Warning! Tire Pressure May Be Too Low!

[RX400h]

I checked the pressure on my Michelins (I just got my 2007 RX400h last weekend with 18" alloys). They are set to 32 psi from the dealer.

I've had my RX 400h for just over a week. I checked the cold tire pressure. 37psi from the dealer.

I intend to maintain them at 37-38 psi. Its a fair balance between comfort and milage economy, keeping in mind that ride comfort is subjective.

Dealer is Metro Lexus, Brookpark, Ohio.

Keep in mind that dealerships often forget to lower the pressure that is set at the factory. Apparently, keeping the pressure near 40 psi prevents flat spots from occuring when the vehicle is shipped from Japan. The dealerships are supposed to reduce the pressure to that which is recommended by Lexus.

If I were you, I'd keep an eye on the tires' center tread wear at that high a pressure. I estimate that 32-34 is ideal for the Goodyears, based upon the wear pattern I have been seeing when the pressure is 30 psi.

Dave

[markatty]

I have 28,000 miles on my Michelins and am starting to see some additional wear on the outside of the tires. I've raised my inflation from 30 to 34 psi, but didn't want to go to max psi as per below.

I bought an RX-7 back in the 80's and my dealer signed me up for performance driving school. (If you ever get a chance to do this go. It's the most fun you can have in 30 second intervals.) At the school the instructors would rub a large grease pencil on the edge of the tires and you would drive around a circle faster and faster until you lost traction.

On the RX-7 you could hear under-inflated tires as they would squeal at lower speeds. Really underinflated tires (like street pressures) would also chatter and the car would "hop" sideways. If the tires were properly inflated about a 1/4" of the grease pencil would rub-offed the sidewall. Underinflated tires would rub it all off and over inflated tires wouldn't rub any off. The idea was to keep as much tread on the road as possible during hard corning. We started with 45 psi and did multiple runs in both directions. Interestingly, each tire took a different psi and varied as much as 3 psi.

Here's a description of the process from the web.

Now if l drove on dry race tracks every day that would be the end of the story, but rain, snow and comfort make it a different story. High pressure tires do give a rougher ride, but they are also less effective on soft surfaces like snow and sand. Over sand we go down to 4 - 6 psi in our Jeep to get a fatter footprint. I also let some air out when I know I'm going to be on snow most of the time and not be at highway speeds. At highway speeds underinflation can be deadly, since it allows sidewall flexing and at highway speeds the heat build-up can do in a tire surprisingly fast.

The problem with lower winter pressures is that much of the driving is on wet pavements and slush. Here you need higher inflation pressure to press the tire down through the water to prevent hydroplaning.

As to tire inflation saving gas Edmunds didn't see a significant effect , but then they didn't see a significant effect with A/C and that does make a difference on the RX-400.

Bottomline 34 psi has been working for me, since I don't like to constantly adjust the tires except for extreme conditions.