Tire Pressure Fluctuations?

I've never owned a vehicle that actually told me what my tire pressure was at any given time. A few mornings ago, temps were in the single digits, and I had a low tire pressure warning when I took off to a meeting that was an hour away. The menu display showed the tires were all at 29 psi.

30 minutes into my drive the tire pressure warning went off, and all the tires were reading 34 psi, which is where I had them set per the door sticker.

I had no idea tire pressure fluctuates that much with temps and driving time. I know it's all physics, but have you guys noticed that much variation? Also, at what temps do you set your cold tire pressure? It seems, if I wait for a frigid day to set the cold pressure, I'll end up driving around with too much pressure most of the time. Any thoughts on this trivial topic?

Matt

 

Yes, it is the ideal gas law, pressure is inversely proportional to temperature. I usually set the tire pressure to 35 in the summer and will see up to 40 PSI during longer drives. When I go skiing, I’ve seen 30 psi on particularly cold days. Perfectly normal and happens to every car. The rule of thumb I’ve heard is 1 psi for every 10 degrees.

 

Thanks. I vaguely recall what you confirmed from my college physic courses, but it was my worst course, and I didn’t retain much of it. I guess I’ll set my tires to around 37 psi now, and that should prevent the low pressure warnings on the cold days.

 

^ X2..

I set my cold pressure at whatever cold means for that season, but usually in the morning when the sun is up but everything is still cold. 3-5 psi change throughout the day is normal for me; 30 degree temperature swings in a day is pretty standard, which tracks with @xc-tc 's ballpark rule of thumb.

 

In the morning when it's cold and hasn't been driven yet, you can reset the TPMS with a button under the dash (I don't recall the exact procedure offhand but it's listed in the owners manual is pretty simple - like hold down the button until the TPMS light blinks on the dash, or some such). Doing this should reset the threshold for the low pressure warning. I believe the threshold is 10 psi from the set pressure, or 20 psi minimum - whichever is greater.

 

Depending on where you live, finding that happy spot for psi can be tricky this time of year. So far our temps around here have ranged anywhere between 30-55 degrees. What I do is run 2 addition pounds from normal, and I set it on a day that was in the 40's. Not much more you can really do.

 

Damn! I read my manuals cover to cover, but obviously glossed over that tidbit. Thank you! I’ll try it tomorrow.

 

I usually set my tires in the Winter 2 psi below what I want. Most of my drives are less than 30 minutes. The PSI goes up 1-2 on average. Summer, not sure, same as OP, I never had a truck which measured the PSI. Our Winter temps are 20-40.

 

Looks like you got the right idea. I set the tire pressures about 4 times a year to account for seasonal temperature change. For my particular tire setup (load range E) I like to target a 38 to 39 cold pressure for optimal tire wear. Nitrogen filled tires (pure nitrogen) helps mitigate that pressure fluctuation cause by both seasonal changes and tire temperature, but some good old compressed air works just fine for any passenger vehicle.