Expert Answers
Proper Off-Road Tire Pressure

How many psi do you need to keep in your tires for biking off-road?

Steve Jones's Answer:

	Steve Jones The author of four mountain-biking books, Steve Jones has logged thousands of miles of trails and backroads. Meet Steve Answer Archive Biking Forums

Coop,

When I started biking off-road way back in the days before front shocks and full suspension, I was told to keep"around 40 psi" in both front and back tires. By checking the recommended pressure on the sidewall of my tires, I saw that the manufacturer's recommendation is anywhere from 35 to 50 psi.

If you haven't tried it yet, there is a significant difference in both performance and handling when you have a tire with 35 psi (or lower) versus 50 psi. Generally, a tire with less air pressure gives a more comfortable ride and tends to displace more tread surface.

Comfort and Handling vs. Speed

I will make the assumption that you aren't into racing much, if at all. If you are a racer, you will want to run tires with as much pressure as you think you can handle, and I mean that literally. You see, a tire with around 45 psi (what many racers pump their tires to) is very rigid, but the advantage in that, so far as racing goes, is that you have less drag and friction by reducing the surface areas between tire and trail. The disadvantage comes at a price in "handling forgiveness." Your steering and "line" needs to be much more precise with a harder tire — hit a curve or a rock or root at too steep an angle and you will have the handlebar twist violently enough to come out of your grip.

Since I bike with little or any consideration for overall speed, I tend to put less air pressure in my tires. Surface friction just isn't that big a deal for me. But I do pay attention to how much air pressure goes into each tire. Here's why.

I've found a "softer" tire tends to skid less, and the less you skid, the more control you have. Also, the less-inflated tire gives a smoother ride, and for someone like me who doesn't have full suspension (a "hardtail"), some extra cushioning can be achieved by running tires with less pressure.

Other Pros and Cons

But I've made another observation about tires with less pressure in them. During a period of time when I tried running tires harder (about 45 psi), I picked up more thorns that caused flats. The reasoning, I believe, comes from the fact that the tire with more pressure had less "give" when I ran over a thorn, so the sharp object penetrated. What I do know is that I have never had a thorn give me a flat while running a slightly softer tire.

But I do appreciate the need for having enough pressure. For example, run a tire too soft, and when you come off a drop and land hard, you will have a greater likelihood of receiving a pinch flat, or what is also known as a "snakebite." What happens is the tube gets pinched in between the rim and the ground because there's not enough pressure in the tire to keep the tire from becoming completely squashed flat.

I tend to run my back tire a little harder than the front. The reason comes from how weight shifts more to the rear on climbs. Having more pressure in the rear compensates for this weight shift. But it still won't be enough compensation for you to keep from occasionally checking the back tire to see if you've flatted on a long uphill grind.

And the Winner Is . . .

So, to finally answer your question as to how much: I believe most recreational riders will be better off having about 35 psi in the back, and around 30 in the front. At least this is what I tend to put in them, but I confess I seldom check pressure with a gauge. After you develop what feels right to you (and you should check different pressures to see what satisfies your needs best), you can squeeze the tire and get a pretty good idea about needing air or not. You can also get on the bike and ride around and look down to see how your tires stand up. Just be careful not to run into anything while you're looking down.