IRacing Formula Vee

IRacing has introduced the Formula Vee to its offerings. While it is introduced as a “Rookie” car, it has and will continue to attract a community of experienced drivers as occurred with the Skippy. These experienced drivers will compete using an “open setup” where drivers use setup optimizations to achieve advantage.

This series of WS Speed Analytics will explore and test the optimizations of setup adjustments. 

First, here is the iRacing Manual on the iRacing Formula Vee. Click on link.

IRacing Formula-Vee-Manual.pdf

The Formula Vee has a very long history. Starting in 1962-63 it became and continues to be a popular car in SCCA and other worldwide venues.

Here is one of the best info manual to introduce you to the car. There is a lot of info that does not apply to the iRacing FV but it will provide a valuable foundation. 

Getting_Started_In_Formula_Vee 

Here is a website with more interesting info about the FV.

The US FV Enthusiast Website

The FV in real life runs a Type 1 air cooled 1200 cc engine. The Type 1 engine without cooling fan was offered in the Beetle in Mexico in 2003 with1600 cc. Displacement can be changed by replacing cylinders and crankshaft. According to the iRacing manual, the iRacing FV has a 1400 cc engine that produces 76 ft-lbs of torque and 69 Hp with a max RPM of 7400. Not sure where iRacing got this spec but no matter, "it is what it is" and that is all that matters.

Here is an excerpt from the "Getting Started" book. Note "a very good engine" on the dyno in a real life FV produced 58 Hp. Pretty sure my engine built by Neumeister was 60 Hp as it had set the track record at the runoffs the year before. Note peak Hp occurs around 5400 RPM and peak torque around 3700 RPM. In real life competition, drivers take the engine to above 6500 RPM but the risk of losing a connecting rod or bearing is high. My educated estimate is the iRacing FV engine has a peak Hp at around 6000 RPM and like the real life engine, optimum shift RPM is 6500-6600 RPM in 3rd which drops to 5000-5200 RPM in 4th depending on how rapid the shift. 

This screenshot is a cockpit cam of me in 2011 at Summit Point in my Vortech FV-note the GPS top speed of 110mph. The iRacing FV is slower despite having more power. I think the iRacing FV does not have as good aero design as the Vortech.

Neumeister's Vortech at Runoffs

My Vortech at VIR (note the half NACA duct)

Here is the car airborne

The biggest difference between the Formula Vee and most other race cars is the unusual rear “swing axle” design. Significant camber change occurs when the rear drops and rises, but the odd characteristic is that when the chassis rolls in a corner, the outside camber become more negative while the inside tire becomes less negative and often goes into positive camber range. The net result is the car has a natural tendency to oversteer on corner entry when throttle is released, the rear rises, and the chassis rolls.

The first step for building a good setup is to build a "first try" setup. Start with the iRacing baseline and then search in every available free forum/online resource including Garage61.net where setups are shared. (See what others are using.) Then test at a track of your choice. I chose VIR North and after examining four different setups and several iterations, I settled on my "StroutX3"

Since the FV is a very low HP car, the first order of business when building a "optimum" setup is to research the settings that produce the highest top speed. We can then test settings that might improve cornering to see their effect on top speed. For this we go to the Talladega oval.

Note the top speed of 99 mph and lap time of 1:36.932.  This was with zero toe in on rears and 1/32 toe out on front. I was quite surprised to see the top speed was considerably lower than real life FV's. 

Increasing tire pressure produced very modest improvement of about 0.05 seconds in lap time and given the probability that more tire pressure might decrease cornering power, I went back to the 17/17.5 psi settings and changed the front toe to zero. This changed lap time by a significant 0.164 seconds to 1:36.768 (still topped at 99 mph so less than 1 mph improvement). However, I returned to VIR North and saw significant improvement (0.4 seconds) on the long front straight. I could not see any significant loss of cornering power or turn in precision at VIR North with the zero front toe setting. (Top speed at Nordschleife testing was 104 mph)

So we have finished the "rolling resistance" testing. Now we test aero drag variables. The iRacing FV has no wings and a flat bottom. So the only adjustment for Aero is "rake" or the angle of the bottom of the car relative to the pavement. This is determined by measuring "reference" points on the chassis: front and rear.   

The StroutX3 set has a rake of 3.123. I dropped the rear to the max (limited to -2,5 camber) and dropped the front to 1.85 increasing rake to 3.156 and the car went slower. (This was good because front setting below 1.95 results in the nose dropping and hitting the ground during hard braking.) I then tried reducing the rake to 2.966 by raising the front, keeping the low rear and the car went slower. So the 5.082/1.959=3.123 is close to optimal. To check that I raised the nose to 2.012 which caused the rear to change to 5.067. This rake of 3.055  produced a very small increase in speed dropping lap time by 0.012 seconds. 

So let's conclude that the front spring preload should be 0.5 or 0 (1.959-2.012") and the rear spring perch offset should be 3.606" (5.082-5.067") to achieve least aero drag. I suspect the 0.5 front spring preload will produce a slight incline of the flat bottom and may have some minor downforce.

A word about Pushrod Offset setting of 1.187.  On a Zero Roll Resistance Suspension with only one spring and damper, ride height is adjusted with a combination of Spring Perch Offset and Pushrod Offset. There is droop stop rod on the iRacing FV as shown in the pictures which is assumed to be fixed, so then the total droop is affected by Pushrod Length. In maximum droop, the suspension will change the rear camber from negative to positive. Not enough droop and the rear wheels will lift off the ground too easily. Too much droop and the car can be very unstable under heavy braking.  My suggestion is to set the Pushrod Offset in the range of 1.0-1.2 and adjust the Spring Perch Offset to get the rear ride height of 5.082-5.067 with qualifying fuel load.

Now let's take the car to Nordschleife to check droop where we know the car goes airborne in Pflanzgarten. As the car is in the air, note how the rear tires go into positive camber. Even so, the car went thru this section very well.

Now we go to the Centripetal Track circle and drive long enough to burn 0.5 gallons. Third gear with left tire on the 100 meter line. Modulate throttle for steering--keep steering input constant. (This will illustrate to you the Zero Roll Suspension tendency of the off throttle oversteer, on throttle understeer-good practice too) See Short Video below)

Below is the tire measurements with -1.7 front camber. (Remember rear camber changes only with the rear spring perch offset which we will not change.)

Below is the test with front camber set to -1.8. 

It should be easy to see that the right front tire is working harder with the -1.8 setting as the tire temps are higher relative to the rear and there is 1% more wear. So -1.8 is more understeery than -1.7 front camber. The speed (around 77 mph) and lap times of around 18.55 were very close.  Given that -1.8 would offer slightly less rolling resistance and a bit more cornering force--the final decision should be on track testing and driver preference. 

Next we up the rear tire pressure to 18. Hmmm. Tire temps and wear almost the same. Given that in our Talladega test we say a slight increase in top speed, I would go with 17 psi front and 18 rear. The relative 2.2/2.0 pressure rise is slightly better than the 2.2/1.9 so there is better balance in the work the tires are doing. 

Now let's look at the rear spring. All tests to far have used a 200 pound spring in the rear. The FV uses a zero roll resistance rear suspension, the roll resistance is all in the front so the rear spring really only affects the rear compression under load. Changing the rear spring to 175 and keeping the rear ride height and rear camber to the same requires a rear spring offset of 3.370.

Not much change. Perhaps a very small increase in understeer but speed was almost the same.  Given the odd design of the rear axle where rear suspension movement creates a lot of camber change, I would go with the 200 pound spring. On a bumpy track, I would go back to the 17.5 psi rear tire pressure.

Zero roll FV rear suspension 

Now let's increase the front ARB from .625 to .750. This WILL change the roll (not rolling but chassis roll) resistance. Because all the chassis roll resistance is in the front, changing the front ARB changes handling differently than on a car with springs on all four wheels. A stiffer front ARB will reduce body roll and reduce the nasty adverse change to the inside rear tire camber a bit. It also appears to improve front tire grip (less sliding and less temp increase) by reducing the camber change in the front during cornering. Tire wear is reduced, hot tire pressure is lower.  Clearly there is more total "grip". 

Here is a video of the centripetal test

An unknown regarding the iRacing FV is how much bump steer and toe out in turns is in their design. These are important characteristics, and close attention is paid to them in real life. But we get what we get here. 

Now about the dampers or shocks. These are important adjustments that affect the "transient" handling. Off the throttle and on the throttle transfers weight rear to front and front to rear. Higher damper settings make the transfer occur faster. 

On throttle:  I have a tendency (due in part to injuries) to apply throttle very quickly so my preference is minimal front setting=0. Others who have better throttle modulating skills may like setting at 1 to be better. 

On braking: A high setting of 5 on the rear makes transfer from rear to front occur quickly. The dampers appear to be single acting so they only damp when extending.  The stiffer setting for the rear slows the rate that the rear axle drops so weight is removed from the rear and added to the front faster.  I like it to occur a bit slower so I prefer 4. (A setting of 5 would increase trailing throttle oversteer and oversteer on corner exit-maybe faster.)

Finally, the static front weight distribution is 46%/54%. During braking a lot of the rear weight is transferred to the front, so you want considerably more than 46% brake bias. You will see front brake bias set in the range of 61-67%. 

Here is video. 99 mph to full stop-100% brake pressure.  The first is Brake Bias at 63.2%. Good braking-handled well in real race with moderate trail braking. If trail braking deeper, raise to a slightly higher number.

Next is a test at 61.4%. Stopped in 15 feet less distance but a bit unstable--required steering control input. Only a Top Gun with fighter pilot reflexes or someone who never reaches 100% braking could use this low setting. 

 

Below is the iRacing Baseline setting of 67%. Front brakes lock and requires almost 25 feet more stopping distance than the 63.2%. 

Take the "StroutX3" settings that I raced at VIR North that are shown above-modify according to these tests (Change to 18 psi rear tire pressure, increase front ARB to 0.750 and test increasing front camber to -1.8) ...The rest is testing on track and adjusting the car to your personal taste—then call your setup FAST.

I tested the setup at several tracks. Ovals: Bristol, IRP, Milwaukee Mile, and Tsukuba Outer. (Tsukuba is excellent for testing and practicing trail braking, trailing throttle oversteer and corner exit neutral handling)  Road: VIR North and Nordschleife. I ended up being slightly faster with the stiffer rear damper setting. 

Here is my final result. (BTW this is very close to the setup shared by Brian Styczynski so much appreciation to him for that)

or more rear damper:

The above is for practice and a 15 minute qualifying session.  The one below is for a 30 minute race using 4 gallons.

or more rear damper:

A note about shifting. Because of severe leg injuries I use paddles for clutch. When shifting up I use right shift and lower left clutch; shifting down I use left shift and lower right clutch. (This requires a bit of programming on my VRS Pro Wheel) When driving the FF1600 with dog type transmission, as long as the clutch and shift overlap the shift occurs without lifting. The FV uses an old fashioned system that is more sensitive to the clutch needing to be fully engaged if power shifting at full throttle. Similarly when downshifting even when (especially when) manually blipping.  So it takes practice to begin pulling the clutch paddle a mini second before pulling the shifter. I got the timing wrong for the first 10 hours of testing and racing and missed many shifts. Using auto blip is slow. So being fast in the FV is mastering precision power shifting. You should also master doing this with a perfectly timed small throttle lift and fast enough action so as not to exceed 7000 RPM when the clutch is disengaged. A missed shift not only costs time but if someone is following close it can cause a collision.

Different opinions about shift points. 3rd to 4th at "4 bars" or around 6600 RPM (85 mph) will drop the RPM when into 4th to just above 5000 RPM. Any higher than 6600 RPM probably is counterproductive. Shifting at 84 mph to be in 4th early using the downshift into 3rd to help rotation into a corner sometimes is beneficial. 

Gear Choice

Gear Choice

There is often a debate as to which gear is the best for a particular corner.

A general rule of thumb is that the best gear at the time of throttle application is the one that provides maximum acceleration from apex to corner exit.  

Each transmission is different, but most transmissions have a 20% difference between 3rd and 4th gears.  Given the same speed, the engine in third gear will be running at a 20% higher RPM than in fourth.  

Example:  5800 RPM in the Corvette in 4th is about 7200 RPM in 3rd. 

This is a part of the actual HP and Torque curve for the Corvette GT3.  It has a very "flat" torque curve (blue line).  Most modern racing engines have a reasonably "flat" curve.  Lower performance engines have torque curves that fall off at higher RPM-racing engines less so.

The iRacing version of the LT6 engine has a max torque of 460 ft pounds at 6300 RPM. Let's estimate at 5800 RPM torque is 440 ft pounds. And, at 7200 RPM torque is 420 ft pounds.

Force=Mass times Acceleration.   Acceleration = Force divided by Mass.   

Transmissions essentially MULTIPLY torque so 3rd gear has 1.2 times the torque of 4th gear.

OK. The Corvette has 5% less torque at 7200 RPM than at 5800 RPM but 3rd gear increases the torque by 20%. Greatly simplified:  3rd gear at 7200 RPM has 14% more torque and acceleration than 4th gear at 5800 RPM.  So initially, the Corvette will accelerate significantly faster in 3rd gear.   (Torque actually increases from 5800 to 6300 RPM, so the average increase is probably closer to 10%.)

Now, redline is about 7800 RPM, so using 3rd gear at the apex with 7200 RPM will require upshifting much sooner than if 4th gear was used.  Shifting down to 3rd on corner entry and up to 4th before corner track out takes time.  The downshift tends to slow the car in corner entry and acceleration is reduced when upshifting.  These reductions in speed must be compared to the increase in acceleration by using the lower gear. 

Another factor to consider is that the 10-14% more torque in the lower gear, in addition to increasing acceleration, also increases the risk of wheel spin and traction control intervention. 

So, the only real answer as to what gear is best is only determined by lap time. Often, there is very little difference. 

The "keep it in 4th" driver will probably see a bit more understeer both in corner entry and exit. But, no time or mental concentration will be lost in shifting. The "downshift to 3rd" driver will see less understeer on corner entry and exit. If using 3rd results in an RPM below 6800 at the apex the time duration with higher torque at the wheels and higher acceleration will most probably more than offset any time lost in upshifting. 

The Corvette will not allow downshifting if it would overspeed the engine. In most cases, the advantage, if any of using 4th rather than 3rd is that often in the process of downshifting, speed and momentum is lost. This speed and momentum loss can be minimized by downshifting as close to the apex as possible--the increased load on the rear tires will rotate the car without having to scrub off speed with steering input at the apex. 

 Author's Note:  I generally use the lower gear only for a very brief period-just before the apex and just after for a "burst" of extra acceleration and assistance in getting the car to rotate without as much steering input. 

IMPORTANT: The discussion above takes on a whole different perspective when dealing with a low horsepower winged formula car like the F4.  In the F4, maintaining speed and momentum is of paramount importance. Corning grip increases substantially with higher speed-likewise corner grip decreases with lower speed. If you feel able to use a lower gear, you may be slowing down too much on corner entry. 

Keep in mind that aerodynamic forces from wings and underbody channels increase at the square of speed. For example a 5% higher speed increases downforce by 10%.

Corvette Z06 GT3 Part 1

This is a series focused on setup development for the Corvette.

Before you start, be sure to read the iRacing User Manual for the Corvette

Chevrolet-Corvette-Z06-GT3_manual_V2.pdf

Rule #1. NEVER EVALUATE A SETUP ONLY ON A FEW LAPS OF TESTING. IT TAKES A MINIMUM OF 25 INTENSE PRACTICE LAPS TO DRAW ANY CONCLUSIONS. EVEN THEN THERE IS A HUGE POTENTIAL FOR AN INCORRECT CONCLUSION. 

The first task in developing a setup is to select the gearing most suitable for the track/s.  You need to know that you are allowing the car to reach the best top speed on a long straight in a draft. You also need to know which gearing best suits the corner exits of the track you are running. In many race cars you can change each gear set--1st thru top gear.  iRacing offers two basic gear combinations: FIA and IMSA.

Below is a chart showing the max speed in mph for each gear in the set:

At this point, the question is “Where do I start?” 

Start with a setup that you trust is reasonably close to your goal and modify it. Use iRacing “canned” setups, setups from VRS, Apex, Coach Dave or your League Engineer

Note that the FIA set allows a higher top speed in 5th and 6th AND more torque (lower speed=more torque multiplication) in 1st-3rd gears.

To choose what is best, test the top speed possible at the longest straight of the track/s you will be running at. Let's consider Road Atlanta, SPA, Mosport, and Suzuka. Testing indicates max top speed not in a draft is:  Road Atlanta 162 mph, SPA 158 mph, Mosport 155 mph, Suzuka 159 mph. 

Add 3% to these top speeds to adjust for maximum 2 car draft: Road Atlanta 167 mph, SPA  163 mph, Mosport 160 mph, Suzuka 164.  Although the IMSA gearing would be suitable for the top speed requirments, you also have to consider how the gearing works in corners.

Note the FIA gearing torque is higher than the IMSA:  20% more in 1st, 8% more in 2nd, 5% in 3rd, equal in 4th, 4% less in 5th; and 4% less in 6th. Bottom line: The FIA gearing will allow significantly higher acceleration (and potential wheel spin) in 1st thru 3rd resulting in higher speeds at the beginning of long straights--this speed "carrying thru" the entire long straight. 

On the other hand, the IMSA gearing will allow more acceleration in 5th and 6th gears. 

The "best choice" depends on the track. In a theoretical "drag race" for example at SPA: after exiting the hairpin in 1st gear, the car with the FIA set would reach Eau Rouge sooner with the car having the IMSA set catching up by the end of the Kemmel Straight. A driver with the FIA set defending the entry at Les Combs would have an advantage. The driver with the FIA set would almost always have an advantage in a race. 

In hot lapping the gear sets most probably do not produce different lap times. 

As can be seen by the chart, the rear wing setting results in only a small change in top speed. The difference between 9.5 and 8.5 are not significant. The difference between 9.5 and 7.5 and especially 6.5 is significant and would make a difference in lap times if the driver is able to cope with the reduced grip in the corners. 

Testing grip at the Centripetal Track

The vast majority of downforce on the Corvette comes NOT from the rear wing but rather the sophisticated air tunnels under the car. Rake or the difference in ride height from front to rear and total ride height WOULD have a significant effect on downforce. (The car needs to be as low as possible--just so high as not to drag on curbs.) The rear wing tends to be more of a fine tuning of the understeer/oversteer balance. Running a test at the Centripetal Track with 190 foot, there was less than 0.5 mph difference between each incremental change from 9.5-8.5-7.5-6.5. The most noticeable difference was the car had an understeering tendency at 9.5 and an almost oversteering tendency at 6.5.  A driver unable to cope with the oversteer tendency would do better staying with the 9.5 on all tracks where top speed is less than 160 mph. 

So, once you choose the gearing and the wing, move on to the adjustments that determine: 1) Brake bias for max stopping power and optimum trail braking that fits with driver's preference; 2) Adjustments that affect the understeer/oversteer balance in all corners--giving priority to the corners leading to the longest straights; and 3) Adjustments that affect the "transitions" and weight transfer front to rear, and side to side, during corner entry and exit. See Parts 2, 3 and 4 of this "series" on the Corvette.

Corvette Z06 GT3 Part 2

Corvette Z06 GT3 Part 2

Choosing Brake Bias, Anti Lock Brakes and T/C

Front Brakes Locked

Brake Bias refers to the % of total braking power directed to the front. The higher the Brake Bias the more likely the front wheels will lock up under braking--obviously this is a bad thing because once the front tires are locked up the driver can no longer steer the car. The lower the Brake Bias the more likely the rear tires will lock up--this is bad as generally the car will immediately spin.

On cars with Anti Lock Braking, turn off the ALB or more correctly the ABS and attempt to execute "Threshold Braking" from 100 mph. Adjust the Brake Bias lower if the front tires lock up-higher if the rears lock up. You can see what's happening by looking at the RF/RR or LF/LR replay views. When you have lowered Brake Bias to a point that the rear tires lock up and handling is unstable, on the Corvette with 5-7 gallons of fuel load, you will be at close to 51.8. Raise the setting to 53.8 to insure you NEVER lock up the rear brakes. 

Front and Rear Brakes Locked at 51.8

In addition, set the ARB and T/C to 2 to allow the computer to help you drive. Very skilled and experienced drivers can run with ARB and T/C at 1. Less skilled and experienced drivers may find the ARB and T/C setting at 3 to be easier to drive.

Another reason for the higher Brake Bias is that even though the rear tires are not locking up, applying brakes in the corner in order to Trail Brake will reduce the sideways grip of the rear tires and the car will have more oversteer.  Increasing Brake Bias will reduce corner entry oversteer but the price that is paid is lower total braking power--you will have to brake earlier with higher Brake Bias. You can brake later with lower Brake Bias as you are utilizing more total braking power--utilizing more of the potential braking from the rear. 

Keep in mind that GT cars have less relative downforce and more weight transfer. Brakes need to be applied earlier than formula cars and weight transfer can make the car feel loose under heavy braking-a fact you should have noticed in the testing described above.

Drive the car and experiment with small changes to see what best suits you. This setting can be changed from the cockpit during the race. Highly advanced drivers will change this setting for different corners during the race!

Traction Control is also adjustable from the cockpit. As mentioned above, it is allowing the computer in the car to help you control two things--wheel spin and yaw. Yaw is the rotation of the car when changing direction. T/C comes with a price--if you exceed a certain predetermined set of conditions (too much wheel spin or yaw) the computer takes almost complete control of the car away from the driver. Much more difficult for driver to "save" with high T/C setting. You have surrendered some of your control as a driver to the computer. (And the guy or gal who wrote the T/C computer software).  It should also be noted that T/C functions by applying brakes and reducing throttle—so T/C will almost always slow you down.

Be aware that the optimum Brake Bias depends to a great extent on how much brake force is being applied.  The Corvette is a heavy 3000 pound car with a higher center of gravity than a formula car--weight is transferred from the rear to the front during braking. The harder you brake the more weight is transferred. The weight distribution on the Corvette is 40% Front/ 60% rear. Under heavy braking this may change to 55% front and 45% rear, so Brake Bias settings depend to a degree on how heavy you tend to push on the brakes. 

The Corvette allows you to choose the type of brake pads. It has been said that the low friction pads allow more “modulation” but this is a myth-you will just have to push harder on the pedal. Muscle memory is most accurate at medium levels of leg/ankle/foot force.

In addition, the Corvette has a large displacement engine, so downshifting is like applying the rear brakes only. If you are an early downshifter, you may want a higher Brake Bias to avoid spins.

Cockpit Adjustments

Corvette Z06 GT3 Part 3

Corvette Z06 GT3 Part 3

Balance

Corvette with slight "fast" oversteer in Rivage

When a car understeers, the driver gets to see what he is about to run into. When a car oversteers, the drivers cannot see what the car is about to run into because they are going backwards. In either case, excess understeer or oversteer is BAD. 

In essence, understeering is caused when the side force provided by the front tire's grip is less than the side force provided by the rear tires's grip. But the term understeering is even easier to explain from a driver's standpoint with an understanding that a car that has understeer is requiring more steering than should be needed--it is "rotating" less than it should. Oversteering is when the car is "rotating" more than it should. A more technical term is "slip angle" which is the angle the tire's travel differs from where it is pointed. When the slip angle is higher on the front tires than the slip angle on the rear, you have understeer. In order for a tire to produce a sideward force, there must be a slip angle.

Every race driver needs to train diligently to become hyper sensitive to both of these conditions of understeering and oversteering. And the car will have different levels of understeering or oversteering in different corners and will depend a lot on what input the driver applies and when the input/s are applied. 

The goal is to achieve a car that is "balanced" with not too much understeer or oversteer-especially in the corners leading to long straights.

Drivers should learn that they can partially overcome or correct oversteer or understeer by changing their inputs and the timing of those inputs. This is not ideal, but is better than being seriously slow because of a slow set up or than running off track or  spinning out of control. The most common way to compensate for understeer is to trail brake further into the corner. The most common way to compensate for oversteer is to brake earlier and end trail braking earlier and avoid early downshifts—and to delay throttle application slightly on exit.

They can also make adjustments to Brake Bias, Rear Wing. ARB,s, T/C and Anti Lock Brake settings in the cockpit. (see Part 2 pictures)

Tire Pressure

Here you are dealing with iRacing’s infamous “Tire Model” that attempts to replicate the real world. In this respect, sometimes reducing tire pressure will increase grip, sometime it does not. Sometimes increasing it will increase grip. Start with the pressure in the “canned” iRacing setups and experiment.

Toe out/Toe In

Most race cars including the Corvette perform best with Toe Out on the front tires and Toe In on the rear tires. The Toe Out in the front is where the tires point outward toward the sides. This helps the car "point" on corner entry by providing an immediate higher slip angle on the inside tire at the beginning of turn in--recognizing that the inside tire has to turn thru a smaller radius. 

Most race cars including the Corvette perform best with Toe In on the rear tires. This tends to increase the slip angle on the outside rear tire on corner exit as it increases sideward thrust. 

If the car is understeering on corner entry--try increasing Front Toe Out. If the car is oversteering on corner exit-try increasing Rear Toe In.

Both Toe In and Toe Out increase drag and slow down the car and wear out tires--too much is bad.

Camber

Negative camber is where the tires lean in at the top. Negative camber generally makes the tires produce more side thrust--a good thing. But there is a limit and excess camber is counter productive. Too much camber leads to the inside edges of the tires overheating--especially during braking. Camber reduces the size of the contact patch between the tire and the track--making that part of the tire work harder, causing overheating. On formula cars there is air flowing over the entire face of the tire, but in GT cars the inside edge of the tire gets less air flow--overheating is worse.  Camber needs to be only enough to allow the largest possible tire patch size during cornering and no more. 

During qualifying, tire overheating is less of an issue. But during a race it can be serious. Most iRacing 'canned' setups have too much camber.

Testing has determined that traditional concerns regarding tire overheating is not an issue at track temps below 100F, so maximum Negative camber is fastest.

Caster

Positive Caster pushes the outside tire down when turning. This action transfers weight to the inside rear tire reducing understeer. More positive caster reduces understeer and increases oversteer. Unfortunately, iRacing does not provide for adjustment of caster on the Corvette. I am sure it has a lot.

Rear Differential Setting

The more clutch plates and the higher the preload, the more force is applied to make both tires rotate together with less "differential" action. This is a good thing in that the power is better applied to both tires and there is more force pushing the car out of the corner-especially as the steering is almost straight. It can be a bad thing in that high diff settings make the car have understeer on corner entry and corner exit. 

Conversely, if the driver becomes accustomed to this differential caused understeer and has developed a habit of overcoming the understeer with early downshifting, late heavy trail braking, low Brake Bias and excess early throttle application--then getting into a car without the excess differential action will result in annoying spins, 

The ideal differential setting would be enough force to reduce wheel spin on corner exit without any significant understeer through the corner. One important note: with low differential force, it is important to keep the inside tire firmly on the ground as the differential will not transmit much power thru the outside tire.

Anti Roll Bars

The Corvette has a cockpit adjustable anti roll bar in the front and rear.

The numbers are not intuitive-the higher the number, the lower the stiffness.

An anti roll bar causes the inside tire to be lifted  by the outside tire during turns when the outside tire is pushed up relative to the body. Another way of thinking is the bar allows the inside spring to assist the outboard one. On the front this transfers weight to the inside rear tire increasing understeer or reducing oversteer. 

So a stiffer front bar (lower number) makes the car understeer. A stiffer (lower number) rear bar makes the car oversteer.

To make sense of the numbering, think the higher the number the more grip. So a high number in the front increases front grip reducing understeer. A higher number in the rear increases grip reducing oversteer.

Rake and Ride Height

Generally speaking race cars are fastest when they sit as close to the ground as possible without hitting the track or curbs. Ride height depends on springs selected--the weaker the spring the higher the ride height at rest and the further it drops when subjected to aero loads and weight transfer. So be sure the car does not hit the ground. 

Rake is the front to rear incline. Changing rake by lowering the front will tend to increase front downforce and the total downforce at the same time.  Increasing aero downforce always comes at a cost producing more drag. 

Finding the Optimum Settings

Run the car 4 laps (1 out plus three complete) at speed and check tire temps and wear. 20C, Mostly Cloudy, October 1 in Northern Hemisphere at 10AM.  The inside of the tires should not have worn in excess of 1-2% more than the outside on the front tires and 1% on the rear tires.

The average temps of the front tires should be only slightly higher than the average of the rear tires. If the front tires have an average temperature more than 10 degrees hotter than the average of the rears, then the setup and driver's actions are causing too much understeer.

Average Front Tires 171.5 F Average Rear 160 F      11.5 F Difference=Excess Understeer

27 F difference inside to outside on Fronts   98/95=3 % delta (too much camber)

Average Front Tires 168.3 F Average Rear 160 F      8.1 F Difference=Safe But Understeer

23 F difference inside to outside on Fronts    98/96=2 % delta Good for GT car.

Keep in mind that this 4 lap "Test run" is for illustration purposes and a guide. Running more than 4 laps on a track that is hotter will yield different figures. The goal is to avoid camber settings with an excess difference in temperatures-inside to outside (but still alllowing some difference) and to "measure" the relative understeering tendency. 

The iRacing "high downforce sprint" has considerably more understeer than the 55PLUS V3 setup and the front tires are more likely to overheat making handling less consistent. V3 was faster than the iRacing setup. Understeer is usually slower. 

The V3 setup was designed to be "easy" to drive. Other setups with less understeer would be faster. 

The next Part will deal with Dampers and Springs. Both of which are important.  They tend to affect the way the car transitions from straight to corner entry to apex to corner exit more specifically to individual corners than the overall performance of the car over the entire track. Springs and Dampers affect how fast a car transfers weight in corners and when changing from accelerating and decelerating during braking and throttle application.

Corvette Z06 GT3 Part 4

 Corvette Z06 GT3 Part 4

Springs and Dampers

To begin, let's introduce the concept of "static" vs "dynamic" forces.

Springs "absorb" the weight placed on each of the four wheels of the car. Stiff springs absorb this weight with less compression. Soft springs absorb this weight with more compression.  Springs are rated a Pounds per Inch.  A 1200 pound spring is compressed 1 inch when 1200 pounds is placed on it. 

From a "static" point of view, springs are selected based in part on how much compression distance is desired when the car is at rest. A weaker spring allows the wheel to move up and down more distance than a stronger spring. We will call this concept--"compliance".  A weak spring has more compliance than a strong spring. 

From a "dynamic" point of view, springs absorb energy as the car is being driven and weight is changing due to accelerating, braking, turning, impacts from bumps and dips and changes in the road surface. Weaker springs will allow the wheel/s to move more  (stronger will allow less) distance when these forces are applied. So cars with weak springs will be feel "soft" with more lean when turning and more dive/lift when braking and accelerating. Cars with heavier springs will feel "stiff".

The Corvette seems to be "happy" with 599 and 1142 springs. There are some setups using 599 and 999 but this softer rear spring is to compensate for an ultra low rear wing and high differential stiffness.

Shock absorbers don't absorb shocks. That is what springs do. Shock absorbers are more correctly called Dampers as their role is to resist and slow down the movement of the wheel. Without this damping function, springs would "yo-yo" up and down for a time. Dampers are related to the dynamic performance of the car.

Dampers work in two directions--they: 1) Resist or dampen the compression of the spring and; 2) Resist or dampen the rebound or decompression of the spring. The higher the compression setting, the more resitance to compression. The higher the rebound setting, the more resistance to decompression of the spring. 

In essence from the driver's point of view, the damper settings control the dynamic performance of the spring/damper combination. High compression and spring settings make weight transfer occur more rapidly--this can be good when wanting to change direction in a chicane for example.  This may be bad if too high as weight transfer from rear to front can make corner entry difficult as the front tires may be temporarily overloaded.

Similarly, high rebound forces also cause a more rapid weight transfer and may actually keep the tire off the ground. Lower rebound settings allow the spring to decompress more quickly keepng the tire on the ground. 

A car that is difficult to handle under braking can be "tamed" somewhat by reducing front compression damper settings and reducing rear rebound settings. This however comes with a price as the car will "dive" more and will take longer to recover.

A car that is oversteering excessively can be "tamed" somewhat by reducing the rebound on the rear dampers and increasing the compression on the front dampers. Conversely, a car that is understeering excessively can be "corrected" by the opposite-reducing front compression and increasing rear rebound.

To complicate the matter, the dampers can be adjusted for "rapid or high speed" movement and "slow" speed movement. 

So making these adjustments will require us to go back to that requirement that the driver be "hyper sensitive" to oversteer and understeer in various corners.  Damper settings can improve the handling by changing the dynamic performance of the spring/damper combination that will dramatically affect the handling. 

iRacing provides a very useful tool for analyzing this. Run a fast lap and with camera view, look at the tire's contact with the track in the corner of interest. You can actually view the tire contact patches from under the track whose size is proportional to the weight on the tire. Often, the oversteer or understeer is the result of the tire being lifted off the track momentarily. Changing damper settings can remedy the problem.

View tire contact from under the pavement

Inside rear tire is off the track in the right-hand high-speed turn

Reduce low speed rebound on rear to reduce oversteer

Do not just make changes to dampers and run a couple laps and conclude "I was faster with that change so it was good."  It takes more than a couple laps to draw conclusions. Focus more on reducing undesirabe understeer or oversteer. 

In conclusion, choosing the "correct" setup selections requires a great deal of experimentation and a very good sensitivity of the car's handling. Ultimately, there will be compromises and tradeoffs--safety vs speed. The "fastest" setup is often quite difficult to drive and hence increases the bad consequences of mistakes. We are all human and make mistakes and we are all different. Most often the setup that is slightly slower but safer wins the race.

Once you feel you have the best setup for you, drive the car for 25 laps and compare your lap times. You may choose to make more fine tuning as you progress.

I encourage you to read some of the older articles here-Setting up the Ferrari GT, Braking Dynamics, Aerodynamics and The Diving Turn.