iRacing GT3 R Porsche 911 Racing Car User Manual
- June 5, 2024
- iRacing
Table of Contents
iRacing GT3 R Porsche 911 Racing Car User Manual
DEAR iRACING USER,
Congratulations on your purchase of the Porsche 911 GT3 R! From all of us at
iRacing, we appreciate your support and your commitment to our product. We aim
to deliver the ultimate sim racing experience, and we hope that you’ll find
plenty of excitement with us behind the wheel of your new car!
GT3s have proven to be some of the most popular road racing cars in the world in recent years, and few brands have quite the road racing pedigree of Porsche. It should stand as no surprise, then, that the Porsche 911 GT3 R is both a beloved and successful piece of kit. Immediately successful out of the gate thanks to a win in its first attempt at the Bathurst 12 Hour, you can find the 911 GT3 R running at the front of the field everywhere from the IMSA Weather Tech Sports Car Championship to the Intercontinental GT Challenge. The 4.0-liter flat-six boxer engine produces a whopping 543 horsepower, more than enough to propel you to the front of the pack
The following guide explains how to get the most out of your new car, from how to adjust its settings off of the track to what you’ll see inside of the cockpit while driving. We hope that you’ll find it useful in getting up to speed.
Thanks again for your purchase, and we’ll see you on the track!
Introduction
The information found in this guide is intended to provide a deeper understanding of the chassis setup adjustments available in the garage, so that you may use the garage to tune the chassis setup to your preference.
Before diving into chassis adjustments, though, it is best to become familiar with the car and track. To that end, we have provided baseline setups for each track commonly raced by these cars. To access the baseline setups, simply open the Garage, click iRacing Setups, and select the appropriate setup for your track of choice. If you are driving a track for which a dedicated baseline setup is not included, you may select a setup for a similar track to use as your baseline. After you have selected an appropriate setup, get on track and focus on making smooth and consistent laps, identifying the proper racing line and experiencing tire wear and handling trends over a number of laps.
Once you are confident that you are nearing your driving potential with the included baseline setups, read on to begin tuning the car to your handling preferences.
GETTING STARTED
Before starting the car, it is recommended to map controls for Brake Bias, Traction Control and ABS adjustments. While this is not mandatory to drive the car, this will allow you to make quick changes to the driver aid systems to suit your driving style while out on the track.
Once you load into the car, getting started is as easy as selecting the “upshift” button to put it into gear, and hitting the accelerator pedal. This car uses a sequential transmission and does not require a clutch input to shift in either direction. However, the car’s downshift protection will not allow you to downshift if you are traveling too fast for the gear selected and would incur engine damage. If that is the case, the gear change command will simply be ignored.
Upshifting is recommended at the illumination of the last two yellow shift lights on the dashboard. This is at approximately 9000 rpm.
LOADING AN iRACING SETUP
When you first load into a session, the iRacing Baseline setup will be automatically loaded onto the car. If you would like to try any of the other iRacing pre-built options, you may select it by going to Garage > iRacing Setups > and then selecting another option that fits your needs. Because this car uses slightly different chassis and body configurations on different types of tracks, it will be necessary to load a setup from the same track type to pass tech inspection. For example, a setup for Talladega will pass at Daytona, but likely will not pass at Bristol.
If you would like to customize the setup, simply make the changes in the garage that you would like to update and click apply. If you would like to save your setup for future use click “Save As” on the right to name and save the changes. To access all of your personally saved setups, click “My Setups” on the right side of the garage. If you would like to share a setup with another driver or everyone in a session, you can select “Share” on the right side of the garage to do so. If a driver is trying to share a setup with you, you will find it under “Shared Setups” on the right side of the garage as well.
Dash Pages
The digital dash display in this car features three selectable pages (Race 1, Race 2 and Qual) as well as numerous light clusters to convey critical information to the driver. Race 1 and Race 2 are largely identical aside from the upper left cluster; Race 1 uses this cluster to display critical engine parameters (oil temperature, oil pressure, water temperature and water pressure) while Race 2 uses this space to display relevant fuel calculations (fuel used this stint, fuel consumption per lap, fuel pressure and current fuel level). ‘Qual’ forgoes most of these detailed parameters and instead displays only lap time, predicted lap time and total fuel remaining.
RACE 1
ROW 1 LEFT
RACE 1 Currently selected dash page
DRY Currently fitted tire
HEADLIGHT ICON Current headlight setting (non-adjustable)
ROW 1 CENTER
NUMBER Currently vehicle speed (km/h or mph)
ROW 1 RIGHT
LAP Current session lap
AC-0 Currently selected A/C map (non-adjustable)
ROW 2 LEFT
OIL TEMP Engine oil temperature (°C or °F)
OIL PRESS Engine oil pressure (bar or psi)
WATER TEMP Engine water temperature (°C or °F)
WATER PRESS Engine water pressure (bar or psi)
ROW 2 CENTER
LARGE NUMBER Currently selected gear
ROW 2 RIGHT
LAP TIME Last lap time
TIME DIFF Difference to last lap
PRED LAP Predicted current lap time
ROW 3 LEFT
MAP-# Currently selected engine map
TH-S # Currently selected throttle map
S12-3 ensor backup function position (non-adjustable)
G12-6 Gearbox backup function position (non-adjustable)
ROW 3 CENTER
TYRE PRESS Tire Pressures (left front, right front, left rear, right rear)
ROW 4
MIL Malfunction indicator
ABS-# Currently selected ABS map
TC-C # Currently selected TCC map
TC-R # Currently selected TCR map
RACE 2
ROW 1 LEFT
RACE 2 Currently selected dash page
DRY Currently fitted tire
HEADLIGHT ICON Current headlight setting (non-adjustable)
ROW 1 CENTER
NUMBER Currently vehicle speed (km/h or mph)
ROW 1 RIGHT
LAP Current session lap
AC-0 Currently selected A/C map (non-adjustable)
ROW 2 LEFT
FUEL USED Fuel used (Litres or US gallons)
FUEL PER LAP Fuel used per lap (Litres or US gallons)
FUEL PRESS Fuel pressure (Bar or psi)
FUEL LEVEL Fuel remaining in the tank (Litres or US gallons)
ROW 2 CENTER
LARGE NUMBER Currently selected gear
ROW 2 RIGHT
LAP TIME Last lap time
TIME DIFF Difference to last lap
PRED LAP Predicted current lap time
ROW 3 LEFT
MAP-# Currently selected engine map
TH-S # Currently selected throttle map
S12-3 ensor backup function position (non-adjustable)
G12-6 Gearbox backup function position (non-adjustable)
ROW 3 CENTER
TYRE PRESS Tire Pressures (left front, right front, left rear, right rear)
ROW 4
MIL Malfunction indicator
ABS-# Currently selected ABS map
TC-C # Currently selected TCC map
TC-R # Currently selected TCR map
QUALI
ROW 1 LEFT
QUALI Currently selected dash page
DRY Currently fitted tire
HEADLIGHT ICON Current headlight setting (non-adjustable)
ROW 1 CENTER
NUMBER Currently vehicle speed (km/h or mph)
ROW 1 RIGHT
LAP Current session lap
AC-0 Currently selected A/C map (non-adjustable)
ROW 2 LEFT
LAP TIME Current session lap
FUEL LEVEL Fuel remaining in the tank (Litres or US gallons)
ROW 2 CENTER
LARGE NUMBER Currently selected gear
ROW 2 RIGHT
PREDICTED LAP TIME Predicted current lap time
ROW 3 LEFT
MAP-# Currently selected engine map
TH-S # Currently selected throttle map
S12-3 ensor backup function position (non-adjustable)
G12-6 Gearbox backup function position (non-adjustable)
ROW 3 CENTER
TYRE PRESS Tire Pressures (left front, right front, left rear, right rear)
ROW 4
MIL Malfunction indicator
ABS-# Currently selected ABS map
TC-C # Currently selected TCC map
TC-R # Currently selected TCR map
LOCKUP LIGHT CLUSTERS
When the front wheels lock, purple LED’s illuminate on two pods located on the instrument binnacle corresponding to the road wheel that’s locking (e.g. left side lights in purple indicate a front left lockup). The number of lights indicates the severity of the lockup, with one light being a minor lockup and four being severe. This light illumination behaviour is identical for the rear wheels with the exception that these are indicated by yellow LED illumination instead of purple.
TRACTION CONTROL ACTIVATION
When traction control is active all lights in the lockup light clusters illuminate in blue along with four lights on the digital display illuminating in purple.
PITLIMITER
When the pit limiter is active (and you are under the pit speed limit) a large green box that includes the current road speed will display across the top of the dashboard while the left and right lockup light clusters will also illuminate completely in green. Should you be above the pit speed limit the green box will switch to orange.
SHIFT LIGHTS
ADVANCED SETUP OPTIONS
This section is aimed toward more advanced users who want to dive deeper into
the different aspects of the vehicle’s setup. Making adjustments to the
following parameters is not required and can lead to significant changes in
the way a vehicle handles. It is recommended that any adjustments are made in
an incremental fashion and only singular variables are adjusted before testing
changes.
Tires & Aero
TIRE SETTINGS
COLD AIR PRESSURE
Air pressure in the tire when the car is loaded into the world. Higher
pressures will reduce rolling drag and heat build-up, but will decrease grip.
Lower pressures will increase rolling drag and heat build-up, but will
increase grip. Higher speeds and loads require higher pressures, while lower
speeds and loads will see better performance from lower pressures. Cold
pressures should be set to track characteristics for optimum performance.
Generally speaking, it is advisable to start at lower pressures and work your
way upwards as required.
HOT AIR PRESSURE
Air pressure in the tire after the car has returned to the pits. The
difference between cold and hot pressures can be used to identify how the car
is progressing through a run in terms of balance, with heavier-loaded tires
seeing a larger difference between cold and hot pressures. Ideally, tires that
are worked in a similar way should build pressure at the same rate to prevent
a change in handling balance over the life of the tire, so cold pressures
should be adjusted to ensure that similar tires are at similar pressures once
up to operating temperature. Hot pressures should be analysed once the tires
have stabilised after a period of laps. As the number of laps per run will
vary depending upon track length a good starting point is approximately 50% of
a full fuel run.
TIRE TEMPERATURES
Tire carcass temperatures, measured via Pyrometer, once the car has returned
to the pits. Wheel Loads and the amount of work a tire is doing on-track are
reflected in the tire’s temperature, and these values can be used to analyse
the car’s handling balance. Center temperatures are useful for directly
comparing the work done by each tire, while the Inner and Outer temperatures
are useful for analysing the wheel alignment (predominantly camber) while on
track. These values are measured in three zones across
the tread of the tire. Inside, Middle and Outer.
TREAD REMAINING
The amount of tread remaining on the tire once the car has returned to the
pits. Tire wear is very helpful in identifying any possible issues with
alignment, such as one side of the tire wearing excessively, and can be used
in conjunction with tire temperatures to analyse the car’s handling balance.
These values are measured in the same zones as those of temperature.
AERO CALCULATOR
The Aero Calculator is a tool provided to aid in understanding the shift in aerodynamic balance associated with adjustment of the rear wing setting and front and rear rideheigh ts. It is important to note that the values for front and rear ride height displayed here DO NOT result in any mechanical changes to the car itself, however, changes to the rear wing angle here WILL be applied to the car. This calculator is a reference tool ONLY.
FRONT RH AT SPEED
The Ride Height (RH) at Speed is used to give the Aero Calculator heights to
reference for aerodynamic calculations. When using the aero calculator,
determine the car’s Front Ride height via telemetry at any point on track and
input that value into the “Front RH at Speed” setting. It is advisable to use
an average value of the LF and RF ride heights as this will provide a more
accurate representation of the current aero platform rather than using a
single corner height.
REAR RH AT SPEED
The Ride Height (RH) at Speed is used to give the Aero Calculator heights to
reference for aerodynamic calculations. When using the aero calculator,
determine the car’s Rear Ride height via telemetry at any point on track and
input that value into the “Front RH at Speed” setting. It is advisable to use
an average value of the LR and RR ride heights as this will provide a more
accurate representation of the current aero platform rather than using a
single corner height.
WING SETTING
The wing setting refers to the relative angle of attack of the rear wing, this
is a powerful aerodynamic device which has a significant impact upon the total
downforce (and drag!) produced by the car as well as shifting the aerodynamic
balance of the car rearwards with increasing angle. Increasing the rear wing
angle results in more total cornering grip capability in medium to high speed
corners but will also result in a reduction of straight line speed. Rear wing
angle should be adjusted in conjunction with front and rear ride heights,
specifically the difference between front and rear ride heights known as
‘rake’. To retain the same overall aerodynamic balance it is necessary to
increase the rake of the car when increasing the rear wing angle.
FRONT DOWNFORCE
This value displays the proportion of downforce acting at the front axle for
the given wing and ride height combination set within the calculator
parameters. This value is an instantaneous representation of your aero balance
at this exact set of parameters and it can be helpful to pick multiple points
around a corner or section of track to understand how the aerodynamic balance
is moving in differing situations such as braking, steady state cornering and
accelerating at corner exit. A higher forwards percentage will result in more
oversteer in mid to high speed corners.
Chassis
FRONT
ARB BLADES
The configuration of the Anti-Roll Bar arms, or “blades”, can be changed to
alter the overall stiffness of the ARB assembly. Higher values transfer more
force through the arms to the ARB itself, increasing roll stiffness in the
front suspension and producing the same effects, albeit on a smaller scale, as
increasing the diameter of the sway bar. Conversely, lower values reduce the
roll stiffness of the front suspension and produce the same effects as
decreasing the diameter of the sway bar. These blade adjustments can be
thought of as fine-tuning adjustments between sway bar diameter settings. 3
ARB blade options are available ranging from soft to hard.
ARB OUTER DIAMETER
The ARB (Anti-Roll Bar) size influences the stiffness of the front suspension
in roll, such as when navigating a corner. Increasing the ARB size will
increase the roll stiffness of the front suspension, resulting in less body
roll but increasing mechanical understeer. This can also, in some cases, lead
to a more responsive steering feel from the driver. Conversely, reducing the
ARB size will soften the suspension in roll, increasing body roll but
decreasing mechanical understeer. This can result in a less-responsive feel
from the steering, but grip across the front axle will increase. Along with
this, the effects of softening or stiffening the ARB in relation to
aerodynamics should also be considered, smaller and hence softer ARB’s will
result in more body roll which will decrease control of the aero platform in
high speed corners and potentially lead to a loss in aero efficiency. 2
configurations of ARB diameter are available; 35 mm (softest) and 45 mm
(stiffest).
TOE-IN
Toe is the angle of the wheel, when viewed from above, relative to the
centreline of the chassis. Toe-in is when the front of the wheel is closer to
the centreline than the rear of the wheel, and Toe-out is the opposite. On the
front end, adding toe-out will increase slip in the inside tire while adding
toe-in will reduce the slip. This can be used to increase straight-line
stability and turn-in responsiveness with toe-out. Toe-in at the front will
reduce turn-in responsiveness but will reduce temperature build-up in the
front tires.
FRONT MASTER CYLINDER
The Front Brake Master Cylinder size can be changed to alter the line pressure
to the front brake callipers. A larger master cylinder will reduce the line
pressure to the front brakes, this will shift the brake bias rearwards and
increase the pedal effort required to lock the front wheels. A smaller master
cylinder will do the opposite and increase brake line pressure to the front
brakes, shifting brake bias forward and reducing required pedal effort. 7
Different master cylinder options are available ranging from 15.9 mm / 0.626”
(highest line pressure) to 23.8 mm / 0.937” (lowest line pressure).
REAR MASTER CYLINDER
The Rear Brake Master Cylinder size can be changed to alter the line pressure
to the rear brake calipers. A larger master cylinder will reduce the line
pressure to the rear brakes, this will shift the brake bias forwards and
increase the pedal effort required to lock the rear wheels. A smaller master
cylinder will do the opposite and increase brake line pressure to the rear
brakes, shifting brake bias rearward and reducing required pedal effort. 7
Different master cylinder options are available ranging from 15.9 mm / 0.626”
(highest line pressure) to 23.8 mm / 0.937” (lowest line pressure).
BRAKE PADS
The vehicle’s braking performance can be altered via the Brake Pad Compound.
The “Low” setting provides the least friction, reducing the effectiveness of
the brakes, while “Medium” and “High” provide more friction and increase the
effectiveness of the brakes while increasing the risk of a brake lockup.
FUEL LEVEL
The amount of fuel in the fuel tank. Tank capacity is 120 L (31.7 g).
Adjustable in 1 L (0.26 g) increments.
CROSS WEIGHT
The percentage of total vehicle weight in the garage acting across the right
front and left rear corners. 50.0% is generally optimal
for non-oval tracks as this will produce symmetrical handling in both left and
right hand corners providing all other chassis settings are symmetrical.
Higher than 50% cross weight will result in more understeer in left hand
corners and increased oversteer in right hand corners, cross weight can be
adjusted by making changes to the spring perch offsets at each corner of the
car.
IN-CAR DIALS
DISPLAY PAGE
Changes the currently selected digital dash page. 3 options are available,
Race 1, Race 2 and Qual as previously described in the dash configuration
section of this manual.
BRAKE PRESSURE BIAS
Brake Bias is the percentage of braking force that is being sent to the front
brakes. Values above 50% result in greater pressure in the front brake line
relative to the rear brake line which will shift the brake balance forwards
increasing the tendency to lock up the front tyres but potentially increasing
overall stability in braking zones. This should be tuned for both driver
preference and track conditions to get the optimum braking performance for a
given situation. It is important to note that differing combinations of master
cylinder size will necessitate differing brake pressure bias values, this is
because increasing or reducing the split in master cylinder size difference
between front and rear axles will produce an inherent forward or rearward bias
in brake line pressure.
TRACTION CONTROL SETTING (TCC)
The position of this traction control switch determines how aggressively the
ecu cuts engine torque in reaction to rear wheel spin. 12 positions are
available. Settings 1-11 range from least intervention/sensitivity (position
- through to highest intervention/ sensitivity (position 11). Position 0 disables the traction control completely. Position 5 is the recommended baseline setting. More intervention will result in less wheelspin and less rear tire wear but can reduce overall performance if the traction control is cutting engine torque too aggressively and stunting corner exit acceleration.
TRACTION CONTROL SETTING (TCR)
The position of this traction control switch determines the slip sensitivity
of the traction control (how much slip is allowable before torque cut is
implemented) rather than the overall intervention strength. Settings 0-11
range from least slip sensitivity (position 0) to most slip sensitivity
(position 11). Position 0 does NOT disable the traction control as it does
with the TCC setting. Position 5 is the recommended baseline setting.
THROTTLE MAP SETTING
Throttle map setting refers to how changes in the drivers pedal position
result in changes in provided engine torque. 5 positions exist, position 4
results in a linear torque map relative to throttle position (e.g. 10%
throttle position results in 10% engine torque, 50% throttle position results
in 50% engine torque and so on.). Position 0 emulates a non-linear S-shaped
map similar to a cable throttle which results in reduced fidelity in the
middle portion of the throttle range. Positions 1-3 are hybrids of the
position 0 and 4 throttle mapping styles.
ABS SETTING
The current ABS map the car is running. 12 positions are available but only 10
maps exist. Position 1 has the least intervention/ support while position 10
has the most support. Position 10 is the same as position 11 and position 0
disables the ABS completely. Position 4 is the recommended baseline setting.
More intervention reduces the possibility of and the duration of lockups
during braking but can result in longer braking distances if the system is set
overly aggressive for the amount of available grip.
ENGINE MAP SETTING
The fuel map on which the car is currently running. Position 4 is the base map
and produces maximum power but the most fuel usage. Positions 3 through 2 are
for fuel saving under green flag conditions and will reduce engine power
output correspondingly. The lower the number the better the fuel economy but
the lower the power output. Positions 1 and 0 are for saving fuel under safety
car conditions and are not recommended for normal usage.
FRONT CORNERS
CORNER WEIGHT
The weight underneath each tire under static conditions in the garage. Correct
weight arrangement around the car is crucial for optimizing a car for a given
track and conditions. Individual wheel weight adjustments and cross weight
adjustments are made via the spring perch offset adjustments at each corner.
FRONT RIDE HEIGHT
Distance from ground to a reference point on the chassis. Since these values
are measured to a specific reference point on the car, these values may not
necessarily reflect the vehicle’s ground clearance, but instead provide a
reliable value for the height of the car off of the race track at static
values. Adjusting Ride Heights is key for optimum performance, as they can
directly influence the vehicle’s aerodynamic performance as well as mechanical
grip. Increasing front ride height will decrease front downforce as well as
decrease overall downforce, but will allow for more weight transfer across the
front axle when cornering. Conversely, reducing ride height will increase
front and overall downforce, but reduce the weight transfer across the front
axle. Minimum legal front ride height is 50.0 mm.
SPRING PERCH OFFSET
Used to adjust the ride height at this corner of the car by changing the
installed position of the spring. Increasing the spring perch offset will
result in lowering this corner of the car while reducing the spring perch
offset will raise this corner of the car. These changes should be kept
symmetrical across the axle (left to right) to ensure the same corner ride
heights and no change in cross weight. The spring perch offsets can also be
used in diagonal pairs (LF to RR and RF to LR) to change the static cross
weight in the car.
SPRING SELECTED/SPRING RATE
This setting determines the installed corner spring stiffness. Stiffer springs
will result in a smaller variance in ride height between high and low load
cases and will produce superior aerodynamic performance through improved
platform control; however, they will also result in increased tire load
variation which will manifest as a loss in mechanical grip. Typically the
drawbacks of stiffer springs will become more pronounced on rougher tracks and
softer springs in these situations will result in increased overall
performance. Corner spring changes will influence both roll and pitch control
of the platform and ARB changes should be considered when altering corner
spring stiffness’s in order to retain the same front to rear roll stiffness
and overall balance. When reducing corner spring stiffness the ARB stiffness
(either via blade or diameter depending on the size of the corner spring
change) should be increased to retain the same roll stiffness as previously.
11 options for spring rate are available ranging from 200 N/mm (1371 lbs/in)
to 400 N/mm (2286 lbs/in) in 20 N/mm (114 lbs/in) steps. Spring perch offsets
must be adjusted to return the car to the prior static ride heights after any
spring rate change.
LS COMP DAMPING
Low speed compression affects how resistant the shock is to compresion
(reduction in length) when the shock is moving at relatively low speeds,
usually in chassis movements as a result of driver input (steering, braking, &
throttle) and cornering forces. In this case -24 is minimum damping (least
resistance to compression) while 0 is maximum damping (most resistance to
compression). Increasing the low speed compression damping will result in a
faster transfer of weight to this corner of the car during transient movements
such as braking and direction change with increased damping usually providing
an increase in turn-in response but a reduction in overall grip in the context
of front dampers.
HS COMP DAMPING
High speed compression affects the shock’s behavior in high speed travel,
usually attributed to curb strikes and bumps in the track’s surface. Higher
compression values will cause the suspension to be stiffer in these
situations, while lower values will allow the suspension to absorb these bumps
better but may hurt the aerodynamic platform around the track. At smoother
tracks more high speed compression damping will typically increase performance
while at rougher tracks or ones with aggressive kerbs less high speed
compression damping can result in an increase in mechanical grip at the
expense of platform control. 0 is maximum damping while -24 is minimum
damping.
LS RBD DAMPING
Low speed rebound damping controls the stiffness of the shock while extending
at lower speeds, typically during body movement
as a result of driver inputs. Higher rebound values will resist expansion of
the shock, lower values will allow the shock to extend faster. Higher rebound
values can better control aerodynamic attitude but can result in the wheel
being unloaded when the suspension can’t expand enough to maintain proper
contact with the track. When tuning for handling, higher front low speed
rebound can increase on-throttle mechanical understeer (but reduce nose lift)
while lower values will maintain front end grip longer, helping to reduce
understeer, but will allow more splitter lift. Excessive front rebound can
lead to unwanted oscillations due to the wheel bouncing off of the track
surface instead of staying in contact. 0 is maximum damping (most resistant to
extension) while -24 is minimum damping (least resistance to extension).
HS RBD DAMPING:
High-speed rebound adjusts the shock in extension over bumps and curb strikes.
Higher values will reduce how quickly the shock will expand, while lower
values will allow the shock to extend more easily. Despite not having as much
of an effect on handling in result to driver inputs, High-speed rebound can
produce similar results in terms of aerodynamic control and uncontrolled
oscillations if set improperly. 0 is maximum damping while -24 is minimum
damping.
CAMBER
Camber is the vertical angle of the wheel relative to the center of the
chassis. Negative camber is when the top of the wheel is closer to the chassis
centerline than the bottom of the wheel, positive camber is when the top of
the tire is farther out than the bottom. Due to suspension geometry and corner
loads, negative camber is desired on all four wheels. Higher negative camber
values will increase the cornering force generated by the tire, but will
reduce the amount of longitudinal grip the tire will have under braking.
Excessive camber values can produce very high cornering forces but will also
significantly reduce tire life, so it is important to find a balance between
life and performance. Increasing front camber values will typically result in
increased front axle grip during mid to high speed cornering but will result
in a loss of braking performance and necessitate a rearward shift in brake
bias to compensate.
CASTER
Caster is the vertical angle of the steering axis relative to the side view of
the chassis. Positive caster angle is where the steering axis is leaned
rearwards from this viewpoint, the more caster the larger the total trail of
the contact patch behind the steering axis. More caster angle will result in
the mechanical trail being a larger proportion of the felt steering weight
relative to the tires pneumatic trail. This will result in a heavier overall
steering feel but a possible loss in felt feedback from the tire. Increasing
caster angle will also have secondary effects such as an increase in dynamic
camber when turning the wheel through large steering angles which can be
beneficial in chicances or hairpins. As well as this the more caster angle the
greater the jacking effect during cornering which will result in lifting the
inside front wheel while lowering the outside front wheel. This jacking effect
will also result in the unloading and potentially lifting of the inside rear
wheel which can aid in rotation around tight corners.
REAR CORNERS
REAR RIDE HEIGHT
Distance from ground to a reference point on the rear of the chassis.
Increasing rear ride height will decrease rear downforce
as well as increase overall downforce and will allow for more weight transfer
across the rear axle when cornering. Conversely,
reducing ride height will increase rear downforce percentage but reduce
overall downforce while reducing the weight transfer
across the rear axle. Rear ride height is a critical tuning component for both
mechanical and aerodynamic balance considerations and static rear ride heights
should be considered and matched to the chosen rear corner springs for optimal
performance. Minimum legal rear ride height is 50.0 mm while maximum legal
rear ride height is 87.5 mm.
SPRING SELECTED/SPRING RATE
Similar to at the front axle, stiffer springs will result in a smaller
variance in ride height between high and low load cases and will
produce superior aerodynamic performance through improved platform control at
the expense of mechanical grip. This can be
particularly prominent when exiting slow speed corners with aggressive
throttle application. Stiffer springs will tend to react
poorly during these instances especially so on rough tracks which will result
in significant traction loss. Spring stiffness should
be matched to the needs of the racetrack and set such that the handling
balance is consistent between high and low speed
cornering. As an example case, a car which suffers from high speed understeer
but low speed oversteer could benefit from an
increase in rear spring stiffness. This will allow for a lower static rear
height which will reduce rear weight transfer during slow
speed cornering while maintaining or even increasing the rear ride height in
high speed cornering to shift the aerodynamic balance forwards and reduce
understeer.11 options for spring rate are available ranging from 200 N/mm
(1371 lbs/in) to 400 N/mm (2286 lbs/in) in 20 N/mm (114 lbs/in) steps. Spring
perch offsets must be adjusted to return the car to the prior static ride
heights after any spring rate change.
LS COMP DAMPING
Low speed compression affects how resistant the shock is to compresion
(reduction in length) when the shock is moving at
relatively low speeds, usually in chassis movements as a result of driver
input (steering, braking, & throttle) and cornering forces. In this case -24
is minimum damping (least resistance to compression) while 0 is maximum
damping (most resistance to compression). Increasing the low speed compression
damping will result in a faster transfer of weight to this corner of the car
during transient movements such as braking and direction change with increased
damping usually increasing the cars tendency to
understeer on throttle application.
HS COMP DAMPING
High speed compression affects the shock’s behaviour in high speed travel,
usually attributed to curb strikes and bumps in the
track’s surface. Higher compression values will cause the suspension to be
stiffer in these situations, while lower values will allow the suspension to
absorb these bumps better but may hurt the aerodynamic platform around the
track. At smoother tracks more high speed compression damping will typically
increase performance while at rougher tracks or ones with aggressive kerbs
less high speed compression damping can result in an increase in mechanical
grip at the expense of platform control. 0 is maximum damping while -24 is
minimum damping.
LS RBD DAMPING
Low speed rebound damping controls the stiffness of the shock while extending
at lower speeds, typically during body movement
as a result of driver inputs. Higher rebound values will resist expansion of
the shock, lower values will allow the shock to extend faster. As at the
front, high rebound stiffness will result in improved platform control for
aerodynamic performance and overall chassis response but it is important to
avoid situations where the shock is too slow in rebounding as this can result
in the tire losing complete contact with the track surface. Provided this is
avoided,, an increase in rebound stiffness can help to ‘slow down’ the change
in pitch of the car as the brakes are applied, increasing braking stability
and off-throttle mechanical understeer. 0 is maximum damping (most resistant
to extension) while -24 is minimum damping (least resistance to extension)
HS RBD DAMPING:
High-speed rebound adjusts the shock in extension over bumps and curb strikes.
Higher values will reduce how quickly the shock
will expand, while lower values will allow the shock to extend more easily.
Despite not having as much of an effect on handling
in result to driver inputs, High-speed rebound can produce similar results in
terms of aerodynamic control and uncontrolled
oscillations if set improperly. 0 is maximum damping while -24 is minimum
damping.
CAMBER
As at the front of the car it is desirable to run significant amounts of
negative camber in order to increase the lateral grip capability; however, it
is typical to run slightly reduced rear camber relative to the front. This is
primarily for two reasons, firstly, the rear tires are 25 mm (~1”) wider
compared to the fronts and secondly the rear tires must also perform the duty
of driving the car forwards where benefits of camber to lateral grip become a
trade off against reduced longitudinal (traction) performance.
TOE-IN
At the rear of the car it is typical to run toe-in. Increases in toe-in will
result in improved straight line stability and a reduction
in response during direction changes. Large values of toe-in should be avoided
if possible as this will increase rolling drag and
reduce straight line speeds. When making rear toe changes remember that the
values are for each individual wheel as opposed to paired as at the front.
This means that individual values on the rear wheels are twice as powerful as
the combined adjustment at the front of the car when the rear toes are summed
together. Generally, it is advised to keep the left and right toe values equal
to prevent crabbing or asymmetric handling behaviour; however, heavily
asymmetric tracks such as Lime Rock Park may see a benefit in performance from
running asymmetric configurations of rear toe and other setup parameters.
REAR
ARB BLADES
The configuration of the Anti-Roll Bar arms, or “blades”, can be changed to
alter the overall stiffness of the ARB assembly. Higher values transfer more
force through the arms to the ARB itself, increasing roll stiffness in the
rear suspension and producing the same effects, albeit on a smaller scale, as
increasing the diameter of the sway bar. Conversely, lower values reduce the
roll stiffness of the rear suspension and produce the same effects as
decreasing the diameter of the sway bar. These blade adjustments can be
thought of as fine-tuning adjustments between sway bar diameter settings. 3
ARB blade options are available ranging from soft to hard.
ARB OUTER DIAMETER
The ARB (Anti-Roll Bar) size influences the stiffness of the rear suspension
in roll, such as when navigating a corner. Increasing the ARB size will
increase the roll stiffness of the rear suspension, resulting in less body
roll but increasing mechanical oversteer. This can also cause the car to “take
a set” more quickly at initial turn-in. Conversely, reducing the ARB size will
soften the suspension in roll, increasing body roll but decreasing mechanical
oversteer. This can result in a less-responsive feel from the rear especially
in transient movements, but grip across the rear axle will increase. 2
configurations of ARB diameter are available; 35 mm (softest) and 45 mm
(stiffest).
DIFF PRELOAD
Diff preload is a static amount of locking force present within the
differential and remains constant during both acceleration and deceleration.
Increasing diff preload will increase locking on both sides of the
differential which will result in more understeer when off throttle and more
snap oversteer with aggressive throttle application. Increasing the diff
preload will also smooth the transition between on and off throttle behaviour
as the differential locking force will never reach zero which can be helpful
in reducing lift-off oversteer and increasing driver confidence. Typically
diff preload should be increased when there is noticeable loss in slow corner
exit drive and/or over-rotation during transition between the throttle and
brake in low to mid speed corners.