How to Find and Fix Leaks in your Tubeless Tires
All you need to know about leak detection and repair to get rolling again
The Bubble Test
The first step in repairing a leak is locating exactly where the air is escaping from your tire. The bubble test is the best way to pinpoint the exact location of a puncture. You can find multiple leaks with this type of test too, which is a common problem with some types of thorns.
However, the bubble test is not always a reliable way to locate leaks between the tire bead and the rim strip. Air that leaks from anywhere around the circumference of the tire bead will almost always come out at the inflation valve. The spoke nipples typically seal well enough that air will not make it through the spoke holes.
Here's how you do it: Immerse the tire and rim in water. You need to have a fairly large container for the water in order to submerge the full tire and rim for 4 or more spoke holes at a time. A bathtub, sink, large utility basin is ideal. You will be able to find the puncture by observing where air is bubbling from the tire.
If an initial bubble test shows that the leak is inside the rim cavity (bubbling through the inflation valve clearance hole in the spoke bed of the rim) and you want to isolate a leak location, then seal the valve outlet area with an oil based clay or other non-permanent caulking material and try to force the bubbles out of the spoke holes near the leak. It is generally easier to substitute parts to cure this type of leak. You can't perform a bubble test on a tire that's not mounted to a rim or if the tire leaks air too fast to immerse.
The Aural Test
Another way to find the location of a leak is to inflate the tire and listen for the distinct sound of air escaping. Not all leaks are detectable in this way since you need to be in a pretty quiet environment in order to hear it. You can detect some internal leaks by slowly rotating the wheel as it is partially submerged in water (about 6 inches deep). As you rotate the wheel and an internal leak is submerged, you will hear the sound caused by the bubbling water inside the rim. You cannot see an internal leak, but you can find its general location in this way. This can be helpful when you are trying to find a leak between the tire and rim strip. If you hear a puncture leak in the tire, another way to confirm its exact location is to test the likely spots with saliva. If you cover suspected hole with saliva, the noise of air escaping will get louder and will also be visible.
If you have a tire that leaks but you can't inflate it enough to use the bubble test or hear the leak, you have to substitute components (rim strip, valve, or tire) to isolate the cause and repair the leak. You can replace everything that might be leaking air to fix it fast, or you can replace things one at a time to find the defective part.
Leaks at the valve
Remove and inspect the valve. If it is damaged, it will need to be replaced. If you are out on the trail, you will need to install an inner tube to complete the ride.
Leaks under the tire bead
This type of leak requires new parts or using an inner tube. In an emergency, a caulking adhesive or thick, non-hardening adhesive (such as traditional sew-up tire glue) can seal up a small leak between the tire and rim strip temporarily. This method should only be used as a temporary measure to complete a ride when spares are not available.
Leaks through the tire casing
Occasionally you might have a leak in an otherwise serviceable tire casing that allows air to escape at an unacceptably high rate. A bubble test will reveal the location(s) of the leaks. Normal patching methods will work, or a fluid tire sealant such as Super Juice might reduce the leak rate too. If sealant is used, you should hold the wheel sideways (rotational plane horizontal) to allow the sealant to cover the leaks.
Regular patches from a standard patch kit will work on the inner surface of a tubeless tire. "Glue-less" patches will work too. The same rules for patching a tube apply here: the inner surface of the tire must be clean, dry and abraded lightly to be patched reliably.
It is often possible to repair a damaged tire casing in order to ride out on a given day. This solution is only good for an emergency repair, so replace the tire before your next ride. Here's how to do it: Use a dollar bill or some other fibrous material to cover the fracture in the casing on the inside surface of the tire. There is a limit to the size of the hole you can repair this way. Applying some adhesive on the material you're using to cover the fracture can help hold the reinforcing material over larger holes. You will need to install a tube in the tire after you repair this type of leak unless you are using a fibrous material that is not permeable to air and is sealed to the casing well. You should not inflate the tire more than necessary to finish the ride.
If All Else Fails
You can always use a tube in a tubeless tire to eliminate the issue of a leak and be able to ride home. You will have to remove the inflation valve to install the tube, and you can also exchange the rim strip for a lighter one to save a little weight.