The text accompanying the tuning parameters provides a ton of helpful informationbut can be a bit daunting in that it doesn’t really guide you you in how or where to start. It’s more like crib notes where you know basically what you’re doing but just need a reminder of some specifics.
That said, my approach to tuning in this is essentially the same as previous forza games:
Decide on spring constants. I use the simple calculation of (vehicle weight) * (weight bias) / 2. For instance, a 2000 lb car with 60% of its weight in front would start at 20000.6/2 = 600 lb/in in front and 2000(1-0.6)/2 = 400 lb/in the rear. This would mean that the curb weight alone will compress the suspension 1 inch and should limit overall swing to 3-4 inches or less. This is great for a smooth course but can be completely unusable off-road. But because it’s based on the car’s weight balance, it should be fairly neutral as long as the tire widths aren’t very different. For fatter rear tires, you’ll want to use a stiffer rear suspension. In Horizon in general, I would drop all the spring values 20-50% from these initial rates and raise the ride height to allow for travel.
Next, I set sway bars to the minimum. They won’t stay there. This is only temporary to adjust the shocks. Shocks complement the springs. Without shocks, springs bounce. But where springs provide a force in oppositition to displacement, shocks provide a force in opposition to rate of change. That is, if you squeeze a spring to the same level of compression quickly or slowly, it will push back with the same force. But if you squeeze a shock slowly, it will eventually fully compress and if you punch it hard it might not compress at all. Another way to look at it is that springs store energy while shocks dissipate it. Properly tuned shocks dissipate the energy that would otherwise lead to oscillation in the spring.
Shocks offer two adjustments: bound (sometimes called bump or jounce) and rebound (usually called rebound). These settings control how rapidly the suspension can transfer weight in response to road conditions and driver input. Bump is the compression rate and rebound is the extension rate rate. Bump controls how quickly the wheel can be pushed up into the wheel well and rebound controls how quickly (and forcefully) the spring can push it back down into the road. Since bump is acting against the monentum of the whole car (imagine reaching the bottom of a hill or entering loop-de-loop stunt) it will have to be stronger than the rebound, which is acting only against the unsprung wheel/suspension parts. They’ll also have to be balanced against the combination of spring stiffness and suspension travel you want. For the initial spring rates above, starting at about 8-9 in front bump is reasonable, with the front rebound about 20% lower, and the rear parts related to the fronts through the weight bias similarly to the springs.
Alignment needs to be set with telemetry. It starts with caster. Caster is analogous to rake on a motorcycle. The reason it is important and should come first is that it makes camber more negatative as the wheel is turned from center to lock. With a good caster setting, the wheels can be almost straight up when car isn’t turning but tilt enough to keep the contact patch level through a turn. The real-world penalty is stiffer steering but I don’t think this is modeled in Forza. A little negative camber can be a good thing. It can make up up for what caster might not be able to accomplish alone as well as providing a little extra straight line stability. What you need look for is that the tire is heating evenly across its contact patch. You should aim for a difference of 0-5 deg F warmer on the inner edge than the outter edge
Usually, if your caster is good, you won’t need much more than about a half or maybe a whole degree negative in the front. On rear wheel drive cars, it is rare to need more than about half your front camber setting on the rear axle. I usually set it to about -0.6 front and -0.3 rear. This is generally reasonable for FR and AWD cars but will need to be adjusted to keep tire temps in line. FF can deal well with ridiculously negative rear camber. MR and RR, I’ll admit I don’t know well but would try to extrapolate from FR.
Toe is pointing the wheels toward or away from each other and generally shouldn’t be needed except for very fine tuning. Toe in can improve straight line stability but decrease a car’s turn-in ability. Toe out can improve turn-in to the point the can feel like it “wants to turn” even if its driver doesn’t. Some recommend a little front toe out but my own belief is that it’s better to get the handling situated by spring/damper/sway bar settings. That is, the suspension is the core of the handling while the alignment refines it slightly, kind of like course/fine knobs. Real world cars generally have slight front toe in to feel stable at highway speeds and because typical drivers are safer dealing with understeer in a panic situation than they are with oversteer. Also, toe-in warms the outer edge of the tire and toe-out warms the inner edge.
This would be enough for a (probably hairy) first test ride. You’ll want to note the car’s characteristics entering corners, apexing, and exiting corners. Telemetry data would tell us what to do with the tire pressure and alignment. The goal is to keep each tire’s cross section evenly heated, to keep all 4 tires at similar temperatures, and for those temperatures to be in the 180-210 F sweet spot for traction. Camber, caster, and toe will all affect the tire temps one edge of the tire while pressure will affect the whole tire cross-section. More pressure generally mean cooler contact patch. At extremes, low pressure will cause both edges to warm and the center to cool while high pressure will cause the center to warm while both edges cool (think of the tire as a balloon and it should make sense why).
Next, we can set about refining the suspension we crudely pieced together above. If the car is completely unmanageable off road, it will need softening all around and possibly increased ride height. The corner entrance characteristics are most affected by front bump and rear rebound (think about what each of those reflects and how a car behaves under braking and it should be clear why). Apex performance is mostly dictated by sway bars. Corner exits are mostly dictated by front rebound and rear bump. Spring rates affect all aspects. For this part, think of understeer as a loss of front traction and oversteer as a loss of rear traction. The parts above can be softened to increase an axle’s traction or stiffened to decrease it . And we’re talking relatively, so stiffening the front is similar to softening the rear. If the overall suspension is too stiff (or ride height too low), you might have very sudden snappy, fishtailing problems. If it’s too soft, it’ll feel unresponsive (understeer tuning can also make a car feel unresponsive even if the suspension is otherwise alright).
Braking usually isn’t worth adjusting. Generally biasing forward causes understeer under heavy braking (binds front wheels) and oversteer with rear bias (binds rears). With telemetry, it can be tuned to lock all wheels together (which maximizes braking efficiency).
Differentials can be tricky but are straightforward. On AWD, setting the center diff controls how much the car acts like FWD or RWD, and is usually set to 60-80% rear on most real world cars (more FWD translates to understeer and getting beyond about 85% rear just begs the question of why not just go RWD full time). On actual FWD or RWD, you use accel to try to maximize traction on the drive axle during throttle-on. You’ll know you have enough when burnouts stop leaving a single skidmark. You might have too much if the drive axle loses traction on throttle through corner (this also happens by applying too much throttle). Decel setting can alter a car’s balance under braking or just lift-throttle conditions. The default settings for both tend be a bit higher than necessary.
Oh, and I almost forgot gearing. It’s easy. Tweak the final drive until you find the best top speed. This will set both the final drive and top gear ratio. Then, fiddle with first (and maybe second) to optimize 0-60 time. Then space the gears somewhat evenly, with the higher gears maybe a little closer together. Take note of the peak torque and power of your engine and verify that you’re remaining in a desirable rev window with a test drive.
Anyway, that’s the basics. I’m sure errors and omissions will be pointed out. This isn’t meant as the be-all end-all but rather a primer and a jumping point for discussion of theory.
