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How Much Pressure Do You Run In Your C3's Tires?

Joined
Mar 9, 2009
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1,026
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Yemen
Knowing this will almost certainly freak most of you out I'll go ahead and tell you what I run in my small block '82 and big block '71. Are you sitting down? In my small block '82 I run 20 psi front/17 psi rear and have done so for 25 years. And in my big block '71 I run 24 psi front/17 psi rear and have done so since I bought it in 2009. With those low (and correct) pressures I get 50,000+ miles out of my tires with perfectly even tread wear. As my '71 is my daily driver it gets driven about 25,000+ miles per year so it's due for a set of new tires every two years. Since I bought my '82 in 1988 I have put about 12 sets of tires on it and since 2009 I have put 3 sets of tires on my '71.

You are certainly thinking those pressures are way too low and unsafe but I'll explain why those are the correct pressures for a C3: Prior to the advent of the modern low profile/high pressure tires that began showing up in the mid '80's the mid 70's thru early '80's Corvettes, Camaros, Chevelles, Novas, GTO's, Firebirds, Skylarks, 442's, and such ran huge high profile/low pressure 225 thru 255X60R15 tires that had internal volumes that were twice as big as the modern low profile tires. The huge 225 thru 255X60R15's have a load rating of 1875 pounds @ 35 psi per tire but when mounted on these lighter 3500 pound cars the tires only required half the pressure to support half the maximum 7500 pound load. Meaning the huge 225 thru 255X60R15's were way bigger than needed for the lighter loads they were supporting. Fine and dandy but as the 3000 mile oil change intervals increased over the years to 5000 to 7500 to 10,000 to 12,000 to 15,000 miles the dealers who serviced these cars only saw them once in a GREAT while (often a year or more) so a slow leak could result in a dangerously low pressure by the time the car was finally brought to the dealer for servicing. So the lower 20 psi/17 psi was perfectly safe as long as those lower pressures were maintained................which very few people did because the average owner doesn't have an air compressor and self-service gas stations often didn't have one either; leaving it up to the dealers to check them maybe once per year. So by 1982 the "big three" manufacturers were forced to recommend MAXIMUM pressures to cover their lawsuit-weary butts.

The really nice thing about running the lower pressures is your C3 car will ride real smooth. And no, the tire will not come off the rim during hard cornering because 20 psi is more than enough to maintain tire-to-rim contact even in a high speed full broad slide on asphalt. If I were going to road race my C3's on paved tracks or run them at the Bonneville salt flats I would definitely pump them up to 30+ psi. But for every day street use the lower pressures are perfectly safe AS LONG AS those lower pressures are maintained.

Comments?
 

Timrock

Member
Joined
Apr 16, 2016
Messages
7
Location
Waxhaw, NC
Corvette
1978 4-sp Coupe
1978 C3 steering is way to sensitive

1978 Coupe:

It is too much work driving my car! There is no play or give in the steering. The slightest bump and the wheel jerks. The car is in great shape and does not need front end work. The alignment is good. The car rides straight. Why is the steering so sensitive? Is there a way to "loosen" it up and give it a tiny bit of play?

I have just read the piece by toobroketoretire and I'm thinking that might be the answer to my problems. Tire pressure! My car has the 25560R15s. I have them set at 32lbs. The car rides really hard and is hard to handle. I really would like my wife to be able to drive this car, but as of now that's not likely. I'm gonna drop the pressure and see if that resolves the the issue?

I see that this issue is very common on the web, and have been reading about it, but there does not seem to be one good answer. Should I have the car re-aligned? The recommended settings seem to be all over the place. What are the proper settings? If the car is not fun to drive, why have it all?

I do have to replace the steering pressure vlave because of a slight leak, but that can't be the cause.

Please help!!
 
Last edited:
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
Drop the pressures to 20 psi front and 17 psi rear and you'll immediately notice a world of difference. It'll ride real smooth and the tires will last 3 times as long. Now days the tires are HIGH pressure/LOW profile and require 35-45 psi. But the old balloon 255X60R15's are LOW pressure/HIGH profile that only require half the pressure because of their huge internal volumes.
 

C3forME

Well-known member
Joined
Jan 22, 2003
Messages
174
Location
Long Island, New York
Corvette
1977 Coupe
32 PSI cold tire pressure
 

dougelam

Well-known member
Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
Knowing this will almost certainly freak most of you out I'll go ahead and tell you what I run in my small block '82 and big block '71. Are you sitting down? In my small block '82 I run 20 psi front/17 psi rear and have done so for 25 years. And in my big block '71 I run 24 psi front/17 psi rear and have done so since I bought it in 2009. With those low (and correct) pressures I get 50,000+ miles out of my tires with perfectly even tread wear. As my '71 is my daily driver it gets driven about 25,000+ miles per year so it's due for a set of new tires every two years. Since I bought my '82 in 1988 I have put about 12 sets of tires on it and since 2009 I have put 3 sets of tires on my '71.

You are certainly thinking those pressures are way too low and unsafe but I'll explain why those are the correct pressures for a C3: Prior to the advent of the modern low profile/high pressure tires that began showing up in the mid '80's the mid 70's thru early '80's Corvettes, Camaros, Chevelles, Novas, GTO's, Firebirds, Skylarks, 442's, and such ran huge high profile/low pressure 225 thru 255X60R15 tires that had internal volumes that were twice as big as the modern low profile tires. The huge 225 thru 255X60R15's have a load rating of 1875 pounds @ 35 psi per tire but when mounted on these lighter 3500 pound cars the tires only required half the pressure to support half the maximum 7500 pound load. Meaning the huge 225 thru 255X60R15's were way bigger than needed for the lighter loads they were supporting. Fine and dandy but as the 3000 mile oil change intervals increased over the years to 5000 to 7500 to 10,000 to 12,000 to 15,000 miles the dealers who serviced these cars only saw them once in a GREAT while (often a year or more) so a slow leak could result in a dangerously low pressure by the time the car was finally brought to the dealer for servicing. So the lower 20 psi/17 psi was perfectly safe as long as those lower pressures were maintained................which very few people did because the average owner doesn't have an air compressor and self-service gas stations often didn't have one either; leaving it up to the dealers to check them maybe once per year. So by 1982 the "big three" manufacturers were forced to recommend MAXIMUM pressures to cover their lawsuit-weary butts.

The really nice thing about running the lower pressures is your C3 car will ride real smooth. And no, the tire will not come off the rim during hard cornering because 20 psi is more than enough to maintain tire-to-rim contact even in a high speed full broad slide on asphalt. If I were going to road race my C3's on paved tracks or run them at the Bonneville salt flats I would definitely pump them up to 30+ psi. But for every day street use the lower pressures are perfectly safe AS LONG AS those lower pressures are maintained.

Comments?
Danger
Follow this advice with fair warning!!!
NO ONE SUBSCRIBES TO HIS WAY OF THINKING
The Sixties & Seventies are past us now and the rest of us learned from their mistakes and this one is still living it!



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Vettehead Mikey

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Joined
Aug 26, 2003
Messages
3,486
Location
Not that far from Ottawa
Corvette
1973 Coupe
Danger
Follow this advice with fair warning!!!
NO ONE SUBSCRIBES TO HIS WAY OF THINKING
The Sixties & Seventies are past us now and the rest of us learned from their mistakes and this one is still living it!

Not to mention in this particular case with the factory 70- series tires the correct pressures as listed on the door jam sticker are 20 front 26 rear. With the larger P255/60R15 tires the pressures for max load are 29 front 32 rear. See picture below.



corvette-472930-decal.jpg.png


Recommending pressures less than the OEM ratings is foolish.
 

Tom Bryant

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Nov 9, 2000
Messages
7,367
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
On our '81 the sticker for 225/70/15 tires says 35 front and rear. When new every bump was a sharp jolt. Someone in the Corvette club told my wife to run 30 psi. We have ran 30 ever since and it makes a good difference in ride quality. I've been very happy with that pressure. We just put on set of tires number 3. I still have the originals that we wore down about 80% and they measure the same all the way across. We had Eagle ST tires on it after that for many years. They were still at about 75% tread depth when I changed them last summer due to age. They looked good with very little weather checking but they were just too old for me to trust them on the interstate if we went on a trip. They were also worn evenly all the way across so I'll stick with 30 psi on the 225s. If 30 was too much they would be worn more in the middle. Even tire wear equals maximum tire contact area (patch). A maximum tire patch will give you maximum traction when accelerating, braking and cornering. Too low of a tire pressure will allow the tire to cup in the middle under severe braking and acceleration and cause a loss of traction. It will also allow the tire to roll over on it's sidewall during hard cornering and loose cornering traction.

The car may ride better with lower pressure but I would suggest that if you want to try it get yourself a tread depth gauge and measure each groove all across the tire at regular intervals, say 3000 miles. Keep a record. If they start to show more wear on the outside increase the pressure. When you get to the pressure where your tires are wearing evenly all the way across you are at the perfect pressure for that size tire on your car. Other cars with different tire brand or wheels or car weight will have a different ideal psi. You just need to experiment to find what's best for your car.

Tom
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
When you get to the pressure where your tires are wearing evenly all the way across you are at the perfect pressure for that size tire on your car. Other cars with different tire brand or wheels or car weight will have a different ideal psi. You just need to experiment to find what's best for your car.

Tom


That's exactly what I have been saying and that's why the huge 255X60R15's only require a scant 20 psi in the front and 17 psi in the rear to wear perfectly even. As people never bother to check their tires the manufacturers were forced to recommend maximum pressures to protect their lawsuit-weary butts.
 

dougelam

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Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
That's exactly what I have been saying and that's why the huge 255X60R15's only require a scant 20 psi in the front and 17 psi in the rear to wear perfectly even. As people never bother to check their tires the manufacturers were forced to recommend maximum pressures to protect their lawsuit-weary butts.
As usual wrong again!!!

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dougelam

Well-known member
Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
Its not your choice of tire pressures, most people will experiment with them, its the comments on tire wear and manufacturers recommendations assumptions that is not correct.

I run 28psi front and rear on 02 vert with perfect tread wear and an acceptable ride.

Recommend tire pressure is based on fuel economy AND safety!!!
The suspension and braking systems are engineered around this.

A REAL ENGINEER WOULD KNOW THIS

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Last edited:

kpic

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Mar 29, 2014
Messages
2,292
Location
Columbus, NC/NE Georgia
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1997 boosted silver coupe

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