Yamauchi: Tire Physics Remain Gran Turismo's Toughest Challenge

Kazunori Yamauchi sat down with evo magazine at the FAT Ice Race in Zell am See, Austria, earlier this year, and in the course of a wide-ranging conversation about Gran Turismo's past and present, he offered a candid assessment of where the series still struggles most: tires.

The admission is notable partly because it echoes something Yamauchi has been saying for years. Back in 2017, when he accepted an honorary doctorate in Modena, Italy, he identified tire modeling as the franchise's most intractable simulation problem. Nearly a decade later, the problem persists. What makes it so stubborn is not the broad strokes of tire behavior—suspension and drivetrains can be modeled with remarkable fidelity to reality—but rather the granular details. Specifically, the contact patch: how the tire's footprint on the road shifts and behaves as heat builds, rubber wears, and track surface conditions change. "The level of grain that happens when you have certain conditions on the track, it's something that we just don't have yet," Yamauchi told evo. Even collaboration with tire manufacturers hasn't fully closed the gap between simulation and the real thing.

The challenge has only grown more complex. A single car in Gran Turismo 7 now takes roughly eight months to develop—a figure that encompasses both the visual model and the physics work needed to make it behave authentically. That's a far cry from the original Gran Turismo, where each car took about two hours. The Nürburgring Nordschleife alone consumed four years of development time. Modern vehicles, particularly electric cars, have made the job harder still. Electronic management systems for drivetrains and differentials vary wildly from manufacturer to manufacturer, and EVs demand an even finer level of detail. Yamauchi noted that the Polestar 5's behavior on ice differs markedly from a Porsche Taycan's—a distinction that matters to players who care about authenticity. He personally test drives each car before it ships, a final checkpoint to ensure it feels right.

What's perhaps more surprising than the tire challenge itself is Yamauchi's acknowledgment of corporate pressure from Sony. When asked whether his bosses at the company have ever pushed him to cut corners or complained that development was taking too long, he was direct: "Up to about Gran Turismo 5, yes. Nowadays, not so much." That admission carries weight. Gran Turismo 5's development cycle was one of the most publicly scrutinized in the series' history, marked by two significant announced delays. The fact that Yamauchi felt comfortable naming that era as a period of corporate impatience suggests the relationship between Polyphony Digital and Sony has genuinely shifted. The studio now appears to have more latitude to pursue the level of detail it wants.

The car list itself follows no single master plan. Some vehicles arrive because manufacturers approach Polyphony with new models. Others make the cut because Yamauchi personally wants them included. Player requests can tip the balance too—community feedback has drawn his attention to cars he might otherwise have overlooked, including the enduring appetite for 1990s Japanese machinery and more utilitarian vehicles. When asked which manufacturers he's turned down, Yamauchi declined to answer, delivering the response with what evo describes as a wry smile.

Meanwhile, the work continues. Update 1.71, which arrived this week, brought yet another revision to the tire physics algorithm, touching slip behavior, rolling resistance, heating, wear, and grip loss. The update notes don't mention contact-patch behavior or graining, suggesting those remain areas of active development. The fact that Yamauchi keeps returning to tire physics—that he's willing to discuss it as an unsolved problem even as his team ships update after update—speaks to how seriously Polyphony Digital takes the simulation. For a game that has grown to encompass players from teenagers to those over 60, and that has become influential enough that early Gran Turismo players now hold senior positions at car manufacturers themselves, getting the details right matters. The Polestar 5's recent time-trial campaign drew 160,000 players, a testament to how much real-world automotive companies value the exposure. That kind of reach demands precision, and precision, Yamauchi's comments make clear, is still a work in progress.