That 40 psi is more like a shipping air pressure.
A couple brand new vehicles we bought over the years were delivered with 40-45 psi while the mnfr recommended psi was 32.
One dealer cracked me up, giving me their signed pre-delivery check-off list all checked off, but they sure missed checking the tire psi.

 

Yup they pump em up because they lash/ chain them down when shipping and don't want flat spot tires. I've been to a few driver's schools many years ago that had me use my street car and they asked us to put pressure up to 40-45 so that we wouldn't have so much 'roll over' on the sidewalls going around turns. Plus your feedback through the steering wheel is amped up. You feel all the road imperfections and wheel slippage.

 

How fortunate that those two service departments had proprietary tire pressure "charts" that overrode the manufacturers specs

 

WTH does Lexus/Toyota engineers know? Everyone is their own rocket (tire) scientist. This debate about PSI can go forever and no matter what anyone says - everyone will be wrong. Why even bother reading owner’s manual? Just do whatever you want. No need to ask for satisfactory confirmation.

 

I haven't seen the Lexus chart, but did see the Audi chart. Audi said the spec for tire pressure was when it was under full load. They set the tire pressure to the "comfort" setting to improve the ride when the car was not under full load. I always wondered if this was an acknowledgement that the spec was to maximize mpg, not safety or comfort. Either way, it was an actual Audi decision, not the dealership.

This is from the 2017 Audi A6 manual. I don't have the car anymore, but I believe the Maximum load settings matched the door sticker. The Normal load settings were the comfort settings.

 

My new 2025 NX350h is recommended at 33psi in the manual but they came at 37/38 from the dealer. Guess I should let a little out. No real surprise, my last Mercedes always came back from service 4-5 PSI above recommended.

 

Look at your driver's door sticker showing tire size and recommended pressure. Look at your tire pressure readout from the TPMS on centre stack once in a while. Buy a pressure gauge and air pump. Adjust accordingly.

Here endith the lesson!

 

Always follow the door jamb label for proper tire inflation. The 18" and 20" all call for 33psi "cold" The reason they typically come back from service with higher pressures is that the technicians use a temperature chart that basically equates to 1 psi for every 10 degrees F above "cold". But what is cold? I live in norther California and my typical winter low temp is around 35 to 40. So if I inflate to 33psi with the car sitting overnight, I should see 37 to 38psi with it 70-80 degrees outside. More pressure if I've been driving for a while and the tires get warmer. I've seen this on my GS, RX and NX. Hope this helps...

 

Yes I hear you. Cold is not a very good word to use. It's meant to be based on the average daytime temps for the area your car-tires are currently seeing. In some areas around the world daytime temps are much higher than overnight temps constantly. Arizona and New Mexico are prime examples. So right now in late May I'm experiencing overnight lows around 48 F daytime highs around 64 F. I don't drive typically overnight so I focus on daytime highs. With the car / tires 'cold' meaning I haven't driven anywhere in at least 1/2 hour AND you're tires are not in direct sunlight I would set at 33 psi for a couple of reasons, temps will be rising over next month or so and 33 is a good baseline, with temps a few degrees warmer soon, that 33 psi will be 34 or 35 cold during daytime, still not bad a pressure. Driving will result in 37 psi when tire hot, also ok. When my cold tire temps (guessing when air temps are 75-80 F) are showing around 35-37 I'll adjust again down to 33 psi when tires are cold. It's a game of cat and mouse in an area that sees all 4 seasons like where I am.

If you're seeing cold tire temps with 36 or 37 psi and don't adjust you're not going to get a 'perfect' ride, it'll be a little harsh, but will improve steering response as sidewall is a little stiffer and if left for 1,000's of miles you'll wear out your centre treads faster than treads at the edges too. In my climate you can typically set to 33 cold at every trip to get your oil changed which is usually 3-4 times a year and be done with it, no major drama, just take a boo at your tpms readings every once in a while to make sure everything is kosher.