[LostCause]

I think the reason for a square contact patch was well developed earlier in this thread. Using an ideal tire width, a square contact patch minimizes overall wheel deflection (stationary and moving).

The rationale bicycle riders use against excessively high tire pressures is that slipping begins to occur. I don't think the issue has anything to do with patch geometry. If slipping and road surface deformation can be limited, higher pressures should theoretically be ideal.

The circular contact patch issue seems logical, but I'd assume it would look more like a rounded off square than a circle. Without a more advanced mathematical technique or a super-specialized scale, I have no idea what the pressure distribution is like. For that reason, I think a list showing "ideal" and "actual" car widths to achieve a square contact patch should be made. If we get an idea of how far off the ideal is from reality, it'll be easier to say what width tire is ideal for a given car.

To that end, I'm going to measure the contact patch geometry of a few cars I have access to and I'll post the difference between ideal width (taking into account weight distribution) and the actual needed width (if I don't far exceed max PSI). Also, I'll post contact patch width vs tire width.

FrankLee already posted his data:

1993 Ford Tempo - 2520lbs Loaded (Front - 1590lb Rear - 930lb)

Ideal CP: Front - 119mm Rear - 106mm
Actual CP: Front - 127mm Rear - 127mm
Actual/Ideal: Front - 107% Rear - 120%

Actual tire width: 185mm
Actual CP width: 127mm
CPW/TW: 69%

While it's not perfect, it should give a general idea...

- LostCause