Quote:
Originally Posted by CapriRacer
Further, while it is true that NEW passenger car tires have bursting pressures over 200 psi, this is a one time event. If you read up on fatigue resistance, you'll find that if something is loaded repeatedly, like rolling the tire with a load, the fatigue resistance drops dramatically. In the range of value normal for tires - 106 cycles - the fatigue resistance is 20 to 25% of the one time value.
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The The International Tire and Rubber Association burst tests I linked to that found a minimum burst pressure of over 300psi was (mostly) of used tires, not new ones.
I'd agree that running at, or even remotely close to that for extended periods would be inviting trouble, but, again, the "max" recommendations on the sidewall have literally
nothing to do with the individual tires capacity.
The number is set not by the manufacturer or car maker, but by an independent organization that has permanent set standards based on tire size only.
The number really seems to be based more on tradition than any test or safety concern.
It was set once, by law, and never altered (as far as I can gather from the DOT website) since 1948.
Manufacturers have to run speed and durability tests on new tires, but the pressures they run them in are taken as a given.
I can't find any thing explaining what, if anything, the 'max' pressure ratings were originally based on - but it is clearly not anything to do with an individual tire's actual burst pressure, strength, or performance (since, as people here have pointed out, they aren't even tested at any higher pressure to see whether they preform better or last as long or are as strong)
As far as the car's "recommended" pressure on the door jam, as Ralph Nader pointed out back in 1965, that number is based on
comfort for passengers, at the expense of safety, efficiency, handling, tire life, etc.
Can anyone find any concrete evidence that running at (or even above) the max rated pressure has any drawback other than a harsh ride and possibly less puncture resistance?