Flats suck, but they happen to everyone. So, learning how to repair a flat mountain bike tire is an essential skill — right up there with “using the pedals” and “holding onto the bars.”
Spending five to ten minutes repairing a flat is immeasurably better than spending an hour walking your bike back to the parking lot, so check out our guide below and comment with any questions you might have on the process.
Before you dive into the nitty-gritty, though, you’re going to want to make sure you’ve got all the tools you need on the trail to get the job done, so we’ll go over those first:
Pre-Ride Prep: Gather your repair materials.
The materials you’ll need to fix a flat can vary a little depending on the kind of tires you’re running.
Ultimately, it all depends on how prepared you want to be, but we recommend the following for each type of setup:
Those who ride tubeless should only need:
- Air Pump
- Tire Plug Kit
- Multitool
- Tire Levers
- Spare Tube (For emergency use only!)
If you’re riding with tubes, however, your kit will look slightly different:
- Air Pump
- Patch Kit (Glue & Rubber or “Scab” Style Patches)
- Multitool
- Tire Levers
- Spare Tube (For serious blowouts, or when you just don’t feel like messing with patches.)
Now that you’ve got your kit together, let’s talk about what to do when you notice you’ve got a flat tire.
Step 1: Get off the trail!
Trailside repairs should be just that — done on the side of the trail. There’s nothing worse than coming down a fast section to find an unexpected mountain biker broken down in the middle of the path. Go ahead and find a nice clear spot off to the side of the trail before you start your repairs — it’s the polite thing to do!
Step 2: Get your tires off the ground.
To make the process as easy as possible, we’re going to want to get our tires off the ground so they’re easier to work on. Typically, you’ll accomplish this in one of two ways.
The first method is to find a low-hanging branch on a small tree, and suspend your bike by placing the branch underneath your seat, creating a makeshift workstand for the job.
Not every reader will have trees where they ride, and personally, I find the tree-limb method a little overkill, so I will usually just look for a relatively flat, clear spot beside the trail, and flip my bike upside-down, using the handlebars and seat to balance the bike.
As long as you’re able to easily remove the front or rear tire (hopefully not both) without potentially damaging your derailleur, you’ll be fine.
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Step 3: Remove your wheel if needed.
Riders using tubes will always have to remove their wheel from the bike to fix a flat, so if you’re running tubes, just go ahead and pull your wheel off. If you’re running a tubeless setup, chances are you won’t need to remove your wheels to address your flat.
Regardless of which setup you run, when you go to pull your wheel, just make sure that you keep up with your axle and any parts that go along with it. Quick-release axles, for example, will have a separate nut and a set of springs that can be easy to lose in the woods.
As a best practice, once you’ve got your wheel off the bike, go ahead and reinstall your axle into the fork or the frame to ensure all the parts stay together and your axle doesn’t pick up any potentially harmful dirt or grime off the ground.
Alright, now let’s talk repairs.
How to Repair a Flat Mountain Bike Tire For Tubeless
Tubeless tires are arguably the best thing to happen to mountain biking since suspension forks. They rarely get flats, and when they do, the fix is often as easy as letting your tire sealant do its job, and then airing up again. Off you go.
Occasionally, however, we will get a puncture that even the best sealant can’t fix, and that’s when our tire plugs come into play. The good news is that even when we need to repair larger punctures in a tubeless tire, we don’t typically have to take the wheel off the bike.
To repair a large puncture in a tubeless tire, start by finding the area causing the leak. It should be plenty obvious, as the area will have sealant leaking out and bubbling up around it.
Once you’ve found the area, simply load a plug into your tire plug tool, and push the plug down directly into the puncture, leaving a small amount sticking outside of the tire. Once your plug is in the hole, pull up sharply on the handle of the tool to set the plug in place. Your tire sealant should do the rest by sealing up any imperfections around the plug and restoring an airtight seal.
Now, simply inflate your tire to the desired pressure, and get back on the trail.
If you can’t repair your tubeless puncture with sealant and plugs, chances are it’s time to pull the wheel and install the emergency tube in your pack, which means the next section is for you, too.
How to Repair a Flat Mountain Bike Tire With Tubes
Knowing how to repair a flat mountain bike tire with tubes is essential even if you run tubeless, because when push comes to shove, the guaranteed repair for a tubeless puncture is — you guessed it — sticking an inner tube in your tire to get you home.
With that being said, let’s take a look at how to deal with tubes out on the trail:
Remove the tire from the rim.
When you get a flat on a tire with tubes, your first step once you’ve got the wheel off the bike is to remove any remaining air that you can from the tire.
If you’ve got automotive-style shrader valves, you can do this by simply pushing down in the center of the valve until air stops flowing.
If you’re running presta valves, just unscrew the valve core a few turns from the top, then press down to release air.
Once you’ve got the tire deflated, you’ll want to go ahead and break out your tire levers. Use the levers to dig down between the rim and bead of the tire and spoon the first several inches of bead up and over the rim. Once you’ve got a foot or so of bead off the rim, you should be able to easily use your hands to push the remaining portion of the tire off the rim one section at a time.
Once you’ve got your tire and tube off the rim, it’s time to find your leak.
Finding Your Leak
Do this by first slowly rotating the tire in your hands and looking for any obvious culprits like thorns or other sharp objects still hanging out of the tread.
Remember, our goal with tube tires is to locate the puncture in the tire, then repair the same spot in the innertube, so keep the original orientation of the tube in your mind so you can find the puncture easily once you’ve found the affected area in the tire.
We check the tire first because if there are still any sharp objects lodged in it after we’ve taken the time to repair our tube, it’s just going to be flat again after pedaling a few feet, and we’ll be back to square one.
If you don’t immediately find any obvious punctures on the outside of the tire, carefully run your hand along the inside of the tire, both at the tread and along the casing, to see if you can feel any sharp objects poking through.
If you still aren’t able to find any issue, then it’s time to move on to inspecting the tube itself.
At home, this is easy, because we can submerge a tube in water and look for any air bubbles escaping. On the trail, however, we don’t have that luxury, so to inspect our tube for leaks, we simply use our hand pump to add a few pounds of air to the tube, then slowly rotate the tube around, listening and feeling for any air escaping.
Once we’ve located the source of our leak (remember there may be multiple if we experience a pinch flat), it’s time to start our repairs.
Patching The Tube
Depending on the type of repair kit you’ve got, this may or may not involve using glue.
Regardless of which type of kit you carry, start by roughing up the area around the puncture with the metal grater or sandpaper provided in your kit.
Once you’ve scoured the area thoroughly, apply your patch.
If you’ve got a glueless kit like the Park Tool GP-2, you’ll be able to simply press the patch on firmly, work out any visible air bubbles, and move on.
If you’ve got a traditional “glue-and-patch” style kit, you’ll apply a thin layer of glue around the puncture, and then apply your patch firmly after allowing the glue to sit for a few minutes to ensure it’s tacky enough to form a seal.
Once you’ve got your patch in place, now it’s time to test your fix by adding air to the tube again and listening/feeling for any leaks. You’ll want to thoroughly check the area you repaired, and also give the tube a few more turns over in your hands to ensure you haven’t missed a spot.
There should be no air leaking from the patch or anywhere else on the tube before we move onto the next step.
Re-Installing Your Tire
Once you’ve got your tube repaired, it’s time to get the tube and tire back onto the rim.
To do this, start by letting the air back out of your tube, and sitting the rim back inside the tire. Next, using your hands, work the outside bead of the tire back onto the rim with your hands. It should pop back on fairly easily without needing the tire levers.
Once you’ve got one side of the tire back on the wheel, locate the valve hole on the inside of your rim and reinsert the tube into the open side of the tire with the valve lined up inside the hole in the wheel. Go ahead and tighten down the outer valve nut about half way to ensure the tube can’t move around and pull your valve out of the hole.
Next, start working the open side of the tire back onto the rim, beginning with the area above the valve and working your way around from there.
You want to work as much of the tire onto the rim as you can with your hands, taking care to ensure that the tube inside isn’t getting caught between the tire and the wheel.
Once you’ve got about 70 percent of the tire back onto the wheel, you’ll start to feel tension around the bead that you likely won’t be able to overcome with your hands alone.
At this point, it’s time to break out the tire levers again, and start carefully working the last of the bead back onto the rim, being extra careful not to pinch the tube with the levers as you finish the process.
Once the last of the tire is back on the rim, there’s nothing left to do but air up your tire again and reinstall your wheel. You’re good to get back on the trail!
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