Tuning tip: The right pressure in road bike tyres
Tyre pressure is a factor that many road cyclists underestimate. Yet it offers incredible tuning potential and costs virtually nothing. However, many factors influence how much air in the tyre is just the right “amount”, e. g., weight, tyre, and rim width as well as terrain. Learn from Alpecin Cycling all you need to know about tyre pressure and get advice on how to determine the ideal air pressure for your needs.
The more the better – for a long time this motto applied with regard to air pressure in road bike tyres. The idea behind it was that narrow, firm and fully inflated tyres were more aerodynamic and had fewer punctures; in a nutshell: that they were faster. A myth that lasted for a long time and has not completely disappeared up to today.
“Eight or even ten bar air pressure in road bike tyres is no longer a thing,” says Felix Schäfermeier, product manager at tyre manufacturer Schwalbe. After all, no one still uses narrow 19- or 21-millimetre tyres for road cycling.
The wider the tyre, the lower the air pressure
Thanks to wider road bike tyres of 25 millimetres or more as well as special constructions such as tubeless tyres and wider rims, tyres can now be ridden with air pressures of around 5 bar and below – at a body weight of 70 to 80 kilograms.
It is true that a tyre inflated “as firm as a rock” is less prone to pinch punctures. But it does not adapt to the road surface and thus loses the desired contact with the ground. It bounces, so to speak. The wattage applied to the pedal literally fizzles out. This aspect increases the effective rolling resistance – the rougher the surface, the higher the rolling resistance of a firmly inflated tyre. In addition, the rider feels it in the form of a lack of grip, for example in bends, but also in form of a significantly poorer comfort, or “souplesse” as experts call it.
Air pressure – the ideal balance between comfort and performance
But the road is no laboratory. Even here in Germany, the asphalt is not as smooth as a sheet of paper or a pane. In other countries – especially the cycling nations – it is even rougher. “When rider and bike bounce on the asphalt, bluntly speaking, there is no continuous contact with the road surface. That leads to an enormous loss of energy,” says Schäfermeier.
With a lower air pressure, on the other hand, the tyre can deform and “glide” more gently over the rough road surface. And not to forget the gain in comfort due to the lower air pressure. “Impacts are absorbed much better. Less air straightens out the bumps, so to speak,” Schäfermeier elaborates.
However, riding with low air pressure can in fact have one disadvantage – poorer aerodynamics. But this only holds true for 28-millimetre or even wider tyres on a very narrow rim, when it is squeezed into a so-called light bulb shape. “However, the differences only become noticeable at speeds beyond 40 km/h and are in the lower single-digit wattage range,” says Schäfermeier. The aerodynamics of wide tyres can be improved when combining them with wide rims of 21 millimetres and more.
Tyre width, rim surface & Co.: These factors determine the correct air pressure
How much tyre pressure is ideal depends on many different factors.
Tyre width and type: As a rule of thumb, lower air pressure is needed, the wider the tyre gets. A difference of two millimetres in tyre width can make a difference of 1 bar. “Tubeless tyres can generally be ridden with less pressure than clinchers, as the tubeless construction eliminates the risk of pinch punctures or snakebites,” explains Schäfermeier. Many tyre manufacturers recommend reducing the air pressure in their tubeless models by 0.5 bar to 1 bar compared to clinchers of the same width.
Keep in mind that the construction of the tyre may also have an impact on the air pressure. The more stable the carcass construction, for example due to an additional puncture protection layer, the lower the air pressure can be for these rather stiff tyres – without increasing the risk of punctures.
Weight and load distribution: For the system weight – consisting of rider and bike – the following applies: The lighter the “package”, the lower the pressure. But also load distribution should be adjusted. As a rule, 0.2 to 0.5 bar less on the front tyre. On triathlon and time trial bikes, where a lot of weight bears on the front due to the riding position, this marginally lower air pressure brings comfort gains and reduces the red muscles’ fatigue.
Road surface: The rougher and more rugged the road surface, the more sense it makes to lower the air pressure to enhance comfort and grip. The latter minimises energy loss and improves rolling resistance. Air pressure should also be reduced on wet roads – between 0.5 and 1 bar less may improve grip. The lower air pressure increases the contact area of the tyre, more rubber is in contact with the road.
Rim width & construction: “Wheel and tyre should always be considered a system, as they interact in terms of performance,” says Schäfermeier. A wider rim (inside diameter) provides better support for the tyre so that it can be ridden at lower pressures – compared to the same tyre on a smaller rim. “It does make a big difference how a tyre sits in a rim,” Schäfermeier elaborates.
A tyre in a hookless rim, e.g., takes up a different, larger volume than in a classic hook rim. This in turn means that with hookless rims – using the identical tyre – less air pressure is needed. Hookless rims are usually only compatible with tubeless tyres, regardless of whether they are used with a tube or tubeless. The maximum permissible air pressure according to ISO standard is 5 bar, which to a certain extent requires a wide tyre-rim combination.
The ideal air pressure: find it via trial and error
In any case, it is worth experimenting with the air pressure. As already mentioned, air is for free and the gains in performance and comfort are enormous. Whether on wet asphalt during a race or on a multi-day bike packing tour. To tinker with tyre pressure is by no means rocket science but requires just a little bit of trial and error – and will reward the adventurous with a really great set-up.
Investing a little time to experiment with tyre pressure is therefore definitely worthwhile. By the way, this applies not only when it comes to the road bike, but even more so when it comes to bikes you’ll go offroad with.
Useful links on tyre pressure
For road bikes, tyre manufacturer Schwalbe has drawn up a list for different tyre widths and rider weights. For example, with road bike tyres that are only two millimetres wider, air pressure may be one bar less.
With “Pressure Prof”, Schwalbe also provides cyclists with a tool to determine the optimal air pressure. So far only for mountain bikes and e-mountain bikes, but the tool will soon be expanded to include road bikes and gravel bikes: