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Pinch flats are one of those annoying things that all cyclists have to face at some point in their riding careers. But what is a pinch flat exactly, how do you repair a pinch flat, and how do we avoid them happening again in the future?
What are pinch flats on a bike
Pinch flats are a type of puncture flat that you typically get on bike inner tubes.
Most punctures occur when you get a spiky object (think: nail, screw or thorny goathead) that punches a round hole through the wall of the inner tube. Or a long sharp object (think: glass shard or rock edge) that slices a gash into the tube wall.
Pinch flatting is a very specific type of puncture though. It happens when the inner tube of your tire is folded and pinched between the metal wheel rim and an object on the ground. The object could be a rock, pothole or kerb edge.
This ‘pinch’ creates a distinctive pair of small slashes (which looks very much like its alter ego: a snake bite) in the inner tube rubber, resulting in air escaping and causing the tire to go flat. Because the sidewalls and tread of the tire are generally not punctured or damaged when this happens, pinch flats are typically easier to fix than other types of flats since it is just a matter of replacing the inner tube.
Common causes of pinch flats
There are many reasons why bike tires keep going flat but, thankfully, pinch flats are a type of puncture that is easier to avoid once you know the main reasons why they happen.
In fact, there is really only one cause of a pinch flat and that’s underinflated tires.
Having low air pressure causes the sidewall of the tire casing to collapse when it runs over something hard. This then forces the inner tube to become pinched between the wheel rim and the object, with the metal rim edge cutting the two slice marks into the tube rubber. For this reason, it’s important to make sure that your tires are properly inflated before you ride.
Pinch flats are more common on mountain bikes (MTBs) than road bikes, hybrids, BMXs, or city/commuter bikes. Why? There’s a couple reasons.
Firstly, because the trails that mountain bikes are most used on are rocky and filled with sharp edges. Secondly, because in order to get good grip on these rough trails, MTBers typically run their tires at lower (in some cases, far lower) pressures than you’d normally have on bike tires used on roads, pavement and other smooth surfaces.
Unfortunately, riding a road bike won’t automatically make you immune from pinch flats. Even when road bike tires are at their maximum pressures, because they are comparatively skinny tires, they are only ever going to be filled with a small thickness of air cushioning.
How to repair a pinch flat
So, when a pinch flat happens, what can we do to fix the problem and carry on with our bike ride?
Well, there are two routes you can go down for fixing any kind of puncture – patching the hole in the tube or replacing the inner tube with a fresh new one.
Both have their pros and cons and I’ve expanded on drying times for bike tire patches in more detail here.
Because of the general shape of a pinch flat (the classic two slash ‘snake bite’), patching is quite difficult.
Do you use one massive repair patch (and hope you’ve got good adhesion across the entire surface area)? Or, do you use two smaller repair patches (even if they might overlap) and run the risk that there’s still a weak spot where the two patches meet?
In my view, neither is a great option. And, in any case, I’m not a big fan of repairing a tube mid-ride only for it to burst again at a weak repair a few miles later.
For that reason, my preference is to always replace the holed inner tube with a fresh new one.
To that end, I carry a small saddle bag on my bike at all times with the necessary gear to carry out the repair:
- This has a new tube (or one that has been punctured previously and I’ve taken the time at home to do a proper job of repairing, rather than a quick-and-dirty fix mid-bike ride)
- Plastic tire levers
- CO2 tire inflator and a couple CO2 cartridges
When you’re mending a pinch flat (or any puncture in fact) it’s good practice when you’re carrying out the repair to check that your tire pressures are sufficient for the terrain and that there are no sharp edges on the wheel rims.
How to avoid future pinch flats
Can you protect your tires and prevent pinch flat punctures? Yes you can and there are a few ways to do this. Let’s take a look.
Keep tires (and tubes) pumped to their recommended pressures
Underinflated tires are the #1 cause of pinch flats, so the best way to pinch flat-proof your bike is to check your inner tube pressures regularly (i.e. before every bike ride).
I like to keep a bike floor pump with tire gauge at home to top up my pressures before I set off for a cycle. I also keep a CO2 tire inflatator and CO2 cartridges in a saddle bag so I can easily deal with tire pressures that are too low mid-ride.
As an aside, I’m a fan of CO2 tire inflators for most bike rides. However, if I’m going for longer bike journeys (e.g. bikepacking trips) then I’ll take a mini bike pump, rather than weigh myself down with armfuls of CO2 cartridges.
Avoid hitting sharp edges – such as kerbs, pot holes, or sharp rocks
Easier to do when you’re traveling along at moderate speeds on the roads or pavement than if you’re charging down a steep ‘n’ gnarly mountain bike trail, I know!
If you have no choice than to hit an obstacle when you’re cycling, then try and take the pressure off the wheel(s) when you do. Either by shifting your balance back onto the rear wheel (to relieve pressure on the front wheel caused by riding over an obstacle) or by standing on the pedals and shifting your balance forwards onto the handlebars (to relieve pressure on the rear wheel).
Doing either or both of these can make a huge difference to the impact that a wheel will take hitting an obstacle – and therefore the potential for a pinch flat. It’s always worthwhile practicing any new manoeuvres like this on a smooth surface in a safe, traffic-free location first.
Check your wheel rims for damage
When you’re checking your tire pressures before a ride (remember to do this!) also have a check of the wheel rims on each side. If you find dents or sharp edges, then it may be worth taking them to a local bike shop for repair or replacing the rims with new ones.
The sharper a wheel rim, the more likely it is to slash through your inner tube when you hit an obstacle.
Consider going tubeless
Tubeless tires can potentially completely protect your bike from getting pinch flats. Why? Well, tubeless tires do away with the need for inner tubes. Instead, the edges of the tire are sealed onto the wheel rims and this keeps the air pressure inside the tire.
No inner tubes means that there’s no tube to get punctured with a pinch flat.
A properly set up tubeless tire will also contain a sealant which can seal up small holes in the tire wall or tread. Whilst this isn’t a guarantee to eliminate pinch flats completely it should mean that they happen less often.