Chris,
now you've gone and complicated things!!!!
Foam tyres and rubber tyres (slicks) and then spiked tyres are completly different animals!!!
Foam tyres work essentially on frictional coefficients (lower shore and addatives increasing this coefficient) with the surface being run on. Now we get into talking about friction couples, slip angles, contact patch presentation yada yada yada. As most cars that run foams have very little roll induced camber change (is this the case with the Blaze being an off-roader .... can the camber links be set to acheive this?) the contact patch presentation is fairly consistent. In this case wider should = more grip.
If we are going to get technical the construction of the foams (how open celled the foam is) also has an effect as the edge of the "pockets" in the foams surface will increase available grip due to it providing more frictional couples.
Slicks (rubber) again are relliant on surface area and frictional coefficients, again softer rubber = higher friectional coefficients therefore it should equal = more grip.
Spiked tyres are slightly different though.
The rubber compound and contact area (combined area of all contacting spikes) is responsible for the grip level on hard pack surfaces ..... however if the spikes are soft and long they will fold over with lateral load and thus their characteristics will change (and they are likely to wear like crazy!).
The spike pattern is responsible for grip in softer conditions (ie. when there is little hard surface to contact) such as sandy soils, long grass / astro as they dig in / drag through. Here the stiffness of the spikes, due to compound AND construction will make a difference.
Hopefully that helps a little mate.
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