re tyre profiles and contact patches

[Jay Negrin <jmnegrin@domain.elided>]

Michael Smith, in AD1097, makes several references to tire ocntact patch and
profile.  I am assuming that profile equals aspect ratio, and that all of the
argument in re steering effort, contact patch area and such are for tires of
the same width, differeing primarily in aspect ratio.  That would make sense
for all of what I read.  

I believe, though, that many of us have gone with lower aspect ratio tires in
order to increase the width of the tire, while keeping the same (or close)
diameter.  I, too, would expect similar performance from, say a 205/55 14, a
205/60 14 or a 205/55 15, on appropriate wheels of course. However, I would
expect increased performance (if all other factors were equal) from any of the
above mentioned sizes compared to a 185/70 14.  Given the wider tire, I would
expect a larger contact patch, and following that, higher steering effort,
especially at low speeds or when standing still.  (That does happen when at
VERY low speeds, such as when attempting to park.)

The differences in performance that I would expect with the same width tires
of different aspect ratios (all other factors equal, of course) is that the
shorter tire would react quicker to steering inputs, as the shorter sidewall
should be stiffer, acting less like a spring, and more like a solid.  Absolute
limits of adhesion, and other perfomrance parameters should, I expect, vary
little. 

another tuppence from Southern California
Jay Negrin
AROSoCal

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