The door says 42psi, but my SC keeps pumping them up to 45 psi. Are there any benefits to pumping higher than 42psi?
First off if they drove the car then set the PSI they are setting it hot to 45, not cold to 45. Totally different when and how you check the PSI.
I don't have an X but on all my current cars I tend to stay between door jamb and sidewall max. Which means I'm running higher than the average driver of whatever car I'm driving in. So if the service center set me at 45 and the sidewall max is 51 I'd stay in that range (when measured at the coldest time of the day, with tires not driven on recently). If you check them and they were 45 hot, but cool down to 42 in the middle of the night then they really did set them to 42. In that case I'd use the cold number to start my comparison.
As to the question of what Higher cold PSI gives you:
* better resistance to heat changing PSI
* more range (longer coast, more regen, less power to maintain speed)
* increased resistance to hydroplaning (to a point, then when severely overinflated braking gets worse than recommended PSI)
* improved handling in some conditions (more precise steering and better cornering stability to a point, too high gets into over steer)
- increased risk of puncture by foreign objects (flat tire)
- increased risk of damage when hitting a pothole
- possibly harsher ride (air suspension will hide this negative)
= Will move wear towards the inside of the tire. Depending on the weight of the vehicle and the PSI used this could increase, decrease, or not affect tread wear life. If you are replacing tires because of how Tesla aligns the vehicle causing excess wear on the tire edge, a higher PSI might extend the life of the tires.
The range difference is more noticeable at low speeds, at high speeds aero effects dominate and will make the tire PSI less important to range.