But doesnt adding mass to the car affect the acceleration properties of the trye in that the radius of the trye will decrease and rotation acceleration is dependent on radius? Also the contact patch will be larger which will change the tryes grip properties. In the real world if I want to stop my car when it is fully loaded as compared to lightly loaded It takes longer to stop when I apply equal brake pedal pressure. Also adding weight changes the C of G and thus the weight transfer you talk about so the net result is that added weight will effect braking performance. A fully loaded 40 tonne truck will never stop as quickly as my 1000 kg car. Also a fully loaded wheel barrow takes a lot more effort to stop than a unloaded one. This example does have a air filled tire! I agree fitting better tires is the first step because they can handle greater acceleration forces, but it is the brake system that adds the acceleration force (deceleration in this case) to the tire. If the brakes can not slow the tire down at its maximum rate then all is wasted.