1engineer
Moderator
So, last week my wife and I did another of our road trips back to Florida to watch some soccer and go to the beach. As some of the older members know, I do some of my best "imaginative" thinking while driving lol. Anyway, I of course did my pre trip checks that most of us do and one of the items is tire pressure. I probably do this a bit different than most of you because I note not only the pressures of each tire but also the ambient temperature. Why? Here is a simple explanation here http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=73 but suffice to say tire pressure, for us, will increase 1 psi for every 10 degrees temperature rise.
I checked my tires and gauged them to 35 psi, which is optimal for this trip and the ambient temp was 65 degrees. I always check the tires the night before (no sun heating up one side) and after the vehicle has sat for awhile so no frictional heat either. My truck was lightly loaded with about 600 lb (two people, gear, bike, dog).
My route was basically all interstate for around 700 miles. I77, I26, I95, I275 and I10 got us within 100 miles of our destination.
I pulled into a gas station in South Carolina to get fuel and boiled peanuts and decided to check the tires. I always do a tactile check when getting fuel (back of the hand held to the tread) because over the years I have driven some heavy trucks and pulled heavy trailers. Tire temperature is critical in those applications and some of that has just carried over to daily life. Anyway, because the ambient temperature was 95 degrees by then I decided to gauge the tires. Every tire was 40 psi and that was about what I expected. Max pressure on my tires is 45 psi so I was well under max.
The question is how did my tires gain 5 psi? Well, 3 psi is easily explained by simple temperature rise of 30 degrees. The other 2 psi? That came by the rolling resistance of the tires which causes friction (adhesion - coefficient is called mu) which causes the tire to heat which causes the air in the tire to expand and - *poof* 2 psi rise in pressure!
Now why did I think this warrants a thread here? Many of you will be going on vacation or long trips this summer and many of you will be carrying a much heavier load. You could be pulling a trailer (tongue weight) + all your gear and easily have an extra 1200 lbs added to the GVW of the 4Runner. Check your tire pressure! Especially those of you with more aggressive tread! It's extremely easy to add 5 psi to each tire as evidenced by my data and observation. More weight + wider aggressive tread + temperature change = a problem waiting to happen. In the 2K miles I drove last week I witnessed well over 20 vehicles with flats or blowouts. Check your pressure and make sure you can stand a 5-8 psi change in pressure and still be within spec. Hope this helps some of you.
I checked my tires and gauged them to 35 psi, which is optimal for this trip and the ambient temp was 65 degrees. I always check the tires the night before (no sun heating up one side) and after the vehicle has sat for awhile so no frictional heat either. My truck was lightly loaded with about 600 lb (two people, gear, bike, dog).
My route was basically all interstate for around 700 miles. I77, I26, I95, I275 and I10 got us within 100 miles of our destination.
I pulled into a gas station in South Carolina to get fuel and boiled peanuts and decided to check the tires. I always do a tactile check when getting fuel (back of the hand held to the tread) because over the years I have driven some heavy trucks and pulled heavy trailers. Tire temperature is critical in those applications and some of that has just carried over to daily life. Anyway, because the ambient temperature was 95 degrees by then I decided to gauge the tires. Every tire was 40 psi and that was about what I expected. Max pressure on my tires is 45 psi so I was well under max.
The question is how did my tires gain 5 psi? Well, 3 psi is easily explained by simple temperature rise of 30 degrees. The other 2 psi? That came by the rolling resistance of the tires which causes friction (adhesion - coefficient is called mu) which causes the tire to heat which causes the air in the tire to expand and - *poof* 2 psi rise in pressure!
Now why did I think this warrants a thread here? Many of you will be going on vacation or long trips this summer and many of you will be carrying a much heavier load. You could be pulling a trailer (tongue weight) + all your gear and easily have an extra 1200 lbs added to the GVW of the 4Runner. Check your tire pressure! Especially those of you with more aggressive tread! It's extremely easy to add 5 psi to each tire as evidenced by my data and observation. More weight + wider aggressive tread + temperature change = a problem waiting to happen. In the 2K miles I drove last week I witnessed well over 20 vehicles with flats or blowouts. Check your pressure and make sure you can stand a 5-8 psi change in pressure and still be within spec. Hope this helps some of you.
