rivera156

Well, I have been back and forth for 2 years debating what psi I should have on my 18" 's. Tell me what size and psi on your tires and why? (dealer/tire retailer recommended, etc.) I currently have 225/40/18 on Pirelli P7000. Feedback is appreciated.

sung35

I set it at 35 psi. Lexus recommend 30 psi front and 32 psi rear. Since 18" tires has less wall and probably less room for air, and my tire max load is 51 psi (Bridgestone S-03 Pole Position), I guess having a little more pressure in the tire would be appropriate. Higher than 35 would be too stiff and probably results in road noise. Lower than recommendation increases traction (not at below 28 psi), but then the tire's life will be short (hence cost) and the tire has more chance of blow tire.

Just my .02 cents.

Hung

rivera156

Thanks. I hope to get more repsonses.

bitkahuna

iTrader: (20)

I don't think dealers have a clue what to pressure to use on aftermarket rims. I even kept the factory 17's at 35. I think most manufacturers recommend low pressures to offer a more comfortable ride.

I keep my 19's around 37 and I'm probably going to try 40 for a while.

PHML

iTrader: (33)

I have 19s. My psi is 46 all around to prevent damage to the wheel due to short sidewall. Max psi on those tires are 51.

D2-AUTOSPORT

On my 17s, I'm running 36psi all around

On my 20s I run 38psi in the front and 36-38psi in the rear

On my 16s, I hated them so much i never checked during the 2weeks I had them on the car

rivera156

Thanks guys. I am now testing them at 33psi as recommended. to see if i get better milage

Gojirra99

On my SC430(18"), 35
On my G35 coupe(19"), 36

D-MAN63

I have mine at 40psi with 20" rims.

drnkcarlos

18's on SC - 34psi for the front(225/40-18 on 9J wheel) and 36psi for the rear(235/40-18 on 10J wheel)

elclassico

ive got the same tires and same size. i have them at 35 all the way around, and im getting road noise, im going to do 32 and see if it helps, didnt have road noise before , bu tas the tire is wearing im getting more road noise? so this means overinflated i assume? i will post result soon, tthanx!

SoCalSC4

Yes, there is less volume for air, but pressure is pressure.

I run mine at about 34 front and 32 rear for everyday use. I run the front a bit higher because of the negative camber (with the car being so low), and the slight forward weight bias of the GS. I might actually increase this to about 36 psi on my next set of tires (unless I get the camber issue handled). With the wide 285 tires on the rear, I find that more pressure just wears out the center of the tire more quickly....

On long trips with a good deal of load in the car, it is a goos idea to actually run a bit more pressure- the tire manufacturers like this because it basically lets the tire perform closer to it's true load rating. A long haul with lots of weight in the car invariably generates more heat n the tires- running higher pressures will help to combat this.

I think running more than 40 psi on these cars does nothing but destroy the ride quality. I haven't heard anything from any of the tire guys I know that says running higher air pressure will minimize the chances of rim damage. Obviously, running too little pressure will expose the tire to more potential for damage, but this would mean in the low 20 psi (or lower) range.

A sharp impact with an overinflated tire will actually put much of the force of the impact into the sidewall, sometimes creating a sidewall blister. One way or another, given a large enough impact, you will either damage a rim or a tire- the difference is the rim is designed to bend, and not lose air pressure. A tire could "blow out" (this is fairly uncommon now) causing a sudden loss of air pressure and a car control nightmare. Remember the Firestone debacle? Tall SUVs like to get upside-down if you lose a tire...

445187

I don't understandwhy everyone has MORE pressure in the rear

There is more weight in the front, the front is responsible for the majority of turning, the rear (being lighter) seems like it would have more chance of losing traction under hard accelleration or turning because of being stiffer (more air pressure)...

Cold some engineer please explain?
Jeff

htc

I have 18X8.5 with 245/40/18. I think 36PSI cold is a perfect setting.

lexforlife

iTrader: (7)

as per expert advice from my good friend indio

i now as of the last few months run 40lbs in front with about 36 in rear.. i have found that because of the neg camber with have to deal with , the lower pressure amplifies the wear on the inner edges wearing the out unevenly and producing increased amounts of shimmy esp during warm up. i have found since mainting exactly 40psi i have virtually no shimmy or vibration during warmup even after 1day or 2 of not driving (flatspotting) . every week i check my pressure and fill before driving (helps having a big air compressor in your home garage).

i use less air in the rear for 2 reasons , 1 is that the rear pressure helps to aid in ride comfort whereas the front determines how well the car handles and responds and 2 because having excessive air in such a wide tire promotes more wear in the middle but i have also dicovered that for us guys running 19in stagg setup that using the 275 also aids in the fast wear of the rears as opposed to the fronts because the rears are spinning faster then the fronts for the od is smaller .. since going to 285/30 in the rear od is now matched and after 3 months of hard use there is no uneven wear on either front or rear...the 40 lb front psi has prevented any tire wear from inside and the ride also got more comfotable vs running 34-35 go fig