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Tuesday, January 22, 2019
When Rock Meets Rim: Attempting to Repair Larger Holes in Tubeless MTB Tires By Brian Gerow
This scenario is as common as it is unfortunate: You mount a new tubeless tire and roll out to test it on your favorite track. Maybe you push a little harder than usual through a corner or rock-garden to check the grip. Then you hear it: the ever-dreaded “pang!” of a rock striking acutely against your rim and cutting your tire. You find the hole and realize it is too large for any tire plug to fill. Find a dollar bill or candy wrapper to cover the puncture, tube it, and head on home.
If you’re like me you spend more money than you can actually afford on your bike. People who look at it without knowing you might think you also have diamonds on the soles of your shoes. The truth of the matter is that you paid a good chunk of your weekly salary for that tire, and you can’t afford to buy a new one any time soon. Let’s see if it’s repairable.
I tried to repair this hole trailside with tire plugs, but even after folding the plug in half twice the sealant couldn’t fill it in. I threw my only tube in and rode delicately for the rest of the day.
Once you’re back home, remove the tire and tube, drain any remaining latex, and mark the location of the puncture on the inside and outside of the tire. This will make the hole easier to locate. Place a piece of tape on the outside of the hole as a waypoint for later.
Clean the inside of the tire where the puncture is with dish soap and water until there is no sealant left near the hole. Depending on your chosen sealant, this may require some hefty elbow grease. Clean about a 5cm (~2in) radius around the hole to give yourself plenty of room to work with. Once you have a nice clean circle around the hole you will want to wipe the surface with rubbing alcohol to remove any leftover soap or oils.
Take a piece of fine sandpaper or a ball of steel wool and rough up the cleaned area. Sand the tire until all of the clean surface is dull and marred with abrasions, but not so much that you start making the tire thinner.
This next step is a bit subjective, depending on the size and location of the hole in your tire. If the hole is too large for a tire plug to fill, you have some work to do. Try the following steps.
Cover the hole with a large inner tube patch, using ample glue to be sure it stays put.
Once the glue has dried you will want to cover the patch with 2-3 layers of Gorilla Tape or some similarly robust tape.
Mount the tire and set it up tubeless as you normally would. Pump the tire slightly higher than the pressure you prefer to ride with so that you will be able to see how the hole reacts with weight and impact pressure. If the patch is not bulging out of the hole when you put your weight on the bike, and the hole remains mostly closed, you are ready to ride. Remember that this is a repair to save your tire and some cash, and may not result in the tire performing as well or lasting as long you had hoped.
Sandpaper, epoxy, and a chunk of old tire.
If the hole appears somewhat open on the outside of your tire after patching and remounting the tire you can try adding layers of epoxy to fill it in, which will also help keep things together.
If the rubber patch is bulging out of the hole you will need to add another layer of backing inside the tire to relieve the pressure. Remove the tire, take off the tape, and clean the area as before. Next, cut a piece from an old tire that is large enough to cover about 2cm on either side of the patch. I like to cut a piece from the center of the old tire’s tread, as that is the strongest part. After making sure that the initial inner tube patch is still securely glued, and the surface is re-sanded and clean, slather a healthy layer of epoxy on the non-tread side of the chunk of tire and glue it over the area where the hole is. Keep applying pressure to the whole tire chunk until it is fully dried. Most epoxies have minimum temperature requirements and drying times, so be sure to read up. Once the epoxy is secure and dry, re-mount the tire as before.
With the thick patch glued inside your tire, your wheel will now be out of balance. You may want to add a similarly sized patch to the opposite side of your tire to keep it rolling properly.
For sidewall tears that are far enough from the tread, I like to add an inner tube patch to the outside of the hole to help the repair last longer and to add strength.
The finished product. Knowing that I will ride this particular tire for at least another six months, I opted for the burly fix. I tried to capture the puncture in a photo after re-mounting the repaired tire, but there is nothing to see. The hole is no longer visible, and the tire maintains its shape where the patch is.
BONUS TIP: If your tubeless setup is leaking air at the valve, wrap the base of the valve in PTFE tape (aka plumber’s tape) before inserting it in the rim. The tape will compress and seal any small gaps.
The above may seem desperate, but I have patched tires that rolled through an additional year with these tricks. If your tire still has tread life left when it tears, it’s likely worth trying to fix.
This Sardinian goat has rock protection sorted out.