I just bought a set of Low rolling resistance Continental ContiProContact(Grand Touring All-Season) for one of my other cars.

They come side wall rated at 51 psi as do many modern higher performance tires.

I drove away from the tire shop and car just didn't seem to drive right. So I check my inflation and I have only 32 pounds. So I get on 5 different tire manufacturer sights and they all talk about inflating your tires as per manufacturer specs on the door jam.

Why can't they just come out and say that max pressure 51 psi tires need to be inflated to 45 psi or a max psi 44 tire runs best at 33 psi?

So I take the car back and tell them I want 45 psi and the manager tells me that you only put in what it has on the car type list which was 32 in my case. I said what if 51 or even 80 lbs tires did not exist when this car was made. So I think that it is stupid of you to assume that the book is always right.


Where can I find proof of how much air you need to run in a modern performance tire?

 

I don't think there is any proof for what PSI you need in your tires, I think it is going to end up going off a few different things, weight of the vehicle, suspension, and owners preference. I personally run between 32 and 34 in my vette and it runs great. On my wife's Miata 30 seems great while in my truck 36 seems to be the magic number. I personally think 45 would be a bit much and cause the middle of the tire to wear a bit quicker.

 

my new nitto 555's came mounted at 42 psi. I thought that was high. When I asked, they told me that's where they are supposed to be.

 

At Porsche we inflate for Max load 44lbs rear and 36lbs front for comfort 39 & 33 lbs

 

How could the manufacturer of a given tire come up with one fixed number that's correct for every one of the dozens or hundreds of car types that it will be installed on?

 

How about a range? I do know that my Vette tires are @45 and they end up with even ware across the face if I have the camber set right. My Cross over vehicle kind of wallowed down the road and around the turns with 32 psi and looked low. I will monitor my ware

 

Best way to find out your own psi= get a yellow or white piece of chalk.(the big piece kids use on streets/sidewalks) draw a thick straight line across the tire. Slowly drive forward and make one or two complete rolls. Look on driveway and tire for wear off/on. Increase or decrease psi till that tire has even wear of chalk line. Each vehicle is a little different with weight and Passengers. This is what I do with my Big jeep tires.

 

Exactly. The tire pressure on the car placard is for the tires it came with.

When they are changed to a different size, make, style, etc, and the application is correct, then you go with that tire's specification found on that tire.

 

Tire pressures as recommended on the door jamb spec plate can't account for every possible tire which an owner may eventually install on a given car, especially as technology progresses post-production. Thus, construction varying among tire lines, there is simply no one inflation pressure which when applied to any tire will yield an optimum contact patch on a given car.

Also, vehicle manufacturers have been know to recommend pressures on the low end of a tire's acceptable inflation window to improve ride comfort. Such was apparently the case for my DD (1996 Caddy STS) which came with 32 psi recommended. Even on the original tires, this proved significantly below that necessary to result in uniform tread wear. On those tires, it actually took ~40 front and ~36 rear to even out temps and wear. With the new assymetrics I recently installed, I'm now at ~44 front and ~40 rear, and thanks to the improvements in tires since my DD was built, it both rides and handles better than ever.

And, who can forget the Ford Explorer/Firestone inflation recommendation controversy? Yes, I prefer to set inflation pressures on pretty much everything based on pyrometer readings rather than rely on what a manufacturer might recommend.

 

UPDATE - I finally got to talk to a "Real" factory tech. Just as I suspected.

Modern higher pressure tires like the ones rated at 51 psi max. They are made to run at 36 -51 psi. car weight blah blah blah all come into acount. Do not use factory door jams or vehicle specified air pressures.

Then I ask about something I had heard years ago about driving "W" and "Y" rated tires up around their max speeds 168 and 186 MPH. The answer was because of the rotational speed and the power applied to achieve those speeds that they have a formula for exceeding the max 51 psi. This only applies to cars doing 1 mile drag racing and open road races and just that high for the event only and then returned to more typical sub 51 psi. So if you are testing your ZL1 Vette and planning on going 200 mph consult your tire man because you might need closer to 60 psi and use nitrogen for less variation.

This came from both the Continental and Goodyear racing tires reps.

 

I use 34 on my Firehawks -seems good so far.

-W (anecdotal only)

 

I start with the standard from the door, then check the tire temps across the tread with my handly tire temp gauge

There isn't a "standard" pressure because the tire may be used on any number of vehicles. So the manufacturer's recommendation on the car is what carries...because they selected the tire and the inflation given is based on their testing.

 

Are they W or Y rated for high speed

 

I run with the tire manufacturer's recommended pressure- it's on the sidewall. The load rating is at the recommended pressure. IF I run the tires on my pickup at the door sticker, I'm not only replacing them at 30k instead of 75k, the thing drives like a drunken ford.

 

I've always run tires at max. pressure as stated on the sidewall. Have done this on several different vehicles (trucks, sedans, sports cars). It has never resulted in uneven tire wear, excess temps, or bad handling. Many years ago, shop manager at the Goodyear shop I bought tires at said the same thing, run max. pressure, not the sticker rating. That said, I think testing and adjusting, as stated above, is probably the best method. This whole situation is complicated by running non-standard tires. You should be the judge of what works for your vehicle and individual driving style. If it feels bad, adjust until you find the "sweet spot" and keep it there.

 

If you runs pressures at the max sidewall pressure they're going to corwn and you'll wear the center of the tire well before the sidewalls are worn out. Braking will suffer because you no longer have the proper contact patch.

Door jam numbers are obvioulsy derived from multiple variables but a vehicle needs a certain number or air molecues to support it. Tire volume X pressure = the number of molecules needed.

 

Chiming in again, I'm surprised the discussion still seems to be around art vs. science on this. When I got started in autocross, I was taught how to use a pyro to find the *right* inflation pressure for a tire on a particular vehicle. I agree with jim2527 that it's all about maximizing the contact patch...which is what a pyro allows you to do.

https://www.pegasusautoracing.com/pr...asp?RecID=2515

 

It is all aobut the contact patch, and IMCO a tire pyrometer is an essential tool anyone who considers themselves serious about perfromance should own. For those who can't justify the expense, tho not as accurate for this specific use, an IR type is a worthwhile alternative I highly recommend to any enthusiast. IMOE picking arbitrary numbers (even if suggested by a manufacturer) and hoping against uneven wear happening isn't the most sound scientific method for establishing proper pressures.

 

Me too.
The manufacturer's suggested tire pressure is a compromise at best. Ride comfort takes priority over performance and wear (and don't forget the tires are warranteed by the tire manufacturer not the car manufacturer ).

 

The chaulk line has always worked for me, that and never forgetting a tire rotation.