Finding the right tire pressure involves a large number of related variables such as tire size, rim width, bike and rider weight and of course ride style and conditions.
Perhaps the most important variable to consider is bike and rider weight. Ultimately the tire is a spring with air pressure determining how soft (or hard) that spring is. The more weight the spring is supporting the more air pressure will be needed to keep the spring from being in a constant state of compression and unable to absorb obstacles.
As Volume Increases, Pressure Decreases.
The total volume of air that the tire can hold is directly related to the width of the tire. This is important, as you of course remember from high school, due to Boyle’s law which basically says as volume increases pressure decreases and vice versa.
With current trends heading towards wider rims and tires, riders need to reduce pressure accordingly. The trick is knowing exactly how much to reduce by so having an accurate way to measure tire pressure is extremely important since in some cases just a few psi makes a significant difference.
Bottom line, the more you, your bike and your gear weighs the more air pressure you’ll want in your tires. However, the wider your rim and tire is the less pressure you’ll want. Obviously finding the right balance between these two will require some trial and error but we also need to factor in a few other variables such as riding surface.
The smoother the riding surface the less you need to worry about uncomfortable vibrations transmitting through the tires, bike and into our bodies. You also need to worry less about flat tires due to jagged objects or a bump compressing the tire to the point where it contacts the rim. Determining tire pressure on rough terrain such as gravel or single track of all types is the most complicated because on the one hand you want to reduce pressure to allow the tires to absorb the varying surface but without risking a flat tire or rim and wheel damage. This challenge is why tubeless tire technology has become the standard for mountain bikes and gaining popularity for road and gravel since there is no danger of pinch flatting an inner tube.
Common wisdom has historically held that higher tire pressures (to a point) reduces rolling resistance which increases speed. This way of thinking was derived from testing tires and tire pressure on a smooth metal drum. The issue with this approach of course is that you don’t actually ride on a smooth metal surface. Recent findings now indicate that on real road and trail surfaces a tire with lower pressure that absorbs imperfections provides a smoother ride which, as it turns out, is usually a faster ride as well since the bike spends less time traveling up and down and more time traveling forward. This concept is somewhat counter-intuitive since many riders associate the sensation of speed with the jarring effects that an over-inflated tire provides but numerous academic and real-world studies confirm lower pressures are in fact faster as a rule of thumb.
Now that you have a basic understanding of the variables to consider you can begin to determine the best tire pressure for you. Like many things cycling related, the process is involves some trial and error which is why an accurate and reliable measurement is so important. It’s also why having that measurement available all the time is important. The best approach is to simply monitor and record the pressure you typically ride at and take note of perceived comfort, traction, speed and anything else you feel is important. Having pressure displayed on your handlebar computer with the help of TyreWiz will make this task much easier and intuitive. It also allow you to make precision reductions in pressure out on the road or trail so start a little high and go from there. Within a few rides on your go-to routes you’ll have a good idea of what is working and be able to make informed adjustments as conditions change.