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?
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.
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.
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.