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 no

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.