Tire pressure experimentation
Car tested: 2022 Model Y Long Range - 7 Seater. ContiPro RX 255/45R19 on 19x9.5 Gemini, all stock. This starts due to my curiosity on why german manufacturers in my experience always provide 'normal load' and 'full load' tire pressure. For example, GLE 450 in my case recommends 31 psi all around for 'normal load' (up to 4 person) and 38/44 front/rear for full load (another person + baggage). I suspect that 42 psi recommended by Tesla is rated for worst case 'full load', which in my case is 5712 lbs GVWR. What if under normal load (which 4500 lbs + 200 lbs driver weight in my case) is just at 4700 lbs, a full 1000 lbs less than 'full load'. So I'm trying to test in 42, 38, 34, and what I run with finally (36 psi). So I begin testing 'unscientifically' the comfort and driving dynamics. I wish I can run longer test to test out wear, but here goes my takeaways on different PSI. NOTE: This test is mostly just me driving alone. Your experience might and WILL differ if you carry passenger or heavier cargo. 42 psi: Ride is surprisingly decent and not as bad as forums communicate. It's tight and controlled over rough road and high speed with a slight 'skittish' feel, but you feel every single bumps. Steering is very light and easy if that's what you like, and highway curves felt 'nervous' to me at 70 - 80 mph. Car felt slightly jittery and produced unpleasant noise over slightly rough roads or worse. Very quiet on new road though. After 100 miles drive at mostly 70-80mph, and it went up to 44 psi at end of drive. I would reduce pressure a bit if it was my WRX back then since 2 psi jump towards end of long drive is usually sign of 'overinflation'. 38 psi: Ride is much better, felt as tight and controlled as 42 psi, but with a lot less bumps transmitted to the cabin. Somehow the distracting and unpleasant noise from 42 psi are all gone. Curves on 70 - 80 mph highways are more confident and inspiring rather than nervous on the 42 psi. Although comfort is a huge improvement from 42 psi, this would still be on the rough side for me (reminds me of my college days WRX). After 100 miles drive at mostly 70-80mph, tire pressure went to 42 psi (could be slightly less, but tpms only displayed whole number). So I felt good about this inflation. 34 psi: First of all, I'm surprised that TPMS are not triggered at this point. I was expecting ride to be comfortable, but this turned out wobbly and floaty. The bumps are well absorbed, but car felt slightly bouncy for a split second after each bump (and Philly roads are quite bumpy in general). This was unpleasant and felt wrong. Highway stability at 70 - 80 mph straights felt surprisingly good, but curves definitely rolled car into sidewall a bit and it didn't feel nice. Over 100 miles drive at mostly 70 - 80 mph, it went from 34 psi to 38 psi, so I don't think there are any heat issue (otherwise it would've went higher to 40 psi +). I wouldn't recommend 34 psi on long highway rides though, curves are not confident inspiring. 36 psi: This is the final favorite pressure. Tire absorbs minor bumps very well, and larger bumps are damped really nicely. No wobble like 34 psi, yet it absorbs the bump equally well IMO. Highway stability is amazing, and surprisingly curves at high speed felt very confident and 'grippy'. Over 100 miles drive at mostly 70 - 80 mph like above, it ends at 40 psi warm (again this is TPMS rounding to nearest whole number). This becomes my favorite instantly, especially since TPMS is not triggered. TLDR; if you are familiar and understand the risk (and return) of tire dynamics, feel free to experiment. It's amazing how much vehicle dynamic changes with different tire pressure.