Race and Vehicle Simulations

As underdog stories go, the conception and development of Kunos Simulazioni as a force in the simracing arena is an emotive one.  The well documented (AutoSimSport December 2011, and here) conception, release and subsequent development of netKar Pro, as a bedroom project turned to reality, is a human story that reflects the sacrifice and passion of a small developer trying to make it in the cut-throat world of video game development.

Many years on, the team are an established business, and working, as is widely known, on a scratch built project to build on their reputation as the class leaders in vehicle dynamics and tyre physics; Assetto Corsa (AC).  netKar Pro, for all its faults, is still regarded by many as the benchmark when it comes to physics in simracing, despite the best efforts of the competition.  This has resulted in a fervent following for AC, with every screenshot on Facebook and every one of Stefano Casillo’s tweets becoming revered as an indication that AC is the sim that everyone in the community is waiting for.

Whether this fervour is realistic is another matter, numbers show that plenty of other sims in development have similarly excited fans, and the consistent user numbers on the iRacing servers leave us in no doubt as to the current top dog.  But, AC is coming on well, so as the proposed release date of “in 2012” is coming to an end, I took a trip out to Vallelunga to see how the sim is coming along.

Over the weekend of the 24^rd and 25^th of November the Autodromo Vallelunga Piero Taruffi was abuzz with the sights and sounds of the 6 hours of Rome sportscar race, and a busy paddock building belied the quiet, calm, working atmosphere that takes precedence in the Kunos Simulazioni offices.  With Stefano, head buried in some code, and Marco, similarly focussed on his screen, the real fun looked to be being had by Nicola Trivilino from DrivingItalia.net, who was pedalling a Lotus 98T around Imola in the Kunos “Sim-rig.”

Once the pleasantries were over, and discussion about my delayed aircraft was duly laughed about (just a left side engine failure on the ground, nothing to be concerned about, erm!), it was time to level some questions at the team.  So, 2012 is coming to an end, where is AC at now?  “I’d say we’re at about 80% of the way there” Aristotelis Vasilakos offers, “most of the main core of the sim is done now, and so we’re mainly now focussing on the little things, making the GUI right, finishing up setups screens, that sort of thing.”

“It looks like we will be delayed beyond the date we originally aimed for.” Marco Massarutto, Project Director, “There are a few good reasons for this, some of which we can’t really get into, but a lot of it is just a matter of making the sim right.  We’d rather put out the best product we can, a little later than expected – than release something that doesn’t work, on time – I think that’s natural.  As such I think we’re looking at quarter one 2013, sometime around March, for release now. However, we hope to get the ‘tech demo’ out sooner, hopefully this year.”

Software development is always tricky to predict, and arguably, a complete scratch-built product in just under a year seemed an ambitious time line.  Is this due to any nasty surprises along the way?  “Not at all” Marco re-assures, “everything has been going very well, in fact, some things much better than expected.  But the fact is we are a small team, and people can only do so much, and sometimes, when dealing with other companies, timescales are not always in your hands.”

Positivity can be taken from this, but what’s been going so well?  Stefano pipes up “I’ve made some nice breakthroughs on the multiplayer side, and to my surprise it’s really come together.  I don’t need to tell you, I was having nightmares about the multiplayer code, after the trouble I had with netKar, but we’ve brought in some new technology on this side that has really improved the experience.”  This inspired Stefano to throw up a server, on a hosted box somewhere on the internet, and connect two clients to it.  Promptly, Stefano and Aris set to the track in a pair of Pagani Zonda R’s, a car with the sort of speed that would have destroyed netKar’s online code.  It was smooth, defined and cars behaved normally and properly, not a jump in sight.  Both drivers ran each other very close at times, with some real wheel to wheel stuff and at no point did the multiplayer falter.

Marco then pulled up a video of an online race in the Lotus 49 with Kunos employee and track modeller extraordinaire Simone Trevisiol, based in Thailand, and similar levels of smoothness and precision were seen in action.  Good news for those that might have feared for AC on this front. “We’re not done yet, there is still a way to go with finalising and tuning the code, but I am very happy with how it is now, and I hope I can make it even better” Stefano’s confidence on the subject is welcome.

“We’ve really got the physics together a little better too, now, I think” Aris comments. “The last time you tried it, in March; things were quite rough and raw, now we’ve refined a lot.  We’ve taken an engineering and mechanical approach to the cars in the sim.  This has meant sometimes fighting car manufacturers quite a bit to get the information we need to ‘plug it in’ to the sim. Once we have the information, all the data goes into the sim and so every car’s suspension geometry is accurate, every aspect of the car’s layout correct, and this links back to the physics engine. It makes sense really, but in the old days of car modding it hasn’t always been this way for sims.  Fundamentally, if we plug in the correct data for the car into the sim, and it doesn’t drive right, then we have to look at what is wrong with the base physics model that isn’t working right, and not play with the car to make it ‘feel’ the way it should.”

As Nicola steps out of the rig to commence his interview with the Kunos team in Italian, I jump in, strap on the headset, and get into a zone.

The sim now has a clean, clear and stylish HTML based GUI, which makes navigation simple and easy.  The basics are there, this sim is about the driving, and so aside from options and configuration, there are sections detailing the driver profile and stats, online, offline, quick race, practice, blah blah.  We all know what a racing sim does by now I hope, and a GUI is just a transport to get there. This one is pretty, and functional – good news. A welcome addition appeared to be an “achievements” section, which is yet to be fleshed out, but should include some basic “gold star” type in-game awards to aid boast value and potentially help with online matchmaking. However, this section of the GUI is “placeholder” for now.

Once you’re set, it’s a simple choice to select a car and a track to find yourself nestled in the pits in some of the most gorgeous cockpits ever seen.  AC is beautiful, the DX11 graphics engine that we’ve all seen at work in the various screenshots posted is just as pretty when on the move.  From the outside of the car the in-car driver animations look so fluid and accurate that it can be hard to tell it apart from reality at times!

My aim for the visit was to really get into depth with the sim, and do some good, hard, laps.  This meant keeping to tracks I know, and working with cars that I am au fait with the basic engineering of.  So, first things first, I took to a Lotus.  I used to run a Mk1 Exige many years back, and have generally been invited to my preferred Lotus dealership to try out new models whenever they are released.  This has allowed me to keep up with new models on the whole, though I have yet to drive the new Exige S, with its Toyota derived V6.  So naturally I took that out first!  The “progress” of Lotus over the last twelve or so years has been to try to compete with the likes of Porsche in the middle market for sports cars.  The net result of this is that successive Lotuses have become a little more user friendly, and usable as road going cars, at the same time this has brought about technology such as ABS (accurately and delightfully modelled in AC) and a slightly more manageable balance on track.

What this means, of course, is more understeer, and thus driving the Exige S quickly can become an exercise in keeping the front wheels in check, getting her slowed in good time, and turning into the corner with minimal scrub.  This exercise is replicated in AC very accurately, and as the laps tick away, you start to appreciate the balance of the vehicle and adjust your style to match.  On road based tyres, the tyre model continues to feel planted and solid.  While road tyres are not as laser sharp as slicks, and a road going car’s steering rarely as precise; this difference feels very nicely implemented in AC.

One thing I have touched upon in previous articles concerning AC, is the overall approach to the sim that the player has to take.  Unlike many other simracing products, the cars in AC feel very much under your control, and this presents a very different approach for the player.  There is rarely any “what the hell happened there” moments of snap oversteer or understeer, the cars behave in a way that (to a driver) feels very much the way you would expect they should.  This means that keeping the thing on the track is never really very tough, provided you know which way the corners go, and you have a basic understanding of the capabilities of the car in your hands.

The net result of this is that cars almost feel rather easy to drive initially, as they arguably should be.  Not many cars are difficult to drive at reasonable speeds, and as I pedalled the Exige S around the Silverstone GP track I found myself getting closer and closer to the limit as I pushed the braking and turn in phases deeper and deeper into the turn, the feedback from the wheel through the front tyres allowing me to understand their tolerance for exactly how much I could blend longitudinal and lateral loads.  Slowly getting quicker and quicker, the confidence I could maintain in the car continued to grow as I was not getting any nasty surprises.  Brake a bit too late, run wide and understeer through the turn; on the throttle a little too early, the back steps out gently and you can modulate your right foot to keep it in check.  The tyre scrub, however it may be induced, causes a reduction in speed, which, provided there is enough room, will bring the car into check as the excess speed wears off.  You know, general car driving stuff.

Then, that confidence got the better of me, as I threw her into Stowe a little too fast, with a bit too much braking causing a forward weight transfer, the rear broke away.  Like it would in real-life, this made me metaphorically “jump” in my heart as I realised I was committed to the turn with too much speed and this could become an accident.  None of it was unexpected really, I had been building my pace more and more, and this was going to happen soon.  The car, broadside well wide of the apex, slid onto the exit kerb and then the lovely flat green-painted concrete, where my corrections straightened her out, and I was on my way.  A minor moment, in some sims, in fact, sometimes the sort of moment you might have every other corner; in AC your control of the car is so solid and understandable that when this happens it makes your heart leap.  When your brain becomes so immersed in the experience, that genuine, heart leaping “Oh no, I’ve stacked it” feeling can grab you.  When crashes are a regular thing in a sim, you become jaded to them, they are normal.  When a crash only happens once in a blue moon, they can cause much more of a shock to the system because you’d spent so long with everything under control.

With this in mind, Aris sat down with me to suggest I take out a car that I am much more likely to crash: The Pagani Zonda R.  With an AMG derived 6.0 litre V12 borrowed from the Mercedes CLK-GTR, putting out 750 brake horsepower and a monstrous 710Nm of torque at 7500rpm with a kerb weight of 1070Kg, this should be a much trickier beast to keep hold of.  “You’ll be amazed” Aris states “What the Pagani engineers have done with the rear suspension geometry to make this thing drivable is amazing.”  Out of a slight fear I took it to the wide open straights of Monza, and sure enough, I was amazed.  The car has a lot of grip, as cars of this level should have.  No car has a rear tyre profile this huge without being fairly grippy.  Whilst it was easy enough to spin the car around on the throttle if you were trying to, provided you were making some effort to feed the power in, the traction from the car was very nicely controllable.  Once the rears gripped up, would launch you out of a corner with the force of an F15 Eagle.

Keeping the Pagani on the track was not difficult, and at no point did I slide off or lose control.  However, as Aris re-assured, this was a car that could bite you.  As you start to push the performance envelope the car’s awkward balance becomes quite apparent, under hard braking the huge anvil of an engine in the rear tries to get to the front of the queue, and so the back starts to squirm around.  Aris jumped in the driving seat for a few laps of hard running to demonstrate, and as the attached video shows, taking your braking a little too deep into Ascari, or the Lesmos can result in a tricky dose of entry oversteer. Though not necessarily in a “terminal” way.

Next we moved back to the Silverstone GP track, and took out the BMW E30 DTM car. Whilst still in early stages of development, still using the road-going E30’s cockpit and bodywork, this car formed the backbone of BMW’s DTM assault in the early 1990’s, and was a homologation special that evolved the basic road car to an extreme level.  With chassis stiffness almost akin to a fast single-seater, the 360hp 2.5 litre 4 cylinder lump can propel this mere 960Kg car to remarkable acceleration.

What was most notable in this car, with such stiffness, was how controllable and usable it was on track.  Positively delightful to drive, pushing the sharp, responsive front-end into a turn would hook the car up into the mid-corner, allowing you to get on the throttle much earlier than you expect, and earlier with every lap.  This car is superbly balanced and capable, its taut chassis allows you to understand what every tyre is doing at each stage, and bouncing the car over the Abbey chicane kerbs felt very much under control, and placing the car where you wanted it became more and more natural with each passing lap.  I mention to Aris that I have to try something else now or else I could drive this car forever!

The next step was the Lotus 49, which I drove on my earlier visit in March.  Much has changed since then, albeit in subtle ways.  On the historic Monza layout the 49 felt so at home but also, in keeping with my experiences so far, very manageable.  No GPL style “deaths” here, I ran several laps, albeit at a track I know well, without incident, and started to really enjoy the gentle powerslides out of the Lesmos, and feeding in power on the exit of Parabolica.  I’ve not driven a real Lotus 49, not many people have, but of the numerous virtual versions I have driven, this is the one that has felt the most like a racing car, like a car designed to win races, to grip, to allow the driver to shine.  It’s another car I feel I could drive forever.

The same can’t really be said of the next on the list, the Lotus 98T.  1985’s Lotus propelled Ayrton Senna to his first win at Estoril in atrocious conditions, and driving this thing makes you wonder about the sheer talent of the man.  The idea of driving it on a wet track sends shivers down the spine; on a dry (modern) Monza the ferocious power delivery, from the 1.5 litre V6, throwing out 1200hp, takes a bit of deft footwork in the first four gears to keeping the back end safe under acceleration!  At only 540Kg, the 98T generates a fairly huge amount of downforce, so corner speeds can be reasonably high, but the turbo lag, and resulting power delivery make for a car that can be very difficult to be confident with when it comes to mid-corner throttle application.  Once again, AC surprises, as the car is never really outside of your control.  But the overall enjoyment of the experience is a little tainted by the reality that this car has just plain has too much power to be usable.  So it’s a case of sitting back and waiting for the car to be safely straight and ready before getting on the throttle and receiving a space shuttle-like punch out of the turn onto the ensuing straight.

It is lunch time, and I still haven’t crashed any of the cars, which is a bonus because it saves me looking like a buffoon.  But that aside, this may be the first sim I have found so easily accessible to drive – Easy to drive, hard to drive fast – pushing the car too far results in time lost, but rarely huge accidents.  The nature of the tracks helps, but at the same time, if you feel things going wrong, the natural response is almost always the right one, and the dynamics of the vehicle respond to inputs exactly as you would expect.  I’d been up since 4am and not eaten a thing, and yet here it was at nearly 2pm and I was asking if I could just stay behind and do more laps. AC had caused me to forget to eat; I doubt it will be the last time.

After a brief fettuccine al pomodoro and amusing chats about the good days of misspent youth thanks to Geoff Crammond, we returned to the offices and I sat down to some nice, long runs.

Experimenting over a series of cars, such as the Lotus T125, P4/5 Competizione and BMW Z4 GT3, I was permitted to enable debug overlays for tyre temperature, slip, camber, caster, toe, and all that exceedingly fun, real-time telemetry action, and analyse how the tyres held up to differing levels of abuse.

The tyre model is so tightly defined across the surface of the tyre, that running over kerbs can cause a “flick-flak” of heat build-up on the parts of the tyre hitting the leading edge of the kerb, and flatspots will come back and haunt you as they always find their way back to the bottom of the wheel to allow themselves to grow.  All very cool stuff, but how do the tyres themselves stand up?

Well, aside from my protestations to Aris that I needed more pressures all round, there was a very pleasing response to input from the tyres under hard running.  At Silverstone, a track that features lots of fast switch backs, it can be very easy for a driver to overwhelm the front tyres, and witnessing this I could feel a general drop off in performance as the fronts began to overheat.  Quite naturally, this does not involve any serious loss of grip, or terminal understeer, but rather gives you a clear feeling that the fronts are becoming more “gloopy” under load, and the resultant loss of grip is very apparent on balance and laptime.  Scaling back the loads, you can see the temperatures come back down again, into the operating window, and find a good level of “attack” to maintain the temperature needed to achieve optimum cornering pace.  This is easier, or harder, in different cars, depending on downforce levels, weight, layout, etc, but tyre management is a clear skill required in AC to consistently get good times. However, I might add, good tyre management is not the difference between good laptimes, and being in the wall.  An overheating tyre is not going to result in wild drop off in grip, just a mild reduction which you notice as you have to wind in more steering lock, or brake a little deeper to scrub off more speed on turn-in.  No sudden switch to “ice.”

One thing remains “off” at present, and that was the feeling of the tyres at cold, and the speed at which they got up to temperature.  Cold tyres felt too grippy on the whole, and within half a lap or so were up to operating temperature.  Aris, when questioned, confided that this was something that had not been fully worked out as yet, as so far the focus on tyre temperatures was on optimising the heat build-up or deprecation under normal high-speed running.  This makes sense, and at this stage I would say the latter is looking very well sorted.  Currently, also, the tracks are quite static, aside from varied grip from differing surface materials. It is expected that by release variable track temperature will be modelled, possibly even down to differing times of day and shadows, and there are plans for a dynamic “rubbering up” of the track to take place, though that is currently a feature somewhat in its infancy.

By this time I had been lapping constantly for nearly ninety minutes, and despite the efforts of Marco with his stethoscope to try to distract me, I wasn’t stopping!  But the darkness beckoned and with it my return flight.  So I finally stepped out of the chair, at which point Aris demonstrated the “drift mode”.  A feature that a “purist” like me finds rather silly, but it does really show off the deftness of the tyre model, that lets a driver literally drive around like a raving maniac and stay alive.  Scoring points for “time spent sideways” is something I’d never thought of for a sim, but it certain raises a smile.

Heading home, via a lengthy plane, train, bus run, I had plenty of time to think about the sim that I had driven, and where AC is really heading to fit into the marketplace.  There’s no huge-scale online matchmaking and race series to compete with iRacing, and I don’t think Kunos expect to do so.  But when it comes to the sheer pleasure of just plain driving, AC scores huge points, and will pull in the discerning simracer with its addictive driving model and varied cars.  My advice: book off the month of March.