Quantifying aero and tyre

performance using ChassisSim.

Introduction

• Quantifying tyre and aero performance is key

to engineering a race car.

• This is thought to be impossible from race

data.

• However it is done on a daily basis using

ChassisSim.

• We’ll discuss the how and why.

Linking Data to the simulator – Creating a

monster file • A monster file is constructed from a single flying lap.

• This is exported at 50 Hz from your logger.

• Using the monster file you can.

• Construct the circuit properties

• Perform Baseline modelling.

• A monster file looks something like this,

0 6564 -0.02 0.05 -6.21 -3.3 23.17 28.62 -0.1 100 231.7

1.305 6612 -0.1 0.25 -6.9 -3.95 21.52 25.94 -0.1 100 231.7

2.606 6588 -0.05 0.25 -6.2 -3.71 20.69 24.08 -0.1 100 231.6

3.908 6600 -0.33 0.19 -5.13 -2.63 20.72 24.93 -0.1 100 232.2

5.209 6564 -0.05 0.25 -3.98 -1.62 21.77 26.46 -0.1 100 231.8

Modelling Aerodynamics

CLA, CDA, and aero balance – The metrics of

Aerodynamics

• Downforce - CLA, Drag – CDA and aero balance can be

defined as,

AeroRAeroF

AeroF

xD

AeroRAeroFZL

FF

Fawf

V

DragCAC

V

FFCAC

2

2

21

21

• Keep this in strict SI Units. Forces are in N, speed in m/s,

and density kg/m3 .

Using Race data to construct the Aeromap

• When a car is run on the race track it returns a thin sliver of

the aeromap

• If you don’t have ride height sensors these can be inferred by,

t

S

mk

Fw

i

i

m

s

i wMR

xd 2

2

43

0

210

ddrhrh

ddrhrh

rr

ff

Aeromap Test procedure • The following is suggested as a test matrix.

Run No Setup

1 frh0 and rrh0 + baseline rear wing

2 frh0 and rrh0 + d_rrh + baseline rear wing

3 frh0 and rrh0 + 2*d_rrh + baseline rear wing

4 frh0 and rrh0 + 3*d_rrh + baseline rear wing

5 frh0 – d_rrh and rrh0 + baseline rear wing

6 frh0 + d_rrh and rrh0 + baseline rear wing

7 frh0 and rrh0 + baseline rear wing

8 frh0 and rrh0 + baseline rear wing + 2 holes

9 frh0 and rrh0 + baseline rear wing + 3 holes

• Just to clarify the nomenclature we have, frh0 = Baseline front ride height as specified in the starting setup.

rrh0 = Baseline front ride height as specified in the starting setup.

d_rrh = delta rear ride height.

d_frh = delta front ride height.

Using the Aero Modelling toolbox • You create monster files from each of these runs.

• You then open the Aero toolbox in ChassisSim

• This generates a file called aero_analysis_results.dat

Tyre Modelling

The ChassisSim V3 Tyre Model –

Formulation • The mathematical formulation of the tyre model is shown

below

MAXzcambTCTZx

MAXzcambMTFyTZy

TMaxTZT

TZMAX

TZzcambMTMTMax

FFTFSRfnF

FFCTFfnF

MTFfnM

TFfnF

TFfnFCM

,,,

,,,

,,

),(

),(,

_

_

• For the time being we will focus on the lateral and

longitudinal forces. However the same techniques can

be applied to self aligning torque.

• Effectively this represents an approximation that is put into

a lookup table.

The ChassisSim Tyre Model quick start

• This is all summarised in the ChassisSim tyre model quick start.

• This is what you are going to use to refine the results.

Using the ChassisSim tyre quick start

• Adjusting the init long multiplier.

• Sample camber values

Car Type Lat Camb sensitivity Long Camb sensitivity

Open Wheeler 3 2

GT car 2 2

Sedan 0.5 – 1 0.5 - 1

The ChassisSim tyre force modelling toolbox

• This is the ChassisSim Tyre force Modelling toolbox

• Works off doing track replays comparing actual to simulated

lateral acceleration from looking at race data.

Creating advanced tyre models • Step – 1 – Create the 2D Model.

• Step – 2 – Optimise camber and slip settings

• Step – 3 – Tune in temperature characteristics in tyre

properties

• Step – 4 – Create the 3D Tyre model.

What to expect

• The end result of ChassisSim Tyre modelling.

Conclusion • Modelling tyres and aero from Race data can be done.

• It’s just a matter of procedure and being patient.

• Prepare the monster file and put in your setup.

• Aero – run the test matrix and then use the Aero

modelling toolbox.

• Tyre modelling – tyre quick start and then use the tyre

force modelling toolbox.