Mountain Bike Tire Pressure Explained: Free Improvements

Let’s talk about the fundamental topic of tire pressure for mountain biking. Finding your optimal tire pressure is probably the single most impactful performance boost you can do on your bike that’s absolutely free. As the contact patch between the ground and your bike, MTB tires are responsible for a lot of the overall performance and feeling while riding. It’s also the number one reason for punctured tires (here are some tips on preventing flats).

But finding the right tire pressure for you and your riding style is not that easy.

Generally, mountain bike tire pressures range from 19 psi (1.3 bar) to 36 psi (2.5 bar), which is a wide range. Rear tires tend to need a little more than front tires, but there’s no one single correct number as optimal tire pressure depends on various factors like tire dimensions, rider weight, riding style, terrain, and track conditions.

As you can see, mountain biking throws up a lot more variables than other riding disciplines like road biking, where there’s a more narrow sweet spot for tire pressure with not a lot of fluctuation from ride to ride. Further down I provide you with baseline pressures for front and rear tires based on rider weight.

Quick tips on MTB tire pressure

Let’s round up my most valuable Infos on tire pressure before going into more detail further down. These are my personal principles when it comes to the air in my tires, that I’ve come to with my riding experiences over the years.

Use my tire pressure calculator for a quick baseline of your front and rear tire pressures.

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Use a pressure gauge

Even if your air pump has a gauge on it, it’s always more reliable and handy to use a dedicated pressure gauge. It’s a small, but powerful gadget you can put anywhere so keep it around at all times when going out for a ride. That way it’s always there when you try to figure out how much air pressure you need.

Start high and go down

If in doubt or searching for optimal tire pressure, rather start out by pumping them up a little too much than too low. Too low of pressure can be really expensive you can wreck your tire and rim. Plus, there is no way to get more air into the tire unless you carry a pump around with you. On the other hand, letting air out is much easier and faster to do on the go.

Document your own tire pressures

Write down the tire pressures that you’d like to use for a given condition or track. That way you’ll always know what to go to if it’s hot and hard-packed or raining and slippery. I’m not saying to start journaling. Just grab your phone and save your preferred numbers in your favorite note-taking app. That way you always got your individual pressures – gained from your own experience – at your fingertips wherever you are.

Check your tire pressures before every ride

This one ties them all together. The fact that tires can’t keep the air in them indefinitely, is why this is such an ongoing topic you need to be on top of by checking and setting your pressures for every ride. Further down I go into much more detail on why air is constantly leaking out of your tires.

There you go. That is the basis of tire pressure. There’s a whole lot more to learn and it could be way more complicated than that. But that should give you a good place to start.

Why tire pressure matters for MTB

First, let’s talk about why tire pressure matters at all. Not even the latest carbon fiber superbike is going to improve your riding if your tires are overinflated or underinflated. An expensive suspension fork, lightweight carbon fiber wheels, and the latest bike geometry are all gonna be a waste if you’re going out with your tires not inflated to the correct tire pressure. Sounds overly dramatic? It isn’t.

I don’t know if you know this, but your tires are the only two contact points to the ground. Usually. There can be instances when there’s a third one: the rider. Or so I’ve heard from a friend.

Them generating maximum traction for you is the result of a number of factors. Let’s go through them and start right at the base: the tires themselves.

For tires, it comes down to properties like the rubber compound (soft or hard) and the tire casing itself (stiff or flexible). For the basics on tire compounds and tire casings, I got you covered with the according articles. In general, stiffer tires allow for lower pressures while still keeping their shape.

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Not conforming to the ground is a bad sign. What you want to see is a little bulging when under load.

Then there’s what’s in between the tire and the rim: the amount of air inflating your rubber tube.

Think of your inflated tire like a knobby basketball. Just different in the sense, that you want it to do the exact opposite of what you’d want a basketball to do. You do not want your tire to bounce off the ground. A lot of air and high pressures will do that for you.

When you run more tire pressure, the tire is less able to conform to the ground while riding your bike and it feels like your tires are sliding around too much or even skipping around uncontrollably because they bounce up and down. Like a basketball. Or kids in a bouncy castle.

The wheels are the first point of contact. Whatever feedback comes from the wheels makes it’s way further through the suspension until it reaches you as the rider who has to manage that feedback. When tires and suspension work against each other, you at the end of the line have to manage the outfall.

Instead, why not make it easier on yourself and let tires and suspension work together. More tire pressure is not necessarily providing you with more traction because of how the tire handles impacts from the trail and then passes the feedback onto the rest of the bike.

So, when high tire pressure is bad, why don’t you just run a low pressure? When your tire pressure is too low your tire can flex too much up and down or side to side. Low-pressure tires can feel vague at best or at worst they could peel off the rim on a fast corner. When you are on a roll and commit, you expect your tires to hold up.

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This is an extreme low-pressure example, but not unlike what happens when a tire bottoms out on the rim.

The bottom line is you spent thousands of dollars on your decked-out mountain bike and you rightfully want to get every penny’s worth out of it. But all of that is a waste if you’re not checking your tire pressure before every single ride – which is absolutely free and one of the biggest performance boosts you can get on a bike.

Units of measurement for air pressure

Before we can get into actual numbers, let’s have a quick refresher on the two most common air pressure units: bar and psi.

While we Europeans tend to refer to bar as our standard unit, psi (Pounds per Square Inch) is more common around the world, especially in the UK and North America. It’s just a matter of what you are familiar with, both are equally correct. PSI is just a more granular unit. With bar, the real meaningful numbers are the decimal places.

1 bar ≈ 14.5 psi

1 psi ≈ 0.07 bar

Should you inflate bike tires to max psi?

It’s not recommended for any bike tire to inflate to the highest possible pressure it can handle. This is, even more, the case with tires for off-road use. The reason is that a tire needs to conform to the ground in order to generate traction and absorb minor bumps. High tire pressures improve rolling resistance but to the detriment of handling.

There is in fact a definitive psi number printed directly onto the sidewall of any tire. On my Maxxis Minions, it’s a whopping 50 psi. But please do not mistake those numbers for recommended values! Those are not instructions but legal safety claims.

50 psi tire pressure gonna have a bad time

The correct tire pressure

So when you can’t even trust what your tires are telling you, where do you even start? Glad you asked. There is an extremely simple, yet effective formula for both the front and rear tires using only your weight as a rider including all your gear. Here it is:

front tire psi = rider weight lbs ÷ 7

rear tire psi = front tire psi + 3 psi

Even 3 psi can make a big noticeable difference. Finding your optimal tire pressure is trial and error. This simple formula should be able to give you a good baseline for the right tire pressure for you.

For a bookmarkable chart to look up quickly, I calculated the PSI and bar valuas for every body weight in pounds and kilograms:

How to accurately measure tire pressure

Nothing up until this point is really going to help you if it all fails at actually measuring tire pressure in an accurate and reliable manner. No, your thumbs do not count no matter how long you’ve been pushing them into your tire and pretending that it’s telling you something. All your thumbs are telling you is that there’s air in there, not how much air is in there.

The best move is to get yourself some sort of pressure gauge. I know tire pumps come with built-in gauges and those are a good starting point. But tire pump gauges (often analog) are just not accurate enough for you to measure in a reliable fashion.

A quick word on reliability. Whatever you choose to use, make sure you always use that option. There can be slight variations between gadgets (digital and analog) and temperatures. Most reasons for fluctuations can be eliminated by just using the same tool every time.

My Joe Blow pump has a gauge, but I still got a separate handheld gauge. The pressure gauge I always keep in my toolbag is the Schwalbe Airmax, which I can’t recommend, to be honest. The reason is that it needs to be screwed onto a Presta valve, which allows air to escape for the duration of screwing it on and then off again. Something like the Topeak D2 SmartGauge is much better as it easily slips onto any valve without screwing or swapping adapters. Both are battery-powered, which is worth a mention.

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Tool kit I bring for every ride.

Check pressure before every ride

I’ve said it before, now I’ll finally explain why your bike tires lose air over time, no matter what you do, what tubes you use and no matter how much sealant you use:

Here is why bike tires go flat when not in use:

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Credit: John Robinson

Bicycle tires lose air over time because air molecules are tiny enough to get pushed through solid rubber. The physical elements of air are simply smaller than those of rubber compounds. It’s the same reason why your birthday balloons are going to be just as deflated the next day as you after a proper party.

That’s just the reason why tires will always, in any case, lose air. But there are other reasons as to why air is leaving your tire. You can also lose air from between the rim and the valve stem itself or even from a bad rim tape job.

If you feel like your tires are losing air too fast it could be down to a couple of things. The first thing I would check is the valve stem and rim interface. Just give it a shake and put your ear close to the valve. If anything is lose, you could actually hear more air come out. In the case of air exiting from the valve area, check by tightening that lock nut from where you’re losing your air from. This may include checking on the valve core too. I had a very sudden change in how well my front wheel could hold air. It wasn’t the nut at the interface of the valve to the rim, it was that the valve core itself was loose.

Losing air could be down to some other places as well. Obviously any holes and leaks in either the tire, the inner tube, or a poor seal to the rim.

Or it could be just a really old tire. With time tires wear out and they get tired (sorry, not sorry) from flexing and bending all the time. Like any old rubber, the sidewalls can break down and start to leak air faster.

And of course the less rubber they have the more they are to get a small leak for air to escape before it gets sealed on a tubeless tire. Or the less the inner tube is getting protected by the tire casing and more prone to annoying punctures.

Simply looking at your tire sidewall can also tell you if you’re running too low of pressure. if the tire is falling over a whole bunch sometimes you can actually see those stress marks on the tire sidewall.

old leaking tire
Notice the dark wet spots where the sealant is leaking through.

Just remember that a few psi too low can spell disaster. Picture yourself hauling the mail down your favorite trail, minding your own business. When all of a sudden the next thing going through your mind is “what the hell happened?”. Well, you had 18 psi instead of 23 psi. Not enough to keep that rock from bottoming on your rim and costing you not only your flow but also a ton of money.

If you want to go fast and test your limits, you need to make sure to have your equipment in order so that it doesn’t let you down in an inopportune moment.

Make a habit of checking your pressures.

High-volume tires VS low-volume tires

Let’s talk about high-volume tires versus low-volume tires and why is it they require completely different air pressures.

We’re gonna go back to talking about basketballs. A high volume wide tire (like plus size or fat bike tires) is a basketball and a low-volume tire ball is a handball.

The big tire provides you with more protection as there’s more distance between it and the rim. That’s the reason why it can get away with running less tire pressure while still being able to perform. The lower pressure is also going to allow it to conform to the ground better. This is why wider tires can be found on bikes that need all the traction they can get, like Enduro and Downhill.

Tire pressures based on terrain

If after all that information you are still ready for a complete deep dive, the dudes at GMBN got you covered with their own tire pressure test where they went ahead and did as close to head-to-head and back-to-back testing.

GMBN went the extra mile and tested tire pressure and tire variations in direct comparison.

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