Quote from Bodhidharmazen :

Thats kind of my point with the thread. Where does "realism" begins? How can we measure it?

I think that your answer lies with yourself. I could could go on and on about the merits of LFS, but I am not you, and since everyone is different, one simulator may be better suited to that individual person than another simulator. Compare the two, see which game you like and how it feels to you, and you exclusively, and then decide.

I know how my car drives on track and I know it is possible to get quite close similar handling in rFactor too, but that requires making things differently from how ISI has made (mainly tires and suspension parameters in hdv). Default ZR is handling so weird way that it surely is not realistic in my books.

Don't know then if LFS is more realistic or not, more refined it is, but does it really matter which one is better, both are so different, can't really compare them against each other.

Quote from bbman :

I remember Niels saying that his C6 uses a suspension you wouldn't get into the car (something way too long), so I'm not so sure if there isn't a flaw afterall and it's still nothing more than making up things to get a desired effect...

Yes, the carFactory developer (Kangaloosh) has stated that he had to kludge a few parameters to get the desired behaviour in-game - which he checks by comparing Motec telemetry generated by the car in-game against his own calculations as to how the car would behave given a set of inputs. This certainly doesn't speak well for the way that rFactor interprets/handles physical input parameters.

Quote from BuddhaBing :

Yes, the carFactory developer (Kangaloosh) has stated that he had to kludge a few parameters to get the desired behaviour in-game - which he checks by comparing Motec telemetry generated by the car in-game against his own calculations as to how the car would behave given a set of inputs. This certainly doesn't speak well for the way that rFactor interprets/handles physical input parameters.

Has anyone done a similar thing with LFS?

Kind of, my WIP setup analyser uses real physics equations (where possible) to model a vehicle and seems to match up with both the real world and LFS pretty well. It's certainly not as detailed as a the comparison mentioned above though.

Most of any physics engine is really not that complicated - inertia, weight transfer, force, mass blah blah blah. Stuff that if you get wrong, you shouldn't be designing a sim to begin with. The acceleration gravity imposes is 9.81m/s/s - that sort of thing. Note I'm not saying dreadfully simple, but rather information that is easy to understand and implement if you have the background.

The problem comes with the physics of tire modelling - how tires interact with the road, how they respond under different loads, and how they behave in a variety of different situations. Of course, that is an extremely dynamic problem, and data is not widely available or easy to obtain regarding the more intricate secrets of the subject. Tire modelling is the crux of any physics engine (well, for driving sims :razz

There are a few things that make the LFS tire modelling stand out:
1) Tire flex is modelled. Not just mathematically, but even graphically. This allows for the deformation of the tires in real time. Try experimenting with different tire pressures and note how it affects handling, and how the tires respond to different pressures.

2) The lateral slip behaviour of the tires is much more accurate. Exceeding the lateral limit of grip generally imposes an unwelcome and physically inaccurate unrecoverable slide in ISI sims. This has been discussed at length here on the forum, and generally speaking a dropoff in lateral force does not occur when moving past the peak slip angle for a given road car tire. No publically (and arguably any proprietary) available data shows as drastic of a dropoff as is present. Some data that a member dug up showed a comparably mild drop off with very high camber (-9 degrees) but this is very unusual. This is IMO the largest problem you'll encounter in those sims. To counter, LFS currently has some issues with longitudinal grip at very (very) high slip ratios. It's likely based on developer comments that this is being rectified. Many other sims behave that way though, as the myth of drop-off on lateral grip curves has been around for decades - and is only now being discovered to be false.

3) LFS has a universal physical model which means that the tire calcs are done through a set of proprietary formulae, and are the same for each vehicle. The physics engine handles the properties of each car in the game in the same way. ISI sims have separate physics "files" for vehicles which in my opinion shows that the nature of the physics engine is subpar, since numbers must be "fudged" in order to get the desired response. This was also discussed at length on the RSC forums, and here.

4) The heat modelling on the tires in LFS is also very interesting in that it allows for flatspots. Wear and temperature and done very nicely in LFS, where there tire is divided up into 48 sampling areas per tire (1 around and 3 across) - plus sidewalls and internal air temp.

All of these things allow for a much more dyanmic tire modelling system. I'm not saying it's perfect, but the local expert (who happens to be writing his own sim, and has writen others in the past) who plays all sims also agrees that the end result of the LFS tire model is the best out there at the moment, save for possibly his own and another unreleased pseudo-secret project (perhaps you've heard of Racing Legends).

There's a plethora of other reasons why LFS is my sim of choice, but I think tire modelling is the most important reason, and most related to your original question.

Quote from Ball Bearing Turbo :

Most of any physics engine is really not that complicated - inertia, weight transfer, force, mass blah blah blah. Stuff that if you get wrong, you shouldn't be designing a sim to begin with. The acceleration gravity imposes is 9.81m/s/s - that sort of thing. Note I'm not saying dreadfully simple, but rather information that is easy to understand and implement if you have the background.

The problem comes with the physics of tire modelling - how tires interact with the road, how they respond under different loads, and how they behave in a variety of different situations. Of course, that is an extremely dynamic problem, and data is not widely available or easy to obtain regarding the more intricate secrets of the subject. Tire modelling is the crux of any physics engine (well, for driving sims :razz

There are a few things that make the LFS tire modelling stand out:
1) Tire flex is modelled. Not just mathematically, but even graphically. This allows for the deformation of the tires in real time. Try experimenting with different tire pressures and note how it affects handling, and how the tires respond to different pressures.

2) The lateral slip behaviour of the tires is much more accurate. Exceeding the lateral limit of grip generally imposes an unwelcome and physically inaccurate unrecoverable slide in ISI sims. This has been discussed at length here on the forum, and generally speaking a dropoff in lateral force does not occur when moving past the peak slip angle for a given road car tire. No publically (and arguably any proprietary) available data shows as drastic of a dropoff as is present. Some data that a member dug up showed a comparably mild drop off with very high camber (-9 degrees) but this is very unusual. This is IMO the largest problem you'll encounter in those sims. To counter, LFS currently has some issues with longitudinal grip at very (very) high slip ratios. It's likely based on developer comments that this is being rectified. Many other sims behave that way though, as the myth of drop-off on lateral grip curves has been around for decades - and is only now being discovered to be false.

3) LFS has a universal physical model which means that the tire calcs are done through a set of proprietary formulae, and are the same for each vehicle. The physics engine handles the properties of each car in the game in the same way. ISI sims have separate physics "files" for vehicles which in my opinion shows that the nature of the physics engine is subpar, since numbers must be "fudged" in order to get the desired response. This was also discussed at length on the RSC forums, and here.

4) The heat modelling on the tires in LFS is also very interesting in that it allows for flatspots. Wear and temperature and done very nicely in LFS, where there tire is divided up into 48 sampling areas per tire (1 around and 3 across) - plus sidewalls and internal air temp.

All of these things allow for a much more dyanamic tyre modelling system. I'm not saying it's perfect, but the local expert (who happens to be writing his own sim, and has writen others in the past) who plays all sims also agrees that the end result of the LFS tire model is the best out there at the moment, save for possibly his own and another unreleased pseudo-secret project (perhaps you've heard of Racing Legends).

There's a plethora of other reasons why LFS is my sim of choice, but I think tire modelling is the most important reason, and most related to your original question.

I would say. Center of gravity is not moving, therefore it`s a question about momentum, when you calculate a car, moving, braking or whatever it does

Offcourse tyres and springs, are variables, but the car is a simple box with fixed center of gravity.

Quote from Bodhidharmazen :

Has anyone done a similar thing with LFS?

not in that detail but then again lfs lets you view the phyiscs working in real time via f9 shift-l and f and it at the very least looks reasonable
and if you care to look deeper you can always output the raf data and analyze it to death

btw one of the often overlooked or not quite appreciated things in lfses physics is real time suspension link deformation which is not available in any other sim on the market today

Quote from Ball Bearing Turbo :

but the local expert (who happens to be writing his own sim, and has writen others in the past) who plays all sims also agrees that the end result of the LFS tire model is the best out there at the moment, save for possibly his own and another unreleased pseudo-secret project (perhaps you've heard of Racing Legends).

i think hes rather fond of netkar as well
all annoying virtual cockpit clicks and useless netcode and menus aside the underlying physics are rather good and much less fudged from what i can tell (remember the car sliding down hills while standing still ? classic divide by near 0 behaviour as far as i can tell from the real time slip angle and ratio output it had)

Quote from alland44 :

Offcourse tyres and springs, are variables, but the car is a simple box with fixed center of gravity.

sadly it isnt quite that simple
you see normally a rigid body will spin about its cog a car on a suspension however has a rotational centre thats not the cog so youre forced to transform the simplest things like moments of inertia
so far that sounds easy enough but things get messy when the suspension moves and along with it the rotational centres (not sure if youd ever notice a engine taking that into account)

Quote from BuddhaBing :

Yes, the carFactory developer (Kangaloosh) has stated that he had to kludge a few parameters to get the desired behaviour in-game - which he checks by comparing Motec telemetry generated by the car in-game against his own calculations as to how the car would behave given a set of inputs. This certainly doesn't speak well for the way that rFactor interprets/handles physical input parameters.

To me, this is a KEY point for sims and their physic's, and to somewhat a lesser extent, those that "try" to simulate real cars.

Alot of sims that try to simluate real cars have to have fudged physics to achieve realistic results, to me this says that those engines are wrong, and "trying" to simulate real cars isn't a very good idea.

I theory in any sim, you should just plug the figures in, and it works (pretty much like LFS, using LFStweak).

From Gunn:

Quote :

Originally Posted by Indiana Jim
Realistic and accurate settings should always be the same regardless of what controller you use.

Quote from Gunn :

How can you justify that statement? How can a 240 degree rotation controller have the same input effect as a 900 degree controller? How can a controller with strong FFB ever feel the same as one with weak FFB or no FFB? How can a gamepad control the steering as smoothly and accurately as a wheel?

Please don't misquote You left half of my statement out to state a point. This is what I said:

Quote :

Realistic and accurate settings should always be the same regardless of what controller you use. But I think that can't be achieved given the variety of controllers in the market.

You see, when I drive my real car which has power steering, it needs 7 ounces of force to turn the steering wheel below 40 mph. If you drove it, it would still take the same 7 ounces to turn. The steering wheel force remains the same regardless who drives it. That is reality.

Hehehe.... why should simple statements cause such havoc? It looks like someone could lose his daily bread on account of a word. Okay, I'll troll, you folks argue. LOL

Bye

But all you are changing there is the torque required on the wheel. Same wheel rotation, same sensitivity etc.

Now, replace your wheel with a keyboard (digital inputs). Will your car feel as good? No. So you need different settings and setups to cope.

Now plug in a joypad, with a stubby with stick. Analogue, yes. But hugely sensitive over a short range, and not a great deal of total travel (so accuracy and repeatability become an issue). Again, you'll want different settings to make the car go as fast.

Now plug in a proper joystick - enhanced accuracy over the joypad, but still lacking over a wheel really, so you'll want different settings again.

Now go back to your wheel, but replace the rack with one that gives you 180 of rotation - you'll probably need to change a few things. Less than the others, as you've still got a lot of range for accuracy and repeatability, but it's going to be quite sensitive.

Now replace your rack for one that gives you 100 turns lock to lock. Loads of accuracy (huge movements of the wheel result in tiny steering movements), but terrible sensitivity. So you'd probably change some things there to enhance the car. In this case you could have loads and loads of contact patch offset to enhance the limited feel, knowing that wheel effort won't become an issue.


So, you see, different controllers DO require different settings and car setups, in both reality and simulator-land. You're power steering argument is one of the worst arguments I've ever heard.

rFactor is better.


damn..

I'm serious too.. However, thats only with good numbers entered, who knows how LFS would feel if some numbers improved..

Hard to know if you're judging the physics engine or the numbers entered

Quote from Niels Heusinkveld :

rFactor is better.

:bananadea

Burn baby, burn.

Quote from Niels Heusinkveld :

I'm serious too.. However, thats only with good numbers entered.

And don't forget botched suspension arms!

... you can't seriously be serious about being serious.

If you're serious, you may want to provide some insight as to why before I get the gas and the matches, and the chocolate sauce...

Quote from Ball Bearing Turbo :

No publically (and arguably any proprietary) available data shows as drastic of a dropoff as is present. Some data that a member dug up showed a comparably mild drop off with very high camber (-9 degrees) but this is very unusual.

I'd like to clarify that point somewhat.

While there is data that shows little if any post-peak drop off (e.g. data obtained by engineers at the Yokohama R&D department in this paper: http://scitation.aip.org/journ ... t/vol_34/iss_2/100_1.html), it's not strictly true that significant drop off is very unusual nor that it occurs only at relatively high inclinations. For example, here are some graphs that show substantial drop off even at low inclination angles:

http://i14.tinypic.com/4mmzceh.jpg

http://i14.tinypic.com/6b00wvn.jpg

And here are some graphs showing similar drop off across a range of load and inclination angles for another type of tyre (Formula SAE tyre):

http://i9.tinypic.com/4m94e1c.jpg

http://i11.tinypic.com/668z7g5.jpg

These graphs were taken from Edward Kasprzak's Ph.D. thesis entitled 'Extension of the Nondimensional Tire Theory to General Operating Conditions'. Dr Kasprzak now works for Milliken Research Associates.

I contacted Dr Kasprzak a couple of weeks ago to ask some questions about the data presented in these graphs as well as some general questions about post-peak drop offs. He responded, in part, that "[a]ll tires exhibit falloff after the peak. Depending on the construction and compound it is more or less severe." and "[t]here's always a falloff, but the amount depends on the specific tire. Even things like inflation pressure and inclination angle affect how much falloff there is."

While many of the ISI tyre curves show eventual drop offs down to as low as 60-70% of peak, bear in mind that these curves go all the way out to extremely high slip angles i.e. 120°. In the range of slip angles likely to be encountered in-game, the drop off isn't as severe. Also worth bearing in mind is that the ISI tyre curves - including the location of the peak and the rate and extent of post peak drop off - are modified by load, camber and other factors which means that the raw curve data in the files isn't necessarily indicative of how the tyres will behave in-game after all the modifiers are applied.

That said, I do agree that the way the tyres behave in most of the cars in rFactor just doesn't feel right.

Wow I have learned a great deal with this thread. Thanks to all the posters.

Excuse my ignorance but what is a "falloff"? its when the tyre totally losses its grip?

Also, I do understand that representing the complex physics involved in the relation of the tyres and the road are important to talk about a more "realistic" simulation.

But still, I can think that "how does it feel" to drive a car in a simulation can be accomplished by other means. And I say this because, no matter how awful or limited is the physics simulation in rFactor, I can easily "feel" how the weight transfers with the inertia created by certain movements in certain directions. Its difficult to explain, but it "feels" right.

So, is it possible that even with a lousy simulation one can get fairly good results? (even if those results are just for the modeled car, as explained by someone).

To my hands, cars like the GTI in LFS are indeed modeled to give a realistic feeling of driving a car with such characteristics. But faster cars simply doesnt feel "right". In rFactor I have the sensation that, driving for example the F1, the simulation its "better" than the F1 in LFS. What do you all think? have you driven both?

Quote from BuddhaBing :

curves go all the way out to extremely high slip angles i.e. 120°.

How can it be greater than 90, unless they're pulling some more magic to deal with scenarios of longitudinal force in the direction opposite the vehicles direction of travel - i.e., "pre-dealing" with a rapidly spinning tire while a car is rotating around it's Z axis...

@Bodhidharmazen - All tires require some amount slip to produce their maximum "grip", both in lateral and longitudinal directions. The controversy is over just how much force is lost when the optimum slip angle (lateral) and / or slip ratio (longitudinal) is exceeded. There a number of threads dealing with that topic around here.

I'm also of the opinion that a sim should be as close to empiracally correct as possible, not necessarily to aim for a subjective "feeling" of an experience, since that will vary from person to person. Much better to aim for an objective behaviour and let your brain do the adjusting IMO. RL experience can be helpful, or it can be detrimental depending on the individual. Provided the person has the knowledge about what's happening and can correlate it with what's represented in a sim, it could be useful. But the average driver without some understanding of the physics of driving, tires, and so forth can't usually provide the best insight.

Quote from Ball Bearing Turbo :

I'm also of the opinion that a sim should be as close to empiracally correct as possible, not necessarily to aim for a subjective "feeling" of an experience, since that will vary from person to person. Much better to aim for an objective behaviour and let your brain do the adjusting IMO. RL experience can be helpful, or it can be detrimental depending on the individual. Provided the person has the knowledge about what's happening and can correlate it with what's represented in a sim, it could be useful. But the average driver without some understanding of the physics of driving, tires, and so forth can't usually provide the best insight.

I agree with you, for a simulator "reality" is the ultimate goal. Still, I'm not sure about what you say regarding drivers and subjective sensations. Are you saying that, in a way, simulation software is like "high end audio"?

You know, there are some kind of people who like to call them selfs audiophiles who swear that they can say which equipment sound closer to real instruments. Funny thing is that every audiophile have their favorite brands, and very very often they trash every other brand around. Yes, even those who are regarded as "highest fidelity available" by other respected (self respected) audiophiles.

Quote from Ball Bearing Turbo :

How can it be greater than 90...

That's the point really. The curves go out that far - for whatever reason - but that doesn't mean that such extremely high slip angles are ever going to be encountered in-game. Given that, characterizing the curves by their shape/behaviour at such extremes isn't very useful.

Expanding on that point, let's compare an rFactor slip angle v lateral force curve against the real-world data shown in the following figure taken from Dr Kasprzak's paper:

http://i9.tinypic.com/4m94e1c.jpg

Note that the data has been non-dimensionalized and that the black plot represents a characteristic curve that has been derived from the measured data. Eyeballing the curve, we see that the peak occurs at a (non-dimensional) slip angle of around 1.8 and that it falls to around 90% of the peak value at a slip angle of about 6. In other words, at a slip angle roughly 3-4 times higher than the slip angle at which the peak occurs, the lateral force falls to around 90% of peak.

Now, let's compare that to a slip angle v lateral force curve from rFactor. In this case, I'm using the 1997_GT1_Goodyear_Tires.tbc file from ISI's Panoz car set. Here's that curve:

http://i11.tinypic.com/6azk36t.jpg

The actual data is shown in columns on the left side of the image while the right side shows the curve plot.

At first blush, the curve looks quite a bit different. In particular, it falls off all the way down to about 62% of peak at the far right. 62%? That's a huge drop off, right? The curve can't be right!

Well, this initial impression is misleading, since the curve extends way out to a slip angle of around 120°. Let's instead look at the behaviour of the curve in the same range of slip angles as the real-world data we just examined. Looking at the data table, we see that the peak occurs at step 11. At step 33 (3 times the slip angle at which the peak occurs), the lateral force is still 98% of peak and at step 44 (4 times the slip angle at which the peak occurs), the lateral force is still 95% of peak.

In other words, the rFactor curve actually shows a smaller drop off than the real-world tyre curve within the same range of slip angles.

Note that I'm not making any value judgements about the curves nor arguing that the rFactor curves are correct/accurate - for example, real-world data often tends to flatten off more quickly than the rFactor curves, which generally continue to drop off. I'm only trying to show that dismissing curves out of hand based on their behaviour at extremely high slip angles might be a bit hasty.

Hmm, very interesting.

Any thoughts on the seemingly inverted countersteering behaviour in rF/GTR2?

Perhaps as Todd alluded to it could be due to lat/long combination calcs...

Shotglass - say something quick, before I contemplate changing my opinion...

Quote from Bodhidharmazen :

I agree with you, for a simulator "reality" is the ultimate goal. Still, I'm not sure about what you say regarding drivers and subjective sensations. Are you saying that, in a way, simulation software is like "high end audio"?

You know, there are some kind of people who like to call them selfs audiophiles who swear that they can say which equipment sound closer to real instruments. Funny thing is that every audiophile have their favorite brands, and very very often they trash every other brand around. Yes, even those who are regarded as "highest fidelity available" by other respected (self respected) audiophiles.

Well what I am really saying is that you'll find anecdotal "data" in the mouths of everyone with respect to vehicle dynamics whether they've driven any level of vehicle on the street or track or not. In my experience humans tend to process the same sensory input in a multitude of fashions, just like your audiophile analogy. As an audiophile one could start comparing waveforms of live performances versus a recording and so forth, which would be much more objective (although impractical obviously for lots of reasons, but this is all for the take of illustration) than audiophile Bob arguing with audiophile Tristan over which one sounds better "to them".

I beleive that a sim should not aim to recreate the feeling of driving / racing, but rather aim for the most accurate possible objective representation regardless of the feeling. Theoretically they should meet somewhere, but that's not necessarily the case for each individual right off the bat. LFS has tons of doodads present to aid one in the "feeling" department - adjustment of head movement on every axis based on G forces, FOV adjustment, controller adjustment and whatnot.... With an accurate representation, OR an inaccurate one, eventually your brain will start to "calibrate" itself to the subjective feeling your discern from a said sim. Of course, certain things just don't make physical sense in some sims (different things from sim to sim it seems) and that's a different topic I suppose.

Quote from Ball Bearing Turbo :

Any thoughts on the seemingly inverted countersteering behaviour in rF/GTR2?

Without knowing how the various curve modifiers, grip multipliers and all the rest are applied in real-time, no, I've no idea. It could be anything.

ISI added a pneumatic trail parameter to the tyre files in the most recent rFactor patch so clearly they were still working on tyre modeling until as recently as a few months ago. Pneumatic trail is a pretty fundamental characteristic and its late inclusion - in explicit form, at least, it may have been a derived value before - does make me scratch my chin a bit.

Add to that the fact that several rFactor tyre files use longitudinal traction and braking slip curves that look suspiciously like lateral force curves also makes me wonder how well tyres are actually modeled in-game.

Quote from Ball Bearing Turbo :

Well what I am really saying is that you'll find anecdotal "data" in the mouths of everyone with respect to vehicle dynamics whether they've driven any level of vehicle on the street or track or not. In my experience humans tend to process the same sensory input in a multitude of fashions, just like your audiophile analogy. As an audiophile one could start comparing waveforms of live performances versus a recording and so forth, which would be much more objective (although impractical obviously for lots of reasons, but this is all for the take of illustration) than audiophile Bob arguing with audiophile Tristan over which one sounds better "to them".

I beleive that a sim should not aim to recreate the feeling of driving / racing, but rather aim for the most accurate possible objective representation regardless of the feeling. Theoretically they should meet somewhere, but that's not necessarily the case for each individual right off the bat. LFS has tons of doodads present to aid one in the "feeling" department - adjustment of head movement on every axis based on G forces, FOV adjustment, controller adjustment and whatnot.... With an accurate representation, OR an inaccurate one, eventually your brain will start to "calibrate" itself to the subjective feeling your discern from a said sim. Of course, certain things just don't make physical sense in some sims (different things from sim to sim it seems) and that's a different topic I suppose.

You are using false terms, my friend
Audiophiles don`t live a subjective life. HiFi is very objective, because it`s trying to recreate the IRL experience, at home

You can`t argue about the sound of a violin or cello ! Either its the real sound, or it`s not

Audiophiles uses a lot of money, to get the "real deal" and your argument is the thinnest I`ve ever seen.

If you leave out the term "Audiophile" and put in young people - Then I can accept your reasoning Young ppl give a shit about the quality of sound, as long as it`s high, and there iss a hell lot of base

That`s the same with Lfs and Rfactor. Lfs is classical music and Rfactor is poprock, with noise guitars

How is listening to audio objective when your outer ear isn't even shaped precisely the same as mine? Not to mention THD even on high end equipment is still ridiculous and we'll hear some harmonics differently from person to person etc, but I digress.

I understand what you're saying, but you're missing the premise for my point.

I agree on your LFS rF analogy though.

Quote :

Audiophiles don`t live a subjective life. HiFi is very objective, because it`s trying to recreate the IRL experience, at home

You can`t argue about the sound of a violin or cello ! Either its the real sound, or it`s not

Audiophiles uses a lot of money, to get the "real deal" and your argument is the thinnest I`ve ever seen.

If you leave out the term "Audiophile" and put in young people - Then I can accept your reasoning Young ppl give a shit about the quality of sound, as long as it`s high, and there iss a hell lot of base

Audiophiles DO live a subjective life (at least the headphone ones) because each brand has its own distinct sound- neutral/emphasising certain frequencies and advantages/disadvantages. It's all down to which sound they prefer.