What does 40 psi mean on a tire?

One of the greatest risks to your everyday driving safety is the one thing you can’t actually see: your tire pressure. Since inflation levels are invisible to the naked eye (unless your tire is almost flat), it’s important to understand how to find and maintain proper air pressure, and to be aware of the dangers of driving on over and under-inflated tires.

What's the right tire pressure for your vehicle?

There is a tire pressure marking on the sidewall of your tires, but this isn’t the optimum air pressure for your tires, it’s the maximum.

The words ‘Max. Press. 35 PSI,’ for example, indicates the maximum pounds per square inch pressure needed for your tire to support the weight of its maximum load-carrying capacity. For everyday use, most passenger cars will have a recommended or optimum pressure of 30 or 32 PSI.

What happens when you inflate your tires to the maximum pressure?

The handling characteristics change at max pressure

Since tires inflated to the max can’t give as much on the sidewall, you might see strong cornering performance, but it could be at the risk of your braking threshold. One quick corner and your back end could slide out.

Your tire life decreases at max pressure

When your tires are overinflated, the rubber rounds out at the top of the tire when you’re driving, and the centre will quickly wear out. You’ll also reduce your traction and you could even cause a blowout.

How do you find your recommended tire pressure?

You’ll find the manufacturer’s optimum or recommended tire pressure for your car on a sticker in the door jamb, or in your owner’s manual. Some models even place the stickers on the trunk lid, in the console or on the fuel door.

What happens when your tires are overinflated or underinflated?

When you drive with over-inflated tires, you risk:

• Problems with handling and safety. Your tires can’t give as much on the sidewall, and precise braking could be compromised. You’d also be risking reduced traction.
• Rapid, uneven tire wear. Your tire will wear much faster, and only in the center because the rubber will bulge in the middle, increasing that area’s contact with the road.
• Blowouts. Bald strips can’t dissipate heat as well, and that means your tires can suddenly blow out.

When you drive with under-inflated tires, you risk:

• Tire failure and safety. Underinflated tires greatly increase braking distances and can dramatically affect steering and handling. Also, when tire pressure is significantly low, more of the tire’s tread face touches the road and causes friction. That friction can lead to overheating, which can cause tread separation and blowouts in extreme cases.
• Premature wear, reducing your tire life by 15 per cent or more. Under inflation wears your tires on both outside shoulders because the edges are making excessive contact with the road.
• Poor gas mileage. Vehicles with underinflated tires see reduced fuel economy because they make your engine work harder: underinflated tires put more tire surface in contact with the road, causing more rolling resistance and friction with the road. The result is poor gas mileage and higher fuel costs – up to 1.3 cents per litre! Depending on how often you fill up, that can lead to hundreds of dollars over the space of a single year.

If you’ve been driving with your tires over-inflated or under-inflated, immediately deflate them to the manufacturer’s recommended pressure for your driving safety. If you’re not confident about how to check your tire pressure, follow our handy 5-step Guide to Checking Tire Pressure.

When your tires are consistently inflated to the recommended air pressure, you enjoy greater tire life, performance and safety.

How do summer and winter temperatures impact tire pressure?

Winter

When the temperature drops, air contracts and as the molecules get closer together, the reduction in volume causes tires to lose their pressure. Before you know it, your tires are underinflated. Be sure to check your tire pressure regularly during the winter months.

Summer

Just as cold outside air causes the air inside your tires to contract in winter, warm outside air causes the air inside your tires to expand in summer. The rule of thumb (best understood as our American counterparts put it) is that tire pressure will go up approximately one pound per square inch (PSI) for every 10 Fahrenheit increase in temperature. So, let’s say your manufacturer’s recommend inflation level is 35 PSI, on one of those all-time hot August afternoons, your tire pressure could be somewhere near 40 PSI.

It's also important in summer to keep in mind that driving equals friction between the road and your tires, which equals heat, which equals…you guessed it…an increase in tire pressure. For this reason, regardless of the weather, your air pressure can increase about 5 PSI in the first half-hour of driving before stabilizing. In the sweltering heat of summer asphalt at high speeds for long stretches, that number can rise, and not for the better.

Is 40 psi too much for a tire?

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What happens if psi is too high?

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