Tire wall collisons?

[Dingo-J]

I have a row of tires (using the objects and not a textured wall). Right now if a car collides with a stack of tires (the stadard stack in default objects) it acts like hitting a cone and has no real effect on the car. How do you change this so that tires have a little more "weight" behind them? I found that clicking on "collide" as well as "movable" seemed to help but it also leaves impact marks in the air where the tires used to be before you impacted them - not good. Anyone?