ChuH

Just wondering what air pressure to you guys put in your 18" rims and tires? I have S03 245/40R18 (F) and 275/35R18 (R) tires? Can't get a straight answer from TireRack. They told me that with the situation with the Firestone and Ford issue they do not want to give any recommendation due to legal reason. The local tire dealers told me to put 4 psi lower than the maximum. That doesn't sound right to me. Lexus recommends 33psi on 235/45R17 (I think it is too low for 18"). Maximum PSI for S03 is 56 therefore 4 psi lower than max would put it at 52 psi (Too high hence harsh ride).

Majority of my driving within city limit (35 to 45 mph). Once in a while I drive in long stretch road at higher speed.

Would appreciate some inputs.

Chu....

GS4Will

C,

for 18s, i would do 30-32 psi. the reason being that w18s, you have smaller sidewalls; and the 33psi is for the 16/17' stock. higher psi would make the car feel like goodyear ballon floating on air.

will

ChuH

When I first got the new rims and tires I ran it at 33 psi and I get a hollow cupping sound (difficult to describe) from the front tires. When I increase the cold air pressure to 36 psi that particular sound disappeared. With current 36psi the steering feel got a bit lighter and ride a bit firmer but still comfortable. I would expect putting more air pressure would cause a bouncy ride and less tire contact patch and not what you had suggested as "...feel like goodyear ballon floating on air".

Also running too low of air pressure would increase the chance of damaging my 18" rims.

I was going to check with local Lexus dealer to see what the recommended air pressure for the SC430 is. As I recall the non-runflat tire are 245/40R18 all around and the SC430 is a bit heavier but still base on the GS platform.

Chu...

GS4Will

C,

you described better than i did-more bouncy ride due to less surface contact, like floating on air.

Mean Gene

Chu - I keep my 18" Nittos at 42 psi which is 2 psi from their max inflation pressure. 44 psi was too rough for the wife anyway & 42 seems to yield a nice even treadwear pattern, at least thru the 15k miles on the tires so far.

mkilty

It all depends on how you drive you Lexus. I drive my hard in the corners etc... so with my SO-2's I need to run them at 38psi cold. As they get warm the pressure is near 42psi where I find them much better for handling then if they were 36psi or less.

But that is for my style of driving...

ChuH

I think the ideal air pressure will be 36 to 38 psi. I will leave it at 36 psi for a week and may increase it to 38 psi later. Road here are not smooth and don't want bounce ride either with higher air pressure. I guess I need to do some more trial and error.

Weather here has been terrible for the past 2 weeks. Rain...Rain...go away!!! Need some sun shine in this tropical island!!!

Thanks all!!!

Chu....

bitkahuna

iTrader: (20)

While your thoughts may be logical, I think they're wrong. A bicycle tire is often inflated to 60psi and that's one tiny sidewall!

Many high performance tires are inflated high (35+).

Car manufacturers often recommend low pressures to give customers a comfortable ride. In the case of Ford with the Explorer, that may well have killed people. Tires running on too low a pressure get HOT.

gs4power

Will is right, for shorter sidewalls it's advisable to run lower psi's. (a little bit)

Bycicle tires are a different story, they have a very small volume and the sidewalls aren't nearly as stiff. To mantain the load capacity of the tire a certain amount of air is required, to accomodate the air in such a small volume you need high pressures.

tinygs

So at 30-34 on an 18", am I too low for optimum handling and tread wear????.....Ive never been really clear on this. I take from the first part of this thread that optimal would be about 38? Just want to hear an amen before I go over inflate my tires...Please reply, Tiny.