I got my Goodyears installed on Saturday, and finally got around to checking the tire pressure tonight. 47 PSI! No wonder they rode so rough. I lowered them to 40 PSI, but that still seems high. What's the best PSI to run on the street for this size tire?

 

Depends on the tire. I have that size on my fronts but the tire says to put 51 PSI. These are the highest load rated for their type, bf goodrich whatchamacallits, the ones with the cool tread design. (brain not functioning this early) Others with lowwer load ratings probably require lower pressure.

Anyway, check out the side wall it should say what PSI to run.

 

No, this just gives the MAX psi that the tire can handle, and is independent of the car manufacturer's recommended psi.

 

I asked the same thing awhile back, and am told that the recommended psi for GT500's (which use that sized tire in fronts) is 35 psi.

Here's a link to the thread:

http://forums.bradbarnett.net/showth...ecommended+psi

 

I am currently running 29 psi in my 255/45/18 BFG KDW's. I'm running lowering springs with the stock struts and shocks. I run a little less pressure to soften the ride.

I started at 32 psi, the recommended stock tire size pressure and went down from there. I was as low as 26.5, but I figured that was too low for safety's sake (> 15% below rec psi) and the difference between that and 29 (10% below rec. psi) is only a little rougher and I can live with it.

 

you were joking.... right???

Rule of thumb= 32-35psi

A little more up front when running the 1/4 and maybe a little less out back.
The contact patch on a radial doesn't increase much when you air down your tires.

 

Not joking, tire reccomends 51 psi, thats what I run. Rears 285/40 r-18 has the same 51 PSI on the side wall, thats what I run.

 

Nynvolt, you're not hurting anything except your rear end by running that kind of pressure. But as was noted, that is the maximum pressure that tire is designed to run at maximum load. Basically, it's giving you the limits of the tire, not the recommended pressure. You'll get a better ride AND better handling if you'll let some air out.

Your tires need to have some compliance as they go over bumps, both to help soak up the bump, and to keep the full tire contact patch planted on teh pavement. At maximum PSI, the tire is too full and therefore to hard to have compliance, and what ends up happening is that the tire bounces over the bump instead of soaking it up.

 

This is how I would do it. If I'd just bought expensive new non oem spec tires I'd buy a cheap tire tread depth gauge. Fill to the psi listed on the cars sticker, with tires cold, then measure the tread depth in the center and outside treads every couple hundred miles or so. If the center tread's wearing down faster than the outside, I'd reduce the pressure a couple of pounds. I'd add air if the outside treads are wearing faster than the center. Eventually I'd find the correct pressure when all treads wear evenly.
Filling tires with maximun psi listed on tires, with no load in the car, should cause quick wear on the center treads.

 

No offense intended but at 51 psi, your car would ride like a skateboard to me!

Another indicator is the treadwear. If the center of the tire has less tread depth the outer tread, then you're running too much air. If the outer tread has less depth than the center then you're running too little psi. This assumes you don't have issues with excessive camber or toe...

This is from a nitrogen site (don't buy the hype) but the principles are still basic:

http://www.nitrogentiremachine.com/p..._inflation.htm

 

NO!!!!!! NEVER run the max pressure on the tire. It's the max pressure the tire can handle when seating the bead. If you run with that pressure you're risking a blowout once the tires get up to temperature and the pressure increases. Run your tires REGARDLESS OF SIZE at the pressures listed on the sticker in the door jamb. Running crazy high pressures will adversely affect tire wear, handling, braking and as stated will risk a blow out. This isn't a personal attack, but I can't believe how many folks don't know this.

 

No offense, but I don't think that this comment is fully true either:

I believe that you should NOT run your tires at the pressures listed on the sticker REGARDLESS OF SIZE; why???: increasing wheel diameter (ie- going to 20" rims) causes a change in sidewall width, which will result in a needed change in tire pressure. That's why some cars post different psi recommendations depending on whether you get the optional wheels (ie- 17" instead of 18" on mustangs).

Now, with that said, I still agree that you shouldn't run it at max psi, as it will cause premature tire wear and a harsh ride.

 

That's true, but it's defnitely a safer bet than running the sidewall pressure. You should also run a higher than listed pressure for sustained high speeds, but I'm just trying to get folks to use a good baseline.

 

I will admit, I may be ignorant about this pressure deal, I have always kept my vehicle tires at the side wall PSI, including motorcycles I have owned. I have always assumed that was the correct pressure to run, never been told diffrent. Will call discount tires who I bought the tires and road hazard protection from to confirm. When they installed the tires they filled them to 51 PSI.

Also, I would have to think the tire pressure reccomendation on the door panel sticker would only apply to OEM tires, side wall hight, and tire type would change the correct pressure needed.

 

Keep in mind that with TPSMs on the newer cars, the tires have to be inflated to a higher than normal pressure to "set" the sensors. On my Charger, I had to inflate the tires to 45 PSI, drive the car for 10 miles to "set" the sensors, then readjust the tire pressure. I'm sure that's why the tire shop had my Mustang tires inflated so high. They just didn't tell me to readjust them after driving a short distance, and I didn't think about it 'til 2 days later.

 

Well learn something new every day, tire shop told me to run around 35 PSI but said to check inside the door pannel to be sure. Been driving for 20 years and never knew, thanks for the correction. Guess I'm lucky to never have had a problem.