It's probably changing as S2 gets updated, and unless the developers are publishing the formulas they use (not likely), your best bet is to get on the skid pad and note the g forces as the tires heat up while turning.
Yet another experiement, again with the LX6, set height to .30, set springs, rebound, and swaybars to max, bump to 5.0 (front and rear), and no camber (not needed with maxed out swaybars). Set diff to 60/60 % . This creates a car with near critcal oversteer. You initiate a turn with just a bit of steering, and then relax or counter steer through the turn, the car pretty much drifts through turns. If you keep the car from getting too far sideways, it responds almost imediately to steering inputs. Will keep working on this to see if I can control it. Very little steering lock is needed because once it's turning the fronts are mostly straightened out relative to the car while it drifts, sort of like an alien setup in GPL.
On the drag strip, I tried spinning the car, and grip remains very high, with the car almost sideways, over 1.1 with this setup. I'll have to try to see if I can get smaller slip angles on the slides to see whats going on.
This time I'm just reporting results from LFS experiements using the g meters. I chose the LX6 and road supers since it's a reasonably fast non-downforce car (also I own a similar car).
Under heavy braking the loss in grip if the tires are locked up is small (until they get overheated); looking at the g meter it's hard to even seen an initial loss in grip, but I'll "gestimate" it as less than 10%.
Cornering is a much different issue. I set a huge steering lock factor on the car to see what happens at large slip angles similar to what you get from a big oversteer reaction. The car pulls about 1.15g's in a corner, and drops to about 1.00 g's with both fronts a bit into the red (slipping). As I keep increasing the turn in to maximum lock, the cornering force continues to drop down, ending up below 0.8g's, a 30+% loss in cornering force. This would explain why once you lose it, it's so hard to recover.
With slicks on my Caterham, it will pull about 1.4g's while cornering, but this is not the issue, as I think the amount of grip in LFS is fine. It's the reaction to loss of grip that seems to be exaggerated, which could be a differential or suspension issue and not a grip issue.
This time I'm more of a typical example. The slicks and DOT racing tires for my car and almost all non-downforce cars are bias-ply (do a web search for bias ply racing tires). The amount of grip lost when sliding is much less than that of a typical radial street tire. Even radial racing tires lose less grip than street tires. The reaction to losing it is more severe simply because there is more lateral force on the car.
Depending on the setup, one trick that can be used is driver induced understeer, by steering the front tires inwards a bit past the point of maximum grip (slip angle). It allows a driver to force the car to respond to sliding with understeer instead of oversteer, assuming that it's not a case of very excessive throttle. You can't do this everywhere, or else the front tires will overheat.
Gravel is a special case because the surface (the gravel) moves). For a beter example, try drifting on ice versus pavement, pavement will be easier.
You should try bias ply tires, they will be much easier to drift than street radials. I've already mentioned that higher g forces lead to a faster reaction by the car when you do lose it.
Check out this web site, the recent videos include data logging on the screen:
This happens all the time, from fun runs to formula 1 cars. The cars go off track quite often, and after getting back on track, they're back up to speed in a very short time.
I agree that the tires should develop hot spots, it's just that these hot spots are very small and don't spread out over time. I was sitting still watching two very small hot spots take over 3 minutes to cool down from 120+ degrees to 100 degrees (Farenheight), while the adjacent areas didn't heat up at all. You can repeat this experiement for yourself.
Hmm, one of my posts never made it into this thread, my fault, should have checked.
I wanted to know what type of limited slip differential was being modeled by LFS, and if anyone here that races in IRL think the differential model is correct yet, but as posted it's still in development, so it's probably not there yet.
The point about kinetic friction reducing with speed would probably have some effect on a single pair of clutch plates type differential, but it would be minor. I went a bit off track here, sorry about that.
Similar to your thread at RSC, I wanted to ask if differentials with multiple clutch plates, and selectable ramp rates could be implemented.
As stated, I'm just requesting some improvements for S2, while trying to provide techincal explanations for my requests. I'm assuming that this is a new audience here.
Also S2 is a big improvement over S1. The tire model and limited slip differential have greatly increased the stability. I'm just hoping to see this trend continue.
Ah, the bad old days and my moaning about the LX6 in S1. Well, now all those posts are gone. I left RSC and had them delete all my posts.
optional off-topic reading follows:
I had an issue with their undocumented public warning policy and guilty until proven innocent attitude. When I pointed out that their public warnings violated their rule 4.1 about abuse, harassment, defamation, .... Mbrio demanded I mail a written letter agreeing to their undocumented policies or leave. I chose to leave.
This is true unless one of the tires breaks loose and starts spinning. The more the one tire spins (compared to the other), the less the locking factor, because there is less overall torque being applied to the now faster rotating differential (due to the faster spinning tire), and because kinetic friction decreases with speed. These are minor factors, since the initial locking factor (such as number of clutches, and pressures), can be adjusted to compensate for these factors. The main point here is limited slip, one tire can spin without the other tire spinning.
I found this to be true in my old 1997 Trans-Am. With a certain amount of throttle, I could get just the right rear to spin while taking off on a straight line. With less throttle, neither tire would spin, and with more throttle, both tires would spin. I could get the same thing to happen while cornering hard (except it would be the inside rear tire that spun first).
With a limited slip differential, a certain amount of throttle pressure will result in a one tire spin, and more throttle pressure will result in a two tire spin. The higher the locking factor, the less the difference between these two throttle pressures for one tire spin versus two tire spin. The lower the locking factor, the more the difference between these two throttle pressures.
GPL models this. A lower locking factor will be easier to drive, giving you more warning, since there's more margin between the throttle pressures for a one tire spin versus a two tire spin. A higher locking factor will be harder to drive, because the margin between the two throttle pressures is reduced, but will give you more acceleration out of a corner because you can use more throttle pressure without the inside rear tire breaking loose.
I think of a limited slip differential as a positively stable setup, because there is a margin of throttle pressures between a one and two tire spin. This margin gives a driver a warning that throttle pressure is approaching the limits of what the tires can deliver, indicated by a single tire spinning, by either the sound of the tire spinning, or by the sound of the increased engine rpms.
A viscous differential is not stable. At a specific throttle pressure, the inside rear tire will break loose and initially spin, but once it's starts spinning, the locking factor increases, and the momentum of the inside tire and fluid in the differential may be enough to break the outside rear tire loose, without any change in throttle pressure by the driver. Even if it doesn't cause the outside tire to break loose, the inside tire will cycle between spinning and not spinning with the locking factor following the same cycle. Neither of these situations are stable. A viscous differentinal may be ok for front/rear differentials on a 4 wheel drive vehicle, but it's a bad choice for a rear end differential.
I've actually had some real life experience with this. A long time ago, I bought some even longer time ago used hot rods. One was a 1969 Chevelle SS396 that didn't have a limited slip differential (a bit strange that a hot rod didn't have a limited slip differential). I could floor it in first gear with the result that the right rear tire would spin and smoke like crazy, yet the car just kept going in a nice straight line, not accelerating very quickly because all the engine speed was going to the spinning right rear tire. Donuts were not possible with just one rear tire spinning. One other unusual feature is that the Chevelle had coil springs front and rear (no leaf springs).
Later I got a 1969 Dodge Charger 440 R/T with a limited slip differential. One good test to confirm this was to get one tire wet and see if the car would still spin both tires (it did). When spinning both rear tires, it would get squirrely and require control inputs to keep it aimed in the right direction. Donuts were very easy to do. Unlike the Chevelle, the Charger had no coil springs at all, it had leaf springs in the back, and torsion bars in the front (sort of like sway bars, but attached to the frame and pointed forwards and attached to the front A arms).
Alllow everyone to use the shortcuts. LFS is still in development, it will get fixed later.
Try to enforce a no shortcut rule (not too practical).
Eventually LFS could either detect shortcuts and auto-penalize (GPL, GTR do this), or fix the tracks by putting up tire barriers (or somethings harder, since it's a game), just like they do in real life.
Personally, I like the GPL rule that you must have at least two wheels on or inside the curbing (or other track boundary indicator) at all times. For LFS, Blackwood is a track where this rule is violated on a routine basis, but most LFS players accept it as part of the game.
LFS is not rubbish. I've never thought so, or I wouldn't be planning on buying S3 as I've have mentioned before. Owning a Caterham doesn't have anything to do with what I've posted here. I've compared the LX6 to my Caterham in the past, but that's not the point now. My suggestions are based on what I read from knowledgable sources, not my own experiences with just one car.
My reason for these comments is the fact the LFS is a game that is still in development, and that I'm hoping that the final result is a good simulation where the cars in LFS behave very much like their real world counter parts; the same amount of stability, the same reaction to control inputs, the same reaction to the environment (driving over wet spots, grass, dirt, gravel, weather effects, ...). I also want to experience a simulation that lets me push the cars to the limits of my ability, not to the limitation of the simulation.
As far as comparson to other games, my comments:
Grand Prix Legends has some wierd quirks in it's physics, but it's seems to have captured the essence of a good simulation in that the cars behave pretty close to their real life counterparts (based on expert testimonials), except since there's no personal risk of being splattered somewhere unpleasant, you can push harder than the real drivers did. (Example of wierd quirk, reverse reaction to steering when braking heavy, in this short video gplrs.wmv . This behavior (induced understeer) would be expected while cornering, but not while going straight).
In the original German release of GTR (1.0), with all assists off, just about any minor loss of control of the car meant you ended up facing backwards. This may have been part of the reason that an actual GT class racer commented that GTR was more realistic with some of the assists turned on (as opposed to all assist off), the reason probably being that the physics weren't quite right. It was improved through the various versions, now up to version 1.4.
Nascar Racing Season 2003 is popular, 300 to 500 players online, but most are running superspeedway races, where the only time you lift on the throttle is to avoid drafting into the car in front of you. Little skill required (probably why it is so popular), mostly wreck avoidance, braking points for pitting, and the luck of exiting the pits right into a draft. I've won my share of these, but lost interest when I realized that other than qualifying, no skill was being developed (I went back to hot lapping Nordschliefe in GPL, wanting to get a sub 500 second (8:20) lap time, I got it down to an 8:15.32). The road courses require skill but far fewer players run on all two tracks (few add-on road courses used online). The main thing going for NR2003 is that it seems to handle 40 players in a single race fairly well, and the GTP mod is cool.
Does S2 model limited slip differentials in the manner described?
One of the advantages of this limited slip differential's behavior to decrease locking factor when speed differential between driven tires increases, is that the result is positive stability. If excessive throttle is used, one tires starts to spin and then increases it's rate of spin. Meanwhile, the other tire is getting less and less torque applied to it as the spinning tire continues to increase rpms. It's sort of self stabilizing as long as the excessive throttle input isn't too extreme, or the initial locking factor isn't too high. It gives the driver enough time to hear that the engine rpms are accelerating too fast and lift on the throttle a bit to stop the single tire spinning without losing control of the car.
S1 used a viscous differential. This had a bad quality to it in that the more the difference in speed between driven tires, the higher the locking factor between driven tires. The result was that if one driven tire started spinning while under excessive throttle input, the increase in locking force would soon cause the other driven tire to start spinning as well, reducing stability.
A limited slip differential has the exact opposite behavior. The greater the difference in speed between driven tires, the lower the locking factor. This helps increase stability when a tire starts spinning due to excessive throttle input.
The reason for this behavior is that the coefficient of kinetic friction varies with speed, and is not constant as is often taught in early physics courses. Starting from almost no speed, kinetic friction increases to a peak, which occurs at a very slow speed, then decreases as speed increases.
With a standard clutch, the higher the speed differential between the plates, the lower the coefficient of kinetic friction. In a street car, trying to launch at high rpms by slipping the clutch doesn't work well, because of this. It's better to just drop the clutch at medium low rpms and let the tires spin, which is what magazine testers do when drag testing showroom stock cars.
There are two common methods used for drag racing clutches to overcome this effect. Sometimes both are used. One is to use weights and springs to increase pressure on the clutch plates as engine rpm increases, but this means the driver has to use more foot pressure on the clutch pedal to compensate for the increase in plate pressure, or some type of launch control is needed that doesn't require the driver to manually resist the plate pressure. The other method is to simply use a clutch with a higher initial coefficient of kinetic friction, so that even at high differences of speed between the plates, the clutch friction is still higher than the grip provided by the tires, so the driver can always keep the tires at the limits.
In the case of a motorcycle clutch, or a limited slip differential, this effect can also be controlled by the number of clutch plates used. Adding more clutch plates reduces the difference in speed between plates, and increases the overall kinetic frction. In the case of a limited slip differential, using more clutch plates requires an adjustment to the ramp rates to reduce plate pressure to end up with the same locking factor. If a limited slip differential has indepently settable locking factors for engine acceleration versus engine braking, more clutches will smooth the transition between the locking factors.
I don't know if S2 models this behavior of a limited slip differential, and I haven't thought of a good experiment to verify this.
No, but that wasn't my point. Although over a long period of time, the whole tire should heat up a little.
Two issues here, in LFS the hot spots are extremely small, and extremely insulated. Looking at the HUD temperatures, there can be a huge differernce in temperatures between the inside, middle, and outside of a tire, as well as from segment to segment, and can remain that way for quite a while. As mentioned before, even after 3 minutes, none of the surrounding cooler areas got any hotter.
I would assume this is like a trade secret, no one but the developers are going to know, or are they explaining how they model the tires?
The issue seems to be that there is no conduction of the heat away from hot spots. It's as if the tire surface is a perfect heat insulator. In the FO8, with 1.00 degrees of negative camber in the front tires, while going 50mph, tires at 60 degrees (Farenheight), I locked up the brakes to a complete stop (takes just under 2 seconds), track must have been cool, because most of the tire dropped from 60 degrees to 59 degrees during the 2 seconds, while two inside hot spots appeared, over 120 degrees. Three minutes later, the hot spots were still over 100 degrees, and the immediately surrounding areas hadn't heated up at all
I would have expected the heat to be conducted both deeper into the tread and outwardly away from the hot spot, but LFS isn't doing this . In addition, the hot spot appears to be much smaller than the actual size of the contact patch of a tire, because it's very difficult to move the car slowly and stop the car with the hot spots showing on the live tire temp HUD. The hot spots are extremely small, and dissipate heat extremely slowly.
Sounds offer good feedback as to what's going on. Tire scrub / squeal sounds are good for braking and cornering. Engine sounds are good for applying throttle, as long as the differential doesn't have too much locking factor. If engine rpms are increasing faster than they should, it's an indication that one of the driven tires is spinning.
Assuming that LFS S2's limited slip differential is modeled well, engine sound feedback should work well for throttle application, even on straights. A car can remain stable and in control with one driven tire spinning if the locking factor is low. Since this is player adjustable, the amount of sensitivity is adjustable.
Force feedback can help with steering inputs, depending on how the game models the force feedback. I noticed that with LFS S1, just enabling force feedback improved stability, even though my steering inputs were the same. The game was adjusting my inputs with the force feedback, so in essence, it was an stability assist. I don't know how much of this applies to LFS S2.
One fix is pretty simple, adjust the tire model; specifically the sideways force versus slip angle curve so that it's more horizontal once past the peak force. This is one of the goals of the manufacturers of real racing tires, both DOT and slicks, to make them more forgiving.
There also seems to be some sort of recovery fudge factor that I can't figure out. The car seems to remain unstable for quite a while after going off track. I'm not sure what is trying to be simulated here. I can understand that it would be difficult to drive a high powered car on wet grass, but once it's back on the pavement, the tires quickly dry out.
Let me first state that I bought LFS S1 and S2, and plan to buy S3, but I think there are some issues with LFS:
The cars in LFS over react when the tires are pushed just a bit past the limits.
S2 is a big improvement over S1 in this aspect of the tire model, but it still isn't quite right yet. I don't know how LFS does it's tire physics, but in real life, there is no sudden transition from static (not slipping) to dynamic (slipping) friction. There is almost alway some amount of slippage at the perimeter of the contact patch of a tire. In addition, there is an inwards squirm effect due to the force from a tires sidewalls.
As longitudinal acceleration (or braking) increase, the amount of area at the leading and trailing edges of the contact patch that are slipping increase, until you reach the point where all of the contact patch is slipping. The amount of loss in grip when all of the contact patch is slipping depends on the tire compound and construction. Wrinkle wall drag racing slicks are sticky, but lose a lot of grip if they spin. Performance street tires don't lose quite as much grip, and because many street cars have clutches that don't grip well when there's a big difference between driving and driven rpms at the clutch plate, most auto magazine testers simply drop the clutch at a medium low rpm and let the tires spin to get the best and most consistent launches when doing drag testing.
A similar thing happens with lateral acceleration (cornering). Slip angle is the difference between the direction the tire is actually moving, and the direction the tire is pointed. As slip angle increases, the sideways force increases, and the amount of area that is slipping at the perimeter of the contact patch increases, until it reaches a critical angle of peak sideways force. Increasing the angle further results in less sideways force, but how much less depends on tire design. With an ideal tire, there would be a large range of slip angle past the peak where the sideways force would remain about the same. Most drivers will give up .1g of lateral accerleration if this resulted in a tire that closely approximates an "ideal" tire, which would be more forgiving and allow them to drive at the limits. Some of you will be "tired" of hearing about this, but do a web search for bias bly racing tires, and you'll find that most non-downforce racing cars use bias ply racing tires (DOT or slicks). This is because these tires behave very closely to an "ideal" tire, losing very little grip even when pushed past their limits. Even road racing radial tires are designed to have similar properties.
tires take too long to regain grip after going off track
In real life, race cars often go off track, and back on track, and it doesn't take as long for grip to return as it does in LFS. If a race car travels over a wet patch (grass for example), the tires lose little heat, and dry up very quickly once back on the road, and at most tracks, they don't water the grass just before a race. Gravel traps use fairly large pebbles to prevent them from getting stuck into the tires and later flung off at other drivers.
The tires in LFS heat up much too quickly when sliding
Not much to explain here, the model just seems to be wrong. The hot spots seem to develop almost instantly, and yet take a long time to dissapate.
Segemented tire model
Again I don't know how this is implemented, but a contact patch varies in size depending the forces acting on it (downforce and accelerations), and the circumference of a tire flows continously through the contact patch, not in segments. If you lock up the tires under braking, even for a fairly short period, then look at tire temps while moving slowly, you can see a very small hot spot "segment". This isn't realistic.
I posted that one, it's very low quality, but at least it's smaller than a similar quality .MOV file that's almost 100MB in size. I've been trying to find a better quality version.
There's a patch that can be made to GPL to allow long tracks. Jim Pearson is now working on a full length Isle of Mann track, but hasn't predicted when it will be done.
Nordschliefe came with Grand Prix Legends. Versions similar to this track are available for F1C99-02, GTR, NR2003, and some other games.
There are two basic layouts, on is 14.1 miles long, the other is 1.2 miles shorter, done by a link that by passes the old start/finish straight, uturn, and return straight. I made a picture showing this bypass link in red:
Other changes since the 1967 version used in Grand Prix Legends include smoothing out some bumps, drops, and rises on the track.
Some fast lap times (I think this was on the 13 mile long layout):
Stefan Bellof - Porsche 956 - 6:11 in 1983 practice session.
Derek Bell - Porsche 956 - 6:26 during 1983 1000km race.
There's a on board video of Derek Bell doing a 6:41 lap at Nordschliefe, but I can't find it right now.
Estimated F1 lap time is under 6 minutes. This can be done with F1C99-02 on the 14.1 mile course (I've done a few 5:55's).
The longest race track circuit (ignoring 1000km Baja type events), is probaly Ilse of Mann. They run motorcycle time trials there once a year. It's 37.75 miles long, and is fairly fast. In recent years, top lap times are just below 18 minutes, 126+mph average. It's dangerous, and the fatality rate is pretty high, but then again, so is Nordschleife when it's open to the public as a toll road (mostly motorcycle fatalities, armco is not good for motorcycles).
Even if LFS never includes slicks for all cars, it's good to see that Scawen isn't objecting to allowing players to have fun with the mod offline or with unofficial servers with their friends. Got to respect him for that.
In the case of LFS S2, I think it's the slip angle versus force curve (breakaway grip) and/or the near instant hot spotting that makes the cars less controllable. In a lot of situations, the cars of LFS don't get "loose", they just spin.
If the breakaway grip were nearly the same as maximum grip the cars would be more controllable. Note that in real life, bias ply slicks have this quality that the breakway grip is about the same as maximum grip, making them much easier to control at the limits, so such a tire model would not be unrealistic.
In real life, suspension setups work because they cause one or more tires to slip more than the rest of the tires, setting up the understeer / oversteer characteristics of a car. None of this works if there isn't significant slippage by one or more tires. If the car is overall very close to or at the limits, then one or more tires is past the limits. LFS needs to be able to model this in a stable fashion.