Many cyclists pump up their tires only when they become noticeably soft. They pump them up until they’re hard. Simple!
Is this the best way to do things? Well, not really.
For a start, it helps if you know how much air pressure is in your bicycle tires.
Monitoring bike tire pressure helps you optimize your tires for comfort and speed. It’ll also alert you to problems like slow punctures or faulty valves.
This article will help you decide how much air you should put in your tires.
What Is Bike Tire Pressure And What Is PSI?
Bike tire pressure can be either measured in bars or PSI, but the latter is more common. These units of measurement gauge air pressure inside the tire. Air pressure gives the tire its shape and decides how much the tire flexes as you ride.
Since it uses pounds and inches, PSI is an imperial unit of measurement whereas the bar is a metric measurement. One bar is equal to 100 kPa (kilopascal).
PSI (pounds per square inch) is the unit you’ll normally see written on the side of bike tires. There will be a maximum PSI that you shouldn’t exceed if you want to avoid hazardous tire blowouts or tire deformation.
You may also see a maximum PSI on wheel rims, which contain the tire pressure.
Air pressure is directly related by Boyle’s Law to air volume. The wider a tire is, the more air volume it has, and the lower PSI it needs to achieve the same “hardness”. A lower PSI does not automatically make one tire softer than another (think of car tires).
Air volume is a vital concern if you ever think about using an automatic air pump at a gas station on your bike. Those are designed for car tires with much greater air volume. As such, they may explode a bike tire.
Why Is Bike Tire Pressure So Important?
Bike tire pressure affects three key aspects of cycling: safety, comfort and speed.
The PSI Safety Aspect
From a safety standpoint, it’s always useful to know if the PSI in your tires is too low or too high. You can adjust PSI to suit various weather conditions. Lowering pressure a little increases tire traction on icy roads, for example.
The weather has a direct effect on PSI. If you pump your tires to the max and go riding in extreme heat, they may end up overinflated. Braking heavily on rim brakes (e.g., on steep descents) also increases PSI. There’s scope for disaster in certain situations.
Even in perfect riding conditions, a tire that is too soft and “squirmy” does not corner well and may risk the sidewall collapsing, potentially causing an accident.
PSI And Ride Comfort
Tire pressure directly affects ride comfort because a softer tire absorbs vibration from the riding surface. Conversely, a tire that’s pumped up to a high PSI hits obstacles harder, causing discomfort as you ride.
One way that larger tires allow lower pressure is by their greater air volume and physical size. That lets you run a slightly lower PSI without running much risk of pinch flats, at least on a road bike.
Of course, the chief benefit of tubeless tires is that you can run low tire pressures and the risk of punctures is inherently mitigated. In theory, at least, any puncture is automatically sealed and you can continue on your ride.
The way a tire is made has a bearing on tire comfort and affects how much PSI you need. With supple tires like tubulars or open tubulars, you are effectively riding on air. The sidewalls are flexible and there are usually two layers of casing rather than three.
Supple tires flex more than vulcanized tires, even when their tire pressure is high. And because they don’t have stiff sidewalls to help prop up your weight, it’s inadvisable to run them with a low PSI. These tires give a plush ride regardless of pressure.
PSI And Speed
Tire pressure plays a role in your ability to ride quickly. However, it’s impossible to calculate a precise optimum tire pressure unless the riding surface stays constant throughout the ride. This is rarely the case.
On a smooth riding surface, a high tire pressure reduces the size of the tire’s contact patch and thus reduces rolling resistance. This makes you faster. However, a tire pumped to a high pressure on rough surfaces incurs “suspension losses”.
A nominal ideal tire pressure, then, takes the nature of riding surfaces into account throughout a whole ride. Rider and bike weight also play a part, as this affects hysteresis losses and the likelihood of punctures.
You can take away something from this: maximum pressure is never the fastest choice on ordinary, variable roads or trails. Try knocking a few PSI off for comfort and speed.
Bike Tire Pressure Chart And Pressure Recommendations
Tire pressure calculators and charts usually take your weight into account and the width of the tires you’re riding. A common aim with these calculations is to create a 15% drop in tire height based on the metrics you supply.
The table below displays recommended pressures for a variety of tires at two rider (plus bike) weights. It also shows how pressure drops with increased width and air volume.
Bike Tire Pressure Chart (PSI)
The PSI in the table assumes a 50/50 split between front and rear tires.
Some people prefer a 60/40 or 55/45 split, which means pumping the rear tire to a higher pressure than the front. This accounts for the greater weight that the rear of the bicycle has to bear.
As well as rider and bike weight, any luggage or panniers you carry will increase recommended tire pressures.
Next, we’ll look at different types of bikes and their PSI requirements.
Tires on road bikes have traditionally been pumped up to very high pressures, dating back to when they were insanely skinny at 20mm. Road cyclists for the most part ride on relatively smooth surfaces, so pressures can go a bit higher without causing discomfort.
The above being said, there has been a trend towards wider tires in the past few years, which can be nudged downwards a bit more in PSI. Tubeless tires are also popular, and these afford even greater opportunity to run low pressures.
Maximum PSI in road tires can go to 140 PSI and above, though few would ride them at those pressures. As mentioned in this article, optimum pressures are invariably lower than max. Unless you’re riding on glass, that enhances speed as well as comfort.
Mountain bikes have wider tires than road bikes, with widths that overlap in range with gravel and CX bikes. All these bikes are ridden on rougher surfaces, which is why tubeless tires are common in off-road riding.
Many people run MTB tires at a low PSI relative to their max, though on rougher trails this invites the possibility of pinch flats or worse. So, many riders use a higher PSI on bumpy terrain to avoid punctures or tire damage.
On smoother trails, you’ll gain a lot of comfort with a lower PSI, and if you pick the sweet spot you might get more speed as well. As long as the trail isn’t too gnarly, this is a risk worth taking.
Hybrid bikes are intended to bridge the gap between road bikes and MTBs, so what about their tire pressures? Well, a hybrid isn’t meant for rougher off-road stuff, but its tires are similarly sized to fatter road tires, gravel tires and narrower MTB tires.
If you run hybrid-bike tires at moderately low pressures on a smooth trail, you’ll gain those comfort benefits already discussed. It probably won’t hurt your speed, either, as the lower pressure helps soak up the impedance of a trail.
What about a bike that was never designed for speed and always designed for comfort—the cruiser? This is a bike that won’t be plowing through rough terrain. Rather, you’ll be casually rolling along a beach or around leafy suburbs.
The balloon tires usually found on cruisers are designed to absorb shock or vibration. Maximum pressure on modern balloon tires is in the region of 35-60 PSI. As with all tires, you can run a lower PSI for extra comfort.
How To Check Your Tire Pressure
The simplest way to check tire pressure, albeit unsatisfactorily, is to give the tire a press with your thumb or finger. It shouldn’t yield much. Unless you have magic digits, this won’t tell you what the PSI is, but it’ll indicate whether the bike is rideable.
Video: The Human Pressure Gauge
You can look down on the tire from above, too. It shouldn’t protrude much beyond the wheel rim if it’s properly inflated, though it’s very common for tires to do this slightly.
With standard butyl tubes in your tires, the amount of PSI lost from one day to the next is minimal. Latex tubes, on the other hand, deflate a fair bit overnight. The latter offer better ride quality, speed and puncture resistance, but they’re high-maintenance.
Tubeless tires lose air slowly as long as the sealant is doing its job and the valve works.
A better way by far to check tire pressure is to use a digital tire pressure gauge. This will give you the tire pressure in the measurement unit of your choice. And you’ll know if your bike is good to go or needs more air.
The downside of a pressure gauge is you have to keep removing it between sessions of pumping up the tire.
How To Inflate Your Bicycle Tire
There are a few simple steps to follow when pumping up a bike tire.
1. Choose A Bike Pump
When pumping up a tire at home, a floor pump with a built-in pressure gauge is ideal. Outside, you can use a frame pump or a mini pump. Make sure the pump you buy has the correct type of head for your wheel valves (Presta or Schrader).
2. Determine The PSI
Check the maximum PSI that should be written on the side of the tire. Don’t exceed that when you go to pump air into the tire. In reality, it’s hard to overinflate a high-pressure tire with smaller pumps, but keep the max PSI in mind.
3. Fix Pump Head To Valve
Now you need to attach the pump head (or chuck) to the tube or tire valve. Take off any plastic cap. With a Presta valve, you also have to unscrew the tip of the valve before it will let air in.
Depending on the pump you use, you’ll have to either screw the pump head on or push it on and secure it with a cam lever.
4. Inflate The Tire
Next, inflate the tire. Aim for your desired PSI, taking into account the advice contained in this article. When pumping up a tire, most of the air goes into the tire at the end of each pump stroke. Be sure to push the handle up to the barrel.
5. Remove Pump
When you’ve pumped the tire up, remove the pump head from the valve vertically to avoid damaging the valve. Do this briskly with a push-on pump head to avoid letting out air. Tighten the valve head again if necessary and replace any cap if there was one.