Turn 10 on why Forza Motorsport 5’s physics are ‘impossible on last-generation hardware’

Forza Motorsport 5

Turn 10 Studio’s creative director Dan Greenawalt will talk about the brutal, complicated maths that underlie Forza’s handling model for days, if that’s what it takes to prove the necessity of next-generation hardware for making Forza Motorsport 5 work. “The things we’re doing in physics now are simply impossible on last-generation hardware,” he says. “The amount of power to do the calculations we’re doing was just not available, and we didn’t have the knowhow as an industry to do some of the things we’re now doing.”

Greenawalt offers an example: “We did good suspension in Forza 4, but there was more to be done. We’re adding open-wheel [cars] in Forza 5, like the 1976 Ferrari and McLaren from the movie Rush, so we wanted to reinvestigate what it takes to do a race suspension model, and that benefits all our cars. Now we have more accurate movement as we’re doing a reverse-kinematic model. Basically we’ve measured all movement – the length of the swingarm, the length of the A-arm – we have all that modelled.”

“Tyres,” Greenawalt says, with a full stop. Forza 4 simulated tyre flex using variables ported directly into the game from Pirelli’s own test data, but Greenawalt wanted more.

“I was asking Pirelli, ‘These tyre curves you have, this data… how are you isolating camber from wear from pressure and so on?’” he says. “Pirelli’s take was, ‘We don’t and [you can’t]’. So we found a new partner for Forza 5: Calspan. Calspan is not a name that anybody knows, unless you’re an engineer. The testing that Pirelli was doing on their tyres is called Calspan testing; that’s what all the tyre manufacturers use. [Calspan’s] take was different to Pirelli. It said, ‘We’ll need palettes of tyres,’ so we bought palettes of tyres and sent them to Calspan and [it] did two weeks of testing – morning, noon and night – isolating these variables. We now know things about Pirelli tyres that Pirelli doesn’t know about Pirelli tyres. We know things about Toyo and Yokohama that are going to help write the textbooks in two or three years.”

Greenawalt only mentions Forza’s most conspicuous competitor when he doesn’t mention it – Gran Turismo 6 uses Yokohama tyres and physics powered by a current-generation processor.

“I don’t know about their physics engine,” he says. “But this is a new physics model that wouldn’t have been possible in the last generation, and not just on Xbox 360. We just didn’t have the power to run all of these isolated variables. We made changes to the aerodynamics, we made changes to the mass block – there are a lot of changes that came in – but it’s the tyres where we’re not just on the cutting edge of racing simulation, we’re on the cutting edge of tyre science.”

But for all the millions invested in handling models and tyre flex, it’s not maths that separates Microsoft’s Gran Turismo from Sony’s Gran Turismo; it’s the push to change, to let players play their way and to exploit new ideas as much as new technology. Polyphony Digital’s Gamescom panel showcased a game of escalating complexity worn as a badge of honour, while Turn 10’s Forza 5 demonstration was about explaining a game that’s playable by anyone, any way.

The massive multidiscipline Forza 4 career has been replaced with 42 90-minute mini-careers, each built around a specific class. The Sport Compact category opens up into a series of campaigns – Modern Hot Hatch, Early Sport Compact, Modern Sport Compact – and lets players take them on in any order, as long as they have the car for it.

You’ll start in a mid-range sports car rather than a Ford Focus, but you can step up or down the classes at will so long as you have the cash for it. Every car is fully articulated and those million-polygon models can be explored in firstperson with an intro from Top Gear’s presenters, detailing the differences between an STi and a GTi or framing it in the history of motorsport, movies or automotive design.

“No matter where you go in the game, you get money and XP and level up,” Greenawalt says. “Whether you’re a five-year-old or a 35-year-old race car mechanic, whether in splitscreen or Free Play, multiplayer, singleplayer… we value everyone’s time equally. I don’t ever want to try to fit someone into a cookie-cutter mould, to say, ‘Oh, you’re not into simulation – get out of here’. I believe that’s poor design. Are there arcade games and sim games? No, there are just poor designers. I believe a good designer can come in and we can have excellent physics and we can have that depth, but if you don’t get it, don’t even worry about it.”

But what about being on the cutting edge of physics? What about a once-impossible degree of variable handling? What about writing the textbook on tyres? What does it mean for the player in a racing game made unique by the chance to play how you like?

“It means a car comes to life,” Greenawalt says. “It’s just more alive. And that’s what Forza is about. We want to bring physics that a race car driver can appreciate and put it in the hands of a five-year-old.”