Dear Car Talk:
My home is at a 1,800-foot elevation.
It’s an 8-mile drive straight downhill to sea level, where I do most of my driving. I understand that tire pressure increases by about 0.5 psi per 1,000 feet of altitude. So here is my question:
Should I inflate my tires to the recommended 32 psi when cold in my garage, or should I add a pound to compensate for the higher elevation? I do check my tire pressure at a minimum once per month. — Roger in Maui
First, I would like to apologize to all my other readers who’ve just spent the winter chipping ice off of their windshields for having to read Roger’s letter worrying about 1 measly psi of tire pressure when he drives down to the beach every day.
Roger, the answer is technically yes, you should add an extra pound of air pressure to compensate for the pound you will lose when you drop to sea level. That’s the technical answer. The real-world answer is that it hardly matters.
Your tires can vary by 1 psi without having any effect on the safety or performance of the car. In fact, the heat of the tires from driving down the mountain might negate the altitude-related loss anyway. Just to give you a frame of reference, all cars now have tire pressure monitoring systems. We know that when tire pressure is too low, tires can overheat and fail catastrophically. This is especially dangerous when driving at higher speeds in hot weather, when tires are most susceptible to overheating and where a blowout can be a matter of life, limb and RAV4.
But the tire pressure warning light doesn’t even come on until your pressure drops by around 10%. So, in your case, you’d have to lose more than 3 psi to get even a warning from the system.
That said, it’s always better to be safe, and it’s always safer to overinflate your tires than to underinflate them. So, if you inflate your tires to 33, 34 or even 35 psi, you’ll do no damage to the tires or in any way compromise your handling or safety. And you’ll give yourself more leeway for the altitude change.
As long as you stay well under the maximum pressure listed on the side wall (not the same as the recommended pressure), you can just overinflate a bit and stop worrying, Roger. Aloha.
Got a question about cars? Write to Car Talk write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.
