you never go by whats on the tire. its made for a million applications. you vehicle was designed to operate at a certain tire psi. we get people in the shop wondering why the car doesnt ride right or rides 'messed up'. first thing i check is tire pressure. reset to factory specs and car rides the way its supposed to.

 

here is a bulliten that all dealers and shops go by.........(its still applies to our old cars)

INFORMATION

Bulletin No.: 00-00-90-002J

Date: January 28, 2009

Subject:
Information on Proper Tire Pressure

Models:
2010 and Prior GM Passenger Cars and Light Duty Trucks (including Saturn)
2009 and Prior HUMMER H2, H3, H3T
2005-2009 Saab 9-7X

Supercede:

This bulletin is being revised to add model years and clarify additional information. Please discard Corporate Bulletin Number 00-00-90-002I (Section 00 - General Information).

Important: ^ Adjustment of tire pressure for a customer with a Low Tire Pressure Monitor (TPM) light on and no codes in the TPM system is NOT a warrantable repair. Claims to simply adjust the tire pressure will be rejected.

^ ALL tires (including the spare tire) MUST be set to the recommended inflation pressure stated on the vehicle's tire placard (on driver's door) during the PRE-DELIVERY INSPECTION (PDI). Recommended inflation pressure is not the pressure printed on tire sidewall.

^ Tires may be over-inflated from the assembly plant due to the mounting process.

^ Generally a 5.6°C (10°F) temperature change will result in (is equivalent to) a 6.9 kPa (1 psi) tire pressure change.

^ 2008-2009 HUMMER H2 Only - The H2 comes standard with Light Truck "D" Load Range tires with a recommended cold inflation pressure of 289 kPa (42 psi). These tires will alert the driver to a low pressure situation at roughly 262 kPa (38 psi) due to a requirement in FMVSS 138 which specifies a Minimum Activation Pressure for each tire type. This creates a relatively narrow window of "usable" pressure values and the warning will be more sensitive to outside temperature changes during the colder months. As with other cold temperature/tire pressure issues, there is nothing wrong with the system itself. If a vehicle is brought in with this concern, check for tire damage and set all tires to the Recommended Cold Inflation Pressure shown on the vehicle placard.


Accurate tire pressures ensure the safe handling and appropriate ride characteristics of GM cars and trucks. It is critical that the tire pressure be adjusted to the specifications on the vehicle¡Çs tire placard during PDI.

Ride, handling and road noise concerns may be caused by improperly adjusted tire pressure.

The first step in the diagnosis of these concerns is to verify that the tires are inflated to the correct pressures. The recommended tire inflation pressure is listed on the vehicle¡Çs tire placard. The tire placard is located on the driver¡Çs side front or rear door edge, center pillar, or the rear compartment lid.

Tip

^ Generally a 5.6°C (10°F) temperature increase will result in (is equivalent to) a 6.9 kPa (1 psi) tire pressure increase.

^ The definition of a "cold" tire is one that has been sitting for at least 3 hours, or driven no more than 1.6 km (1 mi).

^ On extremely cold days, if the vehicle has been indoors, it may be necessary to compensate for the low external temperature by adding additional air to the tire during PDI.

^ During cold weather, the Tire Pressure Monitor (TPM) indicator light (a yellow horseshoe with an exclamation point) may illuminate. If this indicator turns off after the tires warm up (reach operating temperature), the tire pressure should be reset to placard pressure at the cold temperature.

^ The TPM system will work correctly with nitrogen in tires.

^ The TPM system is compatible with the GM Vehicle Care Tire Sealant but may not be with other commercially available sealants.

Important: ^ Do not use the tire pressure indicated on the tire itself as a guide.

^ Always inspect and adjust the pressure when the tires are cold.

^ Vehicles that have different pressures for the front and the rear need to be adjusted after tire rotation.


Improper tire inflation may result in any or all of the following conditions:

^ Premature tire wear

^ Harsh ride

^ Excessive road noise

^ Poor handling

^ Reduced fuel economy

^ Low Tire Pressure Monitor (TPM) Light ON

^ Low Tire Pressure Message on the Drivers Information Center (DIC)

 

I'm on the 2nd set of Indy 500's on my 80, and I've found the following:

1. The guys at Firestone are generally pretty stupid when it comes to specialty stuff. I *might* listen to them about my wife's 2000 Accord, but I wear earplugs when they try to say anything about my Vette.

2. I ran 32#s (cold) all around, and the centers wore out first. But it rode well, handled well, and the wear was pretty close, so I'm going to keep them at 30-31 now - that should be about right.

 

i thought i knew what i was doing before i read this thread but now i do not know what to do.

 

30 psi in my BFG's for the last 30,000 miles and no problems. Center has worn a little more than the edges.

 

Ford's in the middle of huge amount of lawsuit litigation due to Firestone suggesting they lower the pressures on their SUV tires from the low 30s to somewhere in the 20s. We all know what happened. Tires overheated at the lower pressure, blew out and killed people. A 2500 lb Honda would be just fine on 26lbs which is what my door says my 77 should be. But folks, we drive cars that are closer to 3500lbs than 2500lbs. There's current mid size 5 passenger 4 doors that weigh less than our Vettes. I've been running 32# for 10 years and cannot tell any difference in wear from inside to outside on the tread. Yeah, it rides a bit rougher at 32 over 26, but it also handles better. You'll also get better gas mileage at the higher pressure due to less rolling resistance. Something else to keep in mind.... how many miles a year do you put on your C3 Vette. I'm around 1000 miles per year and that rate, even if my tire wear was uneven they're going to dry rot before I wear them out. Just MHO.

Bottom line: Play with the pressures. You know 26 is spec and 35 is probably too much. So play in between until you find a compromise between handling and ride quality.

PS: I tried 35 for a few days. Had to go visit the dentist to get a cavity refilled. I like 32 and the ride is acceptable.

 

I run cold psi at 30. My other cars I follow the door sticker. 20's is too low,

 

Whatever the cost of your tires, it is (at least for me) significantly less than the value of my C3. Tires inflated to 35#, and the torture track roads in PA, pretty much serve to bounce me and the car to pieces. Tires are cheap by comparison. I've dropped my tire pressure to 30# and am much happier with the overall driving experience. Even if the tires would wear out prematurely because of this pressure -- i dont put enough miles on it to be a problem. Most likely those tires will be replaced because of age before tread wear.

 

This is correct. why you say? what if you took the same size tire and put it on a car that had half the weight of his Vette and filled it to the max rating..well duh it would be over inflated. For normal wear and tear street use, a tire is inflated to what the manufacture suggests and this is rated to the gross weight of the vehicle.

 

Something to keep in mind on this subject. I sold tires in the 70s when you still had a choice of bias ply or radials when you needed to purchase tires. The radial tires we purchase today are vastly different than the radials we bought in 1975. They're the same in name only. We didn't fully understand radials and all their advantages at the time. In 1975 the sidewalls on some radials were nearly as thick as the tread part of the tire.

Look at a comparable car/tire combination today and see what the manufacturer recommends vs what they recommended in the 70s. Two cars. Same size tires. Pretty close to same weight. (Both cars sit in my garage)

1977 Corvette - Manufacturers recommended tire pressure = 26psi.

1999 Dodge Intrepid - Manufacturers recommended tire pressure = 32psi.

I remember the first set of radials I put on a car, which was somewhere around 1974. Set at the recommended tire pressure on a car that weighed approximately 3700# - 4000#, I could actually feel the tire roll over if I pushed it cornering. Jacked the pressure up closer to 30-32psi and no more problem.

 

As I think it has already been pointed out, that sticker is for a set of bias-ply tires while the modern tires are radials. Rough rule of thumb I use is 1PSI inflation for every 100Lbs of weight so a 3500Lb Vette would be 35PSI inflation. It's better to be overinflated than underinflated. Tire tread wear patterns will help you decide on any final inflation settings.

 

Actually, my 77 came with radials - GR70-15 - and the sticker says 26#.
Had an 86 Cavalier with 195R70-13s and I ran 32psi. Got 70K out of one set of tires with perfect tire wear. That was probably more than needed for that light a car, but I never slowed down takin' corners.

 

I think there's a simple test to help you decide the right pressure for your tires. Find an empty parking lot and mark out a reasonably tight turn (some pebbles should do). With your tires inflated to 26 psi, see how fast you can negotiate the turn before the tires break loose. Increase the pressure to 32 psi and try the same turn. If your tires break loose at a lower speed, drop your pressure back down to 26.

I don't check my tires often enough but as soon as I hear screeching going around a corner, I know I've got a problem. I keep one of those $10 air pumps that plug into the cigarette lighter in all my cars.

 

Not sure we're talking about the same thing here, but nothing I've read or experienced since radial tires came out in the 70s would suggest a radial tire gives better traction at a low air pressure vs a higher pressure. In every car mag I've read, the testers have pumped up the tires to go faster, regardless whether in a straight line or around corners. Autocrossers routinely jack the pressure on their radials to the 40 to 50 psi range. The reason being is that at 30 psi when you're approaching maximum lateral Gs you tire will actually roll over on it's side. Simple physics says maintaining maximum tread footprint offers more traction and control of your vehicle than driving on the side of your tire.

If one never pushes their car to the limit, never tries to straighten out a curvy country road or attempt a curve marked 30mph at 50 mph+, then 26-28psi is all you need. Your Vette will ride better. But I'll put out the challenge to try that 30mph curve at 50 with 26# in you tires and then do it again at 32#. You will feel a difference. You'll feel more in control at 32psi.

 

Exactly my point -- just didn't want to send anyone out on the highway for their first drifting lesson. I'll add to that - the first time someone cuts you off or stops half-way into the intersection you just entered you'll be really really glad you have 32 psi in your tires (and decent tread).


Of course I understand that comfort is a prime consideration when driving a C3 Corvette.

 

Is that a photo of your ride?

 

First Corvette - fully optioned '69 427/390 4-speed convertible. Bought it in 1977 for $3,500. Out for a test drive when someone cut me off.

 

That really sucks! That would be one downside of fiberglass vs metal. Fiberglass doesn't bend... it just sorta explodes. It looks pretty bad. Was it a write off or were you able to put her back together?

 

Walked away with one small scratch but the entire car was bent or broken. Didn't have collision so I sold the wreck for $600 to a Corvette Club friend. Wrote the rest off as casualty loss on income tax. Bought the 72 in my avatar two months later (still have it).

 

Glad you walked away and weren't hurt. Not the way I'd want to part with a 69 though. I'd much rather have a 68/69..... but a 77 was all I could afford.