A little common sense goes a long way.

Sure, it's possible to see a 10+ lb. difference in one day. Start out with a cool morning at a low altitude, drive all day and end up at a much higher altitude with a very hot air and road temp. I've had this a few times going over the Rockies. I just let some air out since I was going to be spending a week at a higher altitude. When I got back to a lower altitude, I added air, so that I was always at 30 while the tires were cold.

But this scenario is rare. Most driving conditions won't see this extreme a swing in tire pressure. Set it at 30 cold, and it will go up a few to several pounds during normal driving. Keep in mind, though, if you don't have a compressor, and have to drive somewhere to add air, your tires most likely will be warm, and if you bring it to 30 at that point, it will be under inflated. Check the pressure at home before you leave, and if you are down x lbs., add x lbs. at the gas station.

 

Less heat buildup? Probably, but I'm not sure it would be significant, nor that it's something to worry about unless you're driving through Death Valley. Tires heat up, I believe, primarily from two factors: flexing of the tread and sidewall, and friction between the tread and road surface. The latter is a bigger factor than most people realize. The tire and the road are interacting at the molecular level, with the road surface constantly tearing off microscopic bits of rubber. Even in a straight line, friction is a significant factor, hence the development of low rolling resistance tires to improve gas mileage. Our tire are very definitely NOT low rolling resistance designs, and friction is going to be roughly the same regardless of tire pressure, as long as pressure is in a reasonable range.

So you'll get a little less flex with a higher pressure, but not zero, so you're still getting heat generated that way. And you're still getting heat generated from friction. So you're still getting temperature rise.

I'm not sure what max pressure for these tires are, but by starting off 4 psi you're also 4 psi closer to max pressure (which is measured hot, not cold). So you're eliminating some of your safety margin.

Finally, let's say that at 30 psi you get a 5 - 6 psi gain (which is probably higher than you'd actually get), and at 34 psi you only get a 2 psi gain. Either way you end up at about 36 psi hot. I suspect you're looking at a smaller gap than that, and starting at 34 psi will result in a higher hot pressure than starting at 30.

The OM recommends higher pressures if you're going to be driving at high speeds (greater than 100 mph, IIRC) for extended periods. There aren't too many places in the US you can do that.

Really the same question. With less sidewall flex, the amount of rise will probably be a little less starting at 34.

 

What I was looking for was a smoother, quieter, ride, had no idea those tires howl like they do. At 65 and over.

 

I agree the car is much louder than I expected at high speeds. People keep saying that non-run-flat tires will reduce this, but I'm not sure I like that idea.

 

meyerweb -- Appreciate the discussion and analysis. That was what I was seeking.