Not long ago, the question of bike tyres was relatively easy. We cyclists just bought a set of 23s and ran them at 110 psi and that was that. They were thought to be faster because of their size, efficient because high pressure meant lower rolling resistance and all was good in the world.
Then pesky science got in the way and decided to get in on the act. Pro teams and tyre manufacturers began looking at tyre size and pressure in a lot more detail. All that smug assurance that 23s were the way to go was quickly shattered.
Tyre pressure has become similarly complicated. Ride at too high a pressure and it can be an uncomfortable experience but can protect from punctures. Ride at too low a pressure and you can roll slower, still risk punctures and tyre damage. So what’s right?
One of the key consideration in any cyclist’s tyre choice is that of rolling speed. Tyre pressure has a huge influence over that. Lower pressures increase the contact area of the tyre on the road. This is good because it adds grip and allows more distortion of the tyre which improves comfort. It’s also bad because it also increases rolling resistance.
So what is rolling resistance?
Rolling resistance is the loss of energy through the motion of the tyre. This will be primarily from tyre deformation as it changes to the road surface and through the loading and unloading of the tyre as it moves around the wheels. There is also a small amount of resistance in the movement between tyre and inner tube if you use them.
A narrow tyre deforms more than a wider one at the same pressure which increases rolling resistance. This is why cyclists and pro teams are switching from 23s to 25s. Some bikes are even building in clearances for 28s now. But there’s a trade off when you get into the realm of marginal gains. A narrower 23 tyre will offer less air resistance than a 25. In some frames a 23 can cause turbulence between the tyre and the frame, adding resistance. It’s a balancing act.
Pressure and comfort
The higher the pressure of your bike tyres, the less comfortable the ride will be. Rather than soaking up some of the vibration from the road, a tyre at high pressure simply sends that energy into the frame and up to the rider. That’s fine if you live somewhere with smooth roads. It isn’t so great if you live in the UK.
Cycling in Britain is all about compromise, we know that. One of those compromises is comfort. Do you run a thin tyre at high pressure and risk discomfort in return for speed? Or do you run wider tyres at a slightly lower pressure to absorb some road buzz? I am definitely in the latter camp.
The roads down here in Cornwall are terrible. I tried running some Schwalbe Ones at my usual 110 psi when I first moved here and after a couple of rides I had to soften them a bit. I tried 100 psi, which was still too much, especially on a frame as stiff as the BMC Time Machine. Eventually, I got it down to 90 psi and while it doesn’t feel quite as fast I don’t need to see a chiropractor after every ride.
The downside to running at 90 psi was that the Schwalbe Ones became more prone to punctures. I had to dig out a set of Continental Gatorskins and while not the most svelte of tyres, they don’t puncture anywhere near as much.
As you may have gathered, there is no right or wrong tyre pressure. It all depends on your bike, the roads you ride and how you ride. If the roads on your rides are smooth and your frame forgiving, you can probably afford to run higher pressures. If you live close to rougher roads or have a stiff frame, you might benefit from lower pressures.