Model validation is vital to any simulation

Printscreen of the LapSim GUI showing the selection of laps to compare

We think it is vital for a lap simulation to have a good correlation with the reality, in case of a race car, close to the on-car recorded data of the race car.

For us this is where simulation starts. The structure of LapSim is based on this principle and we have tried to make it as easy as possible to compare on-car data with simulation data.

Level of correlation in LapSim

Printscreen of the LapSim GUI showing the selection of laps to compare

The two screenshots of the LapSim GUI show a comparison of on-car recorded data to the corresponding simulation model.

In the top figure you see, vehicle speed, engine rpm, throttle position and diff time. The bottom figure shows you the suspension travel of the four wheels.

These graphs give a realistic view of how close the results of the LapSim model should be to the reality.

Approach to get to a good correlation.

The different parts of the vehicle do interfere in the results of the simulation. But some clearly have a much bigger influence on certain results than other. The best approach to come to a good correlation is described in this menu.

The first focus is on the speed of the vehicle, by altering tire grip, engine power and drag. This is done by looking at the speed graph as well as the diff time signal.

When the speed graph over the complete lap resembles, one subsequently starts to correlate downforce levels by looking at the suspension travel, while keeping an eye on the global speed graph. This is an iterative process

Easiest determined by looking at the diff time

Tire grip determines to a large extend the corner speeds at the various corners. In order to estimate the tire grip, one should look at the whole lap.

Subsequently the details of tire grip can be estimated, like camber and vertical load dependence.

Derived out of the speed graph

The vehicles straight line acceleration is mainly determined by the vehicle's weight, engine power and drag.

Since the vehicle's weight is easily measured, by comparing the speed graphs, a good estimate of the engine power as well as the vehicle drag can be made.

Determined out of the suspension heave signals

The vehicles suspension with its springs and suspension travel measurements, can be seen as very large load cells. The principle is the same in a very large scale.

By comparing the travel of the model to the real car and subsequently making adjustments of the model's aero, a good estimate of the vehicles downforce can be made.

Determined out of the suspension roll signals

As the stiffness of the main springs as well as the suspension roll center height is known, any difference in suspension roll can only be caused by a difference in roll stiffness of the model to the real car.

Therefor comparing the suspension roll travel is a very good tool to determine the stiffness of the anti roll bars.

Can cause discrepancies between model and reality

The track parameters have an influence on the simulation results and can therefor interfere with establishing a good correlation between model and reality.

The two main parameters which influence the model building process is wind and banking in certain corners.