ODE car simulation problem

Hi there I'm trying to simulate a car using ODE physics library , and I was successful somehow. However there is some problems that I can't solve , Hope you can help me with them: 1- How can I predict a physical action with ODE. for example if my car is going with the speed of 100 mph , how long(time) it takes to collide with the wall in front. this is important for my AI to adjust the speed when it go to the walls or turning around a corner. with this prediction I can tell the car when to break to not hit the wall or turn around the corner correctly. 2- My car is composed of 5 geoms & boddies. a car-body(cube) & 4 wheels that they connected to the car-body with hinge2 joints. I use the code below for driving the car: dJointSetHinge2Param ( wheelJoints , dParamVel2 , desiredSpeed ); dJointSetHinge2Param ( wheelJoints , dParamFMax2 , torque ); but me car never get to the desired-Speed! it always increase speed to the desiredSpeed/2.5 ! Isn't it strange? I don't know where I'm wrong. 3- Is it better for the wheels to be spherical or cylindrical ? 4- Do you know a Working car code with ODE on the net. thank you