Pressure Calculator Expanded to 25 mm Tires

Posted by: Jan Heine Category: Uncategorized

Pressure Calculator Expanded to 25 mm Tires

The response to our online Tire Pressure Calculator has been tremendous. Cyclists everywhere appreciate a simple tool that allows them to figure out the lowest rolling resistance for their tire size and weight. It makes it easy to optimize tire pressure based on real data.

One common request has been to extend the calculator to narrower tires. Many racers roll on 25 or 26 mm tires, but we simply didn’t have enough data to extend the pressure calculator that far. Now we’ve done some additional testing and can list pressures for tires all the way down to 25 mm, both for soft and firm tires.

Why are there two pressure values? We’ve found in our testing that—at least for supple high-performance tires—there are two pressures where tires roll fastest. One is moderately high, the other quite low. This means you can optimize your rolling resistance in two ways:

• A ‘soft’ pressure for rides on rough roads or for a more comfortable ride.
• A ‘firm’ pressure if you like your bike to have a firm feel.
• Either pressure will optimize your speed by reducing rolling resistance to a minimum.

Lower pressure means less vibration and less energy lost to suspension losses. That makes up for the higher hysteretic losses due to greater deformation of the tire. These two factors – suspension losses and hysteretic losses – are not linear. The result: Mid-range pressures actually roll a little slower than either high or low pressures. (Read more about the science behind this at the link at the end of this article.)

The pressure graphs also show why the ‘Wide Tire Revolution’ is so much more important for heavier riders. A flyweight racer can ride a 25 mm tire at a high, but reasonable, 5.4 bar (80 psi). For heavier rider-cum-bike weights, the line quickly goes off the charts, especially if you like a firm feel to the bike. On the other hand, the lines for wider tires have much less slope. For example, with a 42 mm tire, the pressures for the Clydesdales among us are not much higher than those for lighter teams.

Some readers have asked: How is the Rene Herse tire pressure calculator different from other online tools? All other calculators are based on recommendations that are good estimates of what works in practice. They were a great starting point for determining your tire pressure, especially back when most cyclists ran their tires at the maximum pressure printed on the tire sidewalls.

Here at Rene Herse Cycles, we’re in a unique position to have real-road rolling resistance data from hundreds of tire tests. That has enabled us to create a pressure calculator that gives you the lowest rolling resistance based on actual performance testing. This gives you a sound basis for experimenting with tire pressure and figuring out what works best for you. As always, our goal is not to tell you what to do, but to provide information that allows you to make your own decisions.