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.

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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.