0:04 = start - Welcome to Sebring
At the start of the video, you see 12 customized cars racing down the front straightaway at Sebring International Raceway in Florida, one of the new tracks we have in Forza Motorsport 2. It’s a pretty tight field and the cars are really dicing it out heading into the first turn.

0:13 = Racing Line
In the first cut-away, we show a top-view of the drivers settling into their racing line. You can see the cars hitting their apex and exit points as they weave through the first group of turns. It’s a tight, high speed section of the track – not a lot of room for passing.

0:18 = Camber at Work
The second cut-away focuses on the front left suspension of a Nissan Fairlady Z. In the left pane, we highlight a change in camber as the car is cornering. Camber is the angle of the tire in relation to the road. In this scene, the camber changes due to body roll and the movement in a double “A” arm suspension. In the bottom right pane, you can see the tire tucking up under the fender just a tad – this movement is meticulously recreated in Forza Motorsport 2. We simulate all kinds of suspension movement as well as their physical geometry.

Geek Out on Tires.
Tire simulation is where Forza Motorsport 2 truly shines. Tires are an incredibly complex system and the most difficult thing to get “right” in a simulator. Tires react to hundreds of subtle variables in some pretty amazing ways, yet they’re an afterthought in most simulation racers. Let me use this cut-away to explain a little about what’s going on in the pane, in real life and in our racing simulation.

You might think that an ideal camber setting would be zero degrees, where the tire is perfectly perpendicular to the ground. However, in this situation you want just a slight amount of negative camber – leaning into the direction of the corner. This negative camber allows the tire to wind up like a spring by flexing its sidewall and contact patch. This spring-like tension is required to get peak friction out of the tire.

As you work a tire, the area where the tire comes in contact with the road flexes and deforms. This area is called the contact patch and you have one for each tire. Managing the forces applied to your four contact patches (load, lateral force and accelerative torque) is the secret to driving fast in the real-world as well as in Forza Motorsport 2. You have to be smooth and keep the car’s weight as evenly distributed as possible.

0:26 = Suspension Simulation
The third cut-away is similar to the second. Only this time, it’s focused in more tightly on the suspension. This allows you to see how much the suspension compresses under heavy load. While the math isn’t as complex as the tire system, the suspension has a lot going on as well. Suspension is one of those physics systems we run at a ridiculously high frequency in Forza Motorsport 2. Some simulation games run their physics at 60 frames per second. However, for systems like tires, body inertia and suspension, this physics update rate is far to low. Its ends up making the game feel like driving in molasses – rapid yaw and load changes feel sloppy. This isn’t how real cars feel. We run our suspension at 360 frames per second to make insure that the racing experience is simulated perfectly.

0:32 = Drafting the Competition
In our fourth cut-away, you can see a Nissan Skyline drafting behind a Honda NSX. They are heading down the long straight-away before the final corner of Sebring. By tucking in behind the NSX, the Skyline gets less wind resistance or drag on the car to slow it down. Using the turbulence and change in air pressure behind the NSX, the Skyline is able to gain some ground and set up a pass.

0:50 = We Have Contact
The final cut-away shows why we included Sebring in Forza Motorsport 2. Sebring is a notoriously rough track. Built on an old runway, Sebring’s surface changes from tarmac to concrete and back several times in a lap. Also, many of the concrete slabs don’t match up right. You can see the Skyline hit a bump and get a few inches of air. If you are asking 100% of your tires and the car gets a little bit of air, the landing isn’t going to be pretty. Sure enough, it ain’t pretty.

The Skyline takes out the NSX and they both go careening into the wall. Parts fly everywhere and come to rest on the track – mirrors, wings, front bumper, rear bumper, exhaust tips... It’s a pretty nasty collision. We’ve added a ton to our damage system in Forza Motorsport 2 – more parts fall off and the performance impacts of damage have been dramatically increased.

1:06 = The Checkered Flag
At the very end of the race, you see the customized Fairlady Z taking advantage of the NSX’s misfortune. The Fairlady Z crossing the finish line ahead of the pack.