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.

Basic Set Up Training for Ferrari 488 GTE-Chapter 3

Basic Set Up Training for Ferrari 488 GTE-Chapter 3

Driver Preference:

Camber
Caster
Toe
Differential Setting
Traction Control

In the first two chapters, we covered the "foundation" issues that to a great degree determine the capability of the car.

There are other adjustments that are important, but the way they affect handling to a great degree is determined by driver inputs.

So, let's just review some basics:

We look at the corner in three parts: Corner Entry; Mid-Corner, and Corner Exit.

Corner Entry is where the car is slowed using brakes and/or throttle lift, weight is transferred from the rear to the front tires and the car begins it's "rotation".

This concept of "rotation" is important.  To go around a corner, the car needs to have a force on the car's center of gravity (center of mass is the same) toward the inside of the corner, PLUS the car must rotate around it's center of gravity.

The car has inertia that wants the car to go straight. The car also has "polar" inertia that wants to keep from rotating.

To navigate the corner, the "turning" force created by the tires having a slight "slip" must be in "balance" with the front doing as much work as the rear.  If the front tires are producing more turning force than the rear, the car will over-rotate and spin in an oversteer condition. If the front tires are producing less turning force than the rear, the car will under-rotate and will seek a larger corner radius in an understeer condition. 

Due to "polar" inertia, the car will tend to resist "rotation" during Corner Entry.  Often, the driver inputs during Corner Entry introduce "excess rotational momentum" that must be reduced in Mid Corner and/or Corner Exit to avoid oversteer. So, in essence, the driver is controlling the rotation of the car throughout the corner, using different inputs in different corner segments.

Be aware, Ferrari did a masterful engineering feat in the design of this car. The combination of a short wheel base and transverse mid-engine design produced a car with a very low resistance to rotation--a low polar moment of inertia.  What this means is that the car response very rapidly to driver inputs--including incorrect ones!

Just for entertainment--view the next video. The Ferrari 488 GTE can be "dirt tracked"  or "drifted" around a corner, but this is not the fastest way thru the corner on a paved track.

How the driver introduces the inputs of steering, braking, and throttle modulation during all the corner segments determines to a great degree what settings are best for that driver. How gradually the inputs are applied and the driver's preference for the speed of reaction determines the best settings for him/her.

More experienced drivers will find during their testing that they actually see little difference in lap times when making some setup changes because they adapt and change their inputs to achieve the best outcome. Many times what makes the car faster in corner entry, makes the car slower in corner exit. 

Camber

In my Basic Set Up Training for the FR2.0, I went into a great deal of detail. Here, I am going to be more general. The pic below is fascinating in that it is a real car that was built to prove the existence of what we call "camber thrust".  The more negative camber--the more cornering force produced by the outside corners--if the tire is rounded.  For a wide, rectangular tire, there is a limit.

The Ferrari likes camber in the -2.0 to -3.0 range. Test starting in the middle at -2.5. Changing front and rear can affect the car's understeer/oversteer balance. The limit is usually determined by excess tire temps on the inside edges of the tire. You are essentially trading off the benefits of camber thrust with diminished tire surface as the tire is tilted.

There are two reasons for the negative camber. First is the camber thrust produced. Second is to make up for the amount of camber change that occurs when the chassis rolls.  (Some of this camber change is accomplished with unequal A arms, but often not enough, so a bit extra "static" camber is set. 

As mentioned, driver preference is important. Higher negative camber tends to make the car a bit more responsive to steering inputs during corner entry but may be counter productive during hard braking and hard acceleration on corner exit.

Caster

Caster is often the least understood setting. Just know this:

Higher positive caster forces the makes the car to rotate faster (more oversteery or less understeery)  During a turn, it puts more weight on the inside front an outside rear tires. 

On the Ferrari 488 GTE--start with 8.0. A range to consider is 7.0-9.0.

Toe

Tires do not produce cornering force until a slip angle is produced.  The orange line in the figure below is a racing slick. 

Toe out or negative Toe In on the front tires essentially creates a small initial slip angle on the inside tire that helps the car to feel more responsive to initial turn in and creates a higher slip angle on the inside tire, theoretically increasing overall front tire turning force, within limits.

A slight Toe In on the rear tires creates a slight initial slip angle on the outside rear tire providing more stability under braking and acceleration.

Any setting greater than zero produces drag and reduces top speed to some degree.

Differential

The Ferrari 488GTB has an electronically controlled limited slip differential.  The iRacing 488GTE requires us to choose a setting for the number of clutch plates and the spring preload. Unlike other cars, which provide a choice of "ramp" settings, we only choose the number of plates and the preload

More plates=more friction.  More preload=more friction.  The higher the friction, the more the the inside and outside rear tires are being forced to turn at the same speed--the more like a solid axle. Here is a good video to explain how the system works.

The more friction, the more the car wants to go straight--to resist rotation. Since we are looking to induce rotation and overcome polar inertia in corner entry, you would think you would want low friction. But, alas, during corner entry we are using brakes to slow the car, and when braking and turning at the same time, the inside tire tends to want to lose traction, lock up and cause a spin.  So, having more differential friction is like a poor man's anti-lock braking system, helping to keep the inside tire from locking up--allowing more braking while turning--in other words, allowing more aggressive trail braking. 

So in essence, the correct choice for the differential setting depends a great deal on how much trail braking the driver prefers and/or uses. 

Start at 4/81 and test to 3/44 and 5/125. 

Keep in mind that Front Brake Bias will also effect how trail braking influences rotation. Higher diff setting (more friction) will allow less front brake bias--more rear braking power.

Lower diff setting will require a higher front brake bias. 

To a great degree, the degree of inducement of "rotation" during corner entry depends to a great degree on driver preference and physical ability to react quickly and accurately.  This initial rotation must be slowed at Mid Corner with precise timing or the car will spin. (Always keep in mind that the car will see a brief extra rotation just when brakes are released--as the front tires are then able to devote 100% of tire grip to turning.) 

Theoretically, more friction provides more traction during acceleration, so higher diff settings should be beneficial on Corner Exit. Again theoretically, the more friction, the more the car wants to go straight, making the car understeer on Corner Exit.  But, in Corner Exit, the inside tire is unloaded and subject to losing traction, so high diff settings can create oversteer on Corner Exit--especially if the rear ARB is relatively stiff. Always test for differential caused oversteer during Corner Exit on tight corners, where full throttle is input early.

Traction Control

There are two settings. One sets the amount of electronic traction control. The second controls the speed that the engine power is reduced. 

Start with 2/2 and test 2/3 and other higher settings.  

I found with the car properly setup, this feature did not matter as much as I thought it would except in slower first gear corners under hard acceleration. 

Basic Setup Training--Ferrari 488GTE in iRacing--Part 2

Basic Setup Training--Ferrari 488GTE in iRacing

The Suspension: Springs, Dampers, Tires and ARB

Ferrari's on track.

https://flic.kr/s/aHskxScsFC

The term Vehicle Dynamics describes a field of art, science and engineering that attempts to describe the behavior of a vehicle while in motion. Like Aerodynamics, it is a highly complex field of study. There are thousands of pages written about the subject. The book, Race Car Vehicle Dynamics by Milliken and Milliken is considered one of the most important collections of information. Below are a few links for those interested in doing a lot of reading and thinking,

http://racingcardynamics.com/weight-transfer/

http://www.optimumg.com/technical/page/2/

http://millikenresearch.com/rcvd.html

https://www.amazon.com/Race-Car-Vehicle-Dynamics-Experiments/dp/0768011272

Fortunately, we don’t need to design the car.  We simply need to understand how to make it go fast!  So this article (based on significant testing) will focus on some very basic core principles that can be applied in the process of building a setup that will allow our best lap times for the Ferrari 488GTE

Vehicle Dynamics and Chassis Set Up is pretty much all about making the car go thru corners quickly and that is highly related to how the weight on the tires changes through the corner.

So, since the car is essentially “held up” with springs and tires, it is the springs and tires that we will address first.


Front tires are 30/68/18 and rear are 31/71/18. (First # is width (cm), 2nd is height (cm), 3rd is diameter (inches)) So the rear tires are wider and taller. (Keep that in mind when setting camber.)

Tires are essentially air/rubber springs acting in series with the suspension springs. More tire pressure is stiffer. For 2018S2, it appears that tire pressure choice is either 17.0, 17.5, or 18.0 psi (117,121,124 kpa) cold. Most often, changes in tire pressure will depend on track temperatures--the goal being to achieve a certain "hot" tire pressure. (145-155 kpa depending on track temp. I found no advantage in hot pressures above 155 kpa. Above 155 kpa, the tires seem to skate.) but since they are also acting as springs, on bumpy track or tracks where intentional curb strikes are common, lower pressure deserves a trial/test. On tracks with very high speed corners, where tire deformation may be an issue, raising the pressure deserves a trial/test. 

Below is an informative article about tire pressure. The most interesting fact is inflation pressure affects outside tire differently than inside tire in a turn.

https://www.suspensionsetup.info/blog/what-tyre-pressure-for-racing-2

Most race cars generally use a “coil over” spring or springs.  The coil spring is located around or over the damper. (Americans call them shocks—Europeans call them dampers).The most typical is one coil over assembly (spring and damper) for each wheel. 

A shot of the rear of the Ferrari design  is shown below.

The choice of springs depends on the stiffness desired:

Soft:              1029# Front    1143# Rear

Medium:        1143# Front    1143# Rear

Stiff:               1143# Front    1257# Rear

Extra Stiff       1257#Front    1257# Rear

Keep in mind that each rear tire is carrying 75# more weight with low fuel load and 80# more when heavy with fuel. This is a mid-rear engine car. 

As mentioned in an earlier chapter, the 1029# front spring allows the front to dive considerably under braking, so ride height needs to be compensated--especially on tracks where there is heavy braking--going from 6th to 1st gear. 

For most drivers, their "baseline" setup will use the Medium spring combo and 17.5 psi tire pressure.

The roll stiffness of the car is affected by the springs/tires in combination with dampers and the anti-roll bar. 

Some drivers prefer stiffer springs and smaller or lower ARB settings. Others prefer softer springs and stiffer ARB settings. The choice softer the suspension, the slower it reacts to inputs.

Soft springs with stiffer ARB will feel "flat" in the corners, but will fee more stable under braking. 

Stiff springs and softer ARB will feel about the same as soft springs/stiff ARB in the corners but will react much faster under braking and throttle.

Of course, it is also possible to choose soft springs and softer ARB, or stiff springs with stiffer ARB. 

So again, you have 4 main or "general"  choices:

Soft:            Soft springs/soft ARB   (Rolls a lot)

Medium:      Soft or Medium springs/medium ARB  (Rolls a little--easy to drive)

Stiff:             Medium or Stiff springs/stiff ARB  (Very little roll-harder to drive)

Extra Stiff:   Stiff springs/stiff ARB (Very little roll-very fast reacting-hard on tires) 

Keep in mind that the ARB reduces roll, but it's most important effect is the change in grip on the opposite end of the car.  A stiffer front ARB, will provide more grip to the rear tires when turning. The ARB essentially moves the grip from one end of the car to the other. So a stiff rear ARB will reduce rear tire grip. Also remember that in a rear/mid engine car with high horsepower, you do not want the rear to lose grip--so the rear ARB is generally softer.

NOTE: The ARB essentially takes weight off or lifts the "inside" tire.  Dramatic and sudden loss of grip can occur with an ARB setting that is too stiff as the inside tire can actually be lifted up off the track and the car becomes a tricycle.  This is less noticeable on the front, but can be a handling hazard, creating a "snap" type oversteer. 

The choice of ARB settings:

Soft:           4 Small Front           1 Small Rear   Neutral

Medium:     5 Small Front           1 Small Rear   Slight Understeer

Stiff:            6 Small Front           2 Small Rear   More Understeer and More Traction

Extra Stiff:   3 Large Front          2 Small Rear   More Understeer and Even More Traction

For most drivers, their "baseline" setup will use the Medium spring combo, Medium ARB settings and 17.5 psi tire pressure. Fine tuning can be done by adjusting the front ARB, one "click" up or down to reduce understeer or oversteer. 

Changes to understeer/oversteer occur also with changes in differential settings! ARB changes affect all parts of corner, where changes to differential will have a different effect on corner entry than on corner exit.  A stiff differential will understeer on entry and oversteer on exit. 

NOTE: The "Baseline" set provided by iRacing is considerably stiffer than the examples and settings provided in this article. Some drivers really try to reduce the "momentum" roll that comes from sudden steering moves. The Ferrari is a purpose built race car--but it is twice as heavy as a formula car with a much higher center of gravity--roll absorbs energy--enhancing grip and is benficial within a reasonable range--a stiff suspension can transfer energy too fast--but softer springs and ARB settings require more deliberate and smooth steering and brake inputs. I was more than 1% slower using the iRacing "Baseline".

The issue of high spring stiffness has to do with deformation of the tire. A certain amount of weight is transferred during braking and turning. The increased weight compresses the spring and tire. The stiffer the spring, the more the tire is deformed. So, on setups with very stiff springs..on this car..it is appropriate to increase tire pressure to reduce this deformation.

Dampers only perform their function when the tire and suspension is moving up and down. They essentially reduce the speed or rate of change of weight that is transferred from corner to corner, end to end, or side to side.  More damping..faster weight transfer..less damping..slower weight transfer.

Dampers also "dampen" oscillation, but in setting up the race car, it is the effect on speed of weight transfer we focus on.

If a car has a slight understeer on initial throttle application in mid corner..reducing front damping in rebound will help. This reduction slows the weight transfer from front to rear..More weight on front tires reduces the understeer.

If the car seems unstable under braking or when cresting a hill, again, reducing rebound damping, this time on the rear, will reduce the speed of weight transfer from rear to front.

The damping force in rebound is always greater than in compression, as the damper must resist the force from the expanding spring, where in compression, the spring and damper are working together. Below is an actual shock dynonometer readout on double adjustable gas shocks.

Another example. Sometimes, these cars will demonstrate an understeer tendency in high speed corners. Using the brakes to "trail brake" will obviously move weight to front tires and help, but often just a slight lift in throttle will be enough...by increasing the compression damping on front and increasing the rebound damping on rear, you will make the car more sensitive to changes in throttle. (The "kink" at Road America or T1 at Sebring come to mind.)


One of things I like to do in these guides is to do real track testing. It can be boring, so few go to the trouble. To verify all of the above we take the Ferrari to the Centripetal Track and run about 100 laps.

.
We put the car in the 4th lane from the outer wall in 4th gear--over 117 mph--to simulate a "high speed" turn to test tire grip with changes in tire pressure and spring rates. Dampers won't matter much here because it is more or less steady state. 

We changed tire pressure to 17.0, 17.5, 18.0 and 19.0 psi.  17.5 and 18.0 felt the best and produced the best lap time of 19.38 seconds. But the 17.0 and 19.0  produced almost the same result, 19.39 vs 19.38. Speed was 118 mph.

The spring tests produced the greatest change. The tire tests were conducted with the Medium 1147# all around springs. By changing the rear spring to 1257#, (The Stiff Combo above) we immediately gained 1 mph to 119 and lap time dropped to 19.144!  We tested the Soft 1029#F/1147#R setup and achieved the same result.  Similarly, we tried the #1257F/1371#R combo and achieved 19.180.  At least in high speed corners, the car likes stiffer rear springs to support the extra weight that the rear carries. 

So next we take the Ferrari to our "dynamic" turning test track--Martinsville! Here we will test dampers and tire pressures in corners under braking and acceleration. 

Close to 100 laps. Result was best with 17.5 psi all tires cold. Setting above for springs and dampers. Soft ARB (See above) On some tracks, stiffer ARB would be appropriate.

Using a road track setup, the Ferrari equaled or bettered the best NASCAR cars iRacing World Record at Martinsville. It would be quicker with an assymetrical setup. 

The tests on the Centripedal and Martinsville were in 3rd and 4th gear...1143# rear springs were faster in corners using 1st gear..the car squatted more with more rear traction. 

Keep in mind that these settings are affected by the rear differential settings. (Used  4/81 in the test)  Those are a story for another chapter.