CRAFTSMAN Nascar Truck Vehicle User Manual
- June 25, 2024
- Craftsman
Table of Contents
CRAFTSMAN Nascar Truck Vehicle
Specifications
- Chassis: Double wishbone independent front live axle truck arm rear
- Length: 4877 mm (192 in)
- Width: 1905 mm (75 in)
- Wheelbase: 2845 mm (110 in)
- Dry Weight: 1510 kg (3330 lbs)
- Wet Weight with Driver: 1633 kg (3600 lbs)
- Power Unit: Naturally aspirated steel block pushrod V8
- Displacement: 5.86 Liters (358 cid)
- RPM Limit: 8000
- Torque: 520 lb-ft (705 Nm)
- Power: 680 bhp (507 kW)
Product Usage Instructions
Introduction
The NASCAR Trucks user manual provides detailed information on chassis
setup adjustments to help you tune the car to your preference. Start by
familiarizing yourself with the car and track before making adjustments.
Getting Started
- Load into the car and press the clutch while selecting 1st gear.
- Ease off the clutch pedal while giving it some throttle to get moving.
- Use the h-pattern transmission, only requiring the clutch for starting and stopping in gear.
- To upshift, release the throttle and select the next higher gear.
- For downshifting, blip the throttle while selecting the next lower gear.
- Upshift when the tachometer is fully illuminated in red at high RPM.
Loading an iRacing Setup
Upon entering a session, the iRacing Baseline setup is automatically
loaded. To try other pre-built options, go to Garage > iRacing Setups and
select another suitable option. Ensure to load setups from similar track types
for tech inspection.
FAQ
-
Q: How do I access baseline setups for different tracks?
A: Open the Garage, click iRacing Setups, and choose the appropriate setup for your selected track. If a setup isn’t available, select one from a similar track as your baseline. -
Q: What should I do if the wheel speed and engine speed mismatch?
A: If you downshift too early or don’t blip the throttle enough, it may lead to wheel hop at the rear and potential spinning. Ensure to upshift when the tachometer is fully illuminated in red at high RPM.
DEAR iRACING USER,
Congratulations on your purchase of a NASCAR Truck Series vehicle! 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!Why race
pick-up trucks? For starters, they’re arguably the most popular automotive
vehicle in America, with upwards of 2 million new pickups sold every year in
the United States. And they’re a blast to race, particularly the trucks of the
NASCAR Truck Series. With 625 horsepower pushing their 3450 pounds around
super speedways, ovals, short tracks and the occasional road course, NASCAR’s
trucks are fun to watch and challenging to drive.
The following guide explains how to get the most out of your new truck, 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!
NASCAR TRUCKS | TECH SPECS
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.
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
Once you load into the car, press the clutch and select 1st gear. Give it a bit of throttle and ease off the clutch pedal to get underway. This car uses an h-pattern transmission, but only requires the clutch pedal to get the car rolling and when coming to a stop in gear. To upshift, simply let off the throttle and select the next higher gear. To downshift, give the throttle a blip while selecting the next lower gear. Upshifting is recommended when the tachometer is fully illuminated in red at high RPM. If you downshift too early, or don’t blip the throttle sufficiently, the wheel speed and engine speed will be mismatched, leading to wheel hop at the rear and a possible spin.
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.
DASHBOARD
The NASCAR TRUCKS are all equipped with the Spek Pro gauge system, which combines easy-to-read backlit gauges, warning lights, shift light, and a visual Pit Road Speed helper all into a very intuitive system.
DASHBOARD OVERVIEW & FAILURE LIGHTS
While the gauges for each manufacturer are laid out differently, all three
trucks feature the same gauges and the same functionality.
Each Truck features a large tachometer in the center with five accessory gauges arranged across the dashboard. These five gauges consist of:
- Water Temp Displays the temperature, in °F, of the water in the engine coolant system
- Oil Temp Displays the temperature, in °F, of the engine oil
- Oil Pressure Displays the pressure, in psi, of the engine oil flowing through the oil system
- Fuel Pressure Displays the fuel pressure, in psi, of the fuel flowing to the carburetor
- Volt Displays the voltage of the battery
Under normal operating conditions, these gauges will all display with a white backlight. Whenever a gauge is displaying a value that is dangerous to the engine, they will begin alternating between their normal color and red, such as the Oil Pressure gauge pictured below:
TACHOMETER
NASCAR does not allow the use of either a speedometer or a pit speed limiter, thus the pit road speed limit can only be followed by running a specific RPM in a given gear. To help the driver maintain proper pit road speed without having to look at the tachometer, the Spek Pro tachometer features Pit Speed lights, which illuminate either yellow, green, or red to show whether the vehicle is traveling too slowly or speeding on pit road. These lights are accurate to a track’s pit road speed limit only when the transmission is in 2nd Gear, and are set automatically when loading a track in the sim.
PIT SPEED INDICATOR
If the vehicle is below the pit road speed limit, the tachometer will
illuminate the speed lights in yellow, with 1 light being farthest from pit
road speed and all 7 being moderately slower than the pit road speed limit,
usually just a few miles-per-hour slower than the limit.
APPROACHING PIT SPEED LIMIT
As the vehicle’s speed approaches the pit road speed limit (but is not
exceeding the speed limit), the pit lights will turn green, with 1 green light
being the farthest from the pit road speed limit and 6 lights being just
underneath the pit road speed limit.
AT PIT SPEED LIMIT
When the vehicle is traveling at the pit road speed limit, the 7th light will
illuminate in green and the backlight color will change to green, illuminating
the entire gauge with a green light.
EXCEEDING PIT SPEED LIMIT
When the pit road speed limit is exceeded, the entire gauge backlight will
turn red and the speed lights will also change from green to red. Similar to
the other modes, 1 red light is just above pit road speed limit and each
additional light signals the vehicle is exceeding the speed limit. If the
vehicle continues accelerating after the 7th red light, all speed lights will
turn off and the backlight will return to its standard color.
SHIF T LIGHT
The tachometer is also equipped with a Shift Light mode, which turns the gauge
backlight to red. This is distinguishable from the pit road speeding mode by
the speed lights being off, and will be enabled just before the engine reaches
the rev limiter.
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
TIRE DATA
COLD AIR PRESSURE
Air pressure in the tire when the car is loaded into the world. Higher
pressures will reduce heat buildup, but will provide better grip with higher
loads and higher speeds. Lower pressures will increase heat buildup, but will
provide better grip at lower loads and lower speeds. Cold pressures should be
set to track characteristics for optimum performance.
HOT PRESSURES
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. On left-turn
ovals, the right-front tire should always see the highest buildup on a
balanced car, while the left sides should be roughly the same, but it is
important to monitor the hot pressures after a run and adjust accordingly.
Ideally, the difference in hot pressures on one side of the car should be
roughly equal to the difference between cold pressures after a longer run.
LAST TEMPERATURE
Tire carcass temperatures, measured via Pyrometer, once the car has returned
from the pits. Wheel Loads and the amount of work a tire is doing on-track is
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 while on track. These values are measured in three zones
across the tread of the tire.
TREAD REMAINING
The amount of tread remaining on the tire once the car has returned from 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 three zones across the tread of the tire.
CHASSIS
FRONT
BALLAST FORWARD
To meet minimum weight requirements, tungsten blocks are installed within the
lower frame rails on the chassis. These blocks can be moved fore and aft in
the chassis, directly influencing the car’s Nose Weight value. The Ballast
Forward value is simply a measurement of the location of these tungsten blocks
relative to a reference point in the frame rail. Moving ballast forward in the
car raises Nose Weight, moving it rearward reduces Nose Weight.
NOSE WEIGHT
The vehicle’s Nose Weight is the percentage of total vehicle weight on the
front tires, directly adjustable through the Ballast Forward adjustment. Nose
Weight represents a rough approximation of the longitudinal Center of Gravity
location in the vehicle and has a direct influence on the high-speed stability
of the vehicle. Higher Nose Weight values result in a more directionally-
stable vehicle, good for low-grip tracks and situations where the vehicle is
set up with extra front downforce. Conversely, lower Nose Weight values are
good for high-grip tracks and configurations with high rear downforce levels.
Smaller tracks will also see benefits from lower Nose Weight values, as it
will allow the rear of the vehicle to rotate easier.
STEERING RATIO
The Steering Ratio is a numerical value for how fast the steering response is
in the vehicle’s steering box. This ratio can be thought of as the degrees of
steering input needed to produce one degree of turn on the steering box output
shaft. For example, a 12:1 steering ratio will require 12° of steering input
to rotate the steering output shaft 1°. A steering box with a lower ratio will
feel more responsive to steering inputs and will require less steering input
to reach the amount needed to navigate a corner. A steering box with a higher
ratio will feel less responsive and will require more steering input to reach
the amount needed to navigate a corner.
CROSS WEIGHT
Cross weight is the amount of weight on the car’s Left-Rear and Right-Front
tires relative to the entire weight of the car, displayed in percent. This is
adjusted via the corner Spring Perch Offset adjustments as well as Front ARB
preload and, to a very small extent, the Truck Arm Preload. For an oval car,
Cross Weight is one of the most influential settings for grip level while the
vehicle is in a turn. Higher Cross Weight values will add weight to the left-
rear and right-front, both stabilizing entry and helping drive-off on corner
exit. Lower Cross-Weight values will help the vehicle rotate and keep it
“free” in the corner to prevent speed from being lost, however too low can
result in unstable entry and exit. Due to this vehicle’s design with a Coil-
Bind front suspension, Cross Weight is a major consideration for front end
suspension configuration.
See the section below for more information.
STEERING OFFSET
Degrees of steering wheel offset, achieved with a combination of installing
the steering wheel into the quick release mechanism off-center and adjusting
front tie-rods. This can be used to compensate for chassis settings which
place the wheel off center and is primarily a driver comfort adjustment.
FRONT BRAKE BIAS
Brake Bias is the percentage of braking force that is being sent to the front
brakes. Values above 50% result in more pressure being sent to the front,
while values less than 50% send more force to the rear. This should be tuned
for both driver preference and track conditions to get the optimum braking
performance for a given situation.
TAPE CONFIGURATION
The radiator grille on the front bumper can be run in one of two
configurations: Race and Qualifying. The Qualifying configuration will block
off the grille entirely, increasing downforce and reducing drag, but
preventing air from reaching the engine’s radiator and increasing engine
temperatures considerably. This increases aerodynamic performance but risks an
engine failure after only a few laps.
The Race configuration opens up a portion of the grille to allow air to cool
the engine with a slight loss in aerodynamic performance.
FRONT ARB
DIAMETER
The Front Anti-Roll Bar (ARB, or Sway Bar) diameter affects the roll stiffness
of the front suspension. Increasing the diameter of the ARB will result in a
higher roll stiffness on the front suspension, helping to keep the chassis
flat relative to the racing surface, but can also increase understeer. While
not absolutely necessary, a large bar is typically desired (>2.00”) to
maintain bind in both front springs throughout the corner. For conventional
setups a smaller bar can be used.
ARM ASYMMETRY
The difference in length between the left and right sway bar arms can be
altered via the Arm Asymmetry settings. The “None” setting will set the two
arms at equal length, while increasing the setting will increase the
difference in length of the two arms. This can be used to produce multiple
effects, primarily serving to produce a higher anti-roll force on the right-
front suspension than on the left-front, effectively rolling the chassis to
the left when under load.
This can be used to correct excessive roll without increasing the ARB
diameter. A knock-on effect of asymmetry is a slight increase in front end
heave stiffness, or resistance to vertical travel.
Since the two different lengths of arms cause the bar to be twisted at
different rates, vertical travel will load the ARB, possibly leading to higher
front ride heights on straights.
LINK SLACK
The left-side sway bar linkage can be adjusted to either delay bar engagement
or apply a static load to the bar. The linkage itself is a slider-type
linkage, and any positive link slack will require the left-front wheel to
travel prior to the ARB experiencing any load. This adjustment directly
affects the bar’s Preload, outlined below.
PRELOAD
The ARB Preload is the static load in the bar while the vehicle is in the
garage. Preload adjustments can be used to alter the dynamic loads in the bar
while on track, and can be used to remove or add bar load in the corners and
on the straights.
ATTACH
A quick way to unhook the anti-roll bar to allow for static suspension
adjustments without bar twist confusing things; increase link slack and unhook
the ARB before making spring/ride height adjustments; attach and reduce link
slack (ARB preload) when done.
FRONT CORNERS
COIL BINDING & “PIGTAIL” SPRINGS
The front suspension for the NASCAR Trucks emulates “pigtail”-style coil-bind
springs. Coil-binding is when the coils in a spring are all in contact with
each other, thus creating a “solid” suspension element. Instead of binding the
full spring (coils are in contact all the way around the spring), a “Pigtail”
spring binds only one side of the spring using a specially-shaped lower spring
perch to compress only one side of the spring. This produces both a very soft
initial rate and allows for a very stiff rate at full travel, providing a low
dynamic ride height, a more compliant suspension when compared to a
traditional coil-bind setup, and excellent aerodynamic platform control at the
low heights.
This effect is created with a two-stage, progressive front spring rate. When
the chassis is up above the minimum ride heights the springs will be very
soft, around 200 lb/in. As the suspension travels while on track from building
aerodynamic loads the springs will eventually bind and transition to a much
stiffer second rate, selected in the garage. The point where this transition
happens is controlled by the Spring Angle setting, described in more detail in
its own section. For more information on tuning front ride heights with this
suspension system, see the “Setup Tips” section at the end of this guide.
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 crossweight
adjustments are made via the Spring Perch Offset setting.
RIDE HEIGHT
Distance from ground to a reference point on the chassis. Front heights are
measured at the bottom of the chassis frame rail just behind the wheel well
and can be roughly identified via the skirt rivets at the bottom of the door.
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.
SPRING PERCH OFFSET
Spring perch offset is used to adjust ride height and corner weight. Adjusting
this setting changes the preload on the spring under static conditions.
Decreasing the value increases preload on the spring, adding weight to its
corner and increasing the ride height at that corner. Increasing the value
does the opposite, reducing height and weight on a given corner. These should
be adjusted in pairs (left and right, for example) or with all four spring
preload adjustments in the car to prevent crossweight changes while adjusting
ride height.
SPRING RATE
Spring Rate changes how stiff the spring is, represented in a force per unit
of displacement. Primarily responsible for maintaining ride height and a good
attitude under changing wheel loads, stiffer springs will maintain the car’s
attitude better while sacrificing mechanical grip. Softer springs will deal
with bumps better and increase mechanical grip, however this could cause the
chassis to pitch and roll too much, hurting aerodynamic performance at faster
tracks
SPRING ANGLE
Spring angle changes the position of the lower spring perch within the lower
control arm spring bucket. This value rotates the spring perch around the
spring’s center axis, relocating the highest point of the perch farther
inboard or outboard to change how the spring binds in travel and the spring
rate transitions from the softer initial rate to the rate selected in the
Spring Rate option. Higher angle values will reduce the amount of suspension
travel necessary to reach the spring rate transition while lower values will
increase the amount of travel necessary.
LS COMPRESSION
Low-Speed (LS) Compression affects how resistant the shock is to compression
(reduction in length), usually in chassis movements as a result of driver
input, such as the front shocks under braking. Higher LS Compression settings
will prevent the shock from compressing quickly and can quickly increase the
load transferred to the wheel when the suspension is in compression, but can
prevent the suspension from absorbing smaller bumps and dips in the track.
Lower LS compression settings will allow for better bump absorption, but can
hurt aerodynamic stability due to excessive body movement with driver inputs.
HS COMPRESSION SLOPE
The High-Speed Compression can be further tuned with the Compression Slope
setting. This setting shifts the high-speed adjustment of the shocks higher or
lower, allowing for a wider range of options for various track conditions.
Higher slope settings will produce a more linear compression setting, with
compression force increasing with velocity. These settings are good for very
bumpy surfaces to keep the shock from “blowing out” over large bumps,
preventing the chassis from striking the racing surface. Lower slope settings
will produce a more digressive compression setting, with forces not increasing
significantly as velocity increases. This is good for smoother tracks where
large suspension movement is not expected. When tuning shocks for a track,
change the slope setting first to suit the track, then fine-tune the shock
using the high- and low-speed settings.
LS REBOUND
Low-Speed (LS) Rebound affects how resistant the shock is to extension
(increase in length), typically during body movement as a result of driver
inputs, such as the rear shocks under braking. Higher rebound values will slow
extension 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 extend enough to
maintain proper contact with the track. Excessive front rebound can lead to
unwanted oscillations due to the wheel bouncing off of the track surface
instead of staying in contact.
HS REBOUND SLOPE
The High-Speed Rebound can be further tuned with the Rebound Slope setting.
This setting shifts the high-speed adjustment of the shocks higher or lower,
allowing for a wider range of options for various track conditions. Higher
slope settings will produce a more linear rebound setting, with rebound force
increasing steadily with velocity. These values will give a more controlled
damping characteristic over very bumpy surfaces. Lower values will result in a
more digressive rebound curve, which is good for smoother surfaces.
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. Greater camber angles 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 itis important to find a balance between
life and performance. For ovals, set the left side positive and the right side
negative. For road courses, all four wheels should be set with negative
camber.
CASTER
How much the steering axis is leaned back (positive) or forward (negative),
which influences dynamic load jacking effects as the car is steered. More
positive caster results in a heavier steering feel but decreases dynamic
crossweight while turning, as well as adding straight-line stability. Running
less caster on the left-front will cause the vehicle to pull to the left, a
desirable effect on ovals.
TOE-IN
Toe is the angle of the wheel, when viewed from above, relative to the
centerline of the chassis. Positive toe-in is when the front of the wheel is
closer to the centerline than the rear of the wheel, and negative toe-in (toe-
out) is when the front of the wheel is farther away from the centerline than
the rear of the wheel. On the front, toe-out is generally preferred. More toe-
out typically provides better turn in and straight line stability, but at the
cost of increased tire temperature and wear.
REAR 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 crossweight
adjustments are made via the Spring Perch Offset setting.
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 rear ride height will increase rear downforce as well as
slightly increasing overall downforce and drag. Conversely, reducing rear ride
height will reduce rear downforce and reduce overall downforce and reduce
drag.
SPRING PERCH OFFSET
Spring perch offset is used to adjust ride height and corner weight. Adjusting
this setting changes the preload on the spring under static conditions.
Decreasing the value increases preload on the spring, adding weight to its
corner and increasing the ride height at that corner. Increasing the value
does the opposite, reducing height and weight on a given corner. These should
be adjusted in pairs (left and right, for example) or with all four spring
preload adjustments in the car to prevent crossweight changes while adjusting
ride height.
SPRING RATE
Spring Rate changes how stiff the spring is, represented in force per unit of
displacement. Primarily responsible for maintaining ride height and
aerodynamic attitude under changing wheel loads, stiffer springs control the
chassis attitude better (less roll or pitch change) which is good for
aerodynamics and camber control, but mechanical grip is often better with
softer springs which allow for more track surface compliance but reduce
aerodynamic control. For ovals, a softer left-rear spring (relative to the
right-rear) is desired to prevent the dynamic cross from being too high in the
corners, which will result in a balance shift towards understeer through a
run.
LS COMPRESSION
Low-Speed (LS) Compression affects how resistant the shock is to compression
(reduction in length), usually in chassis movements as a result of driver
input, such as the front shocks under braking. Higher LS Compression settings
will prevent the shock from compressing quickly and can quickly increase the
load transferred to the wheel when the suspension is in compression, but can
prevent the suspension from absorbing smaller bumps and dips in the track.
Lower LS compression settings will allow for better bump absorption, but can
hurt aerodynamic stability due to excessive body movement with driver inputs.
HS COMPRESSION SLOPE
The High-Speed Compression can be further tuned with the Compression Slope
setting. This setting shifts the high-speed adjustment of the shocks higher or
lower, allowing for a wider range of options for various track conditions.
Higher slope settings will produce a more linear compression setting, with
compression force increasing with velocity. These settings are good for very
bumpy surfaces to keep the shock from “blowing out” over large bumps,
preventing the chassis from striking the racing surface. Lower slope settings
will produce a more digressive compression setting, with forces not increasing
significantly as velocity increases. This is good for smoother tracks where
large suspension movement is not expected. When tuning shocks for a track,
change the slope setting first to suit the track, then fine-tune the shock
using the high- and low-speed settings.
LS REBOUND
Low-Speed (LS) Rebound affects how resistant the shock is to extension
(increase in length), typically during body movement as a result of driver
inputs, such as the rear shocks under braking. Higher rebound values will slow
extension 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 extend enough to
maintain proper contact with the track. Excessive front rebound can lead to
unwanted oscillations due to the wheel bouncing off of the track surface
instead of staying in contact.
HS REBOUND SLOPE
The High-Speed Rebound can be further tuned with the Rebound Slope setting.
This setting shifts the high-speed adjustment of the shocks higher or lower,
allowing for a wider range of options for various track conditions. Higher
slope settings will produce a more linear rebound setting, with rebound force
increasing steadily with velocity. These values will give a more controlled
damping characteristic over very bumpy surfaces. Lower values will result in a
more digressive rebound curve, which is good for smoother surfaces.
TOE-IN
Rear toe in this vehicle serves to introduce “Skew”, where the vehicle travels
through the air with a non-zero amount of yaw relative to the direction of
airflow, producing Sideforce. Setting the right-rear to a negative value and
the left-rear to a positive value will add positive Skew, decreasing
crossweight and shifting aero balance forward slightly. Setting the right-rear
to a positive value and left-rear to a negative value will add negative Skew,
reducing sideforce and centering the rear spoiler behind the greenhouse for
some toe settings. Positive skew is useful at large short tracks and
intermediate tracks, while negative skew will reduce drag for superspeedways
and aid in drive-off for smaller short tracks.
TRACK BAR HEIGHT
The rear axle is held in place laterally via a Track Bar, mounted to the left
side of the rear axle housing and to the chassis frame on the right side.
Overall height of the track bar dictates roll center location for the rear
suspension and thus affects roll stiffness, with a higher track bar increasing
rear roll stiffness and shifting the chassis balance to oversteer. Lower track
bar settings will increase lateral traction due to a reduction in roll
stiffness and roll center height. The track bar end heights can also be set to
different values, known as “rake” or “split”. A positive track bar rake, with
the right-side mounted higher, will increase oversteer on corner exit, as well
as adding skew through vertical travel. Negative track bar rake will increase
traction on corner exit, but will remove skew through vertical travel.
TRUCK ARM MOUNT
The rear axle is held in place longitudinally with two truck arms, mounted to
the bottom of the chassis underneath the driver compartment. The forward
mounts can be adjusted up and down, resulting in various anti-squat and rear-
steer configurations. Higher truck arm mounts will reduce rear end grip,
increase rear steer, add anti-squat, and reduce wheel hop under heavy braking.
Lower truck arm mounts will increase rear end bite, decrease rear steer,
reduce anti-squat, and increase the chances of wheel hop under heavy braking.
TRUCK ARM PRELOAD
Due to the truck arm mounting design on the rear axle, most chassis
adjustments will result in the truck arms applying a torque to the rear axle
housing. This preload has an extremely small effect on the chassis balance,
but can be removed to eliminate any potential issues. It is good practice to
reset this value to as close to zero as possible after making adjustments.
REAR
REAR END RATIO
The Rear End Gear Ratio is the ratio between the driveshaft pinion and the
differential ring gear. For all ovals with NASCAR-sanctioned events, this
value is either locked to one ratio or there is a choice of two ratios. Higher
number values produce better acceleration but reduce top speed, lower number
values reduce acceleration
but result in a higher top speed.
ARB DIAMETER
The Rear Anti-Roll Bar (ARB, or Sway Bar) diameter affects the roll stiffness
of the rear suspension. Increasing the diameter of the ARB will result in a
higher roll stiffness on the rear suspension, increasing oversteer, while
reducing the ARB diameter will reduce roll stiffness and increase understeer.
A rear ARB is only available at Road Courses and has no effect on the chassis
on ovals.
PRELOAD
The ARB Preload is the static load in the bar while the vehicle is in the
garage. Since a rear ARB is only available at Road Course circuits, it is best
to keep this value as close to zero as possible when using a rear ARB to
prevent asymmetric handling issues. When the rear ARB is not in use, this
setting has no effect on the chassis.
ATTACH
A quick way to unhook the anti-roll bar to allow for static suspension
adjustments without bar twist confusing things; increase link slack and unhook
the ARB before making spring/ride height adjustments; attach and reduce link
slack (ARB preload) when done.
ARB PRELOAD
The ARB Preload is the static load in the bar while the vehicle is in the
garage. Preload adjustments can be used to alter the dynamic loads in the bar
while on track, and can be used to remove or add bar load in the corners and
on the straights.
ATTACH
A quick way to unhook the anti-roll bar to allow for static suspension
adjustments without bar twist confusing things; increase link slack and unhook
the ARB before making spring/ride height adjustments; attach and reduce link
slack (ARB preload) when done. This option will completely detach the bar and
keep it from being loaded while on track, if desired.
SETUP & DRIVING TIPS
The NASCAR Trucks can produce some of the best racing on the oval side of
iRacing’s service, but as with every car the Trucks have their own traits and
personality. With a high amount of engine power and some of the highest
downforce numbers of all the oval content they are very easy to drive but
require a high level of precision and skill to drive quickly.
Aerodynamic performance is just under what is necessary to be able to run
wide-open at many tracks, so a keen sense of how much grip is available and
skillful throttle modulation is key to fast lap times. Generally, in race
trim, it’s often going to be faster to crack the throttle slightly on entry
and let the truck drive itself into the corner than to stay wide open and
fight the front tires to the line you want to run. In Qualifying trim a wide-
open lap is attainable, but it can be “sketchy”, as the real drivers say.
RIDE HEIGHTS & ATTITUDE
As with all oval cars, the setup process involves hitting predetermined height targets in the corners and finding a way to keep the chassis and body in that position as long and as consistently as possible. Your targets for chassis setup will be a minimum splitter height and a rear height range.
SPLITTER HEIGHT
The optimum splitter height, and minimum ideal height, is around 0.25” or just
above 6mm, measured via the telemetry channel CFSRrideheight. This height
sensor is placed on the leading edge of the splitter along the centerline and
displays the ground clearance to the front of the truck. As this height is
reduced, overall downforce will increase and aero balance will shift forward
slightly. If the splitter is allowed to pass below the minimum height of
0.25”, an aerodynamic stall will occur and overall downforce will drop
significantly. Further, a risk of ground contact from the splitter will occur,
unloading the front tires and inducing heavy understeer.
Tuning the splitter height is relatively a relatively simple process and can be done in three steps:
- Spring Rate selection
- Spring Angle setting
- Spring Perch Offset adjustment
Selecting spring rates is going to come down to personal preference and track
characteristics. Tracks with high loads or very smooth surfaces can use very
stiff spring rates, while rougher tracks or tracks with lower cornering speeds
may see better performance with slightly softer spring rates. Further, some
drivers may prefer one spring stiffer than the other or both the same rate,
but this will come down to testing configurations and finding which you like
the best.
Pigtail-style coil bind springs only bind one half of the spring while the
other half is left to act as a working spring. The Spring Angle setting
rotates the lower spring perch within the lower control arm spring bucket to
change how far inboard the bound half of the spring is on the suspension,
changing how much suspension travel is available before the Spring Rate chosen
in the previous step takes over. Increasing the Angle value will reduce
suspension travel and cause the splitter to run higher while reducing the
angle will allow more travel before the spring rate transition and lower the
splitter. Use this Spring Angle value to get the splitter as close to the
target value as you can, then move to the Spring Perch Offsets.
Since the Pigtail springs work entirely within the main spring, the Spring
Perch Offset values can be used to fine-tune the front-end ride heights once
the height has been roughed-in with the Spring Angle. Increasing the Spring
Perch Offset values (right clicks in the garage) will lower the static ride
height and lower the splitter height when loaded in the corner. Conversely,
decreasing the values (left-clicks) will raise the front of the car and the
splitter’s dynamic height in the corner. If large Spring Perch Offset changes
are needed, it’s usually best to go back to the Spring Angle and change that
value instead of large Perch changes.
REAR RIDE HEIGHTS & REAR SPRINGS
Rear ride heights are best run in a range of heights for most situations. The
trucks will generate the most downforce when the rear end between around 3.9”
and 4.3” (100-110mm). Running the rear higher than this range will add very
little downforce but a lot of drag and is not recommended. Running lower than
this range can reduce drag and downforce for tracks with the highest top
speeds but can risk damaging the underside of the car.
Choosing rear spring rates is much simpler than choosing front spring rates,
as the rears are purely linear and each spring has its own specific purpose.
The simplest way to approach rear springs is to set the Right-Rear spring for
the target rear height and adjust the Left-Rear spring for handling and roll,
with the Right-Rear spring generally being a few times stiffer than the Left-
Rear. Generally you will want the stiffest Right-Rear spring spring you can
handle and then fine-tune the dynamic height with the Perches. For the Left-
Rear, softening the spring will roll the truck to the left and free the
chassis up through the corner while stiffening the spring will raise the left
side of the chassis and tighten the car through the corner.
CROSSWEIGHT
One of the most important settings in the garage is the crossweight, or the percentage of the chassis’ total weight on the Right-Front and Left Rear as a percentage. This value is a major factor in the mechanical handling balance and how the car will get into and out of the corner.
To adjust crossweight without introducing other issues, follow these steps:
- Note the current Front ARB Preload and disconnect the bar. Once disconnected, increase the Link Slack option to a large positive value, which will prevent the bar from influencing other adjustments while disconnected.
- If the bar has a large amount of preload this may cause the ride heights to move into illegal ranges. This is okay, as they should return to legal ranges when the bar is reattached and loaded.
- Using the Spring Perch Offsets, adjust the crossweight by making the following changes:
- Increase Crossweight
- Right Rear – Right Click (Increase value, decrease corner weight)
- Left Rear – Left Click (Decrease value, increase corner weight)
- Left Front – Right Click (Increase value, decrease corner weight)
- Right Front – Left Click (Decrease value, increase corner weight)
- Decrease Crossweight
- Right Rear – Left Click (Decrease value, increase corner weight)
- Left Rear – Right Click (Increase value, decrease corner weight)
- Left Front – Left Click (Decrease value, increase corner weight)
- Right Front – Right Click (Increase value, decrease corner weight)
- If you’re new to the setup process, keep these adjustments to one or two clicks at a time and watch what happens to the chassis. If you’re comfortable with the adjustments, multiple clicks (Shift-Click is equal to 5 clicks) can be made as long as you keep track of everything that’s changing. Always pay attention to the ARB preload to make sure it stays at zero during crossweight adjustments. If it registers a value, simply adjust the Link Slack to remove the preload and continue with weight adjustments.
- Once the desired crossweight change has been made, reattach the ARB and preload the bar to what it was initially. Following these steps you should now have a change in crossweight with almost no change in ride heights or alignment!
Deciding on a crossweight adjustment is usually fairly simple, it will come
down to how the car is behaving through the center and on throttle
application. If the car understeers through the center or has too much rear
traction on throttle causing understeer on exit, decrease the crossweight. If
the car oversteers through the center or the rear tires spin too easily on
initial throttle, increase the crossweight.
It is also very important to focus on crossweight adjustments progressively
through the corner: Start with entry and work on the car around the corner.
It’s very easy to fall into the trap where the rear of the car loses grip on
exit and the driver wants more crossweight to correct that, when the root
cause is understeer through the center of the corner. This understeer will
result in the driver applying too much steering input and over-slipping the
front tires, which “bite” as steering is removed through corner exit and
causing the rear to lose traction. In this situation, adding crossweight will
make the center of the corner worse and potentially make the car “looser” on
exit. This pitfall can be avoided by looking at the tire temperatures screen
(after a steady run without spins) and noting whether the temperatures show
hotter on the RF than the RR tire, an indication that the car is understeering
and the crossweight needs to be reduced. This will often, counter-intuitively,
tighten the car on exit and free the car up through the center.
ADJUSTING FOR WEATHER AND TIME-OF-DAY
Varying weather conditions and race start times can greatly affect the amount
of grip available from the track surface. Hotter track temperatures will
produce less grip and often cause the car to oversteer, especially on
throttle, while cooler tracks will increase grip and shift the balance towards
understeer. To correct for weather and track temperature changes, the only
adjustment needed is crossweight: Increase crossweight for warmer
temperatures, decrease it for cooler temperatures.
FINAL CONSIDERATIONS
Once these areas of the setup are complete you can move onto finer details
like shocks and alignments. These settings will be dependent on the spring
package and track characteristics, so don’t be afraid to test various settings
to see what works for you. The Fixed setups provided with the car are close to
where the car would like to be run as far as heights and weight balance, but
are tuned more towards mild understeer to make the car more approachable. Keep
it simple, make small adjustments, and you should be able to get wherever you
want to go!