Dear Car Talk:
My 2017 Toyota Tacoma calls for 33 pounds of air in all four tires. Where I live, during certain times of year, temperatures can range from a high in the 70s to a low in the 20s and back to a high in the 50s, all within two or three days. This makes tire pressure difficult to maintain. My question is: What are the safe high and low limits for tire pressure? I know if I go with 35 psi, I will have a hard ride and better gas mileage. If I go with 29 psi, I will have a softer ride and worse gas mileage. But for safety, when do I need to actually adjust it, in either direction? -- Gary
It's always better to go too high than too low with tire pressure, Gary (to a point).
As you say, tire pressure changes along with the outside temperature. For every change of 10 degrees in the outside temperature, tire pressure changes about 1 psi. So if you fill your tires to 33 psi when it's 75 degrees out, and it drops to 25 degrees at night, your tires will be at 28 psi. That's too low.
I've been told that most tire-pressure monitoring systems warn you when your tire pressure drops by about 10 percent. For you, 10 percent would be a little less than 30 psi.
Low tire pressure always is more dangerous than high tire pressure. When tires are deflated, more rubber touches the ground, the tires heat up and you're in danger of a blowout. If you remember the Firestone/Ford Explorer fiasco, the aggravating factors that led to many of those flawed tires exploding were heat (high road temperatures) and low tire pressure.
Higher pressure generally is not dangerous, as long as you stay well below the "maximum inflation pressure." That number is listed on each sidewall, and is much higher than your "recommended tire pressure" of 33 psi, Gary.
So, in your case, I'd recommend that you put 35 or 36 psi in the tires and just leave it there. You won't notice any difference in tire wear, handling or braking.
And even if the temperature drops 50 degrees, you'll still have 30 psi or more, which should keep your "low pressure" warning light turned off.
And if the temperature goes in the other direction, no harm will be done. As you say, at worst you'll end up with better fuel economy and a slightly firmer butt massage while you drive around, Gary.