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. 

Set-Up Training Ferrari 488GTE--Chapter One--Aero, Rake and Wing/ Drive Train

The first goal of this chapter is to determine how adjustments to the rear wing, chassis ride height and drive train affects the speed and handling of the car. So, we take the Ferrari to Talladega for speed testing.

http://www.formula1-dictionary.net/downforce.html

Click to article

The above link will take you to an excellent "primer" on downforce and drag.

The illustration shows a modern formula car, but the Ferrari 488GTE uses most of the same tricks. Notice that downforce is generated by more than just the front and rear wings. The body, floor, underside, and rear diffuser has a lot of effect. And, all of these are affected by the "angle of attitude" or Rake of the car--relative height of the rear being higher than the front. 

To determine the downforce produced, we first need to establish the relationship between downforce and changes in ride height. To do this, we make a simple test--check ride height empty of fuel and then full of fuel. The change in ride height can be used to estimate the rate of deflection from added weight, front and rear. This is not a perfect figure, as we do not know exactly the center of gravity of the fuel load, but it will do for our purposes:

For the relatively stiff springs we chose for the test, we determine that the deflection rate is:

Front:  870#/inch. (15.6 kg/mm)
Rear:   750#/inch  (13.4 kg/mm)

For the tests at Talladega, we used three different 6th gear ratios:

1.174    192 mph (309 kph)
1.190    189 mph (305 kph)
1.217    185 mph (298 kph)

The car is probably capable of doing well above 190 mph (309 kph) in a draft or when going downhill. I did not test it at Bathurst or Phillips Island, but 182 mph in the first long straight at Lemans was possible without a draft. At Talladega--there is no downhill so it is sheer power vs aerodynamic and mechanical drag. 

With a full fuel load, we tested a top speed of 179 mph or 289 kph (using 1.174 top gear).
This was using ZERO rear wing and minimum toe (front and rear) with static ride height of 2.243" Front and 2.760" Rear = 0.517" (13 mm) Rake

Estimated Downforce:

Front:  376 #  (171 kg)
Rear:   675 #  (307 kg)

Dynamic Rake:  ZERO  (Front and Rear Ride Height essentially the same.)

We ran the test again with minimum 1.6 gallons of fuel and changed the 6th gear ratio to 1.190. Top speed still 179 mph with engine revs a little higher. (Perhaps marginally faster than with full fuel.  Remember that Tallagega is high banked so corner and top speed is not affected much by weight.)

Next test was to see what effect a change in Rake would do to speed and downforce.  We dropped the front 2 mm (0.80") to 2.226" and RAISED the rear 2 mm (0.80") to 2.943" resulting in Rake of 0.717" (18.2 mm).  This is a 40% increase in static Rake.

Top Speed increased slightly to 180 mph (290 kph).

Estimated Downforce:

Front:  675 # (307 kg)
Rear:   947 # (430 kg)

Dynamic Rake:  0.230" ( 6 mm)

Note: Keep in mind these figures above are for ZERO rear wing! A high portion of the downforce is coming from the underside of the car and all the sophisticated body features. And, lowering the front while increasing rake made a significant difference. There is no doubt the car would have more downforce if we lowered the front more, but there is a limit of how low you can go, as the front dips significantly under braking and the car is pushed down significantly in high speed turns.  Any front ride height below 2.226" (56.5 mm) requires a test for ground clearance under braking and in high speed turns. Be especially careful when using the 1029# front springs--watch how the front wing is driven to the ground braking for the hairpin with 1029# front springs and a front ride height of 2.250".

Note: The pics above is a form of "poor man's" telemetry--I change the Z axis in the replay camera to be able to see under the car to see ride heights. 

More comment: One might wonder why not use stiffer springs and adjust the front ride height lower. Well---iRacing does not allow you to go below 2.175" on the front. So, stiffer springs (>1257#) are actuall slower since downforce will not push the front low enough. The best speed in our Talladega test was with the weakest front springs (1029#) allowed!!! (The 1029# springs were too weak for Sebring's braking zones--see above) Here is a video of our fastest run.

So, let's now test to see how much of this increased downforce was due to Rake vs lowering the front.  Keeping the front at 2.226", we dropped the rear to 2.754" so the Rake was close to our first test with 0.517" (13mm) Rake. (Actually it was 0.528" in this test.) Still running the 1.190 top gear.

Top Speed still 180 mph (290 kph)

Estimated Downforce:

Front: 527 # (240 kg)
Rear:  775 # (352 kg)

Dynamic Rake:  0.040" (1 mm) 

Note: Notice that the downforce decreased but the top speed did not increase.  As is the case in many cars in iRacing, downforce efficiency or drag increase for an increase in downforce improves with a little Rake. 

Next we checked to see what would happen if we raised the whole car 0.30" (7.5 mm) to a higher ride height, keeping the rake the same. The result was very interesting.

Top Speed decreased to 178 mph (287 kph)

Estimated Downforce:

Front: 595 # (270 kg)
Rear:  933 # (424 kg)

Dynamic Rake:  ZERO

Note: Notice that raising the car increased downforce slightly, but the efficiency dropped off dramatically--we lost top speed.

Next, the question you were anxious to ask.  What happens when I adjust the rear wing?  

We set the car with a static ride height of 2.306" Front and 2.862" Rear = 0.556" (14 mm) Rake. 

With a rear wing setting of 2, Top Speed dropped 2 mph (3 kph) to 178 mph.
Estimated Downforce:  

Front:  579 #
Rear:   976#  (about 200# increase from ZERO setting)

With a rear wing setting of 4, Top Speed dropped another 1 mph to 177 mph.
Here we dropped the top gear ratio to 1.217. 

With a rear wing setting of 5, Top Speed dropped another 1 mph to 176 mph.
Estimated Downforce:

Front:   520 #
Rear:    1076#

Dynamic Rake:  Negative 0.270" (7 mm)

Note: One can see that downforce increased the most from ZERO to 2 Rear Wing setting, adding 200# of rear downforce, and at a setting of 5, the downforce increased only another 100#.  One should also note that with the higher rear wing setting, static RAKE needs to increase. 

Well, what does all this mean?

1. Keep the car as low as possible without it hitting the ground under braking, in high speed corners, or when jumping curbs. (A good place to start is 2.226" to 2.306" Front and test from there.) 

2. The car likes a bit of Dynamic Rake. Set rear static ride height higher than the front somewhere in the 0.52" (13 mm) to 0.70" (18 mm) range, depending on spring rates and rear wing setting. Important to note--nothing in life is free--raising the rear to gain Rake and downforce will come at the cost of a higher center of gravity and a bit of tendency for the rear to "roll over" in mid corner. 

3.  Maximum speed is probably best achieved with the 1.190 Top Gear, 189 mph (305 kph) which gives a gain of 9 mph extra speed when in the draft. (1.174 Top Gear, 192 mph (309 kph) did not however cause much lost speed, so it might be best depending on preference and fuel economy.) Best horsepower is about 6500 RPM--4 green lites, the fourth one blinking.(see video)

4) Changing from ZERO to 2 Rear Wing setting will result in a loss of 1 mph if reaching 178 mph +, BUT that change resulted in an increase of 50# more downforce on the front and 200# more on the rear. One should consider the extra corner exit speed gained from this downforce in the corner entering the longest straight and balance that with the slight loss in speed for a very short part of the long straight.  Where maximum speed achieved is less than 170 mph, a setting or 2 should be considered to be minimum. Keep in mind the rear "wing" is not only pushing the car down, it is also "killing" a bit of the lift created by the shape of the body.

5) At speeds below 160 mph top speed (260 kph), a setting of 4 or 5 for the rear wing is probably ideal--choose which based on achieving desired oversteer/understeer balance in critical high speed corners as well as balanced front/rear tire temps/wear/hot pressures.

6) Keep in mind that downforce is proportional to the SQUARE of speed, so downforce increases dramatically at higher speeds---translation: A) You need more wing for tracks having lower top speed; and B) The faster you go thru the corner, the more downforce you have and the faster you CAN go thru the corner. 

7) Keep in mind that while downforce increases proportional to the SQUARE of speed, drag also increases with the SQUARE of speed. And, drag is a force, so since F=Mass times Acceleration...an increase in drag will reduce not only the top speed, but also the rate of acceleration. So you are constantly choosing a balance to achieve the best lap time---and beware that another driver may choose a different balance with a very similar lap time, but with different speeds at different places. 

Transmission Settings:

The Ferrari has 4 possible settings for the Final Drive. Most commonly used is the 2.455 ratio.  The other three being "higher" in number effectively reduce the speed in all gears.

There are three choices for 1st Gear. 2.857 provides 78.9 mph (127 kph) when using the 2.455 Final Drive.  The other choices for 1st gear would reduce speed.  My limited experience with the car indicates that you want and need first gear, and limiting top speed in 1st gear to less than 78.9 mph would be counterproductive--so  run 2.455 Final Drive and 2.857 1st Gear everywhere.

IRacing provides 21 choices for 6th gear. But given that we are going to suggest using only the 2.455 Final Drive, the lowest numerical ratio we would choose is the 1.174 (192 mph). So you only have about 10 to choose from.

My advice is to pick the 6th gear with a top speed that is 105-107% of your desired max speed on the track with no draft and no wind.  Best horsepower is about 6500 RPM--4 green lites, the fourth one blinking.

Choosing 2nd-5th is then a matter of splitting the gears to optimize three issues: A) Gearing for best corner exit speed at specific corner/s on the specific track; and B) The principal of greater speed range in the lower gears than the higher ones; and C) You want to maximize the area under the torque curve for maximum acceleration.

The principal in B) above is simple. In lower gears, you accelerate faster, so you increase speed more mph in less time. So the split between 1st and 2nd should be more mph than from 5th to 6th.  The splits should become progressively "tighter" as you go higher in gear.

You will sense when this is wrong as the car will feel "off" in some gear changes. Or, you may find yourself shifting at an inconvenient place in a corner. Adjust everything for best lap time. 

Example:  (all subject to optimizing for corner exit and drafting capacity)
1st:    78.9 mph
2nd: 103.1 mph (24.2 up)
3rd:  124.0 mph (20.9 up)
4th:  142.8 mph (18.8 up)
5th:  159.7 mph (16.9 up) 
6th:  173.5 mph (13.8 up) 

The principle in C) above is based on the fact that RPM drops when shifting up, so you want to be sure that the engine will pull throughout the range of the next higher gear without bogging down and without acceleration flattening out.