Sounds like someone's been into the sauce
Here's a really interesting video about the scanning process iRacing uses:
http://www.facebook.com/video/video.php?v=403084340826
Anything to say about this Eric?
http://www.facebook.com/video/video.php?v=403084340826
Anything to say about this Eric?
How do you guys like the Jetta? I've lapped in it somewhat but never an official race. I like the idea of fixed setup races for one, and the car feels pretty decent for a FWD. It actually feels more lively than the Solstice and being FWD the feedback is more obvious.
EDIT 2:
The answer is: yes it does, never mind the other BS I posted.
Last edited by Ball Bearing Turbo, .
Yes I agree with you 100%. There's some really good close racing to be had in it but it probably is tainted by some of the rookie happenings.
Though I wish it was the GXP/Turbocharged version. I'm wondering if iRacing is nervous about modelling forced induction; that's one thing I'd really like to see them tackle. Really hoping for a GT glass Porche twin turbo to mess with the Corvette one day.
That's interesting, I didn't know about those requirements. Although I definitely do not get 60 days notice from Blizzard Entertainment, nor would trying to cancel it after it's just renewed do any good. I'm pretty sure that that company has their bases covered however, so there must be more (or less) to it than you've stated.
Are you talking about sub renewal? 
With any service you enter into full well knowing it's sub based, you'd have to be quite a few kernels short of a full cob to get caught out when you didn't want to be... Every single MMORPG operates that way... iRacing is kind of an MMO really you're building an online identity with it, progressing through ranks, earning points etc.
I understood your point about your schedule now, thanks for clarifying.
With any service you enter into full well knowing it's sub based, you'd have to be quite a few kernels short of a full cob to get caught out when you didn't want to be... Every single MMORPG operates that way... iRacing is kind of an MMO really you're building an online identity with it, progressing through ranks, earning points etc.
I understood your point about your schedule now, thanks for clarifying.
I don't understand... racing twice as often in NR2003 was too "time consuming", but racing half as often, which would consume far less time, is unappealing.
If you only want to compete in one series, then you just plan to race at a certain time and away you go. If you want more you can run another series or tweak your setup or run some laps with traffic in practice to be quicker. Not being able to just hit SHIFT R or just wait 5 minutes when it all goes south is what gives iRacing an atmosphere of competition.
Those are very nice cars indeed - amateur racing cars
Yes, that's fine I'm sure they make good training tires because they're forgiving and probably help you get used to that feeling of living on the limit. I still have no idea what your point is or was in bringing it up though?
Indeed that was the first thing I thought of, good call
I agree. I know there's lots of folks who would've appreciated more detail though, yet the general masses of morons probably got sweaty reading it. I guess it was a good compromise. Very good read and good information in the post. Should've been supplemented with videos of Dave wrecking tires though!
I'm really looking foward to the physical model now. I had the impression it was going to be some sort of hybrid, but from what he said that doesn't appear to be the case. Should be an interesting year in sim racing if Scawen releases his as well.
Sure, if you want to be slow go a head and use them and enjoy the sublime scary handling. They have different properties like you stated; those said properties end up making them undesirable for modern motorsport since they've found something better.
I'm sure there's cool things about muskets too.
Way more variables that vary more often than probably many physical systems out there. IF you read what he said, you'd probably see the allusion to the fact that impractical to get enough useful data consistently. Thankfully what he did get was very useful to him.
Dave Kaemmer's Blog on Tires.
Tires are perhaps the least well understood parts of road-going vehicles, despite the fact that they are one of the most studied. Obviously, since they are typically the only part of a car in contact with the ground (if everything is working right), their behavior is critical in determining how a car handles, how well it grips the road, and so ultimately, how fast it can go. It has been said that if horses complained, the pneumatic tire would have been invented in ancient times. But it took until the 1800’s and the invention of the human-powered bicycle before it was discovered that an inflated tube of air (thank you, John Dunlop) covered by vulcanized rubber (thank you, Charles Goodyear) was a darn sight better at rolling across the ground than a wooden hoop covered with a strip of iron. Maybe if the ancients had invented them, rubber tires would be better understood by now. I like to joke that I’ve spent my entire adult professional life studying tires, with a few other odd assignments thrown in. That’s what it feels like, anyway, since everything else seems pretty straightforward by comparison. Needless to say, most people, when they hear that my specialty is tire physics, tend to turn and walk (or run) away. So I couldn’t believe my good fortune when Steve asked if I would write a blog post about the tire model I’ve been working on. This might take a while, so grab a sandwich, or better yet, a strong cup of coffee, and read on:
What is a tire model and why do we need one? A tire model is a collection of mathematical formulas, along with a bunch of numbers to plug into those formulas, that when given some basic information about how fast and in which direction a tire is going, what it’s contacting and at what angle, can spit out the forces that the tire exerts on the car. That’s pretty much it. There are a bunch of other force models needed for a racing simulation as well: the aero model—the forces that air is exerting on the car; spring and damper models—the forces that are exerted by the suspension elements; engine and drivetrain model—the forces that spin the drive wheels; brake model—the forces that stop the wheels from spinning; gravity—a gloriously simple force (from a racing sim’s point of view) that makes things fall and hit the ground. When we know all these forces, we can plug them into a complicated version of Newton’s F=ma (force = mass times acceleration) equation, and voila, we get the car’s and all of its component parts’ accelerations.
It’s important to be able to figure out how moving things accelerate, since what we really want to know at the end of all the math is where all those moving things are at a particular instant (like the instant we draw a pretty picture from the cockpit of an iRacing car). To know where things are at any instant, we need to know where they were a short time ago (their positions), and how fast they were moving between then and now (their velocities). If we know how fast they were moving a short time ago, and we can figure out their accelerations between then and now, then we can do a pretty good job of figuring out their velocities between then and now, and so we can figure out where they are now (at least we can make a pretty informed guess). If this all sounds kind of circular, like we need to know where we are in order to know where we are, then you are understanding it perfectly. Two things save us: one, the fact that in our universe stuff doesn’t teleport around like in Star Trek (in other words, positions don’t suddenly change in unpredictable ways, at least for stuff bigger than elementary particles), and two, the velocity of stuff doesn’t change unless a force is acting on it. The ancients didn’t have that second one quite right. It took thousands of years to figure that out, so don’t feel bad if this is making your head spin.
So this is why we need the force models for sim racing. They give us the accelerations we need (how much the velocities change). We take those accelerations, add them to the car’s and components’ velocities, take those velocities, add them to the car’s and components’ positions, and repeat, a zillion times a second. Every once in a while we draw a picture on screen with the car and all its parts in the correct positions (and with all the other cars and their components in the correct positions). That’s basically it, anyway. We need to do these calculations many times per second because, while the positions and velocities don’t change very fast (not in a thousandth of a second, anyway), the forces can change very rapidly. To get an accurate simulation, we need to compute those forces really, really frequently. We also need to have good models for the forces—that is, the models need to produce the correct forces in any given situation. Most of the forces are surprisingly simple, or at least they can be modeled fairly simply, and any additional complexities (for example, due to temperature) can be handled fairly easily. The two main exceptions to this are aerodynamics and tires, and of the two, tires are more difficult to model.
It turns out that almost all the forces depend primarily on the positions and velocities of the car and its parts. For example, the force exerted by a spring is a fairly constant multiple of how far it is compressed (or stretched). The force exerted by a damper (shock absorber) is a fairly simple function of how fast the damper is being compressed (bump) or expanded (rebound). Aerodynamic forces, while being fairly complex in origin, can be neatly computed from the air speed, air density and a small number of coefficients (fancy term for numbers) that depend only on the orientation of the car relative to the moving air. Gravity is ridiculously simple, always exerting a fixed force in a fixed direction (downward).
The forces exerted by a tire are not so simple, unfortunately. They depend on the position and velocity of the wheel on which the tire is mounted, as well as its angle relative to the ground (its camber). They also depend on the type of surface it’s touching (grass, concrete, asphalt, etc.), the shape of the tire carcass, the tread rubber compound properties, the inflation pressure, the tire temperature (many temperatures, really, around and throughout the tire), the amount of tread rubber wear, the temperature of the road surface, how heavily the tire is compressed into the surface (the load), how fast the wheel is spinning, even the small amount that the tread belt is deflected away from its usual position by these very tire forces! Let’s not even start on surfaces covered with various lubricants like water, coolant, oil, sand, etc.
Gathering real-world data for the iRacing tire model – Dave Kaemmer checks a tire on Calspan’s Tire Industry Research Facility test rig.
Any attempt to measure tire forces inevitably runs into the problem that all these variables are changing all the time. It becomes very difficult to determine just which property of a tire is having which effect on the overall force generated. As you take a tire and steer it on a tire tester, the surface temperature climbs rapidly and heat begins conducting into the tread, changing its characteristics, plus the carcass deflects, which changes the effective steering angle and camber angle. If you try to see what happens at large sliding angles, the tire wears away rapidly, and the temperature skyrockets (producing a lot of noise and smoke, which is pretty cool, by the way). This is not helpful when trying to come up with a good tire model.
There are a couple different ways to attack this problem. One is to measure the forces generated by a tire in as many different configurations as you have the time and money to do (different speeds, loads, pressures, etc.), and come up with “mathematical curve fits” that pass through the measured data as best they can. This is called an “empirical” model, empirical meaning based on observation or experiment. The other way is to try and come up with a theory that predicts what the tire forces would be in all these different configurations. Ideally, such a theory would only need a few basic measurements, and would produce accurate forces in many different situations. This is called a “theoretical” or “physically-based” model.
There are examples of both that have been used in automotive tire simulation for decades. The most well-known empirical model is Pacejka’s “Magic Formula” (that really is what it’s called by PhD’s in the field!), which can give very good results, especially when combined with “Tire Data Nondimensionalization”, which is a method for reducing the many possible tire force curves at different loads into a couple of curves, which can then be modeled with the Magic Formula. There have been many refinements and improvements over the years to this model, and now tire companies will often identify a tire with its “Pacejka coefficients”, the numbers to plug into the Magic Formula to obtain the tire force curves. The refinements have led to models that account for pressure, load and temperature changes, in addition to other improvements. Pure theoretical tire models such as “The Brush Model”, and the “Stretched String Model” have tended to be a bit simpler, and are used more to explain why the empirical models’ curves look the way they do than to predict what those curves will be exactly.
I’ve been talking a lot about “tire force curves” without much explanation. Let’s introduce a picture:
There are several different force curves that we’re interested in with a tire, but this is the important one, and it serves to illustrate a number of things. Plus you probably only have one cup of coffee, and time is running out on me. What you see here is a graph of a tire’s force parallel to the road surface versus a quantity called “slip”. This parallel force could be forward or backward (acceleration or braking), which is called “longitudinal”; it could be sideways (cornering), called “lateral”; or it could be a combination of both together. This curve has roughly the same shape no matter which direction we’re talking about, basically. Slip is a measure of the difference in speed between the tire carcass and the road surface. In the longitudinal direction, the slip is usually referred to as “percent slip”, or % slip. If a rear wheel is spinning at a speed where the tire carcass is travelling at 110 mph, but the car’s speed over the road is just 100 mph, then the tire is operating at 10% slip. In the lateral case, if the car is travelling 100 mph, but it is cornering hard and facing left at a 5 degree angle to its direction of travel, the tire is operating at a “5 degree slip angle”. In both cases, the tire appears to be “slipping” across the road, but in fact the tread rubber is just being stretched when it is in contact with the ground, and then it snaps back into place when it leaves the ground at the back of the “contact patch”. When the slip exceeds a certain amount (as you move to the right on the graph), the contact patch does start sliding (usually near the back of the contact area where the rubber is stretched the most), soon afterwards the force reaches a peak, and then starts falling as the tire’s slip increases still further.
This is just one representative curve which might be the correct curve for a given tire in one particular situation. The difficulty is that as conditions change (and they change very rapidly, all the time) the correct curve changes size and shape. As you drive through a corner, you might travel up one curve, and come back on a different one, because the temperature of the tire has changed, for example. So we need to figure out how and why these curves change. The force versus slip curve has certain characteristics that do stay mostly the same, so let’s look at it more carefully.
Note that there are three main zones in this force curve: 1) the linear zone in green, when turning the steering wheel more makes the car turn more (i.e. more slip = more force)—where we should always be when driving on public roads, 2) the limit zone in yellow, where the steering wheel becomes just a braking device, the tire starts to squeal happily, and racers make their living (more slip = no real change in force), and 3) the scary zone to the right in red, which is exciting, but not fast, and much rubber is disappearing from the tire surface (more slip = less force). We have discovered over the years from a lot of driver feedback in the simulation that the width of the limit zone and the steepness of the scary zone as you fall into it have a dramatic effect on the “drivability” of a car, and whether or not the tire model feels like a real tire. In order for a racing simulation to properly reproduce the handling characteristics of race cars, you need a tire model that reproduces all three zones well.
Right away, this becomes a problem. The reason is that pretty much nobody is all that interested in the scary zone; they mostly want to avoid it (except for the alternate universe of drifting). Even when testing tires, the scary zone just does too much damage to the tires and so it’s very expensive to test there. Hence there’s very little scary data. If you look at enough measured tire force curves, you’ll see that most of them don’t even extend into the scary zone. When they do, you’ll notice that while empirical curve fits can be really good in the linear and even the limit zones, they don’t really fit the data well in the scary zone. But they don’t need to, for most purposes. No tire company can sell their tires using the pitch, “Our tires have really good scary handling.” They can sell them based on how good the wet skid resistance is, since that is a number required to be tested for all passenger tires that are sold. So unlike most of the scary zone, there is a lot of data for the far right, lowest part of the scary zone, which is where wet skid resistance is measured (tire locked up, sliding on wet pavement). But even that is of little help for tire modeling, since the force at that point is as much a function of the pavement surface as of the tire itself. Also, water dramatically changes what that zone looks like, so all that data doesn’t help on a nice, dry, sunny day.
It gets even worse when we consider that the limit zone (the racer’s office) depends on what is happening in the scary zone. This is because what’s really going on in the limit zone is that the tire is doing both some of its linear thing (stretching the tread rubber), and some of its scary thing (whatever that is) at the same time. The limit zone is just a result of the mixing of the linear and scary zones as we increase the slip. So if we don’t really understand the scary zone, we don’t really understand the limit zone either. Up until not too long ago, the scary zone was keeping me up at night. However, when we did tire measurements last year at a tire test facility, we went ahead and destroyed quite a few tires with different constructions and tread compounds in order to see what they did at very large slip angles and at a bunch of different speeds, loads, and pressures. We were able to get some good scary data. I have been digesting that ever since, and am happy to say that I have come up with a model that is both based on some sound theories, and that produces curves that look like our measured data, which is no small thing, since the data is all over the place!
The other good news is that the linear zone is measured and studied a lot, and although it’s pretty complicated (it still depends on load, pressure, camber, tread rubber characteristics, tire carcass shape and stiffness, tread pattern, tread temperature, tread wear, speed, and some other things), it is possible to break it down into understandable pieces, and make some progress toward a theoretical model. That is what I have been doing, on and off, for quite a while now. So I think I have a good theoretical model for all three zones.
Why not just use an empirical model and be done with it? Wouldn’t that be easier? Well, it would be easier to code up the model, but it’s much more complicated to tweak and tune it so it has the right characteristics in all sorts of conditions (different loads, pressures, temperatures, etc.) Empirical models work well when the conditions can be considered to be fixed, as they might be for a passenger car with the recommended pressures travelling at highway speeds and below. But they become unwieldy in the racing environment, with large temperature changes, pressure changes, aerodynamic downforce and high loads from high-speed, high-banked tracks, along with the need to model curb hits well, and so on. There are just too many different things to measure, and it would be too expensive in terms of tires and time to test them in all necessary conditions. A decent theoretical model, though, should give reasonable responses even when the tire is doing crazy stuff, which on a race track is a lot of the time.
At the end of the day, what does all this mean? Well, I hope it means that once I finish this up, driving a race car on iRacing will be even more like the real thing, and the job of getting the tires right for each car will be a lot easier. That in turn will allow us to improve some of the other force models, as well. And that will continue to give us all more insight into what’s going on out there on the racetrack, increasing our enjoyment of the world’s greatest sport!
What is a tire model and why do we need one? A tire model is a collection of mathematical formulas, along with a bunch of numbers to plug into those formulas, that when given some basic information about how fast and in which direction a tire is going, what it’s contacting and at what angle, can spit out the forces that the tire exerts on the car. That’s pretty much it. There are a bunch of other force models needed for a racing simulation as well: the aero model—the forces that air is exerting on the car; spring and damper models—the forces that are exerted by the suspension elements; engine and drivetrain model—the forces that spin the drive wheels; brake model—the forces that stop the wheels from spinning; gravity—a gloriously simple force (from a racing sim’s point of view) that makes things fall and hit the ground. When we know all these forces, we can plug them into a complicated version of Newton’s F=ma (force = mass times acceleration) equation, and voila, we get the car’s and all of its component parts’ accelerations.
It’s important to be able to figure out how moving things accelerate, since what we really want to know at the end of all the math is where all those moving things are at a particular instant (like the instant we draw a pretty picture from the cockpit of an iRacing car). To know where things are at any instant, we need to know where they were a short time ago (their positions), and how fast they were moving between then and now (their velocities). If we know how fast they were moving a short time ago, and we can figure out their accelerations between then and now, then we can do a pretty good job of figuring out their velocities between then and now, and so we can figure out where they are now (at least we can make a pretty informed guess). If this all sounds kind of circular, like we need to know where we are in order to know where we are, then you are understanding it perfectly. Two things save us: one, the fact that in our universe stuff doesn’t teleport around like in Star Trek (in other words, positions don’t suddenly change in unpredictable ways, at least for stuff bigger than elementary particles), and two, the velocity of stuff doesn’t change unless a force is acting on it. The ancients didn’t have that second one quite right. It took thousands of years to figure that out, so don’t feel bad if this is making your head spin.
So this is why we need the force models for sim racing. They give us the accelerations we need (how much the velocities change). We take those accelerations, add them to the car’s and components’ velocities, take those velocities, add them to the car’s and components’ positions, and repeat, a zillion times a second. Every once in a while we draw a picture on screen with the car and all its parts in the correct positions (and with all the other cars and their components in the correct positions). That’s basically it, anyway. We need to do these calculations many times per second because, while the positions and velocities don’t change very fast (not in a thousandth of a second, anyway), the forces can change very rapidly. To get an accurate simulation, we need to compute those forces really, really frequently. We also need to have good models for the forces—that is, the models need to produce the correct forces in any given situation. Most of the forces are surprisingly simple, or at least they can be modeled fairly simply, and any additional complexities (for example, due to temperature) can be handled fairly easily. The two main exceptions to this are aerodynamics and tires, and of the two, tires are more difficult to model.
It turns out that almost all the forces depend primarily on the positions and velocities of the car and its parts. For example, the force exerted by a spring is a fairly constant multiple of how far it is compressed (or stretched). The force exerted by a damper (shock absorber) is a fairly simple function of how fast the damper is being compressed (bump) or expanded (rebound). Aerodynamic forces, while being fairly complex in origin, can be neatly computed from the air speed, air density and a small number of coefficients (fancy term for numbers) that depend only on the orientation of the car relative to the moving air. Gravity is ridiculously simple, always exerting a fixed force in a fixed direction (downward).
The forces exerted by a tire are not so simple, unfortunately. They depend on the position and velocity of the wheel on which the tire is mounted, as well as its angle relative to the ground (its camber). They also depend on the type of surface it’s touching (grass, concrete, asphalt, etc.), the shape of the tire carcass, the tread rubber compound properties, the inflation pressure, the tire temperature (many temperatures, really, around and throughout the tire), the amount of tread rubber wear, the temperature of the road surface, how heavily the tire is compressed into the surface (the load), how fast the wheel is spinning, even the small amount that the tread belt is deflected away from its usual position by these very tire forces! Let’s not even start on surfaces covered with various lubricants like water, coolant, oil, sand, etc.
Gathering real-world data for the iRacing tire model – Dave Kaemmer checks a tire on Calspan’s Tire Industry Research Facility test rig.
Any attempt to measure tire forces inevitably runs into the problem that all these variables are changing all the time. It becomes very difficult to determine just which property of a tire is having which effect on the overall force generated. As you take a tire and steer it on a tire tester, the surface temperature climbs rapidly and heat begins conducting into the tread, changing its characteristics, plus the carcass deflects, which changes the effective steering angle and camber angle. If you try to see what happens at large sliding angles, the tire wears away rapidly, and the temperature skyrockets (producing a lot of noise and smoke, which is pretty cool, by the way). This is not helpful when trying to come up with a good tire model.
There are a couple different ways to attack this problem. One is to measure the forces generated by a tire in as many different configurations as you have the time and money to do (different speeds, loads, pressures, etc.), and come up with “mathematical curve fits” that pass through the measured data as best they can. This is called an “empirical” model, empirical meaning based on observation or experiment. The other way is to try and come up with a theory that predicts what the tire forces would be in all these different configurations. Ideally, such a theory would only need a few basic measurements, and would produce accurate forces in many different situations. This is called a “theoretical” or “physically-based” model.
There are examples of both that have been used in automotive tire simulation for decades. The most well-known empirical model is Pacejka’s “Magic Formula” (that really is what it’s called by PhD’s in the field!), which can give very good results, especially when combined with “Tire Data Nondimensionalization”, which is a method for reducing the many possible tire force curves at different loads into a couple of curves, which can then be modeled with the Magic Formula. There have been many refinements and improvements over the years to this model, and now tire companies will often identify a tire with its “Pacejka coefficients”, the numbers to plug into the Magic Formula to obtain the tire force curves. The refinements have led to models that account for pressure, load and temperature changes, in addition to other improvements. Pure theoretical tire models such as “The Brush Model”, and the “Stretched String Model” have tended to be a bit simpler, and are used more to explain why the empirical models’ curves look the way they do than to predict what those curves will be exactly.
I’ve been talking a lot about “tire force curves” without much explanation. Let’s introduce a picture:
There are several different force curves that we’re interested in with a tire, but this is the important one, and it serves to illustrate a number of things. Plus you probably only have one cup of coffee, and time is running out on me. What you see here is a graph of a tire’s force parallel to the road surface versus a quantity called “slip”. This parallel force could be forward or backward (acceleration or braking), which is called “longitudinal”; it could be sideways (cornering), called “lateral”; or it could be a combination of both together. This curve has roughly the same shape no matter which direction we’re talking about, basically. Slip is a measure of the difference in speed between the tire carcass and the road surface. In the longitudinal direction, the slip is usually referred to as “percent slip”, or % slip. If a rear wheel is spinning at a speed where the tire carcass is travelling at 110 mph, but the car’s speed over the road is just 100 mph, then the tire is operating at 10% slip. In the lateral case, if the car is travelling 100 mph, but it is cornering hard and facing left at a 5 degree angle to its direction of travel, the tire is operating at a “5 degree slip angle”. In both cases, the tire appears to be “slipping” across the road, but in fact the tread rubber is just being stretched when it is in contact with the ground, and then it snaps back into place when it leaves the ground at the back of the “contact patch”. When the slip exceeds a certain amount (as you move to the right on the graph), the contact patch does start sliding (usually near the back of the contact area where the rubber is stretched the most), soon afterwards the force reaches a peak, and then starts falling as the tire’s slip increases still further.
This is just one representative curve which might be the correct curve for a given tire in one particular situation. The difficulty is that as conditions change (and they change very rapidly, all the time) the correct curve changes size and shape. As you drive through a corner, you might travel up one curve, and come back on a different one, because the temperature of the tire has changed, for example. So we need to figure out how and why these curves change. The force versus slip curve has certain characteristics that do stay mostly the same, so let’s look at it more carefully.
Note that there are three main zones in this force curve: 1) the linear zone in green, when turning the steering wheel more makes the car turn more (i.e. more slip = more force)—where we should always be when driving on public roads, 2) the limit zone in yellow, where the steering wheel becomes just a braking device, the tire starts to squeal happily, and racers make their living (more slip = no real change in force), and 3) the scary zone to the right in red, which is exciting, but not fast, and much rubber is disappearing from the tire surface (more slip = less force). We have discovered over the years from a lot of driver feedback in the simulation that the width of the limit zone and the steepness of the scary zone as you fall into it have a dramatic effect on the “drivability” of a car, and whether or not the tire model feels like a real tire. In order for a racing simulation to properly reproduce the handling characteristics of race cars, you need a tire model that reproduces all three zones well.
Right away, this becomes a problem. The reason is that pretty much nobody is all that interested in the scary zone; they mostly want to avoid it (except for the alternate universe of drifting). Even when testing tires, the scary zone just does too much damage to the tires and so it’s very expensive to test there. Hence there’s very little scary data. If you look at enough measured tire force curves, you’ll see that most of them don’t even extend into the scary zone. When they do, you’ll notice that while empirical curve fits can be really good in the linear and even the limit zones, they don’t really fit the data well in the scary zone. But they don’t need to, for most purposes. No tire company can sell their tires using the pitch, “Our tires have really good scary handling.” They can sell them based on how good the wet skid resistance is, since that is a number required to be tested for all passenger tires that are sold. So unlike most of the scary zone, there is a lot of data for the far right, lowest part of the scary zone, which is where wet skid resistance is measured (tire locked up, sliding on wet pavement). But even that is of little help for tire modeling, since the force at that point is as much a function of the pavement surface as of the tire itself. Also, water dramatically changes what that zone looks like, so all that data doesn’t help on a nice, dry, sunny day.
It gets even worse when we consider that the limit zone (the racer’s office) depends on what is happening in the scary zone. This is because what’s really going on in the limit zone is that the tire is doing both some of its linear thing (stretching the tread rubber), and some of its scary thing (whatever that is) at the same time. The limit zone is just a result of the mixing of the linear and scary zones as we increase the slip. So if we don’t really understand the scary zone, we don’t really understand the limit zone either. Up until not too long ago, the scary zone was keeping me up at night. However, when we did tire measurements last year at a tire test facility, we went ahead and destroyed quite a few tires with different constructions and tread compounds in order to see what they did at very large slip angles and at a bunch of different speeds, loads, and pressures. We were able to get some good scary data. I have been digesting that ever since, and am happy to say that I have come up with a model that is both based on some sound theories, and that produces curves that look like our measured data, which is no small thing, since the data is all over the place!
The other good news is that the linear zone is measured and studied a lot, and although it’s pretty complicated (it still depends on load, pressure, camber, tread rubber characteristics, tire carcass shape and stiffness, tread pattern, tread temperature, tread wear, speed, and some other things), it is possible to break it down into understandable pieces, and make some progress toward a theoretical model. That is what I have been doing, on and off, for quite a while now. So I think I have a good theoretical model for all three zones.
Why not just use an empirical model and be done with it? Wouldn’t that be easier? Well, it would be easier to code up the model, but it’s much more complicated to tweak and tune it so it has the right characteristics in all sorts of conditions (different loads, pressures, temperatures, etc.) Empirical models work well when the conditions can be considered to be fixed, as they might be for a passenger car with the recommended pressures travelling at highway speeds and below. But they become unwieldy in the racing environment, with large temperature changes, pressure changes, aerodynamic downforce and high loads from high-speed, high-banked tracks, along with the need to model curb hits well, and so on. There are just too many different things to measure, and it would be too expensive in terms of tires and time to test them in all necessary conditions. A decent theoretical model, though, should give reasonable responses even when the tire is doing crazy stuff, which on a race track is a lot of the time.
At the end of the day, what does all this mean? Well, I hope it means that once I finish this up, driving a race car on iRacing will be even more like the real thing, and the job of getting the tires right for each car will be a lot easier. That in turn will allow us to improve some of the other force models, as well. And that will continue to give us all more insight into what’s going on out there on the racetrack, increasing our enjoyment of the world’s greatest sport!
You just said it - at the back of a large grid. I don't think it has as much to do with the physics as it does LFS' marvellously dreadful graphic subsystem. The amount of detail in the current cars is pretty minimal, and it struggles drawing low poly models in reasonable time. Put 20 in front of you and it acts like the world is caving in. I just tested this last week when comparing the XRR to iRacing's Corvette C6.R. I have no problems staying frame capped, but that's on an overclocked i7 running SLi (but still having to render everything twice so the SLi is a moot point). But the delta between having no or a few cars on the screen versus many cars on the screen is gigantic.
Well that's pretty interesting isn't it, nice to hear a tidbit like that. Although as stated elsewhere in the thread the req'd specs weren't mentioned, I tend to think that it's due to trying to maintain the current minimum spec requirement... After all it's pretty likely that it runs on Scawen's machine - if he's happy with it, he's probably tested it
That being said I agree with this 100%:
I'm not sure how long their perceived vision of LFS running on a Celeron at 100fps is supposed to last...
:hihi:
mhm, just keep telling yourself that
mhm, just keep telling yourself that
From iRacing forums - new blog post:
On to some of the highlights of the things we are working on…..
Tires, yeah, instead of me regurgitating the same stuff I always say Mr. Kaemmer himself is going to write an entire blog post on what he is working on. After being tied to a chair and forced to watch me trying to solve quadratic equations on the whiteboard he finally broke and said he would do it.
Grant is back working on his new transmission model. He made my eyes glaze over yesterday by telling me he had just added in the mass of a hand into his model in trying to determine the velocity needed to get the dog tooth gears to engage. There is still quite a bit of work to be done on this, most importantly that there are aids available that make this new model usable by all of our customers.
One of the most complained about “features” in the sim is that a damaged car is just as fast as an undamaged car. We just figured what fun would it be if you lost the front wing on your IndyCar and it actually required you to slow down? Okay, seriously, we are working on improving the damage model.
I read a hotly debated thread yesterday on what exactly we are doing with the very general statement of “we are working on night racing”. (On a side note, if you ever want to see an engineer melt down describe a project they are working on in the most general description possible and say it’s a piece of cake to complete.) To elevate the suspense we are working on turning Richmond into a track that can be run at night. This may seem like a trivial task but we are modeling a light source from each light at the track. This will be over 100 lights. Kevin Combs will be doing a blog post specifically on this topic in the near future.
This project is just the first step in the long term project of finally getting back to work on improving our graphics engine. Now that Shawn is finally done working on the HoF project he is being set loose on all kinds of goodies to make the product sexier.
Fixed setup racing for hosted and official racing is also being worked on again. This is pretty self explanatory really. The real debate for this feature is what official series to make fixed setup. We have not had serious discussions about this internally yet but my first thought on this is that to start maybe D and under series are fixed setup? What do you guys think we should do for fixed setup series while trying not to add any redundant series?
I am pretty sure I have mentioned this in one of my previous blogs but we have started the process of transitioning to a third party sound engine called FMod. The feature set for this product should allow us to add some cool effects into the model and hopefully increase performance in general. At this time the goal is to have the old system in place as well so if there are any problems for a particular user you can continue to use the old sound engine.
We have heard quite a bit of feedback from our league operators that having more control over a hosted session would make their lives easier and we have listened. We have begun the process of trying to get back into hosted racing the extended admin functionality that we had in our previous products at Papyrus. As we have said many times before just because we did it at Papyrus does not mean we can copy and paste the code into iRacing so I don’t know the exact feature set we will have yet.
Tony “loose lips” Gardner has made a few posts recently about a few cars we are working on. We plan on trying to get the Tour Modified out in June around the same time that Thompson Speedway will be finished up. We also plan on trying to get the Mustang done in June or early July for when Mid Ohio is released.
On the topic of cars we have received a ton of feedback on our aero model and we have started to look at trying to model the draft effects on aerodynamic side force on the car. We think this will improve the side by side oval racing and being able to pass cars a little easier on the outside.
One of the larger projects that we will be working on is being able to find your friends on the service. We hope to be able to allow members to see if their friends are already in a running race, qual or TT, and can allow them to join an open practice and possibly a hosted session with them. We also are going to try and allow you to join an actual race they are competing in to watch it as a spectator.
I got to see some of the videos the other day that are going into the driving school and I must say I came away incredibly impressed with what they have accomplished. It’s going to be a seriously comprehensive training package that I believe everyone from novice to experienced sim racers will find useful. I am really looking forward to that getting launched.
And lastly, the cheerful backbone of our community, the iRacing forums, will be getting an overhaul. I have told Scott that if we don’t see a serious increase of positive thoughts and discussion in the forums you will be stuck with this same outdated piece of software that you have now. So let this be your warning!
Seriously though, we are incredibly excited to get these projects we are working on out to you guys as soon as possible. I think they encompass many of the things you have been asking for and yet only scratch the surface on what we want to accomplish. I hope everyone has a great summer (or winter for you guys down under) and now I am off to try and get this damn song out of my head!
On to some of the highlights of the things we are working on…..
Tires, yeah, instead of me regurgitating the same stuff I always say Mr. Kaemmer himself is going to write an entire blog post on what he is working on. After being tied to a chair and forced to watch me trying to solve quadratic equations on the whiteboard he finally broke and said he would do it.
Grant is back working on his new transmission model. He made my eyes glaze over yesterday by telling me he had just added in the mass of a hand into his model in trying to determine the velocity needed to get the dog tooth gears to engage. There is still quite a bit of work to be done on this, most importantly that there are aids available that make this new model usable by all of our customers.
One of the most complained about “features” in the sim is that a damaged car is just as fast as an undamaged car. We just figured what fun would it be if you lost the front wing on your IndyCar and it actually required you to slow down? Okay, seriously, we are working on improving the damage model.
I read a hotly debated thread yesterday on what exactly we are doing with the very general statement of “we are working on night racing”. (On a side note, if you ever want to see an engineer melt down describe a project they are working on in the most general description possible and say it’s a piece of cake to complete.) To elevate the suspense we are working on turning Richmond into a track that can be run at night. This may seem like a trivial task but we are modeling a light source from each light at the track. This will be over 100 lights. Kevin Combs will be doing a blog post specifically on this topic in the near future.
This project is just the first step in the long term project of finally getting back to work on improving our graphics engine. Now that Shawn is finally done working on the HoF project he is being set loose on all kinds of goodies to make the product sexier.
Fixed setup racing for hosted and official racing is also being worked on again. This is pretty self explanatory really. The real debate for this feature is what official series to make fixed setup. We have not had serious discussions about this internally yet but my first thought on this is that to start maybe D and under series are fixed setup? What do you guys think we should do for fixed setup series while trying not to add any redundant series?
I am pretty sure I have mentioned this in one of my previous blogs but we have started the process of transitioning to a third party sound engine called FMod. The feature set for this product should allow us to add some cool effects into the model and hopefully increase performance in general. At this time the goal is to have the old system in place as well so if there are any problems for a particular user you can continue to use the old sound engine.
We have heard quite a bit of feedback from our league operators that having more control over a hosted session would make their lives easier and we have listened. We have begun the process of trying to get back into hosted racing the extended admin functionality that we had in our previous products at Papyrus. As we have said many times before just because we did it at Papyrus does not mean we can copy and paste the code into iRacing so I don’t know the exact feature set we will have yet.
Tony “loose lips” Gardner has made a few posts recently about a few cars we are working on. We plan on trying to get the Tour Modified out in June around the same time that Thompson Speedway will be finished up. We also plan on trying to get the Mustang done in June or early July for when Mid Ohio is released.
On the topic of cars we have received a ton of feedback on our aero model and we have started to look at trying to model the draft effects on aerodynamic side force on the car. We think this will improve the side by side oval racing and being able to pass cars a little easier on the outside.
One of the larger projects that we will be working on is being able to find your friends on the service. We hope to be able to allow members to see if their friends are already in a running race, qual or TT, and can allow them to join an open practice and possibly a hosted session with them. We also are going to try and allow you to join an actual race they are competing in to watch it as a spectator.
I got to see some of the videos the other day that are going into the driving school and I must say I came away incredibly impressed with what they have accomplished. It’s going to be a seriously comprehensive training package that I believe everyone from novice to experienced sim racers will find useful. I am really looking forward to that getting launched.
And lastly, the cheerful backbone of our community, the iRacing forums, will be getting an overhaul. I have told Scott that if we don’t see a serious increase of positive thoughts and discussion in the forums you will be stuck with this same outdated piece of software that you have now. So let this be your warning!
Seriously though, we are incredibly excited to get these projects we are working on out to you guys as soon as possible. I think they encompass many of the things you have been asking for and yet only scratch the surface on what we want to accomplish. I hope everyone has a great summer (or winter for you guys down under) and now I am off to try and get this damn song out of my head!
I think the forum software is failing to handle the amount if replies; the page listing is screwy.
The excuse given was that redoing the "physics" from scratch for the cars was it's own undertaking, and redoing the bikes is a separate project.
I wouldn't be surprized if that trailer was running on the old physics anyway; since it sounds from what they've been saying lately that it's still a large WIP physics wise.
I don't expect much; I'd still go for it with the old physics (see Morpha's post) if the ridiculous "roads made of slabs" problem was fixed. That was the only real game breaker. Nobody (in their right mind) is expecting an iRacing competitor physics wise, but the game is just good fun regardless
I'm hoping that TDU2 at least catches some of the psdeuo-sim approach that seems to be contagious lately. Kind of like Shift - not totally sim, but much less arcade than other NFS games. Of course, it'd be really something if the hardcore mode was like a proper sim, but sadly that probably isn't a realistic goal. They should just pay Scawen loads of cash for the current LFS physical model and implement that
The stupid thing is that they don't put enough effort into the hardcore mode. They should just rename it SIM mode and actually make some attempt to license technology to do that. The only people that played "hardcore" mode anyway were people who would only love the game more if it actually was realistic. It should simply have arcade mode, and sim mode. Of course I guess part of the BS marketing is making morons think they're driving a remotely realistic representation of the real car however.
I wouldn't be surprized if that trailer was running on the old physics anyway; since it sounds from what they've been saying lately that it's still a large WIP physics wise.
I don't expect much; I'd still go for it with the old physics (see Morpha's post) if the ridiculous "roads made of slabs" problem was fixed. That was the only real game breaker. Nobody (in their right mind) is expecting an iRacing competitor physics wise, but the game is just good fun regardless
I'm hoping that TDU2 at least catches some of the psdeuo-sim approach that seems to be contagious lately. Kind of like Shift - not totally sim, but much less arcade than other NFS games. Of course, it'd be really something if the hardcore mode was like a proper sim, but sadly that probably isn't a realistic goal. They should just pay Scawen loads of cash for the current LFS physical model and implement that
The stupid thing is that they don't put enough effort into the hardcore mode. They should just rename it SIM mode and actually make some attempt to license technology to do that. The only people that played "hardcore" mode anyway were people who would only love the game more if it actually was realistic. It should simply have arcade mode, and sim mode. Of course I guess part of the BS marketing is making morons think they're driving a remotely realistic representation of the real car however.
Last edited by Ball Bearing Turbo, .
Dev's stated that they will not be in at release, but that they will come later on after release.
Damn you all... 1.5 hours till I get home :irked:
Pretty disappointed here. 
I was really really hoping for some language packs.
I was really really hoping for some language packs.
Not usually an issue here afaik. I always stop, I'm not even sure if I've seen someone not stop before. What pisses me off is when j-walkers expect you to stop, that bugs me. Walk another 50 feet! We're so bloody polite here, that last night on a fairly busy 2 lane road, some old lady (not from Canada...) jay walked right freaking across all four lanes of traffic, nowhere near a cross-walk - when there's a light 100 feet in either direction (Ok maybe 200... but still, this isn't a casual road - it was packed at rush hour).
Heh, man that's wierd. He updated it like crazy, everyone was excited about it pre-S2... I think you like it just because you never tried it.
That's wicked, I could feel the adrenaline watching the video heh! nice!
FGED GREDG RDFGDR GSFDG