Setting Material pairs Tires and Tracks

Working on a racing game here and I'm trying to get the friction working in the callbacks.
What I need to know is how can I set a material pair between the Tire and the Track as the Tire? Or where should and could I set friction(and the side slip info for that matter)?
The simple tire does not have a Newton body member and access to the materialID info that a normal car body does.

the tires have the same material as the chassis body.

for a detailed example, see the Stunt Playground source code.