Don’t just pump your tires up to the max
Many newer road cyclists are a little confused about what tire pressure to use when pumping up the tires on their road bikes, so today I’ll look at tire pressures. Because it isn’t quite as simple as pumping your tire up to the recommended maximum pressure.
Get it wrong and it could all go belly up. Have you ever been riding in a bunch when you suddenly hear a massive bang and wonder who fired a gun? It’s usually someone’s tire exploding. Well exploding might be a little over dramatic, but basically that’s what happened. A massive blowout. It’s certainly happened to people near me, it gives you quite a fright.
The first thing to observe about tire pressures is that each tire, if you look, will specify a pressure. This you find on the sidewall of the tire. This pressure recommendation is not the recommended correct tire pressure, it is the maximum. The tires that I use, for example, specify 120lbs max pressure. This does not mean that you should pump your tires up to 120lbs.
So what governs the tire pressure you should use?
There’s a number of factors. The first of these is the width of your tires. Narrower tires require a slightly higher pressure than wider tires. Generally road cyclists tend to use 23c or 25c tires, however it is possible to ride on either narrower or wider tires.
Tire pressure and rider weight
Secondly, and most importantly, your tire pressure should be adjusted according to your weight. The heavier you are the greater pressure you should use to support your weight.
Here’s recommendations made by Zipp for tire pressures for one of their tires (the Tangente Clincher). I DON’T include these recommendations here for you to use, as these are for a specific tire. I include these to give you an example of how your tire pressure can vary according to your weight.
Notice that there is a variation in tire pressure of more than 15lbs between a light rider and heavy rider. Women should take note in particular, being, on average, lighter than men.
(Note also there is a slight variation between front and rear tires)
Tire pressures and rolling resistance
As a general rule a tire which is pumped up harder will provide less rolling resistance on the road than a tire which is not pumped up as hard. However that doesn’t mean you should always pump your tires up to the maximum.
Particularly on a very rough road this can cause problems, increasing the roughness of the ride and, according to some, actually increase rolling resistance, though I don’t know if this has been tested.
The theory is that a slightly softer tire will mold itself to the bumps slightly better than a very hard tire. This of course does not apply to very smooth roads, where rolling resistance will be reduced by higher pressures.
Tire pressures and wet roads
A tire pumped up very hard will have a slightly smaller contact surface on the road than a softer tire, and a softer tire will be more likely to maintain contact with the road over rough surfaces as well as have a slightly improved contact surface in the wet. As a wet road reduces grip a slightly softer tire can help improve your road grip.
What else effects tire pressures?
There is also some other considerations. Get your pressure too low and you increase the risk of flat tires. If, for example, you ride over a rough object or your tire falls into a hole you can get a pinch flat, namely a hole in the tube where the tire squashes the tube onto the rim as it hits the object.
The temperatures to be encountered on the day are also a consideration. I rode an event last year where air temperatures hit 42deg C (about 107 deg F). I don’t know what the road surface temperature would be in those circumstances, but it would be hot.
If you pump your tires up to the maximum in the morning the temperatures of the day may well increase this pressure to the point where it becomes dangerous, and you’re at risk of that shotgun flat I’ve already mentioned, where there is a catastrophic failure of the tube and tire.
There’s lots of issues around tire pressure. So what do you actually do? The general rule is that there is no general rule. It varies.
Road tires should be between roughly 80lbs and 120 lbs. So start somewhere around the middle of that range, adjust up or down for weight, temperature, road surface, recommended maximum pressure and so on, and start to take note of what works best for you. Then you will get an idea of what pressures you should be riding on, for your tires and your riding conditions.
Today’s quick tip. If it’s going to be a very hot day and you’ll be leaving your bike in the car for some time reduce your tyre pressures. Tyre pressures can increase dramatically in a hot car and may well cause a failure. I know someone who almost ran off the road from fright as a tyre exploded in the back of the car on a hot day.