Quote:
Originally Posted by e60.deluxe
the contact patch is gonna be the same for the same PSI. the only way to reduce the size of the contact patch is to lighten the load on the tire or increase the PSI.
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This is a pretty tired (no pun intended) and overused over-simplification. Yes, it will be the same area. But it will not be the same shape. It's the width of the contact patch I am referring to, not the total area bounded by it. But even more directly, it is as originally stated the profile the tire presents the road. A higher aspect ratio entails a larger radius at the the edge of the contact patch, giving a lighter steering effort by minimizing by weight jacking as you turn the wheel. The more pronounded edge of the lower-profile tire is forced into the ground by the caster of the steering system as you turn the wheel to a greater degree, providing more resistance to the steering.
As far as old vs. new, compare the shoulders of a worn-out tire to a brand-new replacement and the difference is visually obvious. If there is sufficient sidewall stability the edge of the used tire will be sharper, rather than the comparitively rounded shoulder of the new tire. And low profile tires inherently have more sidewall stability, allowing them to more effectively flatten the contact patch and sharpen its edge with wear.