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.
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