Home » Bike Maintenance » Basic tools and repairs » Fixing a UST puncture by fitting a replacement tube

Fixing a UST puncture by fitting a replacement tube

The simplest way of fixing a puncture in a mountain bike tubeless tyre while out on the trail is to use a standard tube. You can fix the tyre properly when you’re home – the chances are that if the sealant hasn’t managed to fix the hole on its own then you’re going to need to get the patches out and fitting a tube is a much easier way to effect a temporary fix.

  • Remove the punctured wheel. The first thing to do is locate the hole. If you’re running sealant, it should be obvious as the fluid will have leaked from the hole. If you’re not, then first look for any holes in the tread or rips in the tyre’s sidewall. If this doesn’t reveal the culprit, then pump the tyre up if it’s lost all its air and pass it past your face – you should hear air hissing when the hole is closest to your ear, may see bubbles if the ground is wet or feel the air cooling your cheek. Once you’ve found the hole, mark it or make a note of where it is in relation to any labels on the tyre or rim.
  • Remove one side of the tyre. Some combinations of UST rim and tyre can be exceptionally tight thanks to the extra-secure bead hook required to seal the join securely. Try pushing the tyre away from the sidewall using your hands, and if this doesn’t work then gently stand on the tyre while lifting the rim away from it.
  • Once you’ve released the seal, you’ll be able to work the tyre away from the rim all the way around one side. Try not to disturb the seal on the other side so you don’t have to reseat it later. Unscrew the lockring on the valve, then remove it and any washers, keeping them safe for when you ressurect your tubeless set-up at home.
  • If there is sealant in the tyre, scoop as much of it out as possible.
  • If you’re using a UST rim, you won’t need to worry about a rim tape as there are no spoke holes in the rim to puncture the tube you’re about to fit. If you have a tubeless conversion kit fitted, however, you may find it easier to remove the conversion strip and fit a standard rim tape. A double thickness of electrical tape will do at a pinch.
  • Put a little bit of air into the tube, just enough to make it hold its shape. Fit the valve through the valve hole in the rim and screw on the lockring loosely to stop it slipping out again. Tuck the tube into the tyre all the way around the rim.
  • Start to work the loose tyre bead back onto the rim. An extra pair of hands can help here, by holding the bit you’ve already refitted in place whilst you work your way around the wheel, aiming to finish at the valve.
  • Try not to use tyre levers on tubeless tyres if you can help it; the slight bends this causes in the stiffer tyre bead can make sealing ,very difficult in future. Tubeless tyres and rims can be very tight, so work your way around the rim a small amount at a time, lifting the bead into place and pulling both sides of the tyre down into the well in the centre of the rim to give yourself more slack to play with. The last section is usually the toughest; letting the air out of the tube can help but increases the risk of pinching the tube as you slide the last tight bit into place.
  • Once you’ve got the tyre on, push the valve up into the rim to make sure the tube’s not pinched between bead and hook, then pull it out, screw the lockring fully into place and inflate as normal. Screw on the valve cap, refit the wheel and re-hook the cable if you’re running cantilevers or V-brakes.

The great grass myth

There’s a long-standing story that if you puncture without a spare tube or patch kit, you can get home by stuffing the tyre with grass. This sounds feasible in theory, but in practice it’s either rubbish or requires a special kind of grass that you’re unlikely to ever come across. We’ve tried it and just ended up spending an enormous amount of time harvesting grass by hand and trying to force it into the tyre. This is trickier than you would imagine since the grass compacts as you pack it. Even if you can stuff enough in to give the tyre some kind of shape, the tyre rolls off the rim as soon as you cycle faster than walking pace anyway, shedding all your hard-won grass harvest instantly. If you try to cycle really slowly, the tyre is so soft that it squidges all over the place, making your bike feel like you’re riding through treacle. You might as well leave the grass growing happily where it is and start walking anyway.

“You might as well leave the grass growing happily where it is and start walking”