A good read on tire size

[chrisgerman1983]

I found a good write up on tire size and how it effects grip. It confirms a few thought that i had on PSI and blanket statements about what tire size is "best"
AutoSpeed- tyres, Grip and All That...

[CapriRacer]

Unfortunately, this article to totally wrong.

First, you can NOT calculate the size of the footprint using load and inflation pressure:

Fact or Fiction? Tire contact patch and air pressure.

While the footprint size will go down with more inflation pressure (and up with more load), the physics is not simple and certainly not linear.

In the July, 2011 issue of Road and Track, they tested 3 high performance tires. They included some details about the tires - including the areas of the footprints at the same inflation pressure and load:

Car Tires - Cooper Treads on Goodyear and Bridgestone's turf with No Fear at RoadandTrack.com

Guess what?

The size of the footprints are different for each tire, even though they were measured at the same load and inflation pressure - and the average footprint pressure (load divided by the footprint area) does not equal the inflation pressure.

I'll leave it to the reader to do the calculations.

Second, tires don't behave according to classical friction theory - also known as Amonton's Laws or Coulomb's Law. The rubber in tires penetrates the macro-structure of the pavement surface and that provides more grip. That's one of the reasons car can generate more than 1G cornering power (another reason is aerodynamic loading)

And this is just the start. Sorry, but this article is just chock full or wrong.