## Tune your custom car's performance

Once you've successfully built a custom car model and have it working in Midtown Madness, you can tweak the car's performance characteristics to create a truly unique vehicle.

To tune your custom car model's performance characteristics, you make changes to the values stored in the vp*.mmcarsim file (located in c:\vck\shop\tune ). As you tweak your car's setup, keep in mind that certain tuning values and combinations of tuning values may cause your custom vehicle (or the game) to behave erratically or stop responding (for example, assigning a negative mass value will cause problems).

The Top 16 tuning parameters you can change in vp*.mmcarsim include the following:

- Mass. The Mass value is used to govern how the car's horsepower affects acceleration. It is also used to resolve the effects of collisions. An object with greater mass will sustain less damage when colliding with objects with lower mass.
- DrivetrainType. A value of 0 (zero) specifies a rear-wheel drive vehicle. A value of 1 (one) specifies a front-wheel drive vehicle.
- MaxHorsePower. This value defines how much power a vehicle has. It largely relates to top speed, but, in conjunction with gear ratios, it affects acceleration.
- NumGears. This value defines the number of gears your vehicle has. The maximum value you can enter is 8; this includes neutral and reverse. This leaves a maximum of six available forward gears, not all of which must be used.
- Spring, Damping, RubberSpring, RubberDamp, RubberSpringLat, and RubberDampLat affect the suspension and ride characteristics of the vehicle.
- StaticFric (not StaticFriction). This value determines the general grip of the vehicle.
- GearRatios. Tuning these values in conjunction with the RPM values, is perhaps the most challenging of all the tuning tasks. Combined with MaxHorsePower, the ratios determine the acceleration and top speed capabilities of the car.
- OptRPM, MaxRPM, UpshiftRPM, and DownshiftRPM. These RPM values provide clues to the engine manager regarding optimal times to shift up or down depending on the engine RPM. When you're driving using automatic transmission, these values determine whether the transmission shifts too soon or too late to produce a smooth acceleration curve.