Hi, I just bought a new set of 4 tires recently for my grand prix and I noticed that the gas milage dropped a great deal, I am thinking because I am still running the discount tire pressure in them. But what I was really asking was how much can I inflate these without inflicting damage or wearing too early. These have a recommended max psi of 35 where my other set had a max of 42. I am currently running around 32 when cold. Could this account for a 3-4 mpg drop? Or is there something else I should be worrying about? And yes, if it matters, it is an automatic transmission.
Going GTO once I finally get a job. Stayin pontiac all the way.
Newer tires (thicker tread) have higher rolling resistance. Lower inflation pressure would also increase rolling resistance. You can safely inflate to the max pressure listed on the tire and the tire will wear fine.
The handling of your vehicle might be different at higher pressures so it might be wise to do a careful "test" drive at the higher pressure to see how you car handles.
A 3-4 mpg drop is pretty significant (about 15%). But if there aren't any other variables except the tires and lower pressure, then they are likely the culprit.
My 1997 Grand Am with 205/55-16 tires was absolutely perfect at 44psi. Handling, wear, and pothole-resistance were all heavily improved. That was the car where I first learned about increasing tire pressure and I didn't even care about fuel economy.
I'm surprised you managed to find tires in a modern size with a rated maximum of 35. I thought the 35 max was only used on old-school sizes like the 205/75-15 on my 1980 Buick. I run 38 in those tires, and eventually I may push the limits more.
I'd inflate the tires to their maximum cold pressure (cold pressure means haven't been driven on in 12 hours), drive around for 3K miles, drive cautiously and if the car drives fine and if the wear looks good, stick with it. I've found inflating to their maximum pressure allowed my tires to wear more evenly. Now that I've read what the holy cow has said, I have seen some newer tires say 35 but in that case I usually go to 40 psi. When I say maximum, I usually mean 44 or 51.. but I have occasionally seen 35 psi as the "max" pressure.
There can be a HUGE difference in RR between tires - up to 60%. I would think that cheap tires would be using old - and High RR - technology. That is on top of the difference between worn and new and the inflation pressure difference.