I played around with my new toy 2015 Q70L, its a lease car brand new from dealer.

when I search the tire pressure.
the car computer shown 46psi all around, all four ties.

didn't check the own manual, but as best i know, passenger cars should be around 33-35, isn't it?
but this is from dealer least than a week.. factory setting or just dealer don't care ?

should I lower it back to 35 psi ?

Definitely put it down to where it should be, which is 33 PSI. Sounds like some dealer noob might be inflating it to the max off the sidewall rather than the factory spec which should be on a sticker in your driver door jam.

#dealernoobfail

In our heavier cars, I would recommend a tire pressure a bit higher than the standard recommendation. Set it to 36 psi all round and then adjust up and down only by 1 psi (certainly no more than 2 psi) to compensate for wear. Use a tread depth gauge regularly and decide whether to go up or down.

This 36 psi is the pressure value that is used for tire load tests (the tire manufacturer does this) per the standards, and it will give you an optimal outcome.

Some important things to be aware of:

The tire pressure must be measured cold. Ideally inside a garage in the morning ... even letting the sun warm the tire can increase the pressure a bit, let alone driving a mile or two, which could increase the pressure by 1 to 3 psi depending on speed and distance. If tires are already warmed, then setting to 36 psi will make it too low overall.

Remember to measure every other week or so - pressures can change (usually drop due to normal leaks) by about 0.5 to 1 psi in that period - more often if the weather temperatures change a lot. If you set it to less than 36 psi normally, check more often!

Finally, the car TPMS is really just for making sure that the pressure is not way off. A good gauge is an essential tool. Personally, I use an Accupressure Racing Gauge (available at Amazon) with 0.1 psi resolution. It's accuracy is +/- 0.5 psi, but the relative 0.1 resolution allow me to set everything to within the same 0.1 to 0.2 psi difference on all four tires.

Yes, this is a bit overkill, but not a bad investment to extend the longevity as well as better load capacity safety.

If I buy a new model tire, I learn the correct value for it in time (by monitoring the tread depth) ... It is not surprising that I seem to get the most even wear around 35 psi, almost no matter what the brand or model! I set it to 36 psi whenever I measure, so that the normal 1 psi drop in the 2 to 3 weeks to the next check is not an issue.

Z

The cars come with higher than the recommended tire pressure because dealers do not want the tires to run low if sitting in the parking lot for too long. Also with higher pressure you are less likely to get flat spots which are common in cold climates.

There is no need to over inflate the tires because the tires and air pressure were already selected to suit the car weight. Over inflating will cause higher tire wear in the center of the tire. However, as cooler weather arrives I typically inflate by 1-2 psia to provide margin when temperatures drop and tire pressure decreases.

Keep an eye on the wear pattern of the tire (using a depth gauge) to give you a better indication for the correct tire pressure.

PS since my car came with nitrogen filled tire I can go for many months without having to add nitrogen.

silberma wrote:Over inflating will cause higher tire wear in the center of the tire.

Agreed ... particularly if you are way over by more than a few psi when cold.

silberma wrote:Keep an eye on the wear pattern of the tire (using a depth gauge) to give you a better indication for the correct tire pressure.

The best approach ... yes.

Z

silberma wrote:PS since my car came with nitrogen filled tire I can go for many months without having to add nitrogen.

Ummm ... air is 79% nitrogen. So, adding a nitrogen fill does not necessarily extend the duration ... most likely, you have a good set of valves and no leaks if you can indeed go that long.

Plus, if you fill with nitrogen, since the tire does not start out empty, this doesn't mean you have pure 100% nitrogen in there. In general, as you noted, measuring pressure and topping off is best.

Z

They come inflated to roughly that PSI when delivered. Either the tech who PDI'd it left them there, or they were put there with the idea that it was going to be sitting on the lot for a while. I always put them at 35psi.

...or you had my wife inflate it for you....The other the computer showed it low (below 26 psi) on her quest van so she called me all panicked asking what to do. I told her to find an air station and fill it up. Well she did, all the way to 50 PSI max rating on the tire

Mjkkb2 wrote:...or you had my wife inflate it for you....The other the computer showed it low (below 26 psi) on her quest van so she called me all panicked asking what to do. I told her to find an air station and fill it up. Well she did, all the way to 50 PSI max rating on the tire

I've worked on cars that had over 110psi in them.

WTF? How did the tire not explode? lol.

IlyaKol wrote:WTF? How did the tire not explode? lol.

You'd be surprised some of the stuff you see when you work on cars every day, lol.