looknow12

I tried lowering my tire pressure today to get the best ride. My tires are 18" run flats so I figured I could push them down low. I was shooting for 28psi but over shot to 25. The indicator on the instrument panel lit up and the Information Display read Low Tires. It would be nice to give you the reading. Anyway, I continued to raise them 1psi at a time. Finally I skipped from 30 to 32 and the light and message went away.

So the point I'm making is either 31 or 32psi is the lowest pressure you can set before getting the warning messages.

spwolf

interesting info... and what was the reccomended psi?

highmiles

My GS430 says 33 Front and 33 Rear with 18" Run Flats. Not much room for error if you get a warning below 30.

looknow12

Just for clarification the warning appeared at 30 and might also do so at 31.

Rockville

Because tire pressures are somewhat temperature related we will have less informed owners come in with their low pressure warning light on in their SC430's, GX470's( usually the Spare) and it will probably happen with the similar new GS system whenever there is a sudden drop in temperature. The fix is to add air and wait for the light to go out like looknow12 suggested. I think this is one of the reasons that the techs like to have a pressure cushion of 5 lbs. or so when they do the PDI so that this won't come back to them later. The recommended pressure of 33 lbs. is the same for the 17's and the 18's. There is a little clause about adding additional pressure for high speed running over 100 MPH. You can add up to 6 more lbs if you want. There is a pretty big difference in the ride quality with the additional pressure. The run flats have a very thick sidewall that can support the car's weight without any air at all. You will not feel a handling difference either since the tire's height does not change. Heat will build up so they are limited to 100 miles at highway speed without air. At lower city speeds you could probably go twice as far. When the SC430 was introduced they had a gathering out West at a track where you could drive the car pretty fast and they let the attendees take hot laps. After taking a lap one of the Lexus technical guys was asked about his impressions of the handling and drive feel. He thought that it was excellent. Then they imformed him that there wasn't any air in all four tires! That being said the conventional high speed radials have a more compliant ride and require the addition of a spare tire. The trade off is convenience vs. ride comfort.

looknow12

Not having a flat for the last 10 + years I guess I'd opt for ride comfort, but maybe my time is due.

I suspect over the last decade they have made much progress in tires and that flats have been reduced. I remember 20 years ago by brother had a Saab with Pirelli tires and he had 3 flats in the same year!

dseag2

Looknow, not sure if you saw my post on one of the other threads, but when I had my SC430 w/ 18" wheels and runflats I was told by Lexus service dept. that 36psi was optimum for ride comfort, even though the owner's manual indicated a lower psi. Many other owners were told that as well and found it improved the ride. I know higher psi is usually contrary to ride comfort, but it worked on the SC430 because of the combination of runflats/suspension. You may want to try higher psi and see if it works.

looknow12

Perhaps increasing the tire pressure puts more of the load on the wheel bottoms and less on the rigid sidewalls. I will definitely try it.

Thank you,