Dirt: It’s that painfully slippery surface that causes most of us a 1x or a 2x at some point; a 4x if we are unlucky enough to really lose it.  It’s something that will take a perfectly fine race car and send it 180 degrees backwards into a barrier or sand trap.

For most road racers dirt is evil.  Most oval racers don’t even worry about dirt while racing in their paved coliseums.   But for one group dirt is for racing.  Pavement?  It’s just for getting there.  From short, bullring dirt tracks to miles of rally stages, this group thrives on sim racing in the dirty stuff.

Motorsports on dirt takes many forms across the world.  It’s best known in America for dirt oval racing, while the rest of the world enjoys rallying.  Then there are the off-road racers, who not only play in the dirt but soar over mounds of the stuff.  So the big question that comes-up weekly in the iRacing forums is: “When is dirt coming to iRacing?”

Dave Kaemmer, co-founder of iRacing.com, recently took some time to talk about dirt and the complications it brings from the developers’ standpoint.

Q:     As a motorsports simulation developer what goes through your mind when you see a member of iRacing asking for dirt racing?
A:     I always think about the technical issues first—mostly surface modeling, and graphics.  Then I think about how cool it would be—and it would be pretty cool.  Then I wonder about opportunity costs—might we be better off doing something else?

Q:     What are some of the difficulties about bringing dirt racing into the service?
A:     Surface modeling and graphics.  We’d need to scan some dirt tracks, some off-road courses, and figure-out how to render and manipulate changing track geometry.  Of course, we could keep the track static (not changing), but where’s the fun in that?

Developing artist's conception of iRacing sprint car on dirt? Easy (relatively). Developing practical model of dirt track racing for iRacing? Not so much.

Q:     If and when iRacing brings dirt racing into the service, will multiple forms of dirt racing be looked at, like rally, off-road, and dirt oval?
A:     If/when we do dirt, that would be ideal.  Obviously the surface and force modeling would work for all of them.  We’d need to license and build some different vehicles to do off-road and rally.

Q:     It would seem dynamic surfaces would be key to capturing the feel of dirt racing, and an ever changing track.  Is this something iRacing has looked into? Is it possible to not only have changing grip, but also movement in the surface?
A:     Anything is possible, but the dynamic surfaces are difficult for many reasons, especially in the multi-player environment.  How do we make sure every driver’s track surface is the same, for example.

“We could keep the track static, but where’s the fun in that?”

Q:     How would you approach laser-scanning the track surface when all of these things come into play?
A:     A laser scan would still be good for getting basic topography, and examples of surface ruts, etc. as well as all the usual off track visuals.  Then we’d have to figure out how to “bulldoze” the surface from time to time, and allow it to be modified by the vehicles racing on it.  We might have to move to a different type of laser scanner for doing many mile, point-to-point courses.  For ovals, we’d just do what we already do.

Q:     I have seen some members say that a new tire would need to be developed for dirt.  Would this need to happen or is the tire model something that works no matter what surface it is running on?                                                                                                                                                                     A:     The tire we have is probably good, but we’re need modeling of the dirt itself.  A lot of the forces on a dirt track depend on the dirt and its properties.  On asphalt, we don’t have to worry about the surface breaking up before the tires lose grip.  On dirt, the “tire” forces are more often dirt forces.

“The dynamic surfaces are difficult for many reasons, especially in the multi-player environment.”

Q:     We have seen from a few of your posts about the data you have on grass, the ‘cow’ data.  Have you looked for data on the properties of different types of dirt and clay?
A:     I’m always on the lookout for data.  There’s a lot of research into “terra-mechanics,” primarily since military simulations of tanks have to deal with the physics of dirt.  It’s interesting, but sand, dirt, clay, even gravel are all pretty much the same except for the sizes of the particles making them up; and their water content.  Of course grass and other plants add complications.

Q:     SODA Off-Road Racing seems to be the only dirt game that you have been connected to, through Papyrus.  Did you have a part in that title?
A:     Shawn Nash developed SODA, pretty much by himself.  Still amazes me.  Papyrus was the publisher, but Shawn did it as an outside developer, so it wasn’t our code.  Of course, Shawn is one of our engineers, so if we do dirt he knows all about mud-pumping forces and 20” of suspension travel . . . and lots of other things.

“If we do dirt (Shawn Nash) knows all about mud-pumping forces and 20” of suspension travel . . .”

Q:     Through the years there have been very few titles for dirt racing compared to those for asphalt racing.  Why do you think this is? Is it a lack of market or just something harder to do than a paved surface?
A:     I think it’s a combination of both.  The best-selling dirt games have been rally games, for the most part.  The difficulty of doing it certainly plays a part, since difficult = costly.

Q:     In your mind where does iRacing need to be on the paved racing side before focus can turn to dirt.   Does the status of iRacing’s paved racing even play a role in when dirt comes?
A:     There are still a lot of features on pavement that are probably more cost-effective for us to do, and for which we’d probably find a bigger audience.  Endurance racing as teams, for example—there’s just a huge list of features we’d like to get done.  Consider this as well… would drag racing be a bigger deal?  How about motorcycles?  Of course I know what you’re thinking:  dirt bikes!

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