Grip is proportional to downforce times the coefficients of friction. Since downforce comes mostly from vehicle weight the maximum available acceleration/deceleration (grip) is nearly identical across lighter and heavier vehicles for a given tire compound and tread pattern.
The complexity comes from things like sidewall stiffness (controls available grip near the lateral limit of traction, must be designed for vehicle mass), suspension geometry (tire camber affects maximum grip), tire width (affects contact patch size relative to mass of the vehicle, tire pressure, camber, and sidewall stiffness), and suspension spring rate and dampening (wheel hop, changing camber angle from body roll).
"Since downforce comes mostly from vehicle weight the maximum available acceleration/deceleration (grip) is nearly identical across lighter and heavier vehicles for a given tire compound and tread pattern."
It's literally just physics. Couloumb (static, or dry) friction is F_f = μF_n where F_f is the frictional force (grip) of tires in this case and F_n is the normal force between the ground and the tires due to the mass of the vehicle. μ ranges from 0.8 to 1 or more in modern tires.
Since F=ma and F_n is 9.8 N/kg due to gravity, F_f = μ * 9.81 * m and a = F/m = μ * 9.81 * m / m, and finally a = μ * 9.81 m/s^2.
