Contact patch....

["Mark Battley" <m.battley@domain.elided>]

PLEASE.... not twice in one digest!

>       Simple answer - the larger the diameter, the larger the contact patch 
>- --> more grip.  This works with wider tires too.  But you probably already 
>knew that. 
>
>3. With restrictions in width, a taller tire (with associated suspension
>modifications) might allow you a larger contact patch and therefore less
>heat build up and the possibility of running a softer compound than your
>competitor...

I make no claims to being a tyre expert, but....

Physics 101: Contact patch area is primarily a function of pressure and the
load on the tyre - force = pressure x area. Tyre width and diameter does not
directly change the contact patch area. The contact patch SHAPE will change
(wider tyre = shorter contact patch, all other things being equal), and the
different shaped contact patch with a different height sidewall will
probably result in some sort of change in grip (which may not be an increase
- wide tyres with short contact patches tend to be more prone to aquaplaning
in standing water than a narrower tyre with a longer contact patch). The
contact area will only change significantly if the different tyre behaves
best at a different pressure. 

Of course it's not quite that simple, there is a whole lot more going on at
the contact patch, and how it deforms under the dynamic loads makes a big
difference. 

Mark Battley
Auckland, New Zealand.

1973 Alfa Romeo 2000 GT Veloce
1989 Fiat Uno Turbo 
1989 Fiat Croma
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