I'm rolling on 18 x 8 wheels, the tyres are Maxxis 235/40ZR18 95W. I wanted know what ideal PSI i should have?

I run 40psi with the same tyre but on a 9'' wide rim with no problems.

Thanks mate =] I've also been told that lower profile tires require more air than factory tires to carry the same load, apparently 40psi is around the minimum that should be run in tyres like this. Anybody have recommendations or comments relating to that?

Thanks mate =] I've also been told that lower profile tires require more air than factory tires to carry the same load, apparently 40psi is around the minimum that should be run in tyres like this. Anybody have recommendations or comments relating to that?

A load of rubbish. 40psi was uncomfortable in my magna. It is bone jarring in the renault. 37-38 psi was a better compromise

36 PSI when cold or 38 PSI when hot is plenty.

I run 38 - 42 PSI on my 18's,
42 psi for general around town stuff for better mileage, 38 for car cruises for better grip.
Higher pressures are more likely to attract punctures tho, so too high could be costly, avoid apexing corners and driving through Debris and driving along the gutter, (sneaking through gaps on the left etc....) stay on the road center.
Low pressures are more comfortable, but you'll increase fuel use, and often wear the outer edges of your tyre prematurely. Even lower will stress the side wall of your tyre (very bad).

By increasing the tyre pressure, you lower the contact area on the road, good in the dry, but high pressures are dangerous in the wet.

This test was done on a regular tyre, so add a few psi to suit 18's, but you'll get the point....

Saw the Mythbusters Tyre pressure test.....
Search it.....

Results are in.
35 psi (control)
tyres at 10psi = 3.7% increase in consumption
tyres at 30psi = 1.2% increase in consumption
tyres at 40psi = 6.2% decrease in consumption
tyres at 60psi = 7.6% decrease in consumption.

However, they they did remark at 40 psi you are more likely to get a puncture. Which argues the point over a 40 psi tyre pressure.
I just avoid gutters and driving for the Apex Cornering.....

Stick to the 40 PSI and stay on the well worn parts of the road, to avoid punctures.

They also left this out of their test, a cold tyre @ 38 PSI will be 40 psi at working temps. So 40 psi is actually 42 when they warm up.

.

Ok brilliant thanks guys. From what i've heard so far, i'll probably run them at about 38-40psi. cheers for the replies =]

My stock rims were around 32psi when I bought my car.
They felt like poo so I upped it to 36psi the second day of ownership. After a week I tried 40psi and hallelujah. I was happy.
I've got 18s now and just run them at 40psi. It's not too rough (stock Sports suspension) - just as comfortable as the 16s - and turn in is beautiful and grip in general is good.

From what I've felt in a Magna, I would recommend nothing under 36psi.