Ann M.
Well-Known Member
There's nothing that can spoil a fine bike ride faster than an unexpected flat. Like many bike issues, pinch flats are an annoying but generally preventable problem.
The next time you get a flat and are removing the inner tube from within the tire, take a close look and find where the hole, or in this case, holes or small slashes are and that's the tell tale sign of a pinch flat. You just got “snakebit!” These holes are about ½ inch apart from each other and resemble the holes made by a snake's fangs. Sometimes only one hole is clearly visible and with careful inspection you may be able to see diagonal cord abrasions or impressions from the inside of the tire on the tube where it flatted.
A pinch flat happens when the tire bottoms out on the rim, completely compressing the tube causing it to fail. The number one cause is an under-inflated tire followed by aggressive riding. Riding over stones and rocks or hitting a curb or the sharp edge of a pothole hard enough with low tire pressure allows the tube to be pinched between the rim and the rock or road hazard.
Very narrow rims and tires that are not wide enough for the rim to adequately support a load are also vulnerable to “snakebites” as are softer tires with a less rigid bead. Pinch flats are more common with mountain bike riders who rely on lower tire pressure for better control and handling over rocky trails or jumps. Riders who approach an obstacle on a trail or the street with too much speed are more likely to bottom out a tire and cause a pinch flat. The concern for pinch flats, combined with a drive to reduce weight, is what has lead to more mountain bikers riding "tubeless" tires. This setup combines a special sealed rim and tire with with rubberized goop that spreads out and seals air gaps, simulating a stand-alone rubber tube.
Sometimes, a bike tire is damaged by the compression but that's not very common. If the hit is hard enough, the rim can dent or bend or even crack, making it difficult for the tire to hold air.
More rare is an underside snakebite, a risk on wider fat mountain bikes running low pressure on a softer surface. The tire can roll so far on one side and snap back without pulling off the rim but causing a pinch flat on the underside of the tube. Riders often want to blame a faulty rim strip when the real cause is under-inflation.
There's one other way you can cause a pinch flat and I consider this a form of self sabotage: Improper use of tire levers, particularly at the point where the tire is almost completely on the rim and is very tight. With a little patience, work the last bit of the tire onto the rim by hand if at all possible and you'll be off riding rather than redoing another pinch flat.
So what do you do to prevent a pinch flat? First, check your tire pressure regularly and inflate adequately, especially the rear tire which bears more of a rider's weight. Each tire has a recommended range for inflation imprinted on the side (and we list that on the reviews here at EBR so that you can find it if your tire is dirty or worn down). And, remember to account for hotter weather to avoid over-inflating. Air expands as it is heated, so you could fill a tube in the cold morning and see it getting firmer or even overfilled throughout a hot day. Same thing applies when changing altitude, the air pressure in a tire will raise as you go up in elevation because the outside air pressure lowers due to decreased atmospheric pressure. Use a little finesse riding over rougher spaces and you'll have less flats and a more enjoyable ride.
Consider investing in better grade tires with more layers of tread or rigid wire beads rather than a lighter weight folding tire. These can handle lower tire pressure and will have stronger sidewalls that are less likely to deform to the point of causing a pinch flat. If you're a commuter, multi-layer tires like the Schwalbe Marathon (which comes in many sizes and includes reflective sidewalls) will last longer and combined with tire liner strips like Mr. Tuffy along with thicker thorn resistant tubes or a liquid sealant like Slime, give you more flat free miles. And yes, you are adding more rotating weight to your wheels so the performance may feel a little different. If the extra weight is critical to a bike's handling, as it can be for a lot of off-road riders, consider a crush core or foam type insert or converting to a tubeless setup. No pinch flat if there's no tube!
The next time you get a flat and are removing the inner tube from within the tire, take a close look and find where the hole, or in this case, holes or small slashes are and that's the tell tale sign of a pinch flat. You just got “snakebit!” These holes are about ½ inch apart from each other and resemble the holes made by a snake's fangs. Sometimes only one hole is clearly visible and with careful inspection you may be able to see diagonal cord abrasions or impressions from the inside of the tire on the tube where it flatted.
A pinch flat happens when the tire bottoms out on the rim, completely compressing the tube causing it to fail. The number one cause is an under-inflated tire followed by aggressive riding. Riding over stones and rocks or hitting a curb or the sharp edge of a pothole hard enough with low tire pressure allows the tube to be pinched between the rim and the rock or road hazard.
Very narrow rims and tires that are not wide enough for the rim to adequately support a load are also vulnerable to “snakebites” as are softer tires with a less rigid bead. Pinch flats are more common with mountain bike riders who rely on lower tire pressure for better control and handling over rocky trails or jumps. Riders who approach an obstacle on a trail or the street with too much speed are more likely to bottom out a tire and cause a pinch flat. The concern for pinch flats, combined with a drive to reduce weight, is what has lead to more mountain bikers riding "tubeless" tires. This setup combines a special sealed rim and tire with with rubberized goop that spreads out and seals air gaps, simulating a stand-alone rubber tube.
Sometimes, a bike tire is damaged by the compression but that's not very common. If the hit is hard enough, the rim can dent or bend or even crack, making it difficult for the tire to hold air.
More rare is an underside snakebite, a risk on wider fat mountain bikes running low pressure on a softer surface. The tire can roll so far on one side and snap back without pulling off the rim but causing a pinch flat on the underside of the tube. Riders often want to blame a faulty rim strip when the real cause is under-inflation.
There's one other way you can cause a pinch flat and I consider this a form of self sabotage: Improper use of tire levers, particularly at the point where the tire is almost completely on the rim and is very tight. With a little patience, work the last bit of the tire onto the rim by hand if at all possible and you'll be off riding rather than redoing another pinch flat.
So what do you do to prevent a pinch flat? First, check your tire pressure regularly and inflate adequately, especially the rear tire which bears more of a rider's weight. Each tire has a recommended range for inflation imprinted on the side (and we list that on the reviews here at EBR so that you can find it if your tire is dirty or worn down). And, remember to account for hotter weather to avoid over-inflating. Air expands as it is heated, so you could fill a tube in the cold morning and see it getting firmer or even overfilled throughout a hot day. Same thing applies when changing altitude, the air pressure in a tire will raise as you go up in elevation because the outside air pressure lowers due to decreased atmospheric pressure. Use a little finesse riding over rougher spaces and you'll have less flats and a more enjoyable ride.
Consider investing in better grade tires with more layers of tread or rigid wire beads rather than a lighter weight folding tire. These can handle lower tire pressure and will have stronger sidewalls that are less likely to deform to the point of causing a pinch flat. If you're a commuter, multi-layer tires like the Schwalbe Marathon (which comes in many sizes and includes reflective sidewalls) will last longer and combined with tire liner strips like Mr. Tuffy along with thicker thorn resistant tubes or a liquid sealant like Slime, give you more flat free miles. And yes, you are adding more rotating weight to your wheels so the performance may feel a little different. If the extra weight is critical to a bike's handling, as it can be for a lot of off-road riders, consider a crush core or foam type insert or converting to a tubeless setup. No pinch flat if there's no tube!
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