Just this past Saturday I finally got a pair of Goodyear Eagle F1 GS-D3s in 245/40/18 installed, and now I'm just wondering what a good PSI to use would be for them? They started out at 34.5 when I picked up the car but I felt it was a little too bouncy and squirmy, so I dropped it to 33. Now it's a little firmer and flatter through corners but still gets squirmy at times, even when taking very mild straightline curves at speeds over 60.

The squirminess is probably in part because the tires are new, but I'm just wondering what PSI I could use to completely eliminate such squirminess, since I would usually get this same squirminess in the OEM Dunlops if they were overinflated by even 1 PSI. Going from 32 to 31 made a huge difference in how the RX-8 felt during cornering with the OEM Dunlops. The RX-8 seems extremely sensitive in that regard in that one 1 PSI made such a huge feelable difference. Should I try dropping below 33? Given the huge cost of these tires I definitely don't want to drop the PSI too low if it means giving up tire life. But neither should tires of this level still be slipping when just simply going through a slight curve on a relatively straightline street.

 

If you can feel a "huge" difference with a 1psi change in a street tire on the street, then I'm not sure why you're asking for help.

 

I do not know how experienced you are at driving like crazy .. (I dont have any track driving experience) but I doubt tread squirm will be affected much by inflation pressure. Think it depends on the tread design and primarily the tread depth.

So for example snow tires that have softer rubber compounds and deeper treads will tend to squirm (by that I mean the car feels like its a bit wobbly .. the effect is felt when you do a very fast lane change or something - that is what I describe as tire squirm). On the other hand if you have racing slicks there should be 0 squirm.

Some of the squirm can be countered by raising the inflation pressure (not decreasing it I believe) but then the tread squirm just seems to appear at a higher speed. Raising the inflation pressure should reduce the tire contact patch and provide less squirm and less grip for acceleration. Lowering the inflation pressure should increase contact patch giving you more squirm and more acceleration at the cost of blowing your tire due to heat.

Finally there might also be an effect from your wider tires (if you have the 245mm width mounted on 225mm oem rims). I dont know what that effect is.

Lastly, tires have this release compound attached to the rubber which helps the rubber break away from the mold, which can cause slightly different handling. This should burn off after 200 miles or so.

Bodi

 

I keep my Pzero Neros that size at 33.

 

i dont know the recomended PSI for that tire but lowering the PSI from suggested will only hurt handling performance.

 

I run my Falken 451's at 32 psi. Never had any problems.

 

i run at 51 PSI .. muwahahah!!

but im running 245/35

 

Different tires like different inflations. The size of the tire is somewhat irrelevant. (Somewhat... a bigger tire can run a little lower inflation as it has more material to distribute heat.)

I good rule of thumb is start with manufacturer recommended pressures and go from there.

Doing that, I found my BFGoodrich KDM2s like about 36 lbs.
Meanwhile, my Pilot Sport Cups like 28lbs. Which, is actually Michelin's cold-inflation recommendation for those tires.

 

I would do that if I could find the Goodyear's recommendation for the F1 GS-D3s. Can't seem to find the recommended PSI on their site though. Don't suppose anybody else knows it or could find it?

 

Actually, I found out about Michelin's recommended inflation pressures on The Tire Rack.

If you can't find that, start with Mazda's recommended inflations.

 

Look at the label on the door pillar. Tire inflation is determined by load. More air is required to support more weight and maitain the intended contact patch. Since tires do differ in construction, you'll need to adjust, but cold inflation should always start at the rating listed for the car, not the tire. For auto-cross, where you're driving very hard for a very short period, you want to up the cold inflation to compensate for the tires not heating up and expanding. Harder tires for track or winding mountain road drives would have similar considerations, but be careful. Go for a drive to heat up your tires, pull over, and use chalk to mark the shoulders. Make sure you get the entire outside tread block, both the driving surface and the shoulder. Then go drive hard some more. Pull over, and see where the chalk is worn off. You trying to get it right at the corner of the tread block, where the driving surface meets the shoulder. If there's still chalk toward the outside edge of the driving surface, you're over inflated, if it's rubbed off on the shoulder, you're under inflated. Obviously this only works in dry whether, so those of us in the Great Pacific Northwest haven't had an opportunity in nearly 3 months, and may not for another month or two. The pressures provided by the tire manufacturers are minimum and/or maximum safe pressures for the tire (usually maximum). They have no way of knowing how heavy your car is, so the car maker provides a starting point on the door pillar.