Simulating vehicle physics -- problem with friction.

I’m working on some code to simulate a vehicle with more than 4 wheels. The vehicle has a suspension and that’s working fine. The way it works is that the code looks at each wheel and solves for the amount of deflection at the wheel needed to touch the ground. The resulting spring force is solved for and applied against the vehicle body. This works well and the suspension moves over uneven terrain as expected. But the vehicle slowly creeps when stopped. It occurred to me that it might be because the code is applying suspension force from the wheels against the vehicle body, leaving no forces against the ground. Or is there? So the question is how do I apply the wheel force against the ground so that frictional forces can take effect?