sleepybobcat

What tire pressure do you use on your RX300?
I've followed the door sticker which said 30psi...
However, that makes the tires look a little flat.

Any recommendation apppreciated....

Bob

Silversport01

I was wondering the same thing.

LexRX

I've wondered the same about tire pressure. I used to inflate to the specks on the tire itself then came to realize I was supposed to go by the vechile manufacturer specs. I also feel that 30psi is way too low. I like to do at least 35 - especially on one with a max psi at 44. Once I inflated it up to at least 40-42psi and drove two hours at 75mph and the heat didn't make it go above the max of 44 (it was actually at 43 psi when i measured it at a rest stop).

So, I really don't know, but won't go as low as 30. I run at least 35, usually higher and it has worked fine for me so far.

Francis

I have 34 in front and 32 in rear. And I feel fine with this setting.

Francis 99' RX

RealMarty

Guys, I'm going to apologize up front if this is stuff you already know. I'm just trying to help here...Also, this turned out to be a long message so I'll give you the most important piece of information again up front -- radial tires look deceiving. Unless they are very under or over inflated it's extremely difficult to tell the amount of inflation by looking at them.

With radial tires, the fact that they look too low can be deceiving...especially if you look at them when they are cold or the front tire is turned to one side. At proper inflation they may well look underinflated. The tire pressure recommended by the manufacturer is a function of the tire size and the vehicle's weight. And they try to figure in the effects of temperatue due to long trips, etc.

If the manufacturer has done their job properly they have recommended the pressure that will put as much tire on the road (the contact patch) as possible at a variety of tire temperatures. Under ideal conditions the tire will have a flat spot on the road at all times that is even across the tire width and probably about 6" front to back (I'm estimating here).

Overinflating will push out the center of the tread and you will get uneven wear in the center of the tire. It will also cause the car to oversteer because the tire is harder and not able to absorb cornering forces. It will also make the car less stable in the rain because of the reduced tire contact patch on the road.

Conversely, underinflation will cause the center of the tire to "sag" and wear out the outside of the tires. It will also cause excessive heat and premature failure of the tire. It will also cause the car to understeer because the tire compresses and, to some extent, absorbs the attempt to change the vehicle's direction.

So, this all having been said, I'm not telling you that the only pressure to run is Lexus' suggestion of 30, but 40 lbs on a 44 max-rated tire is probably too high to get the handling and tire life you paid for. If you want a stiffer ride there's only so much you can do with tire pressure. Beyond that you need to start looking at springs, shocks, sways, etc.

My recommendation is to limit your pressure changes to no more than 5 lbs more than the 30 lb. recommendation and see how it feels. On my GS430 with stock size tires 235/45/17 I run the recommended 33 lbs. I've experimented with 35 and found it oversteered too much at highway speeds after the tire has had a chance to heat up so I went back to 33.

That's my rather long-winded .02. Hope it helps.

RX300TC

I can't believe how many times folks bring this subject up on other car sites... but Marty nailed it with the correct answers.

The bottom line is the manufacturer's specification for tire pressure is calculated to take a lot of parameters into account. You never, ever inflate to the max pressure that is indicated on the sidewall because that's exactly what it is: the maximum pressure!

Sure, you are free to put any pressure you want, but what you might not realize is that you are in fact sacrificing one aspect for another.

I leave mine at the door sticker pressure. If you want a "different" type of ride, then you need to start looking at shocks, springs, etc. Ford tried to give the Explorer a "cushier" ride by cheating on the tire pressure... and they ended up killing people.

mooretorque

Marty, you are, as always, correct in all aspects. I would add one detail: it all depends on the tire spec'd as OEM. Since the tire sidewall is an integral part of the suspension, tuning is usually done with one particular tire, and we all know which one that has been for the RX. Change the tire and you've changed everything, including optimum tire pressure.

DanMeyers1

I like a stiffer ride so I run Firestone LE3 at 37 PSI. I had LE2s and got 61,000 miles (they are rated at 60,000 miles) running them at 37 PSI from day one.

Jhixson

I run michelin at the Lexus recommended pressure of 30. I get really long tire life and even wear.