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Winter vs. Summer Tire Pressure - What is the Proper Inflation?

20 September 2013  |  C, G, & J Inc  |  Heat Transfer Experts
The weather is cooling down and winter is just around the corner. You may have heard it said that you should run different tire pressure in winter than summer or that you need to run lower pressure for better traction in bad weather. There are a lot of misconceptions about tire pressure that can cause significant problems for your vehicle, so let's take a look at what is the correct pressure to use.

Most people will agree that driving with properly inflated tires will produce the best traction, MPG, durability, and safety that you can possibly get from the tires. However, figuring out the proper PSI for a tire seems to spark quite a debate among people. So how do we determine the proper inflation for a tire?

Tire Pressure: Manufacturer Recommendation vs. Max PSI on Sidewall

You may not be aware that your vehicle’s manufacturer has a recommended PSI for tire inflation either on the sticker inside the driver’s door or in the manual. This is the PSI rating you should inflate your tires to. It is designed to provide the most comfortable ride for your vehicle. What about the “Max PSI” on the sidewall? That is the PSI for which the tires will support the maximum carry load. For everyday use, the tires should be inflated to the manufacturer recommendation.

In order to get the proper inflation amount in our tire, we first have to know how much pressure is already in our tire. Clearly that is just a matter of unscrewing the fill valve cap and checking it with a pressure gauge, right? Almost. The time of day and whether or not the vehicle has been driven can alter the pressure in the tire enough that we may not get an accurate pressure reading. Instead, we need to check the pressure in the morning prior to driving the vehicle.

Check Your Tire Pressure in the Morning Before Driving

The recommended inflation amount is based on the tire being “cold.” This isn’t to say the ambient air has to be a certain temperature, but that the tire hasn’t been warmed up by any of the following:

  • Driven for more than a mile
  • Sat in direct sunlight for a long period of time
  • Been in contact with hot pavement, even if parked
  • Warmed by rising day time temperatures

As a general rule, your tire pressure will gain or lose 1 PSI for every 10° F change in temperature. This means that if the temperature rises 20° during the day (as it is known to do in North America), your tire pressure will increase by 2 PSI. So if we check our tire pressure in the afternoon, we may be running low pressure in the mornings when the air is cooler. The best time of day to check your tire pressure is in the morning before driving. This will give you an accurate reading and allow you to properly inflate the tire.

Will My Tires be Over-inflated in the Afternoon if I Fill them in the Morning?

If you measure the PSI in your tire in the afternoon, it will be higher than in the morning but it doesn’t mean they are over-inflated. This is both expected and planned for by the tire manufacturer. They know that the PSI will increase as the tire is in use and the day warms up. You are still okay even if the afternoon PSI is greater than the “Max” PSI listed on the tire sidewall! That “Max” PSI is in reference to when the tire is “cold.” The max PSI is not the “bursting” point for the tire. Do not let air out of your tire in the afternoon just because the PSI is higher than the recommended level; otherwise, you’ll be running under-inflated tires in the morning. Again, the recommended PSI is based on when the tire is “cold” and the tire is designed to handle the extra PSI from normal use.

Check Your Tire Pressure Often: Every Month at Least

Another general rule is that you lose 1 PSI every month after you inflate your tire. Damage to the tire can cause you to loose pressure faster, but assuming your tires are in good shape, you’ll continue to steadily lose pressure. Combine this with the loss of PSI due to the change in temperature, and the beginning of winter becomes the most critical time to check your tire pressure. Imagine this scenario: You checked your tires in August, when it was 75° F in the morning, and filled them up. In November, you’ve now lost 3 PSI since it’s three months later. If the morning temperature is 55° F, then you’ve lost an additional 2 PSI for a total loss of 5 PSI. That’s enough to lose MPG, traction, and damage your tire. Check your tire pressure regularly to ensure you’re not putting yourself or your tires at risk of damage.

Increase PSI when Carrying Heavy Loads

In order to support the added weight of heavy loads, your tires will need to be inflated at a higher PSI (but not more than the max PSI listed on the sidewall!). Exactly how much higher will depend on the load amount, your vehicle, and your tires. Check your vehicle manual for recommendations or call the dealership for the best PSI rating to use for the expected load.

Do not Run Over-inflated or Under-inflated Tires

Regardless of the time of year, you should always run your tires at the proper PSI recommended by the manufacturer. Under-inflated tires will not maintain their shape causing them to lose traction, wear unevenly, and even damage the tire not to mention the reduction in fuel economy. In wet weather, under-inflated tires won’t shed water away from the tire as well as they should creating a significantly higher risk of hydroplaning.

Over-inflated tires become rigid and inflexible making them more susceptible to damage from road debris and pot holes, plus it makes for a rougher ride. Slightly over-inflated tires can provide better steering precision as well as cornering stability but only to a certain extent. This is primarily done for racing vehicles and should only be done by experts. Passenger and other vehicles travelling regular roads should stick with the manufacturer’s recommendation.

Keep Your Tire Pressure Consistent All Year Round

Regardless of the time of year, you should regularly check and maintain the recommended PSI for your vehicle. This will provide the smoothest ride, best fuel economy, longest durability, and greatest amount of safety you can get from your tires. If you are unsure of what your tire pressure should be, you can always bring your vehicle by our shop, and we’ll be happy to check it for you!

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