Tyre pressure has been a critical concern ever since the inner tube was invented, but our understanding of it is changing. It used to be thought that high pressures made road tyres faster and more efficient; now a new trend leans towards running lower pressures. So, what’s the best tyre pressure for a bicycle?
The answer is simple: there is no single ideal pressure. While there are many factors to consider, lower tyre pressures probably have more to offer than high ones.
It may come as a surprise that there’s no optimal pressure for bicycle tyres. It used to be thought that perhaps 120 PSI was a good pressure on a road bike. Any higher and it became too uncomfortable; any lower and it was too slow. But the problem arose when tyres started causing issues in corners before they actually became slower.
A study with professional riders in the Arenberg forest found that every time tyre pressure was lowered, the riders went faster over the same section. There is no perfect tyre pressure; it varies with the rider’s weight and with the road surface, which means it can be optimised — and that makes it strategically important.
One of the biggest findings from these studies is that most riders interpreted the vibrations caused by over-inflated tyres as extra speed. Without those vibrations, most believed they were riding slower, which led them to dismiss lower tyre pressures. Once they got used to the change, however, the riders in these studies note that lower tyre pressures bring greater comfort without sacrificing speed.
Many of us are obsessed with the pressure of our tyres, both on the road and on the mountain bike. The best way to see for yourself whether these studies hold true is this: drop your pressure by 5 PSI and keep it there for a week.
How does bicycle tyre pressure affect the ride?
One of the keys to maintaining good grip and absorption on the bicycle is having the correct tyre pressure. If the pressure isn’t optimal, the bike’s behaviour can become a real hazard.
Without the correct tyre pressure, we’ll face a series of significant drawbacks. When the air pressure is too high, the bike will bounce continuously and you’ll lose grip in corners. Conversely, if the air pressure is too low, you’re very likely to suffer a pinch flat, friction with the ground will increase and you won’t even be able to ride normally. At the same time, the tyres will squirm and you can even unseat the bead on very tight corners.
What factors affect bicycle tyre pressure?
The right pressure will help you stay balanced in all situations. And to maintain that balance, you need to consider certain factors:
Weight: This is arguably the main parameter. Although most of the load on the tyres comes from the rider’s weight, it’s important not to overlook the bike itself and any kit being carried.
Type of terrain: The difference between smoother or rougher tarmac, pavé, gravel tracks, or even proper mountain terrain will largely determine tyre pressure. We need to adjust the bike’s tyre pressure to suit the terrain we’re riding on. Remember that the tyre is the only part of the bike in contact with the ground.
Weather: Any amount of water on the road reduces tyre grip, so it’s sensible to drop the pressure by around 10 PSI. Light rain, or shaded roads that haven’t dried after the overnight dew, can make riding tricky, so working out the right tyre pressure is crucial.
On mountain bikes, rain — or wet terrain — plays a different role. On dirt it increases grip considerably, but on rock it can be a serious hazard. In the first case, it’s wise to stick with your usual pressure for any given day; in the second, when the surface is wet stone, it’s best to lower the pressure so the contact patch is larger and grip improves.
Tyre width: lower pressures can be used with wider tyres (for example, 28c on the road) with a lower risk of punctures.
Tyre casing and compound: these components have a major impact on how the tyre behaves when inflated. The cycling industry uses a variety of tyre casings and rubber compounds, but in the absence of a meaningful baseline, comparisons are difficult.
So while higher thread counts generally produce more supple tyres, the end result also depends on the rubber compound and how it’s bonded into the tyre. The presence of puncture-resistant tape or material can also have an effect.
Type of tyre: tubulars have a reputation for being more supple than clinchers, but this is more a reflection of the construction materials used than of the tyre type itself. Any given pressure that works well for a tubular won’t work as well for a standard clincher or a tubeless setup unless they share the same materials and construction methods.
Rim width: the width of the rim bed has a direct impact on the size and shape of the tyre. Narrow rims create a bulb shape, while wider rims allow the tyre to form a semicircle, which makes it stiffer vertically. So the width (Chart A) and height (Chart B) of any tyre generally increase with rim width, meaning lower inflation pressures can be used.
That’s why experience counts when it comes to understanding the optimal tyre pressure for your bike. In many cases, just by pressing the tyre with your fingers you’ll know whether the pressure is right.
How is bicycle tyre pressure measured?
There are two basic units for measuring pressure: BAR and PSI (1 BAR = 14.5 PSI). BAR is the more international measure, while PSI is a pressure unit used in English-speaking countries. Either way it amounts to the same thing, since 99.99% of pressure gauges include both scales.
Over time, tyre pressure will drop because tyres always lose a little air. That’s why it’s recommended to check tyre pressure before every ride.
It’s also strongly advised, if you run inner tubes, that every time you repair a puncture you make sure everything is in order the day before your next ride. And as many of us already know, the famous tubeless setup (bless it) tends to leak through the punctures it seals, and you don’t notice until you go for a ride and find the tyre almost flat.
What pressure should a bicycle tyre have?
As with suspension, we can calculate more or less ideal settings from a technical standpoint, but that is not the case with tyres. We can use the most common pressure ranges as a reference (MTB tyre pressure with an inner tube is between 1.8 BAR and 2.5 BAR, and tubeless tyre pressure is between 1.2 BAR and 2.2 BAR) until we find the ideal pressure. This should be the lowest pressure possible, without causing a pinch flat, unseating the tyre or making us excessively sluggish.
Finding the ideal wheel pressure doesn’t require a long journey; often, with a few simple exercises — a jump and a few corners on the MTB, or some rough tarmac on the road bike — we can find the wheel’s ideal performance.
It’s best to look for a midpoint within the pressures recommended by the maker. This range takes into account the ideal terrain for the tyre’s design, whether it’s tubeless, tubeless ready or with an inner tube. Then you should test inflation gradually, dropping pressure in 5 psi increments until you feel comfortable.
What is the ideal pressure for a bicycle tyre?
At this point, as you’ve read, there’s no secret formula. Once you’ve done the tests I mentioned earlier, the ideal is to choose the lowest pressure to avoid tyre bounce and reduce the risk of punctures — this will improve traction and grip. But it must be a pressure at which you don’t notice squirm in corners, uncontrolled skids, a sluggish feel or pinch flats / hits against the rim.
The rolling resistance of a bicycle tyre
It’s relatively straightforward to measure rolling resistance under controlled conditions. This allows different makes, models and sizes to be compared and ranked to identify the ‘fastest’ tyres. The influence of other variables — including tyre pressure, the different materials used in inner tubes, and, for tubular tyres, the type of glue used — has also been tested.
The results of these studies have provided a great deal of information about the parameters that can influence rolling resistance. They lead to some clear and established principles, such as rolling resistance tending to decrease as tyre pressure increases, as well as providing up-to-date data on new trends, such as wider tyres. However, there was always the risk that such a controlled laboratory test would overlook other issues at play in the real world.
Current thinking now holds that there are two components to rolling resistance: first, hysteretic losses, which occur when the tyre flexes — these are greater when the tyre is too soft; and second, impact-absorption losses, which fall on the rider and are greater when the tyre is too hard. Each effect appears to be largely independent of the other, so the net result depends on the sum of the two.
These effects are not widely understood, and that’s where the habit of over-inflating tyres comes from. Most riders accept (and even enjoy) the suspension losses in exchange for the hum and rumble of firm tyres rolling on tarmac, and they interpret this kind of feedback as a measure of speed. While it’s true that this vibration increases with speed, any rider who experiments with lower tyre pressure will discover that it’s possible to go just as fast.
The figure shows that at all pressures, the widest tyre (28 mm) has the lowest rolling resistance — expressed in watts in this case — followed by the 25 mm tyres and finally the 23 mm tyres. We should bear in mind that the test is carried out on a single wheel, whereas a bicycle has two wheels, so the actual rolling resistance will be double the value seen in the image.
Riders who tolerate over-inflated tyres are wasting energy. It’s worth noting that these losses appear to be significant at the tyre pressures commonly used (100–120 psi). It’s therefore likely that a great many riders would enjoy an immediate drop in rolling resistance (and an associated increase in efficiency) simply by reducing tyre pressure by 10 to 20 psi, even when riding on smooth roads.
How to avoid punctures or pinch flats on the bike?
Perhaps the biggest objection to reducing tyre pressure is that it will increase the risk of punctures. This is a common fear among riders who use inner tubes; however, riders using tubeless or tubular tyres can’t ignore the risk either.
A pinch flat occurs when the tyre bottoms out against the rim and the inner tube becomes trapped between the road surface and the rim’s sidewalls. Most riders intuitively understand that tyre pressure influences how quickly a tyre will bottom out; however, studies of the forces involved have revealed an interesting finding.
By using a larger tyre, it’s possible to reduce the inflation pressure and still enjoy added puncture resistance. So, for those who suffer from frequent pinch flats or punctures, you’ll get a better result by switching to wider, higher-volume tyres than by over-inflating narrow ones.
In this simulation you can see two situations: a rim strike or pinch flat with no consequences (left) because the pressure is correct, and a rim strike or pinch flat with consequences (right), where you can see that the lack of pressure allows the rim to strike the rock.
The same happens with nails, glass and other objects we encounter on our rides, whether MTB or road — adequate pressure helps reduce this dreaded enemy of riders.
How can you improve bicycle tyre grip?
Mountain bikers are more demanding in this respect than road riders, though for the latter it’s still very important when taking corners and in wet-road conditions.
As I said earlier, lower tyre pressure favours additional grip by allowing the tyre to conform better to the road surface. To this you must also add the compound and contact-patch factors. A soft rubber compound and a larger contact patch both favour grip.
Of course, there’s a limit to how much you can reduce tyre pressure to improve grip. Once the tyre starts to collapse under the rider’s weight, it becomes unstable and that will compromise the tyre’s grip.
Bear in mind that reducing the pressure of a given tyre won’t change its suppleness. This applies particularly to training tyres, since they’re stiffer due to the extra rubber they contain. Such tyres will be more puncture-resistant, but their robust construction means they won’t conform to the road surface as easily, nor rebound as quickly as a supple race tyre. As such, they’ll always suffer additional rolling resistance and reduced absorption of road irregularities.
Therefore, the most effective way to maximise grip is to use larger tyres built with supple casings, inflated to relatively low pressures. Since this kind of set-up also minimises suspension losses, riders can enjoy additional grip and comfort without sacrificing speed.
For road riders hoping to maximise marginal gains, it’s worth noting that there’s a limit to how much larger a tyre can be before it starts to detract from the aerodynamic performance of a deep-section wheelset. The tyre will generally begin to interfere with airflow once its width exceeds that of the rim by 5%. Studies have shown that it’s possible to run a wider tyre (e.g. 25c) on a rim optimised for a smaller one (e.g. 23c), provided the inflation pressure is kept low and the tyre doesn’t develop an excessive bulb shape.
Conclusions
There’s no simple formula to determine the optimal tyre pressure for an individual. And as I said earlier, the pressure your riding companions use isn’t particularly relevant. Instead, the best approach is to start experimenting with different tyre pressures, remembering that 5 psi can make all the difference.
This experimentation may seem slow, but a detailed log will soon tell you which tyre pressures work best on your bicycle in terms of comfort, grip and rolling resistance, and which ones don’t. This is the kind of information that can give competitive riders a strategic advantage, while recreational riders will find themselves better prepared for their favourite ride.
That said, every rider needs a meaningful starting point. One option is to start with a high pressure (for example, the maximum the tyre allows) and then gradually drop the pressure until the vibrations from rough roads start to fade, or until stones on the road are absorbed by the tyre.
That said, all of this is just guidance. Much of the data from private studies (tyre makers) and public ones (universities and independent laboratories) favours wider (25–28c), supple tyres at lower pressures (60–80 psi / 4–5.5 bar), but every rider should feel free to experiment with tyre size and pressure until they’re satisfied with how their bicycle performs.