DeTomaso Mailing List: May 1997, Message #532
     



From: Andy Poling <andy@realbig.com>

Subject: Re: Tires

Date: Tue, 27 May 1997 16:23:57 -0400 (EDT)



On Tue, 27 May 1997 CGMEES@aol.com wrote:

> With all the talk about type and size of tires, is anyone aware of a method

> to determine the "best" size of tire given the weight and horsepower of the

> car.  In listening and reading about the various pluses and minuses of

> various brands of tires, I thought that there ought to be a means to

> determine the best type of tire contact.  As I understand it, the amount of

> tire in contact with the road is determined by the weight carried by the tire

> and the air pressure inside of the tire.  This would mean that with wide wide

> tires you would have a narrower rectangular patch of tire contact while with

> the thinner tires you would get a more square type contact.  Is there any

> benefit for either type of contact to effeciently get the power of the engine

> to the road?



That is correct: a wide tire has a wide (side-to-side) contact patch and a

narrow tire has a long (front-to-rear) contact patch.  The area of the

contact patch is (mostly) determined by the weight of the car, with the tire

pressure being somewhat pre-determined by the limits of the tire and the

proper pressure for the weight of the car.  There are some other things that

affect the area of the contact patch, such as the tire carcass construction,

but they can mostly be lumped together with the air pressure in the tire.



Also, a smaller diameter tire tends to have a wider contact patch, while a

larger diameter tire tends to have a longer contact patch.



What's more (and the answer to your question) the wide contact patch is

optimal for side loads (i.e. cornering) and the long contact patch is

optimal for longitudinal loads (i.e. acceleration and braking).



Thus dragsters run large-diameter, relatively skinny tires for maximum

traction under acceleration.  And road racing cars tend to run smaller

diameter, wider tires for better traction when cornering.



-Andyu

#3822



72 Pantera: power             91 Miata: quickness              96 A4Q: traction

84 RZ350: all the above