Geoff Dymott

Former Senior Performance Engineer

Williams Racing
Ride, Ride Analysis and Simulation
© MIA 2023
© MIA 2023
 Introduction
This presentation will cover the subject of ride, one of the big
compromises for motorsport suspension design and set-up.

We’ll try to cover the following areas:

• The ride and handling compromise

• Damper fundamentals
• Ride simulation and analysis

© MIA 2023
 Ride Compromise 1
All racing cars are set up to be stiff, why?
• Driver feel and speed of response
• Elimination of free play and friction
• Static and dynamic control of centre of gravity
• Aerodynamic platform control

Quiz: which do you think is the most important?

© MIA 2023
 Spring Types
Springs and bump rubbers have a first
order affect on ride, but they are largely
selected from a handling and aerodynamic
point of view first.

Ride considerations do come into things,

but are very track specific. Monaco
traditionally will require very soft springs,
but even this is changing in modern
motorsport.

© MIA 2023
 Ride Compromise 2
So why do we care about ride?
• Contact patch load control
• Aerodynamic sensitivities
• Vibration and shock
• Circuit characteristics and shortest trajectory
• Occupant comfort and NVH

Quiz: which do you think is the most important for improving your
lap time?

© MIA 2023
 Ride Systems
In more open regulations, F1 in particular has come up with a
range of novel solutions to the ride/handling/aero compromise.
• Mass dampers (Renault 2006)
• Inerters (McLaren 2005)
• Warp soft suspension (Williams 2008)
• Pitch links & FRIC (Lotus 2011, Mercedes 2011)
• Active suspension (Lotus 1983, Williams 1987 & 1992)
Inerters are banned as of 2022 regulations, so none are now legal.

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 Damper Types
There are two main types of racing damper, depending on series.
Standalone Coilover
with or without remote reservoir with or without remote reservoir
with or without adjusters with or without adjusters

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 Damper Internals
Dampers basically operate by flowing fluid through orifices. The
size and speeds at which these open determine the curve.
Remote reservoir
and gas chamber

Pressurisation valve

Foot valve
Rod/shaft Piston and
valves/shims

© MIA 2023
 Damper Testing
In series that allow custom dampers, all teams will spend a lot of time tuning
them. Testing is done on a damper dyno, a dedicated single axis test rig.

They may be crank-driven via electric motor (the cheaper type usually seen)
or hydraulic. The latter allows track playback and more complex testing.

© MIA 2023
 Damper Curves 1
Typically, the low speed region is for
body control, including for handling, the
high speed region for wheel control.

Simplest form is a linear relationship.

More usual is a curve with a nose and
more bump than rebound.

Some dampers have an acceleration or

force based blow-off that removes high
speed damping.

© MIA 2023
 Damper Curves 2
If adjustable, there are up to 6 adjusters.
LS & HS bump, rebound and blow-off.
They may also be position dependent.

Adjusting LS affects the nose region (and

usually the HS region too).

Adjusting HS usually just removes peak

damping at the higher velocities.

Curves are set on a damper dyno and are

usually temperature compensated.
© MIA 2023
 Ride Analysis
Ride analysis is notoriously difficult on track.
• Damper adjustments are usually very small (assuming they are
starting from a sensible working window).
• Driver lines, kerb strikes are not at all repeatable.
• Track evolution and tyre age makes lap time comparisons hard.
• Rare to get back to back runs with just a damper change
Any analysis carried out is usually in the form of pushrod load,
damper displacement and upright/chassis accelerometer data.

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4- and 7-Post Rigs
Hydraulic test rigs with four
wheel actuators and up to
four aero load actuators.

Capable of lap replay of

displacement to the four
wheels whilst applying
braking, cornering and aero
loads on the body.

Aero load can be constant or

using an aero map look-up.
© MIA 2023
 Design Verification
Rigs and cars are fully instrumented:

Pushrod loads
Damper displacement
Upright and body accelerometers
Rig contact patch loads
Ride heights

Can be used to verify motion ratios,

spring and damper rates/function and
other physical characteristics.
© MIA 2023
 Frequency Sweep 1

The first dynamic test mode is the frequency sweep. Usually this is a swept
sine wave with a constant aero load. The sweep typically covers 0-40Hz and
reduces in displacement amplitude as the frequency increases (constant
velocity), this mimics typical track imperfections.
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 Frequency Sweep 2

Results are analysed in the frequency domain as transfer functions or power

spectral density (PSD). Usually taking peak values or areas under curve.
These allow direct comparison of all aspects of spring and damper set-ups
and comparison across cars/years/series. © MIA 2023
 Frequency Sweep 3

Test plans can be devised to sweep regions of

damper set-up or spring rate to try to establish
optima or trade-offs.

Care needs to be taken with aero cars, they often

have non-linearities in set-up that require you to
be sure in which section you are running.

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 Lap Replay 1
Using a 7PR, it is possible to carry out a multi-dimensional
system identification process to reverse engineer logged data
on the rig to generate rig actuator inputs (Servotest ICS or
equivalent software).

Playback of these inputs gives repeatable track replay so that

small changes can be analysed.

Analysis is usually in the form of rms values for high pass

filtered contact patch load fluctuations and various
displacements, tracked over a range of set-up changes and
different track segments.
© MIA 2023
 Lap Replay 2
250 1
For analysis, track is
200
divided into segments
or distance chunks.
CAR SPEED [kph]

150

SEGMENT
100 These can be
50
subdivided into
0 0
entry/mid/exit, HS/LS.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
TIME INTO LAP [s]

3
BASELINE SETUP 1 Loads, displacements,
2
accelerations are high-
CHASSIS VERTICAL ACCELERATION [g]

1 or low-pass filtered
0 and processed into
-1
average, standard
-2
deviation or RMS
-3
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
TIME INTO LAP [s] values.
© MIA 2023
 Lap Replay 3
BASELINE SETUP 1

3
SEGMENT RMS VALUES
BASELINE SETUP 1 %CHANGE

2
1.2 1.50
1.1 1.25
1.0 1.00
CHASSIS VERTICAL ACCELERATION [g]

1
0.9 0.75
0.8 0.50

% CAHNGE
0
0.7 0.25

RMS
0.6 0.00
0.5 -0.25
-1 0.4 -0.50
0.3 -0.75
0.2 -1.00
-2
0.1 -1.25
0.0 -1.50
-3 1 2 3 4 5 6 7 8
3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7 7.1 7.2 7.3
TIME INTO LAP [s]
SEGMENT

If testing is carried out well, very small changes in parameters can be

measured. Have to be careful with repeatability due to temperature etc.

Set-ups can be compared visually. It is rare for them to be better everywhere.

The best compromise is required unless one corner is a problem.
© MIA 2023
 Ride Modelling
Increasingly, physical testing is being
replaced by modelling. If correctly
correlated, this can be very accurate and
much cheaper to do. A fully built car can be
hard to get your hands on!

This can be simpler parameterised mass-

spring-damper half- or full-car models or
using full multi-body simulation.

Results are often derived from similar test

programmes as used for physical testing.

© MIA 2023
 Simulators
The use of simulators in ride development
is an interesting topic.

The use of highly accurate laser scanned

track surfaces means that the model inputs
for kerbs and surface roughness can be
very good.

But motion systems may not have a wide

enough frequency range to replicate them
and the problems of driving line replication
and subjective driver comments return.

© MIA 2023
 K&C and CofG Testing
Some expensive vehicle dynamics rigs are used
too little to warrant the purchase cost. Teams
will go to external sites for this.
https://cranfieldimpactcentre.co.uk/moment-of-inertia-and-centre-of-gravity/
Two examples are K&C testing and moment of
inertia/centre of gravity testing.

These rigs are used for parameterisation and

correlation of vehicle models, to check
geometry and to ensure that the car is within
stiffness limits.

https://www.horiba-mira.com/facilities/kinematics-compliance-facility/

© MIA 2023
 Further Reading
Damper Tuning with the use of a Seven Post Shaker Rig
SAE 2002-01-0804

An Investigation of the Influence of High Performance Dampers on

the Suspension Performance of a Quarter Vehicle
SAE 962552

Shock Absorber Handbook, John C Dixon

https://onlinelibrary.wiley.com/doi/book/10.1002/9780470516430

© MIA 2023
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