Fri. Feb 3rd, 2023
Go behind the scenes with DiRT Rally's punishingly realistic road physics


Formula 1 may be known as the pinnacle of motorsport, but the most challenging discipline in racing has to be rallying. Now, in the form of Codemasters’ DiRT rally– available now for PC on Steam Early Access and arriving April 5th on the PS4 and Xbox One – there’s a video game that finally does justice to this sport. More a simulation than anything that’s come before, DiRT rally arguably one of the hardest racing games we’ve ever played. It’s also one of the very best.

To the uninitiated, rallies are point-to-point races against the clock. They run on “stages” – public roads or circuits closed for the occasion, one car after another in a series. Every car has a driver and co-driver. Before the event, they create pace notes—a condensed list of the route with information about the various turns and hazards—and during each leg, the co-driver performs navigation tasks and calls that information back to the driver.

Those of us who race on purpose-built tracks quickly memorize the layout, knowing that the same corner will be in the same place lap after lap. Rally drivers? Not so much. Not only do they have to race over stages that can be tens of kilometers long, they also do so on dirt or gravel roads where the amount of grip varies from corner to corner. Oh, and they have to run in all weathers. Rain, of course, but also snow and ice, depending on the event. As we say: challenging stuff!

Now for a quick confession. As much as I love watching real rallies, I’ve never been the biggest fan of rally games. Codemasters’ Colin McRae meeting left me cold. The rally stages are coming in Gran Turismo did about the same. The cars always felt like the handling was unnatural, and I’d rather be doing something different. Those days are over, I’m happy to report. Within just a few minutes of sitting down with the game, I knew Codemasters had knocked it out of the park. Paul Coleman, DiRT rally‘s lead designer, participates in rallies in his spare time, and his passion for and knowledge of the sport shines through the game.

You get to race in a number of different events. There are traditional rallies, where you compete against AI drivers on real stages used by the World Rally Championship (in Greece, Monaco, Germany, Wales, Finland and Sweden). There are rallycross events, held on circuits that are a mix of tarmac and dirt roads, where you compete against several other cars at once. And finally, there’s the legendary Pikes Peak Hillclimb, which will be held for the 100th time this summer, a 12km run down the Colorado side of the mountain. In addition to single-player events, there are asynchronous online events and competitions, as well as real-time PVP rallycross races.

DiRT rally gives you a range of different cars chosen from different decades of the sport. In career mode, you start with low-powered cars from the 1960s, then progress to faster machines like the deadly Group B monsters of the 1980s or the increasingly sophisticated WRC cars of the 1990s, 2000s and 2010s. There are also specific rallycross cars for those events and a few famous Peugeots built specifically for Pikes Peak.) You can modify the cars between some stages (in line with the real thing, where there are intermediate service stages), and as you progress in the game, your mechanics and support team will gain skills, making your car better (and making repairs faster).

We recently spoke with Coleman to learn about the history of DiRT rally and to discover why it is so challenging. PC gamers who have been playing it for a few months now have made the comparison with Dark souls, a notoriously difficult action game. “I’m not exactly thrilled with that analogy because we never set out to make this the hardest racing game ever; we wanted to make the most authentic rally game ever,” Coleman told us. “Driving the cars isn’t actually difficult, it’s the roads you have to drive them on. Driving one of these cars down a 4m wide goat track in Greece is where the challenge comes from. But if you take it easy and you go through the stages calmly, you’ll get through them; you’re not going to fall off the road. You’re just not going very fast!”

This is certainly true. Try to run flat out right away, and you’ll soon find yourself in trouble, spinning out, or worse – many of the rallies are held on trails that run over hills or along cliffs, and it’s very easy to overcook and end up at the bottom of a gully.

The secret sauce that makes DiRT rally so realistic – and therefore so challenging – is the way the game models the tracks. When development started in 2012, Coleman and his team started with the engine of dirt 3taking authentic stage widths and real roads from real rally stages, then running cars from them dirt 3 down.

They soon discovered that those cars couldn’t handle it. “The old throw dirt 3 cars down there weren’t working and we knew we had to rework our simulation engine. We started doing things with the bike at our disposal, and we got close, but we hit a brick wall in certain areas. And our physics programmer was not willing to touch anything at the time. It was an engine that we had been using for 10 years, and it was very reluctant to go into Pandora’s box and unravel everything,” he said.

A new engine was needed. The hope was to leverage the engine that Codemasters’ other racing franchise (the F1 201x games) had built in 2012, but that quickly turned out to be insufficient. “To a naive person you would think it would all be the same, but to F1 they are essentially a plane with wheels. For us it’s a completely different proposition. The first thing we did when we got a new coder who was willing to unravel all these things was to say, ‘Okay, the most important thing we have as a racing game that no one else has to deal with is the surface you’re driving on.’ And while most other games have tarmac and they can work on the tire model and go from there, we wanted to make sure the surface technology was right first – that foundation you build on – and then start working on how the tire interacts interacts with that,” Coleman told us.

Coleman and his team began reading many articles on fluid dynamics to understand how rocks move across surfaces. “I’ll be honest and say we’re not using fluid dynamics for the game because the CPU power of a home computer or PS4 can’t handle that. What we’re actually doing is a simplified model, which is density,” he said. “The deeper you dig into a surface, the denser it gets and the more traction you find. That works to spin the wheel; it also works to slide the tire.”

“Each surface has different properties. The gravel surface you get in Finland is a very compact, quite fine stone that they use as a public road, while the roads in Greece are dirt roads with very large lumpy, sandy rocky gravel. The density is so very different there, and the nature of the road changes quite dramatically, even between gravel surfaces.” The result is an intuitive experience where things like car weight transfer really matter.

Modeling real stages was also important to Coleman. “With these real stages in it – instead of making the stages like we’ve done before, and designing each corner to be the best corner ever – we said this is a road like the one used in real rally events, and we embrace the fallibility of that, that angle is a nightmare to drive around because that’s what rally is, driving a car over a very rough stretch of road and dealing with it.”

Once the basics of the surfaces were good, the next step was to layer in the physics of the tire and how they interact with those surfaces. Next came the cars – the engine, clutch, gearbox, powertrain, and so on – with information drawn from real teams, historic cars and published race reports. The attention to detail becomes apparent as you play DiRT rally with a wheel – you’ll soon find that a 1960s Mini or Lancia needs a lot more steering to take a corner than a modern WRC car with its ultra-fast wheelhouse. And all the while it manages to maintain 60fps at 1080p.

And play this game with a wheel you should. While Coleman expects the controller to be the default input device, with a wheel it becomes utterly convincing – the only thing missing compared to the real thing is the cold and the rain.

By akfire1

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