Ideal Inflation Pressure
The mechanical tests conducted in the woods of Finland reveal a tremendous amount about a tire’s characteristics, but its performance on race day also depends on its inflation pressure. “The tire can adapt [to the road], and it’s the first thing in contact with the road—it absorbs shock, it deflects little roughness instead of just giving it all to the wheel and to the rider in the end,” says Vorm Walde.
Vorm Walde compares the specificity of car tires with the ability to alter the pressure in your cycling tires. “You see a certain model tire on a BMW and on an Audi, but it’s never the same tire. The name is the same, it’s the same model but Audi has different specifications for the same tire because the [car’s] suspension geometry is different, so they dial in the tires a little differently. It’s dialed in to the car model, even though it’s the same tire model. They make those subtle changes to influence the ride, steering stability and driving comfort.”
Just as car manufacturers specify certain tire characteristics to complement their vehicles, cyclists must tailor inflation pressure to maximize performance and comfort based on specific race conditions, including road surface and temperature change throughout the day.
“The riders are the different car models,” clarifies Vorm Walde. “You have to adapt the model to meet the likings of the individual rider. You have to change the tire pressure to make it work for you. There is such a big span in rider weight and riding style it’s impossible to give a rule of thumb for tire pressure. It really comes down to trying it out and playing with it.”
Although Wolf says there is no rule of thumb for selecting the ideal tire pressure for an individual rider, he provides two guidelines for minimizing rolling resistance while avoiding the risk of tire explosion on a hot day.
Reduce rolling resistance: Inflating beyond 8.5 bars (123 psi) you don’t really get a significant reduction in rolling resistance. If you test a 23c or a 25c tire at 6.5 (94 psi), 7.5 (108 psi) and 8.5 bars (123 psi), you will see that rolling resistance decreases the higher the pressure gets. You also see that the savings gets [smaller and smaller] as pressure goes up. Beyond approximately 130 psi, the rolling resistance doesn’t change at all any more.
Prevent blow-outs: “You get your bike ready early in the morning, pump to 9 bars (130 psi), it sits there and warms up and maybe in the afternoon [the pressure is] 40 psi more in the afternoon.” This large increase in pressure can cause the tire to blow, especially if you ride clinchers. “It’s pretty hard to come up with a pressure in the morning, but I would recommend to pump the tires to 7.5 or 8 bars (108 or 115 psi) when it’s chilly in the morning, or if you expect a warm up of more than 10 degrees Celsius [50 degrees Fahrenheit] to account for this rise in air pressure in the tire,” recommends Vorm Walde.