proper tire inflation
I have 235/70/15 Cooper tires on my coupe. I am unclear about the proper tire inflation for the car. A GM restoration document says 24 pounds for the original type tires, but I currently keep about 28 pounds in each tire. These tires are currently 9 years old, with very good tread. For safety, should I replace them according to govt. suggestions, or watch them and use them. I don't drive the car hard. Thanks for any input.
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Re: proper tire inflation
The sticker on the 77's door reads 20psi front / 26 rear as the original tires' inflation. I guess this was GMs best compromise between comfort, control and economy.
In summer, I bump these figures to 24/30 something on Good Year Eagle GT+4's (225s). In winter I go to around 40 to avoid flat spots.
Well, tires THAT old should definitively get replaced. The rubber gets hard, having a very bad influence on the tires' grip. And all that comes without ANY sign of ageing. (If the tire SHOWS its age, it's highest time anyway...)
But I tell you this with tires about just as old as yours... I was thinking about getting new ones next season.
The investment does not hurt anymore, when imagining you loose control and insurance refuses to pay because of poor maintenance. Not good! -
Re: proper tire inflation
I keep my tires around 28ish on my '73 also. I tried higher pressure but the ride was too harsh.
As for the gvm't idea that all tires always go bad at the stroke of midnight on their ? birthday irrespective of how they've been cared for and used. Well, pull the other one.Comment
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Re: proper tire inflation
Sure it isn't irrespective of care and maintenance - but it is a matter of fact that rubber ages and gets hard after some time, EVEN if you care for it and rarely drive...
So at a point ask yourself if you are taking the risk (I still do
) - and be aware that your insurance might decline a resulting claim. 
(And they don't ask if you have been taken utmost care - for them only the age counts. That's all.)
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Re: proper tire inflation
Congress/DOT did not come up with specific tire life regulations because cooler heads prevailed, and they realized that any regulatory "tire life" is purely arbitrary.
Tire life starts with the quality of materials and manufacturing processes and is then highly influenced by environmental factors during service. UV and ozone are tires' biggest enemies. Typical "collector cars" that live most of their lives in garages have minimum exposure to life-limiting environmental factors.
If your tires are at least H-rated and have spiral would nylon cap belts and don't live outside they could easily be safe to drive on for a couple of decades.
If the are T-rated or less without a nylon cap belts, I won't comment other than to say I would not install such tires on any car I own if you gave them to me.
As far as pressure is concerned, it's a function of tire size/load capacity relative to the load the tires are carrying. The 235/70R-15 size has a load capacity of about 1800 pounds, so you have nearly 100 percent load margin. This means you can run low pressure - probably as low as 22-24 psi if not less, but steering response and handling will degrade while ride harshness will improve. Fuel economy will also be less because tire rolling resistance increases with lower pressure. It's a matter of personal preference, but my advise is usually to run them as high as you can stand, but for that size tire and the Corvette's relative low weight, I would not go over 32 psi, cold. There is a point where a lightly loaded tire can actually loose grip if pressure is too high.
DukeComment
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Re: proper tire inflation
Gentlemen,
I have moved the air pressure to 30 for a test. I tend to agree with Mr. Ward, my tires spend their life in the garage, 1-2K per year driving. I will replace in the spring just for peace of mind, I am not sure what I will buy, but they will probably outlast me.Comment
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Re: proper tire inflation
I suggest the V-rated 225/70R-15 102V Goodyear Eagle RS-A. It's the last available "police pursuit tire" in this size of the three I discussed in a circa 2003 Corvette Restorer article on tires.
They will even minimize judging points deduction on most '73-'82 models since they are the original base size from an OE supplier.
DukeComment
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Re: proper tire inflation
I run 32psi in that type of tire. The ride and tire wear don't seem to be compromised and I think I get a little better fuel mileage as it is easier to roll with the extra air. TomComment
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