"Limited CoLLeCtor’s edition
Limited CoLLeCtor’s edition
0207 Part No. X12-87636-01
Ta b l e o f C o nT e n T s
Welcome........................................................................ 2 The Vision
An Interview with Lead Designer Dan Greenawalt ....................................3
Car Manufacturers ........................................................ 18 The art
An Interview with Art Director John Wendl ............................................71
a sampling from the stable .......................................... 80 The sounds
An Interview with Audio Lead Greg Shaw ............................................108
Real-World Tracks .........................................................114 Racing school ............................................................. 126
Turn Types ...........................................................................................129 Basic Turn Strategy ..............................................................................132 Braking and Cornering .........................................................................133 Managing Weight Transfer ..................................................................138 Coping with Understeer and Oversteer.................................................142
Professional Insights
An Interview with Racing Driver Gunnar Jeannette ...............................148
Industry Credits .......................................................... 152 Team Credits ............................................................... 155
All trademarks, trade dress, design patents, copyrights, and logos are the property of their respective owners. All rights reserved. © & p 2007 Microsoft Corporation. All rights reserved. Microsoft, Forza Motorsport, Halo, Midtown Madness, the Microsoft Game Studios logo, OptiMatch, PGR, Project Gotham Racing, Turn 10, Xbox, Xbox 360, Xbox LIVE, the Xbox logos, and/or other Microsoft products referenced herein are trademarks of the Microsoft group of companies.
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ForzaMotorsport.net
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W e lC o M e
Welcome to the Forza Motorsport™ 2 Limited Collector’s Edition, your passport to the world of automobile racing, both simulated and real. Forza Motorsport 2 players have two things in common: a passion for cars and racing, and a consuming desire to win, and this book is designed to feed that passion. In its pages you will: Get a behind-the-scenes look at what went into the making of the most detailed and immersive racing simulation to date. Find a wealth of information on the cars and tracks you can experience in Forza Motorsport 2. Learn about racing techniques that can fuel your success in Forza Motorsport 2.
The V I sI on
an Interview with lead Designer Dan Greenawalt
Lead Designer Dan Greenawalt is the keeper of the vision for the Forza Motorsport franchise. In this revealing interview Dan takes you behind the scenes for a better understanding of that vision, and of the physics that underlie this extraordinarily realistic auto racing simulation. From the tire physics that determine whether your car will stay stuck to the road or spin off the course, to his views on the automotive playground he is creating and constantly improving, to his emphasis on the joy of driving and his plans for the future of Forza Motorsport, this interview provides an intriguing look into the world behind the game.
“I envision Forza Motorsport as the place where car lovers can gather to talk and argue about cars they like and racing they’re interested in. I want to bring people with this passion together regardless of their other differences. My goal for the Forza Motorsport franchise is broad and inclusive.”
Welcome
T he V i s i o n
Q: What are the physics behind the Forza Motorsport 2
racing simulator? What are the components of real-world racing you had to re-create?
We spent a ton of time working on the physics. We used a lot of sources, but especially Milliken & Milliken’s Race Car Vehicle Dynamics, a very reputable source on vehicle dynamics and tuning, with the graphs and the math as well as general theory. It’s used a lot, not only for racing sims, but also by racing engineers. It was the single biggest influence for us; it became the way we spoke. We made a technology demo with five meticulously researched cars to prove our physics engine. In many ways we were just trying to see what we could do. We poured six months into that demo, and the results were really incredible. There were no licensing agreements at this point, so we had cars rolling over, taking heinous damage, shedding parts—but you’ve got to make some allowances when you have agreements with fifty different premium car manufacturers. It was an all-star team of guys who had all been involved in one racing franchise or another—Rally Sport Challenge, Project Gotham Racing®, or Midtown Madness®. The physics was where we were at our purest, and I haven’t seen many simulations that match the accuracy of Forza Motorsport.
Q: so you slowly moved away from an entirely purist
process for six months to get our vision honed. Not just the vision for Forza Motorsport version one, but for the franchise. This helped me get a better vision of where I want us to be in six or ten years—the game I want Forza Motorsport version six to be. This sort of forethought allows us to start planting little road signs in the game, minor features we could develop over time into major ones.
Q: It sounds like your vision of the user experience shifted
over time to become an online multiplayer experience, much more involved in version two.
In many ways, Project Gotham Racing and Forza Motorsport are brother and sister products. We share technology; but more than anything, we share a charter to keep pushing the bounds of online play. Microsoft in general and our teams in particular believe that online play is where gaming is at today. We also believe that the most influential innovations in this genre are going to come in the online space. Our goal every time Project Gotham Racing or Forza Motorsport ships a new version is to make sure it just keeps getting better and better. We pushed the boundaries in the original Forza Motorsport; no game had so many scoreboards. We write to multiple scoreboards at once; no one had ever done that, and we had a seamless online to single-player Career mode. At the Xbox 360™ launch, Project Gotham Racing 3 (PGR® 3) came out with even more fantastic online features, like Spectator mode. Now we’re pushing the boundaries again with our Auction House, tournaments, and other new features. I really want to get us to a new way of experiencing racing games in the future, so we’ve got to keep making forward progress.
approach to an emphasis more on game design and gameplay.
I love physics, and I like working on that aspect of the game in particular. While we were working on the demo, I was also working on the vision and the “pillars”—the features—that support that vision. I had to flesh it out from the top down. We all threw features at the wall to see what would stick. I worked to pull it all together and create a cohesive game design. We repeated this
The Vision
T he V i s i o n
Q: Tire simulation is a big part of the physics model, and
people don’t usually focus on that in racing games. What did you learn in trying to develop a realistic tire formula?
We tried different tire models after our “green light” demo. We kept tuning the physics model, finding bugs, and working on it. New cars exposed new issues. We had two basic ways of expressing the tire physics. The traditional way that simulation racing games do this is Pacejka’s Magic Formula—no joke, that’s what it’s called. It’s got a whole slew of variables you tune and input, and it spits out friction values. But the cars didn’t control the way we wanted and the results didn’t mesh with a lot of our real-world data. I’ve had enough experience tuning with that formula that I can feel it at work when I play some racing simulations. It’s not quite right, but it’s close. Toyo put me in contact with their tire engineers. It was hard to understand the data they were giving me, and I had to ask a lot of questions, but they slowly brought me up to speed to where I could understand what their graphs and data were saying. Pacejka’s formula is close, and really good in most situations, but not all, and not for transitions between states. It just doesn’t feel right. So we went to what could best be described as a table system. We have a table that linearly interpolates between the curves we have for different weights, tire pressures, and other variables. It’s a very big, computationally difficult system. That’s what was nice about Pacejka’s formula when we were using it—it’s very lightweight, where our approach is extremely heavy. That’s why in Forza Motorsport, drifting, for example, is very real and very responsive. Drifting is all about weight transition, and you can control it with your throttle in Forza Motorsport because in our model the movement between those curves is very smooth and precise. We spent a lot of time getting it right. The tire model is amazing, but there are always things to improve. There are things in our physics model I’ll want to improve forever. Forza Motorsport 2 is a simulation, not a complete emulation—no one has ever done that, no matter what they claim. We can’t completely emulate tire technology until the scientists learn it, and they haven’t learned it all yet. Tires
do some funky things. They’ve got load sensitivity, which involves nonNewtonian physics. A tire with a coefficient of friction of 1.0 at 500 kg actually develops a smaller coefficient of friction at 1,000 kg. With 500 kg on the tire, it might require a value of 500 kg force to push it. But with a 1,000 kg load, it might require a value of 800 kg force to push it. Understanding this is huge in understanding how tires function. It’s a big deal to simulate this, though few people know about it. When I told the tire engineers, they were amazed we were doing it.
Q: Please elaborate on why tires are so important in
racing. Why do most people give more thought to parts upgrades than to tires?
People tend to take their tires for granted; you see the tires on your car every day. But turbochargers and computer-controlled fuel injection systems are like alien technology to many folks—they’re high tech and people don’t see them every day. People think they understand everything about tires, and unfortunately tires are the part of the car they usually understand least. Tire compounds are really crazy. We were at an American Le Mans Series (ALMS) race in Portland, Oregon, under very hot conditions, and saw how tires have a huge impact on racing. The science behind tire technology is always changing. We can get amazing performance out of tires, and the tires of today are much better than tires even just five years ago. That extreme rate of rapid iteration doesn’t happen with turbos or many other engine technologies. Your car talks to the road through four little tire contact patches, and it’s how you manage those patches that makes everything work. After the ALMS race the manager of the winning team said the only reasons they won were their drivers and their tires, that both really came through in the heat. The tires have many layers, all of which are meant to react to heat, torque, and force in various ways. If they do what they’re supposed to do, they create the
The Vision
T he V i s i o n
necessary coefficient of friction. When you start twisting that contact patch the tire winds up like a spring and gives you the slip angle required to hit peak friction. Doing that is a very complex process. It’s interesting that different tire compounds, like a Y-rated tire, or a DOT-spec tire, or a racing tire, have very different characteristics. You look at them—they’re just some rubber on a rim. It’s not just the tread that gives tires their characteristics. Tread quality is essential, but it mostly comes down to the composition and construction of the tire. How sticky it is, how it reacts to heat, how the sidewalls flex, all make a huge difference.
Q: Is there ever a reason not to use sticky tires? Q: What is the process of tuning more than 300 cars to
make them feel right?
We use roughly 9,000 individual variables just to define the physics for a single car—not including the tires, but for the variables that define the car and its upgrade parts (from spring rates, damping bump and rebound, to weight, aerodynamics, and so on). Even race cars that can’t be upgraded involve 5,000 numeric values to define each car. It all started when we were figuring out and iterating on the physics, and I was trying to determine whether there were patterns. We were reading Milliken & Milliken as well as other vehicle dynamics books and trying to identify how the cars relate to each other. Basically, we were developing a math model for tuning the cars. The hardest thing is, you can’t find, for example, spring rate data for all 300 cars. You’re lucky if you can get it for 20% of them, from the manufacturers and from research. Sometimes you can get that kind of data on fan Web sites, which can be freaky that way. Sometimes we contacted the spring manufacturers, not the car manufacturers. The manufacturers we contacted were based on the continuum of all of the cars, so we could get a really even spread of data on low-end cars to high-end cars to race cars, finding out about progressive springs versus linear springs, and so on. Then we looked at ride height, the weight of the car, and what we call the “goodness rating,” from reading reviews and learning a lot about each car. We ranked the cars based on their “goodness,” and arranged those values into buckets. For example, we might put a Ford Focus SVT a little lower than a Subaru WRX STi. When we set the spring rates for those cars, and we don’t have the actual spring rates for them, we use a formula, a mathematical model, to automatically tune those numbers for us. Then we put in critical damping, and offset damping with “goodness,” ranking cars by region. A lot of this we call “automagic”—it’s our voodoo magic that we do in the game, and it’s the only thing that makes it possible to tune 9,000 numbers on 300 cars.
As someone who tracks his car, I can tell you that sticky is more expensive to buy and that you’re going to go through them faster because they’re softer, so you have to buy more of them. They also generally react badly to high heat. In that hot ALMS race, most teams were running on their hardest-compound tires. Because of the heat, those hard tires were getting soft and losing rubber, leaving “marbles” all over the track. On a cool day you would go with a softer compound and might only have to pit, say, once an hour. On a hot day you’d go with your hardest compound, and might also have to pit at the same rate. If you had stuck with the soft tires on that hot day, you might have had to pit twice as often. Also, on a hot day the softer tires might blister and fail. In Forza Motorsport, tire pressure increases as the tires heat up. This changes the contact patches and tire friction, and affects your handling.
The Vision
T he V i s i o n
Proving that this automagic model could work to tune the cars was a big part of our getting the green light for version one. And there’s a ton of testing that goes on. We list and graph the numbers we get, looking for anomalies, and then we test the cars by hand. For example, one may come out with a really loose spring rate. Sometimes we find that our formula isn’t taking weight distribution into account as well as it should. Then we rework the formula, reexport all the cars’ values, and retest. That’s a lot of systems—engine systems, such as turbo pressure, rpm, inertia, and so on. Some things we get to research a lot, like all of our stock turbo pressures. We went through and tested them, and made sure that they were in the right stack rank relative to each other and that their results in the game matched our research and knowledgebase.
Q: for the original Forza Motorsport, racing driver Gunnar Q: so we’re really talking about hand tuning.
After the automagic has done its thing, then you go in and hand tune. For instance, getting the nuances of the suspension right is less about oversteer and understeer and more about controlling the car with the throttle through a turn; how getting onto, off of, and back onto the brakes creates oversteer; how braking and throttle techniques affect the car. We’ve got a really good team—guys who are rally drivers, guys who have driven all kinds of cars. So we start tuning that way. But inevitably there are cars no one on the team has driven, like the Lancia Stratos. We had trouble finding reviews on it; we just knew it was a famous rally car, but our physics got a ton of that stuff right. You start putting in the weight distribution, the size of the car, its moment of inertia, and it starts getting better and better.
Q: how do you handle implementing upgrades? When does
Jeanette made some suggestions about cars he had driven, and you were able to change some numbers on the fly to make the car more realistic. Is that something you’re doing for Forza Motorsport 2?
There are two sides to it. Some of the cars drive the way they do because it’s completely predictable. You look at the car’s behavior and it’s easy to see why it behaves that way. If it understeers and you see that it’s front-weighted with no downforce, all the tires are the same size and its spring rate is tighter on the front, obviously it’s going to understeer. In a front-drive car with 60% of the weight on the front wheels, it’s just physics that the car will understeer. So there are a whole bunch of characteristics people comment on—“You really got that right!” I say, “We didn’t have to get it right—the physics got it right!”
the upgrade variable come in?
Some of the upgrade variables are researched heavily in order to create the model. The issue is that our Level 3 upgrades are full racing upgrades, as if you had a million dollars to burn, which very few people have, especially on a lower-class car. No one is going to spend so much upgrading cars like that, so we have some cars people don’t race much, and have no idea how much power that engine can really make. So we have to use some math and our model to figure it out. The car has a certain displacement and configuration, it’s a certain size, has a certain rpm redline and top speed, and we take all those things and put them together and come up with what we think is its theoretical maximum torque and horsepower. But believe me, gas velocity out of the valves and headers can be a real pain to estimate.
The Vision
T he V i s i o n
Q: since you have to account for things you can’t find in
reality but that can exist in the sim, are there times when the potential for so many car modifications seems too crazy and unbelievable even though the math says the model is right?
When I was developing the franchise vision, I hit on the idea early that this is an automotive playground, a sandbox. We could have gone the route of a super-credible, licensed parts catalogue. We could have said, “Exactly what parts really are available for, say, the Mark II GTI? Oh, these parts are available in the real world—okay, then that’s exactly what the player will get—no more and hopefully no less. It’s sort of limiting for cars that for one reason or another have never gotten a lot of race R&D in the real world. Also, we could have exposed the player to the money pit and no-win situations that define tuning in the real world. One t..."
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