I forgot about the 165S15... I don't recall seeing that tire on a US Spec 122S, but I did buy a new '69 142S that came on that size as OE. But notice it only has an "S" between the width and the rim diameter; the "R" is missing. That's because it was another example of the 6.00-15 with different numbers on it, in other words just another bias-ply tire, but in this case it had an "S" speed rating.

Thanks for the link. I wondered where the "Pressure=weight/area" theory (as regards tire footprints) came from, as it has come up on these pages before. Sounds good on the surface, but it ignores the fact that weight is not evenly distributed over the entire contact patch. It also ignores the fact that the sidewall of the tire carries some of the load. The latter becomes extremely important when you move from high aspect ratio tires (like the 165/80-15) to more modern low profile tires. The sidewall on a 40 series tire is very stiff when compared to your "tall skinny" stuff.

That's not to say you can't come up with a specific tire pressure, on a specific wheel position, that will calculate an accurate weight for the load on that particular tire. But I think I can guarantee that if you double (or halve) the pressure in a tire, you will probably *not* see the square inches of footprint halve or double, respectively. And that's with the same tire, on the same wheel, on the same car. Never mind different wheels and different tire profiles from different tire manufacturers.

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Gary L - 142E ITB race car, 73 1800ES
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