MTB Tire Pressure
“What tire pressure should I run?”
I get that question all the time.
It really comes down to a few simple things. It’s the way that these things mix together, work against each other, cancel each other out, and so-on-and-so-forth that makes it all very interesting, and thus, a real tough question to answer.
What I’ll try to do here, is explain the main factors (I can’t, of course, hit EVERY factor in the space of this article) that become relevant in the search for proper tire pressure and send you on you’re way to figuring out what is best for you.
One question a lot of students ask is, what is the best method for measuring tire pressure? “Should I measure my tire pressure with a gauge or by feel?”
The answer to this question is … YES!
Use both. Why? Because most small and inexpensive tire gauges, like the kind you will most likely carry with you in your Camelback or tool box, are not very accurate when measured against one another (one may read 25 psi and another 22 psi on the same tire, and that’s a big difference). However, they are usually pretty consistent with themselves (until the batteries start to go dead). As long as you use the same gauge, you should have a pretty consistent reading. So why use your hand with a squeeze of the tire? Because you’re never going to accidentlly leave your hand on the tailgate of your friend’s truck or back at the hotel room. And, when the batteries in the gauge do start to go dead, you’ll know that even though the gauge is reading 38 psi, the tire is really right around 20. Also, when you use a new tire (same or different brand) your hand – gauging by feel – gives you a better idea of how hard you will actually need to hit an obstacle before that obstacle bottoms out on the rim of the wheel (flatting your tire, damaging your rim, or both) than a number on a tire gauge. Then use the gauge to see what pressure your “feel” relates to and you can get consistent on where you want be with your new tire. Like anything else, this takes a little time and experience, but two gauges are better then one… especially if you can never lose one of them.
Gauges on most tire pumps are usually all over the place. I’m not a big fan of tire pump gauges. A good hand held gauge is the way to go.
The right tool for the job
Next, pretty much all tires are different brand to brand, size to size, different materials, construction, new to old… There are a lot of variables in tire construction. There are also a lot of different uses and intentions. For instance, some of my students are endurance racers. Most endurance races are held on courses that are not very technically challenging and have a fairly smooth surface. A fast rolling, low profile, super light tire with a pretty high pressure (for minimal rolling resistance) would be a great choice for the intention of being fast and efficient for long periods of time on this type of terrain. If the same rider goes out to Bootleg Canyon (all jagged rock) for a fun weekend with their buddies, I would suggest a tire on the opposite end of the tire-spectrum: a large volume tire with big lugs and with great durability. This tire, when run at low pressure, would give the rider more traction (in this terrain, traction is more important then the low rolling resistance for an endurance race) and give the rider a smoother and faster ride because of its ability to absorb bumps (more on this is a bit). With the first tire, the rider may run something like 45 psi, the second … 25? Big difference… Another example: while 30 psi may be way to much pressure for a 135 lb downhill racer on a 2-ply Downhill tire, 30 psi may be way too little for a 220 lb “not so smooth” dude on a super light cross country tire and rim.
Advantages of low pressures are traction and bump compliance. Generally speaking, the lowest tire pressure that you can run without getting a flat will give you the most traction, the most bump compliance, and, thus, the most control. With low tire pressures, tires spread out on the terrain under load and create a larger contact patch – more traction. Also, the tire will absorb bumps – acting like suspension – and help the rider maintain a smoother momentum path over inconsistencies in the trail while maintaining contact with the ground.
Some disadvantages of low tire pressures are that on smooth sections of trail (where searching for traction or bump compliance won’t be priorities) the tires will have a lot of rolling resistance, and, of course, you stand a greater chance of getting flats by either “rolling” your tire off of the rim, or by bottoming the tire out on the rim. Unfortunately, even tubeless tires aren’t a cure-all for this dilemma. In fact, I see just as many flats these days as I did in the days before tubeless because riders still push the limits of what they can run pressure-wise, as they should. Except these days, because bottoming the tire via the impact of an obstacle to the rim is more frequent with tubeless tires, riders often damage their rim in the process. I do like tubeless tire set-ups, but they do have their limits.
The advantages of high tire pressures are low less rolling resistance on smooth surfaces and very little chance of getting flats. The disadvantages: less traction because the tire doesn’t spread out on the surface of the trail (smaller contact patch) or absorb obstacles like it will with lower pressures – it will now deflect off of the obstacles, bouncing, sliding, and deflecting and offering a very a rough and unpredictable ride.
So what tire pressure should you run?
I have two “go to” tire set-ups, and I change them depending on my location and trail conditions. I sometimes change my tire pressure during the ride (I will drop pressure, I almost never add tire pressure, but there are some great hand pumps out there that do allow you to do this practically and quickly – most hand pumps don’t – and without wasting a CO2). I run enough pressure so that I can attack the trail with out getting flats. Also, the weak spot in my riding isn’t my technical ability; it’s my legs and my lungs. So, I’ll give up a little bit of control and traction (and make up for it with technique and by finding the smooth spots on the trail) and benefit from higher pressures and less rolling resistance. If you’re a rider whose fitness is your strength and technical ability is your weakness, you may want to go in the other direction.
Most beginner riders run too much tire pressure and could benefit by dropping it substantially.
How do you find out what works for you? Hopefully this info helps out, but go ride a section of trail with 20 psi in your tires. Now go back and ride the same section of trail with 50 psi in your tires. Now ride with the pressure right in the middle. How did each different run feel? Take notes on all of this, especially as you’re learning. Evaluate what type of rider you are and what terrain you plan on riding.
I also always run a couple/few more psi in the rear than the front. The rear naturally will have a little more weight on it than the front. Also, its easier to lift and maneuver the front wheel, thus, minimize impacts with the front while the rear will probably have to take more of these impacts.
Armed with the above knowledge, hopefully, you’re pointed in the right direction. Oh, and learn how to fix flats before you go too crazy with this…