18 January 2010

Tuning in Forza 3: a guide to the trickier menus.

Note: This tuning guide applies to track racing in Forza 3 and does not apply to drag or drift. It can also apply to real-world cars, as Forza really is a car and race simulator at the heart of it all. Almost everything that works in Forza works because it works in real life.

Having read a lot of blogs lately about tuning cars in Forza 3, I'd just like to say there's a lot of misinformation out there. I think because people aren't familiar with the concepts behind racing and haven't actually driven a real car on the track, they're adjusting things, seeing what that does, and drawing conclusions. This seems intuitive, but at the same time, with this approach, you're working backward. Because Forza 3 really is a simulation of the physical world, to make smart changes, you've got to understand what you're changing, why would be changing it, and how that will affect the physics model, not necessarily the results you think you see once you make the changes -- if you're changing things in the wrong order, or trying to dial out excessive understeer with aero for instance, you're going about things the wrong way and you'll not see the optimal results you want. To properly tune in Forza 3, you've got to tune as if you're tuning a car, not tuning a video game.

The intent of this guide is to take someone who knows nothing about tuning in Forza3 to someone who can properly set up a car and solve handling issues without having to resort to plugging in generic values in a spreadsheet. This is not meant to be a comprehensive guide, nor will it go into advanced concepts any further than is absolutely necessary to explain what you're setting and how it will affect the handling of your car. I may also make very generic statements like "positive caster is always bad" when I really mean "under almost every circumstance you'll ever encounter, this is a bad thing". Unfortunately, covering all the very specific encounters in which an advanced tuner might make this adjustment is outside the scope of this guide.

When you're modifying your car for the track, it's a good idea to get all the settings somewhere in a generic, workable range that works well for most cars on most tracks and then start tweaking from there. The default setting the car comes with is effectively this starting point. Once you're doing your "fine tuning", try changing one thing at a time and seeing if it improves handing or not. If you're changing ten things at once, you may find that you have improved the handling but you'll have no idea why. Worse, you might have done five things wrong and five things right which ended up giving you an overall gain, but you could have a much greater gain if all ten things were working properly.

Alignment
This is really where you should start. Without this, nothing else works. Or at least, works right. This is where you really correct gross handling errors -- a car that's just way too twitchy or a car that just won't turn in like it should or one that just feels unsorted. Once you set this, you can mostly forget about it with a few exceptions. Alignments that work for your car tend to work everywhere. If your car isn't working quite right for a certain track, but it has worked on others, then it likely just needs fine tuning in other areas. Still, this is the single most important part of tuning. A good alignment can turn a difficult car into one that's easy to drive (though it might not be as fast!) while a bad alignment can turn a car that's completely sorted in every other regard into an unmanageable monster.

To understand what we're talking about when we talk alignment, here's a photo.

Camber
Camber is quite simply how much the tire leans from the vertical. Let's just go ahead and state that positive camber is always, always, bad. In general, negative camber is always good. However, like anything in life, too much of a good thing is a bad thing.

Let's start by looking at what we're trying to achieve. In an ideal world, when we go around a corner, the tire would be standing up more or less straight. In a car with zero camber, that is true at rest. However, as soon as we turn the car, the tire rolls over, the suspension starts compressing, the car leans, and suddenly the tire has a lot of positive camber. Which, as we've said, is bad. It's bad because we're working the outside edge of the tire much harder than the inside edge. In a severe situation, we could overload the outside edge so much that the inside edge actually stops contacting the track. As you can tell, all of this works to decrease our friction circle.

To fix this, we have to dial in some negative camber so that when we corner, the tire stands up straight. As with everything, there's a catch. Negative camber means that when the car is going straight, it will be riding mostly on the inside edge of the tire, increasing wear. On a track, that's usually not much of a problem, but if there are enough long straights and a long enough time period -- say, 24 hours of LeMans -- tire wear can be a very big issue with cars that have large amounts of camber. As I said, we can also have too much of a good thing. If you dial enough camber in, you'll exceed the grip of the tire long before you bend the car over far enough to set the entire tread of the tire flat on the track.

Most cars can't use much more than one or two degrees of camber, so 1.5 is usually a pretty good starting point. Drive the car around and see if the inside or outside edge of the tires are heating up in the diagnostic screens. To access the real-time diagnostic screens, press up on the d-pad while you're driving any of your cars. Extra screens are accessed by pressing left and right on the d-pad. You can close the window by pressing down at any time. If the tire is maintaining consistent temperatures between the two sides (don't worry about the middle right now), then you're set up right. If the inside edge is heating up more than the outside, you need less camber. If it's heating up less than the outside, you need more.

Synopsis: Set this at 1.5 to start, drive the car and adjust as follows: if the inside edge of the tire is heating up more than the outside, decrease camber. If the outside edge of the tire is heating up more, increase camber.
Toe
Toe is fairly easy to understand. If you think of your feet as tires, walking pigeon toed would be the same as toe-in (positive toe). Walking with your toes out to the side would be toe-out (negative toe). Let's start with the obvious, any toe out on the rear is a recipe for disaster. Period. With toe out in the rear, you will have a car with virtually no straight line stability and one that will be nearly impossible to predict and control.

Apart from that, toe is all about feel. We won't really have any cool graphs to see where we should place it, because quite frankly, this setting is really all about how you personally like your car to feel and how much trade off you're willing to give in certain areas to get gains in others.

Synopsis: Set this at zero front and zero rear to start. After setting camber, dial in a little toe out on the front. If you want more stability, dial the toe back in. If you want faster turn-in, add more negative toe. The rear should stay at zero toe, however, if you find the rear end to be unstable, you may want to use some positive toe to bring it back under control. After adjusting the car to your liking, check the tire temperatures again. If the outside edge is getting too hot, you have too much positive toe. If the inside edge is getting too hot, you have too much negative toe. Adjust accordingly.
Caster
This one is a little more difficult to understand. Caster is the amount the steering pivot axis is tilted forward or backward. Simple, right? The best way to understand this is that a normal motorcycle has some positive caster. A 'chopper' style motorcycle has a whole lot more positive caster. A shopping cart has negative caster. Luckily, this one is easy to set. In general, more positive caster is better, and most real world people will align with the most caster they can get which is usually limited by steering geometry and other alignment settings. Positive caster tends to just improve straight line stability, which is helpful if you've already setting the car to be a little twitchy. However, at the extreme end of things, it can lead to abnormally high steering effort. Which, in Forza, isn't really a problem.

Synopsis: As much positive caster as you can get.

Anti roll bars
Anti roll bars stiffen the chassis of the car and prevent it from rolling. Pretty much as the definition says. Used in moderation, the bar allows the inside tire in a corner to maintain grip and keeps the car from rolling over too far and affecting camber, caster, and toe settings. If you use too much, it keeps the car's suspension from working as it should and actually decreases grip.

In general, to improve grip at one end of the car, either loosen the anti-roll bar at that end or increase the anti-roll bar at the other. This is only in general, you may find that you may need to do just the opposite to get the handling changes you require. A nice technique is to run the car with the bars set to the middle values, then do a "bar sweep" of each bar individually -- setting one bar to full soft and then working all the way through full hard. At the end of that exercise, you should get a good feel for the balance points of the car and you can do some fine tuning from there.

Synopsis: Set the bars at the middle setting. If the car is oversteering, decrease the stiffness of the rear bar and/or increase the stiffness of the front. If the car is understeering, decrease the stiffness of the front bar or increase the stiffness of the rear bar.



Springs and Shocks
Much like camber, caster, and toe, these are things that work together, but here, they help fine tune the handling you've already dialed in. While you may not adjust alignment much for different tracks and surfaces, you will adjust these and the anti roll bars a lot more often. First, let's talk about the difference between shocks and springs and what they do.

First, the spring is actually the part that supports the car and keeps shocks from being transmitted to the chassis. What we traditionally call shocks are actually dampeners, and they control the natural oscillation of the spring. Without springs, the dampeners would just simply compress and you'd get no suspension travel at all. Without dampeners, the car would continually bounce up and down (like a spring) after hitting a bump. How they work together is this: the spring is force sensitive, the shock is velocity sensitive. In other words, the spring should be used to control how much weight is pressed down onto the suspension. A heavier car will need heavier springs, and a car with higher cornering limits or increased aerodynamic downforce will need them even stiffer than that. The shock is then used to control how quickly the weight transfer and spring compression occurs.

So, once we actually use the springs to control weight transfer and the car no longer sways like a boat, we then use the shocks to make sure that it doesn't feel "springy" either.

A dampener also has two settings: bump and rebound stiffness. This is how hard it is to compress and extend, respectively. Usually, you want these to be equal, but there are times when you might want differing stiffness settings. For example, you may find that you want a high rate of bump stiffness on your car's front end to help slow the weight transfer down during heavy braking. However, you may find that the car oversteers greatly as soon as you get out of the brakes and start accelerating. In this case, you'd want to decrease the rebound stiffness so that the car can quickly transfer the weight to the rear and keep the rear wheels planted.

While stiff is usually better for flat tracks, once you start setting any of this too stiffly, the suspension cannot work properly. If the springs are extremely stiff, the suspension loses travel and shocks that would otherwise be absorbed will be transmitted to the car, upsetting the balance and possibly spinning the car. If the bump stiffness is set too firm, the tire will "skip" over bumps rather than riding over them, again upsetting the chassis of the car. If rebound is set too firm, the wheel can't extend quickly enough over holes and can't recover quickly enough after a bump. Notably, extreme stiffness isn't really a problem on glass smooth raceways, but it can be a major one on rougher tracks like Nurburgring. By the same token, on a rough track, we want to make sure that we don't set anything too softly either. A spring that can't carry the weight of the car or the cornering forces or handle the imperfections of the track will eventually cause the suspension to run out of travel and will bang it up against the bump stop. When this happens, your spring rate immediately and effectively goes to infinite, which causes the car to behave in unexpected and sometimes uncontrollable ways. Meanwhile, shock that's set too soft will allow the spring to oscillate or become overloaded, which will mean that the tire will have problems maintaining contact with the ground.

Again, there are no tools to help you here. You'll just have to use your intuition and "feel" your way around it. You'll also need to figure out just how you want the car to handle. I recommend setting everything to the middle and adjusting from there. First, set your springs so that the car isn't transferring an extreme amount of weight in corners or under braking, then set your shocks to control the handling and quickness of the weight transfer. While doing your adjustments, make sure the car isn't behaving unpredictably or getting out of control in corners or on bumpy parts of the track.

Ride Height

This is a pretty easy one to set. The lower your car, the more aerodynamic it will be, meaning your top speed will be higher, and the ground effect aerodynamics (if there are any) will work better. Of course, the lower the car, the less suspension travel it will have. As above, if you run out of suspension travel, you'll hit the bump stops and cause wildly unpredictable behavior. In general, adjust this for the track. If the track is glass smooth, set it as low as you can, but if the track is rough, set it just high enough that the car remains settled.

Aerodynamics

I think this is one of the least understood sections of Forza. It seems easy on the face of it, but it's actually a little more complex when you dive down into it. Aero effectively increases the weight of the car without actually causing the car to be heavier -- but only when the aero is active. Most modern aerodynamics aren't effective under 60 mph, and they get more effective the faster you go. The reason this is misunderstood is because people only focus on the most obvious effects and don't attempt to understand what all this means.

What does it mean? It means that once the aero starts working the effective weight of the car starts to increase, which in turn means that friction available to the tires increases. If you add a lot of rear areo, for instance, you'll notice the car understeers a lot at high speed and if you have a RWD car, it's not nearly as prone to power-on oversteer. Of course, if you were looking further, you'd notice this only happens at high speed, and you'd notice that you have more grip to do everything -- brake, corner, and steer. In fact, some F1 cars will go around a corner at 100 mph that they couldn't make at 65 mph, simply because the increased aerodynamic forces allow for enough cornering force to make the turn. It seems impossible, but it does work this way.

Of course, since we're effectively increasing weight, if you're really paying attention, you'll find that the suspension doesn't work as well as it used to. The springs won't be stiff enough, the dampeners won't be firm enough, and if everything is soft enough and the ride height is low enough, you can actually compress the car completely down on its suspension. So, when you add a major amount of areo, you are going to have to go back and rework your suspension settings. However, you're also going to have to strike a compromise because the car works completely differently at speed. If the track has a lot of tight corners coupled with a few fast sections, you might bias the suspension settings for the lower speeds and deal with the compromised handling at high speeds. You might make the opposite decision on different tracks.


Then, there's the added element of drag to deal with. The more aero you use, the more drag the car produces and the slower it goes. This isn't very noticeable at low speeds (where the areo isn't working) but it can take a huge chunk of speed off your top end. For a track like Le Mans, where you have very long straights and extremely slow corners, you might go with minimal areo, because where you really need it, you're not going fast enough to use it.

It's this kind of mastery of the compromises between settings that takes you from being someone who can just plug values into a spreadsheet and someone who can actually tune a car for a given track.

Braking Forces

There are two settings here. Brake balance and brake pressure. So long as you understand what we're trying to do, these are pretty easy to set. If you're using ABS, you can pretty much ignore this, but if you're not, this can make a big difference. What we're trying to do here is keep the wheels from locking up, and primarily, to keep one wheel from locking up before the rest. A sliding wheel doesn't have as much grip as one that's not sliding, so we want to avoid that at all costs. At the same time, if you can only get 50% of the braking force out of the rear wheels before the front ones lock up, you're giving up a lot of braking force.

You can mostly set the braking balance using the drag strip. Go very fast, apply the brakes and look for red, locking wheels in the friction telemetry screens. It should be pretty obvious which wheels are locking first and which direction you need to bias the balance to get them to lock up at roughly the same time. Now, the one change you may have to make depends on your driving style. If you're the kind of person to dive into corners and use a lot of trail braking, you may find that you're still locking the rear brakes up in the corners long before you ever fully optimize the fronts. This is because you're trying to do too much with the rear wheels, and you may find that adjusting the bias toward the front may be more effective for your driving style.

Brake pressure is almost completely subjective. If you're constantly locking up the brakes because you can't modulate the amount you're using them very well, a little (or a lot) less brake pressure might help. If you aren't able to get full braking force because you don't press down hard enough, or you can't seem to do it without pressing all the way and locking up the brakes, you can probably use a little less brake pressure.

Differential

This is the one place where I feel the game isn't very accurate to real life. You usually won't find limited slip differentials like this, but it's what we get here, so we have to use them. Let's look at the words "Limited Slip Differential". Every car has to have a differential on the drive wheels. This means one for each powered axle, and in the case of an AWD vehicle, this means another one between the two axles as well, for a total of three. Now, the reason for a differential is that when a car goes around a corner, the inside wheel turns less than the wheel on the outside because it's covering a shorter distance. Without a differential (to balance the difference between the two wheels), the wheels would bind and skip and cause all sorts of handling issues. Of course, once we do that, we have another problem -- all of the torque goes to the wheel that has the least amount of traction. This means it's easier to spin the inside wheel, and once it spins, all the power goes there. Worse, if you lose traction completely on that wheel, you can't accelerate at all.

Off road trucks and dragsters have it easy. They just weld up the differential and don't worry it. This way, no tires slip or they all slip. Simple. Easy. But dragsters don't go around corners, and off road vehicles can use the slip inherent in off road travel to offset the difference the differential would handle. We don't have that luxury, so we have to compromise. In an ideal real world situation, you'd use a Torsen-style differential and be done with it, but Forza doesn't allow us that option.

To make this work, we need to put a high enough setting in the differential that we're not experiencing wheelspin on the inside wheel during acceleration nor inside wheel lockup during braking. We can watch the friction telemetry again and see which tires are losing traction and when. However, be careful, because if we increase the setting too much, you'll lose traction, and we'll get inside wheel locking and popping in the corner, which will unfortunately show up the same way in the telemetry screens.
Gearing (individual gears + final drive)
Everything else considered, gearing is pretty simple, though it seems to be greatly misunderstood. You basically have two sets of gears you're looking at: the normal numbered gears (including reverse) and the final drive. Changing any individual gear ratio only changes that one gear. Changing the final drive changes them all.

Let's start with the final drive. In a normal car, this is found not in the transmission, but in the rear differential. It's usually fairly easy and fairly cheap to change, while a complete custom gearbox can be fantastically expensive and notoriously difficult to tune, so that's usually where people start. As the tuning page so helpfully suggests, a larger rear end ratio will result in faster acceleration. It'll mean that your engine spends more time in higher rpms where it generates much more horsepower and torque. However, it will come at a cost -- your top end will be reduced and you'll be shifting a lot more often. On smaller, tighter tracks without overly long straightaways, having a lower top speed doesn't hurt all that much. On tracks like LeMans it can be crippling. Of course, if you set it too high, you simply won't be able to accelerate fast enough and it doesn't matter how fast you can ultimately go if you can't ever get there -- or only get there in the last five feet of track. This is also car dependent. A torque monster like the Corvette can deal better with gear ratios that are spaced further out (lower final ratio) whereas a higher strung car like an S2000 is going to want gears that are spaced closer together (higher final ratio). So, this is somewhat of a balance you'll have to find depending on the car and the track you've chosen.

Now, let's look at setting individual gears. This is a lot trickier, and real racers will spend days just fine tuning individual ratios for one track. Unfortunately for us, Forza 3 doesn't really give us the telemetry we need to properly and easily set the gear ratios, so we'll have to do it simply by feel. What you'll have to do is consider the track you're racing and think about where you can make changes to your gearbox to optimize your speed. In general, remember that the more time the engine spends in the upper rpms, the faster you'll accelerate, and the smaller your gear ratios are the more time you'll spend in each gear and the higher speed you can reach in each gear.

For example, if you were racing a fairly tight but fast track where you had no speeds over 110 mph and at the same time no speeds under 40 mph, in a normal car, you have effectively eliminated two gears completely -- you'll never go fast enough to need sixth gear and you'll never go slow enough to shift back into first. In this instance, it would be better if you just threw out those gears altogether, and added more ratios in between second and fifth. And with the gearbox editor, you can do exactly that by setting first gear to the same ratio as second, sixth gear the same as fifth, and then equally spacing out all the ratios in between. Of course, this means that we're going to be a little slower off the line, but in a long enough race, we should be able to make up for it.

Conversely, for a track like LeMans, where we've got a lot of very tight low speed corners along with some very long straights, you might find the stock settings are the way to go with a lower final drive, or you might find that you need some really tightly spaced gears on the first few gears combined with some much longer gears on the last few to give you the immediate acceleration you need coupled with the top end speed you'll need on the Mulsanne straight. Exactly how to balance all that is where you'll need skill, luck, and little bit of experimentation.

Tire pressures
Tire pressures are one of the last thing you should touch, after you get your car handling and controlling the way you like. You can't make gross adjustments by tuning tire pressures, this is primarily for finally dialing in the exact handling you desire. The reason Forza 3 drops you here first is because it's the one thing you'll likely change the most often after you do your major tuning. A lot of guides I've seen have recommended just setting the tires around 32 psi hot (which is defined after the tires have warmed up, usually a couple of laps) and that's a decent place to start, but if that's all I did every track day, I'd be slow.

Luckily, in Forza 3, we don't have to deal with differing weather conditions, which cause me to have to tweak my tire pressures every single time I go to the track, but we do have to deal with tire compound, and different compounds respond better to different pressures, so this isn't completely a "set it and forget it" setting. You might even find that it will help to change pressures depending on the track as well -- especially if you decide to tune your cars for specific tracks rather than a generic setting that works well everywhere.

Forza 3 does give us a really nice tool to help determine the optimum tire pressure. The one you'll be using is in the diagnostic screens and it's the very last one that shows the tire temperatures for the left, right, and center of the tires. What we're aiming for is consistent heat across the entire width of the tire when we're driving the car correctly and at speed. If we're heating up the centers of the tire more than the shoulders, we've got too much air pressure. If we're heating up both shoulders faster than the center, then we've got too little. If we're heating up either the front or rear tires too much or too quickly, we've got too little pressure in that end. If we're not heating them up fast enough, there's too much. Now, we can't be perfect, but we're aiming for consistent temperatures across each tire as much as we can. I hate to say it's this simple, but it really is -- but only if you've set up your car properly to begin with. Something as easy as way too much toe can send outside tire temperatures through the roof and negate everything we're trying to do.




Solving Handling Issues:

At this point, you should have a car that behaves pretty well, but it needs a little tweaking. Either you missed something somewhere, or you think it could work better on a certain track. Where do we start then? There's no sense throwing out the baby with the bath water and starting fresh, so lets look at some common handling problems and some quick minor fixes. Again, this assumes a car that's not behaving horribly or set up poorly in the first place. This is fine tuning.

ProblemManifestationSolutions
Steady state understeerAll turns or low-speed turns onlyIf front tire temps are optimum and rears are low, stiffen rear antiroll bar; if front temps are too hot, soften front (most likely).
If front tire pressures are optimum, decrease rear tire pressure.
Improper front camber.
Too much body roll at front, causing excessive camber change.
Steady state understeerHigh-speed turns onlyIf front tire temps are OK, increase front downforce.
If front tire temps are too hot, reduce rear downforce.
Steady state oversteerAll turns or low-speed turns onlyIf rear tire temps are optimum, with fronts too low, stiffen front antiroll bar; if rear temps are too hot, soften rear antiroll bar (most likely).
If rear tire pressures are optimum, decrease front tire pressure.
Improper rear camber.
Steady state oversteerHigh-speed turns onlyIf rear tire temps are OK, increase rear downforce.
If rear tire temps are too hot, reduce front downforce.
Corner entry understeer
Front shocks are too soft in bump resistance.
Too much front toe-in; use a small amount of front toe-out.
Corner exit understeer
Rear shocks are too soft in bump.
Front shocks are too stiff in rebound.
Corner entry oversteer
Rear shocks are too soft in rebound.
Rear ride height is too high (too much rake) compared to front.
Corner exit oversteer
Rear shocks are too soft in rebound.
Too much rear toe-in or any rear toe-out.
Straightline instability
Tire pressure is too low in one or more tires.
Too little positive front caster.
Too much front toe-in or any toe-out in rear.
Straightline speed too slow
Too much overall downforce.
Too much toe-in or toe-out.
Ride height is too high.
Chassis or suspension bottoms
Spring rates are too soft.
Shock absorber bump rates are too soft.
Inadequate suspension travel.
Inadequate ride height.












3 comments:

TicketBastard said...

Someone asked me how to "stiffen up" a car that handles well on a bumpy track but could be better planted on a smooth one without wrecking the handling or doing serious modification in the process.

My response: What you're wanting to achieve is more bump tolerance on bumpier tracks while maintaining the feel you have and like on smoother tracks where the bump tolerance isn't as needed.

You really shouldn't be adjusting this with springs. Remember, springs are force sensitive, but shocks are velocity sensitive. Spring rates are more affected by the weight of the car and how much it will transition as the car moves around, with a little bit of aero thrown in if you're using it. None of that changes from your proverbial bumpy track to the proverbial glass smooth one. While a car that's oversprung will be less noticeable on a smooth track, it's really not preferable to overspring it just to get it to handle.

What you should really be adjusting is the ride height and the bump stiffness. Adjusting the ride height lower will give you a higher top speed, better working aero, but at the cost of suspension travel. However, if the track is smooth, you don't really need the suspension travel and making it shorter will make the car feel stiffer and prohibit chassis lean in corners. Stiffening the shocks will keep the car from rolling over as quickly and will also give you that "tightness" feeling you're looking for.

If you are going to adjust the spring rates or stiffen both anti-roll bars, what you've mentioned will likely give you a better starting point, but expect to have to tweak a lot more and if you had the handling set well before, you'll likely get poorer results overall by doing this.

charlotte said...

wicked write up m8 learnt loads simple but real well done ps kanerose is my tag if u want to send me tunes haha

GRD 4 3L said...

A fantastic write up in general and specific to Forza. The best guide I have read taking the entire car as a whole.

I would love to chat with you regarding the physical attributes that are actually coded into Forza. eg. Rake - is this actually coded into Forza? How would you test for this?
eg. Torsional stiffness - this is coded into Forza but how much stiffness is appropriate?
eg. Wheel/suspension travel telemetry screen - what is it actually showing? The vertical movement of the wheel or suspension compression?
etc., etc. . . .