaced.
If you are already out of breath but can't get the bead hook to play with the tire bead, you can try another technique. Before the emergence of tubeless rims, we would use an inner tube with a diameter smaller than the wheel, such as a 26-inch tube, and cut it in a circle along the outermost edge. Then, insert the valve and stretch the opened inner tube carcass like a huge rubber band on the rim, and then install the tire on the top of the inner tube. The inner tube rubber between the tire and the rim will take up some space from the dents, which usually seals the tire and rides safely.
The tray can also be used to re-dress the inwardly recessed wheels in the egg-shaped direction. I work in a shop in Florence, Italy, where we provide services for a large number of DH racing equipment, and I learned this move to save customers money and get them back on track. Place the part of the rim that is bent inward (toward the hub) between the two plates. Then place an eye-catching board inside the rim and hit it until something is round enough for riding. You usually need to tighten the spoke joints at the bends, unless you can magically "return the wheel back to its original shape." This is definitely not an ideal solution, but it may save your mountain bike holiday or race day.
What are some useful tips for straightening rims that cannot keep the tubeless tyre sealed? Please share with us in the comments below.
I used an adjustable crescent wrench and it worked well. The advantage of a set of pliers is that it has no clamps on the jaws, so you don't need any fabric to prevent scratching the edges, and you don't need to use hand pressure to hold the pliers in place because it may slip off your handle.
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