Your bike’s tires are the only thing that touches the ground when you’re riding.
Any experienced cyclist will tell you that a good pair of tires can make all the difference. Compared to stock tires, high-quality aftermarket tires are suppler, wear out slower, get fewer punctures, and have lower rolling resistance.
If you equip your bike with good tires, you can ride faster and go farther—with a comfortable ride that’s easier on your body. Provided, that is, you keep your tires at the correct tire pressure, which we will talk about in today’s blog post.
When it comes to your bike’s tires, PSI stands for “Pounds per Square Inch.” It’s a unit of measurement from the imperial system that determines how full the tires are based on the air pressure that’s inside them.
Filling your tires to the correct tire pressure the first time you mount them and topping them up every 1-2 weeks is one of the most important habits you need to develop as a cyclist.
Tire Pressure, Explained
Bike tires—whether we’re talking about clinchers with inner tubes or tubeless—are casings made out of fabric, rubber, and a couple of hundred of other chemicals that you mount on the rims to hold air and roll on the ground.
In their simplest form, they are containers for air.
Since air is invisible to the eye, it’s easy to forget that it has mass, volume, and pressure. But when you puff out your cheeks like frogs do, the seeming firmness of the air bubble between your cheeks will quickly remind you of it.
So, when you inflate a tire, you pump more and more air molecules inside it. The more air molecules that get into the tire, the less the free space between them. At a certain moment of time, these molecules get squeezed together so tightly that they’ve nowhere to go… so pressure builds up.
PSI is the metric that lets you measure this pressure, no matter the type of tire and pump at hand.
It’s like the hours on the clock or days on the calendar; you can simply trust it.
Getting Tire Pressure “Just Right”
Pumping tires is a Goldilocks situation:
On the one hand, you don’t want to pump them too little, as they will be too soft and won’t hold their shape well . And yet, you don’t want to pump them too much because they will become too hard (and hold their shape too well).
An underinflated tire has too few air molecules inside, so it’s soft and squishy; it doesn’t have the shape or firmness it needs to provide traction and grip.
As a result, underinflated tires deform while riding and can easily become trapped between the tire and rim (in what is called a “pinch flat”).
An overinflated tire has too many air molecules inside it and, since the tire is a confined container, these air molecules have nowhere to go.
Overinflated tires are too full and too stiff for their own good. They don’t have the suppleness that they need to absorb shocks from the road or carry the combined weight of the bike and the rider, so they’re prone to blowouts.
The tires’ PSI, which you can check with a tire pressure gage—either as a stand-alone device or mounted on a pump—is what helps you get that air pressure “just right.”
The Type of Bike Matters
Different types of bikes have different types of tires.
Road bikes have compact, narrow tires that weigh less, have better aerodynamics, and brake quicker. They hold more pressure and have less contact surface with the road.
Mountain bikes have bulky, wide tires that weigh more and run on any terrain, from sand or snow to mud or rocks, and in all four seasons. They hold less pressure and have more contact surface with the ground.
Hybrid bikes, as their name suggests, are somewhere in between. They have tires that work well on the road, on paths, and on trails so you can use them for commuting and recreation.
Best PSI for Road Bikes
Road bikes are intended for paved roads over rough terrain.
On smooth asphalt, as in long and easy riding surfaces (including racing tracks), a road bike is built light. The structure and all of its components, including the wheel and the tires, are meant to deliver a smooth and/or fast ride.
In the cases where road bikes are being used for kid’s starter bikes (which usually occurs on asphalt or smooth surfaces), or urban commuters are riding them on city roads that have the usual cracks, undulations and potholes, some adjustments may need to be made.
Road bike tires should generally be pumped up to 90-120 PSI. The more inflated the tire, the lighter the touch with the road. They say that road bikes “fly;” if runs effortlessly and, if you stop peddling, it will glide smoothly.
A high-PSI tire will be bouncy, especially on cobblestone roads, very sensitive to shocks, and tend to fly. These may not be the characteristics you look for in the other two cases mentioned above.
For a kid’s bike, the expectation is that the rider is not experienced enough and, depending on how they gain weight and height, the balance is always a question.
You don’t want to put a kid on a super-fast bike; the chances of them taking a tumble are too high. Also, for some starter bikes, costly tires that can withstand high PSI may not be worth it.
The problem with an urban commuter’s bike is different.
While you don’t do off-road as an urban commuter, in many countries, cracks, potholes, slopes, and undulations are a natural part of the course.
As a result, the type of tire used and the PSI employed can vary, depending on how rough the regular route. Her speed is of secondary importance when driving next to cars and pedestrians: safety and stability are much more important.
Best PSI for Mountain Bikes
Mountain bikers ride off-round, on rough terrain. Slickness and speed on the road are not the determining factor in choosing the right tire or determining the right tire pressure for MTBs.
Grip, traction, and an ability to absorb shocks and resist punctures are among the top traits to look for when choosing tires for this kind of bicycles. These tires come in all shapes and forms, with wider tires offering more control and narrower tires offering higher speed.
No matter what kind of tires you’ve fitted your MTB with, a few general principles for how you top them up with air apply:
Mountain bike tires should generally be pumped to 30-50 PSI, although there are situations in which less or more tire pressure may be needed.
Where one falls within that range depends on the specific ground being covered.
The lower the PSI, the more the tires “sag”, which is not good for smoothness or speed but excellent for stability on rough soil since the tire hugs more ground with better grip.
It may be a bit different for gravel bikes. While the terrain is not as smooth as those road bikes ride on, hard-packed gravel makes for a different challenge due to abrasiveness.
Depending on the specific circumstances, experienced riders will customize the PSI, usually still sticking to a low or mid-range, but maybe not as low as for mountain bikes.
Best PSI for Hybrid Bikes
Hybrid bikes are designed and built to be used as both a road bike and a mountain bike (though some would say they’re not particularly good at either). So you can ride them to and from work while having fun in the mountains on the weekend.
As a golden rule, the optimal tire pressure for a hybrid bike is between 50 PSI and 70 PSI, plus/minus 10% depending on the terrain and weight of the rider.
If you use your hybrid bike for commuting to work or for road trips, inflate the tires to a higher value PSI for less resistance and higher speed. Before going off-road on the weekend, deflate to a lower PSI for a larger contact area with the ground and better grip.
What If You Don’t Have a Tire Pressure Gauge?
There are situations in which you need to pump up your tires, but you just don’t have a tire pressure gauge handy.
For example, I once slid out a corner in the mountains, falling down and puncturing the tire. I had Slime sealant and a ball pump in my backpack, but the ball pump had no pressure gauge.
The good news is that there are ways to check your bike’s tire pressure by feel, if imprecise:
Rider’s Feel
An experienced rider will know if the tire is over- or under-inflated just by feel, especially if they have ridden a particular bike for a while.
An over-inflated tire will feel unusually bouncy, too responsive, low on traction and prone to quick changes in direction. Under-inflated tires will feel sluggish, unresponsive and hard to maneuver. A middling obstacle on the ground may cause the bike to trip, even.
The Squeeze Test
This is the same test that you would do if you didn’t have the psi range marked on the tire.
Pinching the tire sidewalls near to the frame would let the rider know if there is tautness, but with a bit of give – which would be the top end of the range the tire can tolerate.
The Sag Test
There are a couple of versions of this:
Firstly, if there is someone riding with you, they can make out if the wheel is sagging due to low psi in the tires.
Secondly, if you ride through a low puddle, and the water splashes up to the level of the tire tread wells, your bike is definitely riding too low.
Summing It All Up
| Type of Tires | Recommended Tire Pressure |
|---|---|
| Road bike tires | 90-120 PSI |
| Hybrid bike tires | 50-70 PSI |
| Mountain bike (MTB) tires | 30-50 PSI |
The PSI on your bike tires is a vital, final component of getting ready for your ride.
As we discussed, dedicated riders can be extremely finicky about their tire pressures—and for good reason. Hopefully, the guidelines above have given you a good idea of how to choose PSIs for your tires so that you enjoy your ride to the fullest.
