Not for nothing Lex, but a higher altitude would mean the ambient air pressure surrounding you would be less, and the hotter climate would mean the tires would be running hot. Logically this would dictate that 30psi or less would yield better ride comfort.

Just a thought....

 

Harrier,

I run my tires between 30 and 32 psi. They seem to ride pretty well with those pressures. Like everyone has said previously, Lexus suggests 30 psi on the tires. It's all a matter of personal preference too...if ya like your ride firm...pump 'em up a few psi...if it's too firm...just release some pressure to your liking.

Don't forget to check the psi in yer spare tire also! Good luck!

 

So, has anyone noticed an improvement in handling by increasing the air pressure? My wife and I are looking at the RX and MDX and noticed that the MDX has a firmer (sportier) ride. Lane changes seem crisper for instance. I was hoping that higher pressures could help sway our decision process towards the RX.

I would also suspect higher pressures may improve gas mileage as well. I run 35-36 psi in my IS and it seems to help.

 

Ok... looks like it's time for Tire Pressure 101 again...

Everything about tire pressure is a tradeoff. The theoretical correct pressure is the one which balances these tradeoffs and has the least negative side-effects when variations are made from the chosen pressure. This is what the vehicle designers shoot for.

The things that are directly affected by tire pressure:
Handling response
Traction/grip
Fuel efficiency
Ride comfort
Tread life

Many of the above characterisitics are inverse to each other when it comes to tire pressure, meaning that if you change pressure to improve one, the other will suffer. That's why the the manufacturer recommended PSI on your door panel is a good starting point. The markings on your actual tire ARE MEANINGLESS... those are only maxium numbers and should never be approached.

Let's look at what happens when one under or over inflates...

Under-inflate:
+ Ride comfort -- The tire side-wall becomes more "compliant", meaning that it is able to flex more because of less pressure in the tire. This will give a more forgiving ride in terms of bumps in the road, ie, ride comfort is increased.
+ Traction/grip -- because the tire is under inflated, more of the tread is allowed to contact the road, thus increasing grip.
- Handling response -- because the sidewalls are more compliant, response time is decreased. Also, the more springyness of the tire makes for unpredictable handling, think Ford Exploder for example.
- Fuel efficiency -- goes down because more tread is contacting the pavement, increasing the coefficient of friction between the tire and the road.
- Tread life -- decreases because the tires were designed to run at a given pressure and maintain a given "contact patch profile" with the pavement.

Over-inflate:
- Ride comfort -- The tire side-wall becomes stiffer, meaning that it is unable to flex as much because of increased pressure in the tire. You will feel more bumps in the road.
- Traction/grip -- because the tire is over inflated, less of the tread is allowed to contact the road, thus lowering grip.
+ Handling response -- because the sidewalls are stiffer, response time is increased. The stiffer tire makes for more predictable handling.
+ Fuel efficiency -- goes up because less tread is contacting the pavement, lessening the coefficient of friction between the tire and the road.
-/+ Tread life -- this is hit or miss, because again the tire was designed to have a certain amount of tread contact the pavement for maxium life. Too much pressure and only the center of the tread will wear, which will be uneven for the overall tire. But overall, over inflate is better than under inflate for tread life.

Hopefully everyone can see that there is no PERFECT setting... only an optimal one that takes all those factors above into account and errs on the side of PASSENGER SAFETY. And that is the one that the vehicle manufacturer chooses (disregard Ford).

Hope this helps,
TC

 

Marke 1: I keep my RX Integrities around 38 psi and the ride is fine on an '03! Handles nice, crisper. Try it.

Need to go to 28 psi or so in the winter if snow is present for traction, and less in sand on the beach - haven't been there yet though with 2WD!

 

I run 38 front and rear.

 

I wish it were more true about underinflating at these high altitudes, but unfortunately that is not the case. One reason is that gas runs over $2.00 a gallon for premium here. I tried it at 30 several times switching back and forth and it never felt right (often dangerous in some cases on turns). Half the time it gets very cold throughout the year. I wake up in July and it is 44 F when I leave for the office.