Forces on a Banked Oval-Part 1

Understanding the forces on the four "corners" of the race car's suspension will help in the determination of the ideal spring and damper setting selection/s.

The race car on an oval experiences rapidly changing forces:  1) From the "Twist" of the banking ribbon transition between the curve and straight; 2) The rapid increase in downforce from the banking; 3) The normal "cornering force" that causes chassis roll in turns; and 4) Forces that result from deceleration and acceleration.





It is useful to think of the race car having three different "roll" axis. The first is a line drawn from front to back of the car. Lets call this the "L axis" for longitudinal. The second is a line drawn from corner to corner. Let;s call this the "X axis" for cross axis. The third is a line drawn thru the center of the car from side to side. Let's call this the "P axis" for pitch axis.

The force/s introduced by the banking transition act from corner to opposite corner about the X axis.  LF to RR; or RF to LR, etc. These forces are momentary but can be quite large and result in substantial spring compression and changes in handling. (See figure above)

The second force is produced by the extra "weight" the car experiences on all four corners because of the banking.

The third force, deemed cornering force is the centrifugal force on the center of gravity of the car that results in a reduction of weight on the inside tires and an equal increase in the weight on the outside tires about the L axis.

An analysis of suspension telemetry will show these forces as "displacements" or changes in ride height.  These changes in ride height are affected by spring choice and damper settings. The car will generally see a force about the X axis on corner entry, followed by all four corners being compressed by banking forces, while simultaneously weight is being transferred about the L axis as the car rolls in the turn. As the car exits the corner, these forces will be reduced. The weight change about the L axis from turning will return to the straight line forces. The banking compression will diminish and the car will see an opposite force about the X axis on corner exit. 

Stiffer springs will absorb less "energy" and hence, the weight transfer about the X axis, the L axis, and/or the P axis will occur faster and with a greater magnitude. Increasing the rebound damping on the shock/damper that is losing weight will cause the weight transfer to occur faster. Increasing the compression damping on the shock/damper that is gaining weight will cause the weight transfer to occur faster.

Weaker springs will absorb more "energy" and hence, the weight transfer about the X, L, and/or P axis will occur slower and with less magnitude. Decreasing rebound damping on the shock damper that is losing weight will cause the weight transfer to occur slower.Decreasing the compression damping on the shock/damper that is gaining weight will cause the weight transfer to occur more slowly. (This second set of facts can be counter-intuitive.)

The next question is usually:  How do I choose to make the car go faster?   The answer is not a universal one as the correct choice of springs and damper settings depends on the track, the conditions (e.g. track temperature and tire design) and driving line. Often the optimal choice is determined by experimental testing--starting with a base setup and making small changes to determine the changes that result in better lap times.

Basic Road Course Setup Building for DW12

Link to Dropbox .sto file
RFC Road Q BASE setup 2016S1

https://www.dropbox.com/s/ri7ryrqcm0bhrmm/RFC2016S1BaseRoad.sto?dl=0

iRacing.com RFC2016S1BaseRoad for IndyCar DW12
(Formatted for PC--see end of article for settings formatted for mobile devices)

FRONT:                                                                     REAR:

Cold pressure: 25.0 psi                                               Cold pressure: 23.0 psi
FRONT AERO:                                          REAR AERO:

Wing angle: 28.50 deg                                               Wing angle: 46.0 deg
Wing wicker: 1" full span                                           Wing wicker: 1/2" full span
Upper flap angle: 11.5 deg                                         End plate wicker: 3/8"
Upper flap wicker: 1/4"                                              Beam wicker: 1"
UNDERSIDE AERO:                                 AERO CALCULATOR:

Diffuser exit wicker: 3/4" (sealed)                              Front RH at speed:  0.500"
Diffuser add-ons: Sidewall ON/Strakes ON              Rear RH at speed:   0.500"
Radiator inlet: 2/3 closed EXT side                           Front downforce:    40.93%

                                                                                    Downforce to drag: 3.040:1

GENERAL:

Wheelbase: 118"                                                         Steering offset: +0 deg
Brake pressure: Medium                                             Ballast forward: -6"
Brake pressure bias: 52.0%                                        Nose weight: 44.7%
Steering pinion: 8 tooth                                   Cross weight: -0 lbs to the left front

FRONT:                                                     REAR:

Corner weight: 404 lbs (44.7% Front)                        Corner weight: 499 lbs
Ride height: 1.114 in                                                  Ride height: 1.596 in
Pushrod length: 25.545"                                             Pushrod length: 21.089"
Spring rate: 1750 lbs/in                                               Spring rate: 650 lbs/in
Camber: -2.13 deg                                                      Camber: -1.60 deg
Caster: +7.36 deg                                                        NA
Toe-in: -2/32"                                                              Toe-in: +5/32"

FRONT:                                                     REAR:

3rd spring: Stiff                                                          3rd spring: Stiff
3rd spring gap: 0.338 in                                              3rd spring gap: 0.321 in
ARB diameter: Small                                                  ARB diameter: Large
ARB blades: Steel
ARB blades: 3                                                             ARB blades: 2
ARB Drop-link position: Wide (Slow)            ARB drop-link position: Wide (Slow)
ARB preload: 0.0 ft-lbs                                              ARB preload: 0.1 ft-lbs

Fuel level: 4.5 gal                                                       Weight jacker: 0

FRONT DAMPER:                                   REAR DAMPER:

Low speed comp: -7 clicks                                      Low speed comp: -19 clicks
High speed comp: -21 clicks                                  High speed comp: -23 clicks
Low speed rebound: -7 clicks                              Low speed rebound: -23 clicks
High speed rebound: -14 clicks                           High speed rebound: -20 clicks

ENGINE:

Engine map setting: 7 (MAP) (Less sensitive)  
Turbo boost pressure: Push to Pass 10x/race

GEARBOX:        Final drive: 17/59

First gear: 16/34          109.3 mph                   Second gear: 17/31     127.4 mph
Third gear: 19/31        142.4 mph                   Fourth gear: 19/28      157.6 mph
Fifth gear: 18/25         167.3 mph                   Sixth gear: 20/26         178.7 mph
DIFFERENTIAL:

Clutch plates: 4                                                           Preload: -50 ft-lbs
Ramp angles: 45 coast/30 power

Just like for ovals, building a competitive setup for road courses requires trial and error testing.  While one could start from scratch for each track, each season, it is often time efficient to build on already existing setups.

This article shares a “Base” setup tested for iRacing’s 2016S1 “Build”.  (Sometimes iRacing makes changes to chassis stiffness and tire grip/slip angle coefficients that may require minor changes to the base in the future.)

This “Base” setup is designed for a “balanced” car—neither “tight=under-steery” or “loose=over-steery”.  For each track, this is a starting point and modifications and adjustments need to be made and tested for optimal performance.

First, run the “Base”  set for 10 laps and get a baseline set of lap times. (You will need to increase fuel level to 7 or 8 gallons temporarily.) Note the top speed. (If you hit the rev limiter in 6^th gear, then adjust it to a higher mph setting and determine the top speed before ending the first stage testing.) Also note the gears used entering and exiting each corner.

Before proceeding further—view Youtube videos of hot laps at the track run by other drivers. Note the top speed and the gears used entering and exiting each corner. Note the driving lines taken and braking points if possible. Check iRacing results and World Records (Only during the last 12 months) and set a “target lap time” for certain track temperature. 

IMPORTANT TERM:   A Balanced Race Car is one where the front and the rear tires are close to the same temperature and wear---this is the goal. With the correct driving line, you will “feel” this with the car not being “generally” loose or tight. But, on road courses, in most cases a compromise is required—some corners the car may seem loose while in others it may seem tight.

IMPORTANT TERM:  Best Camber for Racing Grip is the setting that produces almost equal tire wear from left to right of each tire. (This may not be the best setting for qualifying, but for racing it produces the setting that will provide the best lap times for long runs.) On road courses, because of necessary and desirable negative camber, generally the temperature and wear on the outside edges will be lower.

The first adjustment will be to setup the gearbox so that desired top speed is achieved in 6^th gear with Max Speed Possible (hitting the rev limiter—this is 178.7 mph in the Base Set) approximately 5-6 mph higher than the desired top speed. (This allows for the draft.) Then set 5^th gear Max Speed Possible at 93-94% of 6^th gear; 4^th gear Max Speed Possible at 92-94% of 5^th gear; 3^rd gear Max Speed Possible at 90-93% of 4^th gear; 2^rd gear Max Speed Possible at 87-90% of 3rd gear; and 1^st gear Max Speed Possible at 85-87% of 2nd gear.

Run 10 laps to verify you are reaching the desired top speed. If you are not hitting the rev limiter and not reaching the desired top speed, then you must reduce aerodynamic drag.  Reduce the front and rear wings as necessary to maintain a 40-42% Front Downforce % and a Balanced Race Car tire condition as well as the desired handling in the fastest corner and corner/s leading to the longest straight. Note the gears used entering and exiting the corners and make adjustments as necessary. (The main issue is that you usually would prefer to be upshifting after the track out point on corner exit. Make minor changes to gearing—one step only.)  (This is a different procedure than the typical concept of choosing downforce to improve cornering---the idea is that desired top speed is limited by the gearing and aero settings you choose.)

Finding the right “combination” of wing angle/s, wicker dimensions takes a bit of trial and error using the Aero Calculator as a guide.  Choose the combination giving the highest Downforce to Drag ratio. Here is where you may choose to add aero downforce to improve handling and lap times, even though it may reduce your top speed.

Once a Balanced Race Car and desired top speed is achieved by adjusting wings, run another 10 laps to establish a new baseline set of lap times. Note the presence of tight or loose conditions.

Before proceeding further, carefully consider the choice of spring rates. The “Base” setup produces certain handling characteristics that can be changed simply by changing spring rates. Increasing the front spring rates will make the car tighter. (Drivers who like to brake later may desire this.) Decreasing the front spring rates will make the car more loose. Increasing the rear spring rates will make the car more loose. (Drivers who like to “steer with throttle may desire this.) Decreasing rear spring rates will make the car tighter. (It is not recommended going much lower than 650 pounds for the rear springs that are used in the “Base” setup.) If you change springs, reset ride height back to the “Base” settings and run a few test laps to insure the car is a Balanced Race Car. Adjust aero as needed.

There is no "magic" formula for the correct tire pressure. Best advice is to experiment at each track with increasing and decreasing tire pressure from the base. Generally, tracks with fast sweeping corners call for higher pressure. And, tracks with slow chicanes and hairpins call for lower pressure.

Before making any further adjustments, using ALT L, and some form of telemetry software analysis, note the ride heights on all four corners.  If the car is hitting the track during corners, then ride height needs to be increased. Generally, at corner entry, the optimum ride front height under heavy braking would be not be much more than 0.2 inches—often you will desire it to be near zero.  On the longer straights for maximum speed, front ride height should be no lower than 0.6 inches and it is generally good for the rear ride height to be 0.3 inches higher in the rear than the front. However, one may choose to increase downforce (and drag) by increasing “rake”—raising the rear height above this 0.3 inch figure and running a front ride height on the straights that is less than 0.6 inches which will also increase downforce.

Note that on the DW12 road course setup—you have a choice of “3^rd Spring Gap”. The 3^rd spring comes into play when both sides (L and R) of the car are lowered by aero downforce, braking or acceleration. If the car is running too low at maximum speed or during braking, one can reduce this 3^rd Spring Gap—essentially causing the 3^rd spring to supplement/add to the spring rate of the conventional springs. Retest telemetry after making this change.

After adjusting ride height/s, Run another 10 laps and compare lap times and handling. Note tire wear and temps. On particularly fast tracks, you may gain speed by reducing the rear toe . This benefit will be at the expense of a car that is looser when applying power in a corner.

You will now start making adjustments to remedy the handling issues you observe without adjusting wings. You will focus on improving the handling in specific corners as well as improving tire wear/temps.

First, adjust front and rear camber to optimum. Keep in mind the principle of “Camber Thrust” where tires on the outside of the curve tend to produce more lateral grip with a small amount of negative camber but produce less on the inside of the curve. (See figure below.) Keep in mind that "A Arm" suspensions usually generate more negative camber as they are compressed.  Generally, tire temps should be about 5% cooler on the outside. Next, choose the desired Caster. Higher Caster setting will make the car more loose in mid corner. More front ARB will give more rear traction and make the car tighter. Less rear ARB will give more rear grip and make the car tighter.  Finally, choose the optimum damper settings. Generally, reducing high speed compression and rebound makes the car better able to go over curbs. Reducing low speed rebound settings will give that corner more relative grip; increasing compression settings will give that corner less grip. Keep in mind that changes to grip from damper setting are “dynamic” or momentary—they simply control/affect the speed that weight/cornering load is transferred.

The figure above gives a bit of insight about the high and low speed damper settings.The low speed settings affect the damper when moving at 1-2 inches per second. The high speed settings affect the damper when moving faster than that. The rate of damping force increase relative to speed is different for high speed movement vs. low speed. Rebound damping is higher than compression damping because the spring is acting to accelerate the damper's movement.

Continue running 5-10 laps “Stints” after each change. Be careful that you do not confuse the improvement in lap times due to your improved driving with improvement caused by adjustments you make to the car. Often it is wise to reverse the change and test to see if lap times get worse when the change is reversed. Let your lap times determine the best setup. Be aware that changes can improve performance in one corner while making performance in another corner worse.

Road course setups do not have Qualifying Boost. Instead, they provide 10 Push to Pass Boosts per race. When comparing lap times be aware of Push to Pass Boosts used. Often during Official Practice sessions, other drivers will use several Push to Pass Boosts to get an "impressive" but unrealistic lap time. Push to Pass is NOT available during Road course qualifying. Another "game" some drivers use is to report their "optimal" lap times on the forum. "I am reaching 1:xx.xx)" while their best actual lap was 1 second or more slower. 

For qualifying, generally, set fuel fuel to 4 or 4.5 gallons. (Test this and set so you have only 0.2 gallons at the end of qualifying session.) For the RACE setup, increase fuel to 18.5 gallons, and change the radiator opening to 1/3 blocked. Since the car is heavier, adjust the ride heights to compensate.  

Colder temps generally allow less wing. Hotter temps generally require more wing (downforce). You may want a higher downforce to make the car more stable as tires wear. Generally dropping tire pressure slightly will help on a hot track. Run a full fuel stint to test. These rules of thumb are not always the case—it depends on the track.

Often, it will require 6 to 8 different setups to cover the range of temperatures for qualifying and racing. Cold (70-85F track)  Medium (85-95F track) Hot (95-105 track) and ExtraHot (105F+) For 2 lap qualifying generally you only need Cold and Hot.

This is by no means a complete instruction. There are other adjustments that can be made (like front brake bias, differential settings and ballast forward) and vehicle dynamics are complicated.  Some drivers may prefer a car that is more loose than a Balanced Race Car. These “more advanced” settings should be attempted to further optimize your lap times but will require additional time consuming testing. And, remember that driving lines and throttle modulation are part of how best lap times are achieved. 

Note 1:  On courses with sharp and slow turns like Circuit of the America's, the base setup may introduce a bit of mid-corner over-steer or looseness. This is primarily caused by the rear tires being overtaxed by trail braking. A "drive-around" is to do less trail braking--brake in a straight line and release at turn in or" The "setup" fix is more front brake bias and a higher "Coast" differential setting. 

In addition to my engineering and racing background as well as 30 years of interest/study in the field of vehicle dynamics, a great deal of the knowledge and experience behind the base setup and this guide came from the excellent professional level coaching I received from nearly a year working with Wyatt Gooden. He continues to evaluate setups I build for Team RFC and almost always betters iRacing World Record laps times when doing so.    http://www.wyattgooden.com/

Here are the setting in a format better suited to mobile devices.

RIGHT FRONT: LEFT FRONT:

Cold pressure: 25.0 psi

RIGHT REAR: LEFT REAR:

Cold pressure: 23.0 psi

FRONT AERO:

Wing angle: 28.50 deg
Wing wicker: 1" full span
Upper flap angle: 11.5 deg
Upper flap wicker: 1/4"

UNDERSIDE AERO:

Diffuser exit wicker: 3/4" (sealed)
Diffuser add-ons: Sidewall ON/Strakes ON

Radiator inlet: 2/3 closed EXT side

REAR AERO:

Wing angle: 46.0 deg
Wing wicker: 1/2" full span
End plate wicker: 3/8"
Beam wicker: 1"

AERO CALCULATOR:

Front RH at speed: 0.500"
Rear RH at speed: 0.500"
Front downforce: 40.93%
Downforce to drag: 3.040:1

GENERAL:

Wheelbase: 118"
Brake pressure: Medium
Brake pressure bias: 52.0%
Steering pinion: 8 tooth
Steering offset: +0 deg
Ballast forward: -6"
Nose weight: 44.7%
Cross weight: -0 lbs to the left front

LEFT & RIGHT FRONT:

Corner weight: 404 lbs
Ride height: 1.114 in
Pushrod length: 25.545"
Spring rate: 1750 lbs/in
Camber: -2.13 deg
Caster: +7.36 deg
Toe-in: -2/32"

LEFT & RIGHT REAR:

Corner weight: 499 lbs
Ride height: 1.596 in
Pushrod length: 21.089"
Spring rate: 650 lbs/in
Camber: -1.60 deg
Toe-in: +5/32"

FRONT:

3rd spring: Stiff
3rd spring gap: 0.338 in
Bar diameter: Small
Bar blades: Steel
Bar blade position: 3
Drop-link position: Wide (Slow)
ARB preload: 0.0 ft-lbs

REAR:

Fuel level: 4.5 gal
3rd spring: Stiff
3rd spring gap: 0.321 in
Weight jacker: 0

REAR ARB:

ARB diameter: Large
ARB drop-link position: Wide (Slow)
ARB blades: 2
ARB preload: 0.1 ft-lbs

LEFT/RIGHT FRONT DAMPER:

Low speed comp: -7 clicks
High speed comp: -21 clicks
Low speed rebound: -7 clicks
High speed rebound: -14 clicks

LEFT/RIGHT REAR DAMPER:

Low speed comp: -19 clicks
High speed comp: -23 clicks
Low speed rebound: -23 clicks
High speed rebound: -20 clicks

ENGINE:

Engine map setting: 7 (MAP)
Turbo boost pressure:  Push to Pass limited to 10 times per race.

GEARBOX:

First gear: 16/34
109.3 mph
Second gear: 17/31
127.4 mph
Third gear: 19/31
142.4 mph
Fourth gear: 19/28
157.6 mph
Fifth gear: 18/25
167.3 mph
Sixth gear: 20/26
178.7 mph
Final drive: 17/59

DIFFERENTIAL (RC only):

Clutch plates: 4
Preload: -50 ft-lbs
Ramp angles: 45 coast/30 power

Basic Oval Track Setup Building for DW12

Building a competitive setup requires a great deal of trial and error testing.  While one could start from scratch for each track, each season, it is often time efficient to build on already existing setups.

iRacing provides “fixed” setups for every oval track. Each of these are thoroughly tested by some unknown person or persons to be “competitive” and are almost always a bit under-steery or “tight”. On most ovals, it is useful to take this fixed set and modify it.

First, run the fixed set for 10 laps and get a baseline set of lap times.

One modification is called “fixing the toes”.   Essentially, using the toe in/out settings to make the front and rear wheels “steer” into the turn.  The system will generally only allow -2 on the right rear (toe out) and +2 on the left rear (toe in).  At the same time, generally the front is set with -1 on the left front and +1 on the right front.   There are many theories of why this works.  The most plausible is that the car essentially travels in a “crab” orientation creating some aerodynamic assist in turning but it is also correct to note that this adjustment changes the location of the turning radius center. The driver needs to adjust his sense of attitude (loose vs tight) as the car may seem loose, even though the tires’ slip angles may not be materially different.

The next modification is to adjust the radiator inlet—changing to 1/3 blocked for racing and 2/3 blocked for qualifying. Most fixed sets run the radiator Open.

After making these two modifications, run another 10 laps and compare lap times and handling to the baseline. Also view the tire temps and wear. 

Generally the car will be “tight” or under-steery.  This is usually the result of excessive Relative Rear Downforce and will also be signaled by higher front tire temps compared to the rear.

IMPORTANT TERM:   A Balanced Race Car is one where the right front and the right rear tires are close to the same temperature and wear---this is the goal. With the correct driving line, you will “feel” this with the car not being loose or tight.

Note the % Front Downforce.  Reduce the rear wing downforce slightly as well as reducing the lower beam wicker to ¼”

IMPORTANT TERM:  Best Camber for Racing Grip is the setting that produces nearly equal tire wear from left to right of each tire. (This may not be the best setting for qualifying, but for racing it produces the setting that will provide the best lap times for long runs.) See Figures below. On an oval track, negative camber on the right side and positive camber on the left is essentially creating a "camber angle" and "camber thrust" on both left and right tires. (Forces on both tires to the left to make the car turn left.)

Note the Cross Weight (Left Front +/- Weight). Adjust the left side to less positive camber (often to the least allowed by iRacing). Adjust the right side as required to achieve Best Camber for Racing Grip. ( See figure above--You are compromising maximum lateral grip when cold for better tire performance when tires are hot as well as maximizing the usable tire surface for longest life.) Adjust ride height to restore the original Cross Weight. 

Run another 10 laps and compare lap times and handling. Note tire wear. Repeat with additional changes to wing aero until a Balanced Race Car is achieved.

Once a Balanced Race Car is achieved by adjusting wings, note the Front Downforce %. Reduce front and rear wing as needed to reduce total downforce while maintaining the Front Downforce %.  At some point, reduction in downforce will expose poor handling. The car will be too tight or too loose.

Before making any further adjustments, using ALT L, and some form of telemetry software analysis, note the ride heights on all four corners.  If the car is hitting the track during corners, then ride height needs to be increased. Generally, at corner entry and mid corner, the optimum ride height on the right side would be not be much more than 0.3 inches—often this requires you to lower the car.  On the straights, it is generally good for the rear ride height to be 0.3 inches higher in the rear than the front. (You can tell if the car is too low without telemetry--top speed will be hurt and if you watch carefully in the replay, you can see sparks.)

Having noted these ride heights, make adjustments as needed while maintaining the Cross Weight. Run another 10 laps and compare lap times and handling. Note tire wear.

You will now start making adjustments to remedy the handling issues you observe without adjusting wings.

If the car is tight, adjust ride heights to put more weight on the left front tire. If the car is loose, adjust ride heights to take weight off of the left front tire. (By taking weight off the left front, you are essentially reducing the right rear tire weight at the same time. Most times the loose condition will be reduced by reducing the right rear tire load.)

Run another 10 laps and compare lap times and handling. Note tire wear.

If the car exhibits a tendency to snap oversteer on exit, increase left rear spring or decrease right rear spring. This is called adding "bite". (Alternately try reducing left front spring.) At the same time, reduce rebound dampening on the left rear and reduce compression dampening on the right rear and  try increasing the front ARB. Reduce caster settings. (Higher caster makes the car looser when turning.)  If the car exhibits a tendency to be tight in mid corner and/or exit, do the opposite, plus reduce rebound dampening on the left front.  

The figure above gives a bit of insight about the high and low speed damper settings.The low speed settings affect the damper when moving at 1-2 inches per second. The high speed settings affect the damper when moving faster than that. The rate of damping force increase relative to speed is different for high speed movement vs. low speed. Rebound damping is higher than compression damping because the spring is acting to accelerate the damper's movement.

The challenge here is that each track has a different “Ribbon Banking Transition”. Think of the track as a ribbon of pavement that is twisted as it transitions from higher banking in the turns to less banking on the straights. The shape of that “ribbon” will change the “dynamic” handling characteristics of the car.  As a car comes off the steeply banked turn, the reduced banking on the front straight requires the inside of the track to RISE, placing more force on the left front tire and less force on the left rear momentarily—the car will be loose.  As a car enters a steeply banked turn, the inside of the track will FALL, placing less force on the left front tire and more force on the left rear momentarily—the car will be tight. (Many times this “tight on entry” will not be noticed and will extend to turn exit where the driver will input too much steering to correct for it—causing a loose on exit problem. ) Each track and each corner “twists the ribbon” differently. Adjusting the Cross Weight and relative spring and damper settings for each corner is generally how this dynamic handling is optimized. (This issue is the reason you will often find that the best setup requires a weaker spring on the left front.)

Run another 10 laps and compare lap times and handling. Note tire temps and wear. Keep in mind the important goal of maintaining a Balanced Race Car. (97% RF; 97% RR is good for example.)

Now, experiment with increasing downforce AND decreasing downforce to achieve faster laps. (Keep in mind the goal is to improve or optimize the Downforce to Drag ratio when making changes, if possible.)  Experiment with different tire pressures. Experiment with changing "rake" of the difference between front and rear ride heights--more rake with rear higher than the front will increase downforce and drag. (This requires lots of trial and error testing.)  Be sure to run a full fuel run on what you think is your best setup. On hot tracks, most setups will require adjustments to weight jacker and/or ARB during a full fuel run.

The choice of settings for the various aerodynamic devices on the Indycar is not simple. One confusing aspect is that "negative" wing angles can still produce downforce.  In iRacing, one simple help is clicking the right side box increases downforce.  Generally, the wing is more efficient with a small wicker or Gurney Flap--the theory being there is less turbulence. (Reducing turbulence is a good thing in aerodynamics and in addition to making your car faster---less turbulence creates less draft and makes it harder for your opponent to pass.)

Negative weight jacker takes weight off of the left front, making the car less loose. Positive weight jacker puts more weight on the left front and right rear, making the car more loose. When thinking of the weight jacker, think LOOSE----Negative=MINUS or LESS LOOSE; Positive=PLUS or MORE LOOSE. Adding front ARB will tighten the car. Reducing front ARB will loosen the car. When thinking about the Front ARB, think TIGHT---More Front ARB=MORE TIGHT; Less Front ARB=LESS TIGHT.

Check top speed at the end of straights--adjust gearing as needed. Generally you want 5th gear max to be 3-5 mph higher than your top speed. 6th gear should have enough more max speed to allow for added speed in the draft. Set 4th about 10 mph lower than 5th so that it can be used in corners during the race----in traffic near the end of the race.

Be sure RACE setups do not use Qualifying Boost.  (Do be sure to use Qualifying Boost for running Qualifying setups in Practice.)

For qualifying, generally, you change the radiator inlet to 2/3 blocked, and reduce fuel to 2 gallons. Since the car is lighter, adjust the ride heights to compensate while maintaining Cross Weight. Then, experiment with reducing rear wing and increasing all springs by 50 or 100 # to make the car more stiff. (Tires will have maximum grip and stiffer springs can be faster.)  You may find increasing weight on the left front, i.e. changing Cross Weight may be faster. For qualifying you want a SLIGHTLY UNBALANCED setup with a tendency to be a little loose. (This usually is indicated by rear tire temps about 5-10 degrees higher than the front.) You may also find that increasing camber and caster settings make the car faster. Be careful as the car may become “edgy”.  On some tracks, the second lap of qualifying is slower because during the first lap, you abused the tires to get maximum speed.

Colder temps generally allow less wing and more weight on the left front. Hotter temps generally require more wing (downforce) and less weight on the left front. Remember that the underwing is the most efficient so be sure to maximize available downforce with strakes and ¾ wicker before adding front or rear wings.

Some drivers use the weight jacker in between corners to make the car better suited for each corner. Some actually do this DURING the corner to change the handling between mid corner and exit!

A loose race car is very hard to drive in traffic, so for extra hot conditions, generally the car will need to have more rear downforce and sometimes a stronger left rear spring. (Or weaker right rear.)  A loose condition usually requires a reduction in throttle which causes a weight transfer from rear to front which may make it more difficult and may take more time to stabilize the car where an understeery condition can often be quickly remedied by a slight reduction in throttle.

Often, it will require 6 to 8 different setups to cover the range of temperatures for qualifying and racing.

This is by no means a complete instruction. There are many other adjustments that can be made and vehicle dynamics are complicated. These “more advanced” settings (like choice of wheelbase and assymetrical caster settings or moving weight forward/rearward as well as tire pressures) should be attempted to further optimize your lap times but will require additional time consuming testing. And, remember that driving lines and throttle modulation are part of how best lap times are achieved. 

Note 1: The choice of spring rate for each corner is "relative" to the spring rates on the other corners. The choice of the average spring rate depends on three factors--bumps ride height, and grip. Choosing a higher spring rate will reduce the chassis deflection at high speed from aero downforce--this is good. Choosing a higher spring rate will increase the speed that weight transfers in turns and when grip is lower--this can be bad. Most times the best setting is the result of trial and error testing. Tire pressures change the effective "spring rate" of the tire and tend to produce a similar result as a change in spring rate for that corner--think of the tire and spring as two springs connected in "series".

Note 2: There is an advanced topic regarding the use of significant added weight (100-250#) to the left front tire. In NASCAR this is called Negative Cross or Negative Wedge. In IndyCar it is EXTREME ADDED LEFT FRONT weight. It is a very odd setup that only works on some tracks, at lower temps. The added weight to the left front keeps the front “planted” and extra high rear downforce is used to keep the rear “planted”. The extra drag from the extra rear wing is less than the reduction in scrubbing/friction drag from the front steering tires.  When it works, the car can be an order of magnitude quicker.  Often it works on a cold track (like Iowa at night) but it seldom works on a hot track. The effectiveness depends on the relative temperature vs. grip curves of the front and rear tires. 

Basic Road Course Setup Building for Star Mazda

Link to .sto File

iRacing.com Formulamazda setup:

RFCBaseSM2016S1 v1.0

FRONT:

Cold pressure: 20.5 psi

REAR:

Cold pressure: 20.5 psi

FRONT AERO:

Wing flap angle: 24.0 deg
Wing mainplane angle: 5.5 deg
Wing flap gurney: 1/4" - 6.4mm

REAR AERO:

Wing upper element setting: A1
Wing lower element angle: 7.5 deg
Wing lower element flap gurney: None
Wing end plate vertical gurney: Full Length

AERO CALCULATOR:

Front RH at speed: 0.875"
Rear RH at speed: 1.000"
Front downforce: 54.62%
Downforce to drag: 1.810:1

FRONT:

ARB diameter: Large
ARB blades: 2
ARB preload: -0.0 ft-lbs
Toe-in: -1/16"
Brake pressure bias: 55.7%

LEFT FRONT:

Corner weight: 288 lbs
Ride height: 0.910 in
Spring perch offset: 2.500"
Spring rate: 800 lbs/in
ARB rocker hole: Fast
Camber: -2.2 deg
Caster: +8.9 deg

LEFT REAR:

Corner weight: 398 lbs
Ride height: 1.175 in
Spring perch offset: 2.469"
Spring rate: 700 lbs/in
ARB rocker hole: Slow
Camber: -1.5 deg

RIGHT FRONT:

Corner weight: 288 lbs
Ride height: 0.910 in
Spring perch offset: 2.500"
Spring rate: 800 lbs/in
ARB rocker hole: Fast
Camber: -2.2 deg
Caster: +8.9 deg

RIGHT REAR:

Corner weight: 398 lbs
Ride height: 1.175 in
Spring perch offset: 2.469"
Spring rate: 700 lbs/in
ARB rocker hole: Slow
Camber: -1.5 deg

REAR:

Fuel level: 4.0 gal
Toe-in: +1/16"
ARB preload: -0.0 ft-lbs
Cross weight: 50.0%

LEFT FRONT DAMPER:

Low speed comp: -12 clicks
High speed comp: -15 clicks
Low speed rebound: -7 clicks
High speed rebound: -14 clicks

LEFT REAR DAMPER:

Low speed comp: -7 clicks
High speed comp: -12 clicks
Low speed rebound: -5 clicks
High speed rebound: -12 clicks

RIGHT FRONT DAMPER:

Low speed comp: -12 clicks
High speed comp: -15 clicks
Low speed rebound: -7 clicks
High speed rebound: -14 clicks

RIGHT REAR DAMPER:

Low speed comp: -7 clicks
High speed comp: -12 clicks
Low speed rebound: -5 clicks
High speed rebound: -12 clicks

Gearbox:

First gear: 12/29
69.8 mph
Second gear: 15/32
79.1 mph
Third gear: 15/25
101.2 mph
Fourth gear: 19/27
118.7 mph
Fifth gear: 20/25
134.9 mph
Sixth gear: 19/21
152.6 mph

This article shares a “Base” setup tested for iRacing’s 2016S1 “Build”.  (Sometimes iRacing makes changes to chassis stiffness and tire grip/slip angle coefficients that may require minor changes to the base in the future.)

This “Base” setup is designed for a “balanced” car—neither “tight=under-steery” or “loose=over-steery”.  For each track, this is a starting point and modifications and adjustments need to be made and tested for optimal performance.  

Keep in mind that the Star Mazda has an “open” differential and will handle a bit differently than cars with a spool or locking differential. It is generally driven with a bit of “trailing throttle oversteer” which allows the driver to steer the car with throttle application, to some degree.  This set introduces significant “trailing throttle oversteer” and requires some “maintenance throttle” to hold the rear when turning.

First, run the “Base”  set for 10 laps and get a baseline set of lap times. Note the top speed. (If you hit the rev limiter in 6^th gear, then adjust it to a higher mph setting and determine the top speed before ending the first stage testing.) Also note the gears used entering and exiting each corner.

Before proceeding further—view Youtube videos of hot laps at the track run by other drivers. Note the top speed and the gears used entering and exiting each corner. Note the driving lines taken and braking points if possible. Check iRacing results and World Records and set a “target lap time”. (This is a different procedure than the typical concept of choosing downforce to improve cornering---the idea is that top speed is limited by the gearing and aero settings you choose.)

IMPORTANT TERM:   A Balanced Race Car is one where the front and the rear tires are close to the same temperature and wear---this is the goal. With the correct driving line, you will “feel” this with the car not being “generally” loose or tight. But, on road courses, in most cases a compromise is required—some corners the car may seem loose while in others it may seem tight.

IMPORTANT TERM:  Best Camber for Racing Grip is the setting that produces almost equal tire wear from left to right of each tire. (This may not be the best setting for qualifying, but for racing it produces the setting that will provide the best lap times for long runs.) On road courses, because of necessary and desirable negative camber, generally the temperature and wear on the outside edges will be lower.

The first adjustment will be to setup the gearbox so that desired top speed is achieved in 6^th gear with Max Speed Possible (hitting the rev limiter—this is 152.6 mph in the Base Set) approximately 5-6 mph higher than the desired top speed. (This allows for the draft.) Then set 5^th gear Max Speed Possible at 88-90% of 6^th gear; 4^th gear Max Speed Possible at 87-88% of 5^th gear; 3^rd gear Max Speed Possible at 85-87% of 4^th gear; 2^rd gear Max Speed Possible at 78-84% of 3rd gear; and 1^st gear Max Speed Possible at 88-90% of 2nd gear. (2^nd gear is the most often used gear for slow corner exits.)

Run 10 laps to verify you are reaching the desired top speed. If you are not hitting the rev limiter and not reaching the desired top speed, then you must reduce aerodynamic drag.  Reduce the front and rear wings as necessary to maintain a 48-55% Front Downforce % and a Balanced Race Car tire condition as well as the desired handling in the fastest corner and corner/s leading to the longest straight. In previous seasons the front downforce % was a lower range   Note the gears used entering and exiting the corners and make adjustments as necessary. (The main issue is that you usually would prefer to be upshifting after the track out point on corner exit. Make minor changes to gearing—one step only.)

Finding the right “combination” of wing angle/s, wicker dimensions takes a bit of trial and error using the Aero Calculator as a guide.  Choose the combination giving the highest Downforce to Drag ratio. Here is where you may choose to add aero downforce to improve handling and lap times, even though it may reduce your top speed.

Once a Balanced Race Car and desired top speed is achieved by adjusting wings, run another 10 laps to establish a new baseline set of lap times. Note the presence of tight or loose conditions.

Before proceeding further, carefully consider the choice of spring rates. The “Base” setup produces certain handling characteristics that can be changed simply by changing spring rates. Increasing the front spring rates will make the car tighter. (Drivers who like to brake later may desire this.) 

Decreasing the front spring rates will make the car more loose. Increasing the rear spring rates will make the car more loose. (Drivers who like to “steer with throttle may desire this.) Decreasing rear spring rates will make the car tighter. (It is not recommended going much lower than 500 pounds for the rear springs.) If you change springs, reset ride height back to the “Base” settings and run a few test laps to insure the car is a Balanced Race Car. Adjust aero as needed.

Note: On tracks with fast sweeping corners, often a spring rate that is higher in the rear works well. On tracks with chicanes and hairpins requiring acceleration from a slow speed, a lower spring rate in the rear is usually better. On tracks with chicanes requiring fast direction change, sometimes it is beneficial to increase the front spring rate. Changing springs by a significant amount from the base requires attention to ARB settings. See Note at end.

There is no "magic" formula for the correct tire pressure. Best advice is to experiment at each track with increasing and decreasing tire pressure from the base. Generally, tracks with fast sweeping corners call for higher pressure. And, tracks with slow chicanes and hairpins call for lower pressure.

Before making any further adjustments, using ALT L, and some form of telemetry software analysis, note the ride heights on all four corners.  If the car is hitting the track during corners, then ride height needs to be increased. Generally, at corner entry, the optimum ride front height under heavy braking would be not be much more than 0.2 inches—often you will desire it to be near zero.  Generally, the Star Mazda should be run with low ride heights—just low enough to not hit the track. This produces "ground effects" downforce with little increase in drag.  One may choose to increase downforce (and drag) by increasing “rake”—raising the rear height.  The car will also tend to turn better in mid-corner with a higher rake.

After adjusting ride height/s, Run another 10 laps and compare lap times and handling. Note tire wear and temps. You will now start making adjustments to remedy the handling issues you observe without adjusting wings. You will focus on improving the handling in specific corners as well as improving tire wear/temps.

You may gain speed by reducing the rear toe to zero—you may also increase rear toe-in on slower tracks to help the rear stick better on acceleration. Increasing toe-out on the front can help the car turn in more quickly.

First, adjust front and rear camber to optimum. Keep in mind the principle of “Camber Thrust” where tires on the outside of the curve tend to produce more lateral grip with a small amount of negative camber but produce less on the inside of the curve.  Generally, tire temps should be about 5% cooler on the outside. Next, choose the desired Caster. Higher Caster setting will make the car more loose in mid corner. Finally, choose the optimum damper settings. Generally, reducing high speed compression and rebound makes the car better able to go over curbs. Reducing low speed rebound settings will give that corner more relative grip; increasing compression settings will give that corner less grip. Keep in mind that changes to grip from damper setting are “dynamic” or momentary—they simply control/affect the speed that weight/cornering load is transferred.  

The figure above gives a bit of insight about the high and low speed damper settings.The low speed settings affect the damper when moving at 1-2 inches per second. The high speed settings affect the damper when moving faster than that. The rate of damping force increase relative to speed is different for high speed movement vs. low speed. Rebound damping is higher than compression damping because the spring is acting to accelerate the damper's movement.

Continue running 5-10 laps “Stints” after each change. Be careful that you do not confuse the improvement in lap times due to your improved driving with improvement caused by adjustments you make to the car. Often it is wise to reverse the change and test to see if lap times get worse when the change is reversed. Let your lap times determine the best setup. Be aware that changes can improve performance in one corner while making performance in another corner worse.

Colder temps generally allow less wing. Hotter temps generally require more wing (downforce). But this is not always the case—it depends on the track.

Usually qualifying is done with 2 gallons of fuel. The race is generally run with 4-5 gallons. You may wish to lower the front ride height for qualifying.

Often, it will require 4 to 6 different setups to cover the range of temperatures for qualifying and racing.

This is by no means a complete instruction. There are other adjustments that can be made. (like front brake bias and ARB settings) Vehicle dynamics are complicated.  Some drivers may prefer a car that is more loose than a Balanced Race Car. These “more advanced” settings should be attempted to further optimize your lap times but will require additional time consuming testing. And, remember that driving lines, braking and throttle modulation are part of how best lap times are achieved. Most often, if someone is going faster, it is not because they have a better setup--rather, they are simply using a better technique and moving their hands and feet more quickly. It is not uncommon for a "great" driver to be 2 seconds a lap quicker than a "good " driver using the same exact setup.

Note: Anti Roll Bar or ARB settings essentially affect the car in a similar way as running a higher spring rate, except the ARB only makes the car stiffer when rolling and not in forward/rearward pitch.  A stiff ARB on the front provides more rear tire grip during acceleration.  A weaker front ARB will allow the car to turn in mid corner better. Be aware that stiffening the front ARB can result in the inside tire lifting when turning, causing the inside tire to lock up while trail braking.

In addition to my engineering and racing background as well as 30 years of interest/study in the field of vehicle dynamics, a great deal of the knowledge and experience behind the base setup and this guide came from the excellent professional level coaching I received from nearly a year working with Wyatt Gooden. He continues to evaluate setups I build for Team RFC and almost always betters iRacing World Record laps times when doing so.    http://www.wyattgooden.com/