iRacing BMW M4 GT3 Racing Car User Manual
- June 12, 2024
- iRacing
Table of Contents
iRacing BMW M4 GT3 Racing Car
BMW M4 GT3 User Manual
General Information
- Chassis: Independent double wishbone suspension front and rear
- Length: 5014 mm (197.4 in)
- Width: 2022 mm (79.6 in)
- Wheelbase: 2916 mm (114.8 in)
- Dry Weight: 1285 kg (2833 lbs)
- Wet Weight with Driver: 1411 kg (3111 lbs)
- Power Unit: Turbocharged inline-6
- Displacement: 3.0 Liters (182.6 cid)
- Torque: 475 lb-ft (644 Nm)
- Power: 500 bhp (373 kW)
- RPM Limit: 7000
Introduction:
The BMW M4 GT3 is a pre-release version of the BMW M4 GT3 that will be made available to iRacing members in the weeks after the 2021 Season 1 build. It is the second BMW to join iRacing’s GT3 offerings, succeeding the BMW Z4 GT3. The car will compete in GT3 series around the world and will also run in iRacing’s corresponding official series and special events.
Getting Started:
- Before starting the car, it is recommended to map controls for Brake Bias, Traction Control, and ABS adjustments. While not mandatory, this will allow you to make quick changes to the driver aid systems to suit your driving style while on the track.
- To start the car, select the upshift button to put it into gear and hit the accelerator pedal. The BMW M4 GT3 uses a sequential transmission and does not require a clutch input to shift in either direction. However, the car’s downshift protection will prevent downshifting if it senses you are traveling too fast for the selected gear to avoid engine damage. In such cases, the gear change command will be ignored.
- Upshifting is recommended when the shift lights on the dashboard are fully illuminated in red, which typically occurs at around 6750 rpm depending on the selected gear.
Dear iRacing User,
Congratulations on your purchase of the BMW M4 GT3! 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!
iRacing’s renewed focus on GT3 content continues with an early release of the
BMW M4 GT3 that will make its real-world racing debut in 2021. Revealed at BMW
Sim Live in early December, the new car will compete in GT3 series around the
world in the coming years, and will also run in iRacing’s corresponding
official series and special events.
The BMW M4 GT3 is a pre-release version of the BMW M4 GT3 that will be made
available to iRacing members in the weeks after the 2021 Season 1 build. The
car succeeds the BMW Z4 GT3 as the second BMW to join iRacing’s GT3 offerings.
In the coming months, the in-development car will shed the Beta label for all
members, receiving a comprehensive set of updates to match its final real-
world form.
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 it feels 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 when the shift lights on the dashboard are fully
illuminated in red. This is at approximately 6750 rpm depending on the
selected gear.
LOADING AN i RACING SETUP
Upon loading into a session, the car will automatically load the racing
Baseline setup [baseline. To]. If you would prefer one of racing’s pre-built
setups that suit various conditions, you may load it by clicking Garage >
racing Setups > and then selecting the setup to suit your needs.
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 dash display in this car is non-adjustable and features a single page to display critical vehicle information.
DASH CONFIGURATION (PAGE 1)
-
Left of Display
Traction control intervention indicators for the left rear tire. One light (green) is minor intervention increasing to five lights (red) indicating severe intervention -
Right of Display
Traction control intervention indicators for the left rear tire. One light (green) is minor intervention increasing to five lights (red) indicating severe intervention -
Row 1 Left Left front tire pressure (kPa or psi)
-
Row 1 Second from Left Right front tire pressure (kPa or psi)
-
Row 1 Center Currently selected gear
-
Row 1 Fourth from Right Currently selected engine map
-
Row 1 Third from Right Gearbox oil temperature (Celsius or Fahrenheit)
-
Row 1 Second from Right Currently selected traction control map
-
Row 1 Right Currently selected ABS map
-
Row 2 Left Left rear tire pressure (kPa or psi)
-
Row 2 Second from left Right rear tire pressure (kPa or psi)
-
Row 2 Right Gain/loss in seconds to best lap
-
Row 3 Left Fuel used last lap in kg
-
Row 3 Center Speed in km/h or mph
-
Row 3 Right Last lap time
-
Row 4 Left Remaining fuel in kg
-
Row 4 Center Current engine rpm
-
Row 4 Second from Right Current lap
-
Row 4 Right Current brake pressure bias (%)
-
Row 5 Left Current engine water temperature (Celsius or Fahrenheit)
-
Row 5 Second from left Current engine oil temperature (Celsius or Fahrenheit)
-
Row 5 Third from left Current gearbox oil temperature (Celsius or Fahrenheit)
-
Row 5 Center Currently fitted tyre, dictates ABS/TC and pit limiter corrections (non-adjustable)
-
Row 5 Second from Right Session best lap time
-
Row 5 Right Current applied brake pressure (Bar or psi)
PIT LIMITER
When the pit limiter is active the shift light cluster will flash all LED’s in magenta and the PSL box will appear on the main dashboard screen.
SHIFT LIGHTS
- 1 Green 4800 rpm
- 2 Green 5000 rpm
- 1 Yellow 5200 rpm
- 2 Yellow 5400 rpm
- 3 Yellow 5600 rpm
- 4 Yellow 5800 rpm
- 5 Yellow 6000 rpm
- 6 Yellow 6200 rpm
- 1 Orange 6400 rpm
- 2 Orange 6600 rpm
- All Red 6800 rpm
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 (ALL FOUR)
COLD AIR PRESSURE
Air pressure in the tire when the car is loaded into the world. Higher
pressures will reduce rolling drag and heat buildup, but will decrease grip.
Lower pressures will increase rolling drag and heat buildup, 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 analyzed once the tires
have stabilized 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 analyze
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 analyzing 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 analyze 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 ride heights. 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 SET TING
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 BL ADES
The configuration of the Anti-Roll Bar arms, or “blades”, can be changed to
alter the overall stiffness of the ARB assembly. Increasing the number of ARB
arms 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 number of ARB arms 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
assembly in relation to aerodynamics should also be considered, softer ARB
assemblies 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. 11 configurations of ARB arms are available and range from D1-D1
(softest) to D6-D6 (stiffest).
TOE-IN
Toe is the angle of the wheel, when viewed from above, relative to the
centerline of the chassis. Toe-in is when the front of the wheel is closer to
the centerline 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 buildup 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 calipers. 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.
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
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 tires 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.
ABS SET TING
The current ABS map the car is running. 12 positions are available but only 11
maps exist. Position 1 has the least intervention/support while position 11
has the most support. Position 12 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.
TRACTION CONTROL SET TING
The position of the traction control switch determines how aggressively the
ecru cuts engine torque in reaction to rear wheel spin. 10 positions are
available. Settings 1-9 range from least intervention/sensitivity (position 1)
through to highest intervention/sensitivity (position 9). Position 10 disables
the traction control completely. Position 6 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.
ENGINE MAP SET TING
The fuel map on which the car is currently running. Position 1 is the base map
and produces maximum power but the most fuel usage. Position 2 through 11 are
for green flag fuel saving and will reduce engine power output
correspondingly, position 12 is for saving fuel under safety car conditions.
LEFT/RIGHT FRONT
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 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
should be increased to retain the same roll stiffness as previously. 16
options for spring rate are available ranging from 190 N/mm (1086 lbs/in) to
340 N/mm (1943 lbs/in) in 10 N/mm (57 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 compression
(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 0 is minimum damping (least
resistance to compression) while 11 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 kerns less high speed
compression damping can result in an increase in mechanical grip at the
expense of platform control. 11 is maximum damping while 0 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.
11 is maximum damping (most resistant to extension) while 0 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. 11 is maximum damping while 0 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.
LEFT/RIGHT REAR
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 95.0 mm.
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. 13
options for spring rate are available ranging from 130 N/mm (743 lbs/in) to
250 N/mm (1429 lbs/in) in 10 N/mm (57 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 compression
(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 0 is minimum damping (least
resistance to compression) while 11 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 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. 11 is maximum damping while 0 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. 11 is maximum damping (most resistant to extension) while 0 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. 11 is maximum damping while 0 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
tradeoff against reduced longitudinal (traction) performance.
TOE-IN
At the rear of the car it is typical to run toe-in. Increasing 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.
REAR
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.
ARB BL ADES
The configuration of the Anti-Roll Bar arms, or “blades”, can be changed to
alter the overall stiffness of the ARB assembly. Increasing the ARB assembly
stiffness will increase the roll stiffness of the rear suspension, resulting
in less body roll but increasing mechanical oversteer. This can also cause the
car “take a set” more quickly at initial turn-in. Conversely, reducing
the ARB assembly stiffness 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. 7 configurations of ARB arms are available and range from
D1-D1 (softest) to D4-D4 (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 behavior
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.
BMW M4 GT3 // USER MANUAL
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