I have my tires at 37psi all around. I note that after driving a while on the highway (usually 65-80mph), the psi goes up to 41psi. is it usual for the pressure to increase by 4#? Is 41psi too high for the tires...is it dangerous?

 

What's the recommended PSI for your car? + 4 PSI is normal after the tires warm up.

 

On the gas tank lid, the recommendation for normal loads is 36 all around. And, for maximum load, the recommendation is 39/45...yikes! So, I guess tire psi going up to 41psi is no big deal for these tires.

 

Most PSI measurements stated are for Cold tires. The 36 PSI is a cold reading, so it very well can go up from there and it will do to the additional friction of your tires against the road surface.
Do you remember the Ideal Gas Law from high school physics? PV=nRT? Pressure is directly related to temperature. So as one increases so does the other (since volume in this case is pretty much limited by the tire).

 

Yeah, Hapa, I know that pressure is directly proportional to temperature (but I did forget the formula.) Anyway, my concern was that I thought that I was seeing a higher than expected temperature increase and didn't quite realize that these tires can take a lot of pressure...and now I know. Used to run my BMWs at 35 all around even though the recommendations were 32/35. For the MB, I thought that 37 all around would be a nice compromise as I figured that the lower psi might be a little more wearing on the tires??? Right now at 37psi the ride and control are fine.