I use a calculator to do a bulk of my tuning work for me, but in general terms this is how I treat each component in my tuning process.
There is no die-hard right or wrong in tuning, do what works for you.
TIRES-
I start at 28psi cold, then adjust them for 34psi hot, AFTER the rest of the tune is closer to finalized.
It takes a several miles at race speed to get up to hot temps of 180+
SPRINGS-
I use the springs as my primary gross tuning point for under/oversteer. I reference the weight of the car, the drivetype(fwd,rwd,awd), and the known balances of other settings to come to a basic spring setting. Typically my combined spring value will be approx 36~38% of the vehicles weight, but there are exceptions for specialized builds.
I bias spring strength slightly rearward for FWD.
I bias spring strength strongly rearward for AWD.
I bias spring strength forward for RWD.
ANTI-ROLL BARS-
This is tricky, but in general I use a ratio of front to rear balance that is based inversely on supporting the weight of the car and biased to the drive type. This ratio is designed to compliment the spring bias not work against it from an under/oversteer perspective. In this way I don’t have to worry very much about fine tuning these components.
It also compliments the drive type characteristics of all the cars very well.
This is something new I’ve found that is both real world realistic and seemingly effective for FM5*.
This wasn’t true for former versions of FM.
In addition I use a variable based on vehicle weight that creates a stronger strength for heavier vehicles and a weaker one for lighter vehicles.
Once these values are in I do not alter them to fine tune over/understeer, there are other settings that have finer effects.
DAMPERS-
Bump is adjusted, based on spring strength, to an initial setting that is primarily complimentary to bump absorption and initial weight transfer response. I only adjust bump in certain unstable tunes that don’t like curbs.
Rebound is a bread and butter adjustment that primarily is used for chassis response during the three phases of cornering, turn-in and trail braking, mid-corner transition, and corner exit throttle roll-on. The initial setup is based on a ratio of weight distribution, but also biased to the spring balance(which is already biased to drive type).
A major majority of my fine tuning occurs here as is tweaked around how the throttle and brake inputs make the car react through a corner and over crests.
CAMBER and CASTER-
Rear camber is easy to set at a fixed value based on perceptive rear grip squat and dive situations.
Front camber is the same, except that the added dynamic camber of the caster setting allows for a lower static value, and better braking stability, and initial turn-in response.
Caster is set high, but modified based on chassis weight distribution, with lighter front loading needing more aggressive value.
Both front and rear camber can be modified by downforce, but FM5s telemetry doesn’t seem pickup on this factor like FM4s did.
TOE-
Minimized as close to zero as possible, but frequently tweaked by -.1 or -.2 rear to add stability for a variety of situations.
GEARING-
1st is set to a partial wheel-spin, full or partial throttle launch.
The top gear is set as an overdriven gear for top speed, unless aerodynamic loads are high.
The final drive is set to compliment both first and the top gears.
The middle gears depth are set to compliment the hp and tq curve strengths.
Gear tuning can affect on-throttle and downshift/engine braking chassis balance, so I try to get it tuned early, and then address it to a finer level later on if the chassis is too on-throttle loose.
AERODYNAMICS-
Set for high speed grip.
I favor front to rear ratios of between 1:2 and 2:3
I almost ALWAYS use both adjustable or both non-adjustable parts.
Balance is based on high speed handling feel.
I try to match 120mph G-forces to 60mph G-forces if possible, but it depends on class and feel.
TIRE WIDTH-
Usually a 4-wheel matched set for fwd and awds.
Rwd cars usually benefit from a staggered set of tires, with the rears no more than about 40% wider than the fronts.
DIFFS-
Set to predetermined ratios, but based on a “felt” center that compliments drive type biases.
Adjusted only if spring and rebound adjustments are ineffective.
BRAKES-
Adjusted initially to between 54~52%, but tweaked for trail-braking and raw braking performance.
Staggered tire widths and aerodynamic downforces also affect braking balance.
*While FM5 is a great sim, there are many aspects of the tuning that are not realistic. The differentials for example act very much like mechanical lockers, as opposed to the more realistic and sporty limited slip or torque biasing versions. The alignments and dampers are also very simplified in relation to their real world counterparts.
Still, I try to give FM the benefit of the doubt and try to use realistic ratios for tuneable components.
From what I’ve studied, a real world FWD car with a forward weight bias generally has firm front ARB’s and soft rear ARB’s, even when motion rates and leverages are considered. To make this chassis rotate more effectively in a race situation the rear ARB strength is generally increased to a ratio than may match or even exceed the rear. This ratio helps to neutralize the understeer characteristics of a FWD chassis.
A RWD car with a forward weight bias is less unbalanced from a drivetype perspective, but if we bias the spring strength to properly support the weight of the front without being too firm(understeer) then there is still a strong potential for oversteer. To compliment this potential understeer we must promote turning grip to the front and simultaneously not induce oversteer from the rear. How is this accomplished? By controlling the independent suspension deflections of the rear tires by binding them together with a relatively firm ARB. This is exactly what is done in rear world racecars. Promote front end grip with firm springs and a moderate ARB, and promote rotation of the rear with a firm ARB matched to softer springs.
Where this concept gets interesting is in cars like the RWD rear weight biased Porsche 911 type of chassis.
Because this chassis is naturally unstable with the drivetype and weight concentrating arounnd the rear axle it becomes a very tricky and sensitive car to tune.
The front of the car can be very sensitive to steering inputs and so might benefit from only a very slight spring bias. By this same small amount however it will still need some ARB to keep it stable.
The rear of the car needs somewhat firm support to allow throttle lift turn-in, but also need some ARB to control the roll under acceleration. The fine line here is using the springs to control squat and dive, the ARBs to control braking and throttle stability, and using the dampers to control the speeds at which it all happens.
Again, unsprung motion rates and leverages considered, 911’s typically have springs rates very close to their 40/60 weight distribution, and ARB’s that are close to 50/50 or 45/55.
After literally weeks of trial and error tuning my A-class Ruf CTR2 I came to this realization of balances. Once this car was finally dialed into the equations, my calculator tunes all started to fall into place. The key observation I made was that the weight distribution, drivetype, and ARBs need to be treated as a single tuneable unit, and one that supports the anti-roll balance, spring bias, and steering of the chassis. Another aspect of these relationships is that the damper tuning became very sensitive to even the slightest changes, a very realistic effect in my opinion.
One of the basic versions of this Ruf CTR2 tune can be found in my “Feuerdog Tuning” Marketplace post.
