96 GTS, did you go? I looked around for you but didn't see anyone in a red, striped polo

Got a pic of Doug, Mario, and me. I darn near cut him out of the picture. We were all shoulder to shoulder and then they took a step back without me realizing it. The woman (Mario's publicist) taking the picture kept saying, "closer, closer!" so I kept leaning in more and more. Argh!

Oh well, a photographer took another one of Mario and me at the bar. Hopefully that one will turn out a bit nicer without it looking like I'm trying to hog the whole frame like a bonehead

I live about three blocks away. It's been my Cheers since they opened years ago

Come on down. If on the one out of a hundred chance there's a problem, ask for me ("Todd") and I'll come kick the bouncer's butt to get you in

That won't be needed though I think. It'll be fine and just early dinner for everybody, so just come on over and meet the Pope.

Quote from 96 GTS :

Gah, I'm 20 Not 21 until the end of November. I wonder if I could sneak in.

He's coming at 6:30pm so you might be be able to get in anyway. It's a restaurant/bar and there are often kids having dinner with their parents early in the evening. You might want to give them a call and see. Who knows?

Quote from Tweaker :

Met Mario at Laguna Seca in the paddock once... nice man, and invited my family into his team lounge area where we got to crash their party and eat all their food .

Sold a pit scooter to one of his crew too. Now if only I could get a testdrive in one of their cars

Great story!

Quote from NaturalPoint_Support :

The abilty to use, or not use an axis is fully adjustable, within the TrackIR software. So if you tilt your head, when you drive, and what to turn it off, you just have to disable the roll feature.

And if you do, it's remarkably accurate. A really good piece of hardware. I only wish my Z800 was half as good at head tracking.

Anybody else here happen to be in the Minneapolis/St Paul area? If so and you're 21+, head on down to Tom Reid's Hockey City (sports bar) this Tuesday, August 7th in the evening. Mario Andretti will be there It looks like Doug Milliken ("Race Car Vehicle Dynamics" and others) will come along as well. Should be fun

Yep, I agree totally.

The TrackIR is a very nice, highly precise unit. Great for flight simulators, but I didn't like driving with it at all. To each his own though. Some people can't stand a fixed view, so have at it

I tried flight simulator with TrackIR and quite liked it, although now I've got a Z800 VR headset which is much better with the 3D. The best combo for me would be having both. In racing sims I really don't like look to apex or head tracking. It's distracting and disconnects me from the car. The apex is always visible on screen anyway, so there's nothing preventing me from turning my eyes or head to look at it naturally, so I just never understood the point. In replay videos it looks cool, but when driving it messes me up.

Quote from yoyoML :

You got the effect in reverse. Steering in one way rolls you in the other.

Suppose you're traveling forward, so the front wheel's angular momentum points left. You "steer" to the left by exerting a torque, whose direction points up. The change in the wheel's angular momentum is then in the direction of the torque, which is up. The originally left pointing angular momentum then points left-up, rolling you to the right.

Steer (yaw) left -> roll right. One more reason to countersteer.

Suppose your bike begins to fall to one side: rolls left. The torque that the bike exerts on the wheel points aft. The left pointing angular momentum then points left-aft, yawing the wheel to the left.

Roll left -> yaw left.

You see, that the gyro is "stable" arises from this alternating force and response: yaw left->roll right->yaw right->roll left.... If you had "yaw left->roll left" like you said, then the gyro goes yaw left->roll left->yaw left even more->roll left even more... until it diverges.

Yes, you're right of course. I got it backwards. Thanks for catching it.

Shotglass, ignore what I said on this one.

Quote from Breizh :

The rims in LFS (again IIRC) are calculated on the fly so that Bespoke causes sync errors. It's odd that rims' weight would be accounted for to such precision, but not their gyroscopic force if that force is as significant as jtw62074 describes.

To be fair though, I don't know if it's significant on big cars. With the little RC cars in Virtual RC it makes quite a difference, but those may very well be totally different from regular sized cars. There are quite a lot of vehicle models used in handling engineering that don't bother with the effect either.

EDIT: Here's an interesting video showing a rather bizarre gyroscopic effect

http://www.metacafe.com/watch/ ... _gyroscopic_effect_weird/

Last edited by jtw62074, Sun, 22 Jul 2007 20:46.

Quote from Shotglass :

todd shouldnt a gyro roll to the left if you steer it to the right ? at least thats what my pro gyro testing rig (spinning a cd on my fingernails) tells me

Shouldn't be, no (if you spin it away from you, at least). Although I tried the same thing with a CD on a pen just now it would seem that's right. There's some friction involved there though

This is a nice animation showing it:

http://en.wikipedia.org/wiki/I ... scope_wheel_animation.gif

The wheel is spinning "forwards" at the top into the picture as though you're behind a wheel rolling away from you. They roll it to the left which yaws it also in the same direction. Same thing happens if your input torque is to yaw the wheel. It rolls/banks into the turn.

What should be noted is that there is only a gyroscopic effect if the wheel is both spinning and rotating about another axis. I.e., when travelling straight down a road there is no gyroscopic torque at all. Introduce the slightest yaw/roll velocity and the reaction will appear.

Ooo, another physics discussion

Gyroscopic forces work a little differently than most people think. When a bike/motorcycle begins to tip to the side (roll, ignoring steering here), the gyro torque actually causes a yawing torque on the bike which twists it into the corner, much like steering on a car. At the same time, if you were to yaw the bike through steering, the gyro effect exerts a roll torque that tips you into the corner. This is probably why when riding straight, you don't have to steer left to tip the bike to the right (at least not on my friend's Harley ), then steer again to the right to make a right turn. Just steer right and it rolls into the turn all by itself, no countersteering required at all. I'm very far from being anything remotely close to an experienced rider, but this is what my experience was on that one bike. And when it came time to straighten up the bike again I could just steer it straight without giving a quick input to the right in an attempt to kick the bike upright or do some fancy weight shifting with my behind. Without the gyro effect I suspect this wouldn't work so well.

In a car the effect is similar. When you steer the wheels or the car is rotating to the right in a turn, the gyro effect causes the car to roll into the corner slightly, reducing weight transfer from what the regular steady state calculation would say it should be. The quicker you steer or the quicker the car is rotating, the greater the roll torque (it must be so to conserve angular momentum). This is generally an understeer tendency and therefore a stabilizing effect.

I do gyro in my sim and although I haven't tried it without it in the full sized cars in a very long time, the difference with and without gyro in Virtual RC Racing is very noticeable. Enough to where you'd go back to the setup screen and tweak the car a bit to get the balance back how you had it before. Maybe it's not so much on a 1:1 scale car, I don't know

A few years ago I did some calculations for a motorcycle to see if the effect would be significant for upright stability. The resulting torques were so large I thought I'd made a mistake and rechecked it several times, but it was quite significant even at highway speeds. On a bicycle it would be much lower of course since the moment of inertia of the tires is much lower, as are the rotational velocities.

There is more to the picture of stability of course, such as the other effects mentioned earlier by others (fork angle, etc.), but this is how the gyro effect by itself influences things.

Gregor Veble tried a motorcycle in his engine a few years back. If I recall correctly (this was a long time ago) he found he could make the bike work and be pretty stable without the gyro effect, but gyro helped it quite a bit. I'll have to ask him about it again when he's online next.

Last edited by jtw62074, Sun, 22 Jul 2007 00:53.

Quote from Ball Bearing Turbo :

Concerning dropoff with camber, load sensitivity is the first thing that comes to mind which Todd already touched on. Could it be partially due to much more rapid heat build up in the portion of the tire in contact with the road; or specifically the portion receiving the bulk of the weight transfer - since the surface area handling that weight is reduced... It actually seems logical that this would happen, but I certainly never thought of it before. Obviously that's a simplistic view, but it does make some sense I think. Note that with less load, the dropoff is not as severe, even at -9 deg.

Nice work on the debate BhuddaBing!

Man I love these threads!

Yes, that could very well be part of the picture. Load distribution throughout the contact patch is quite bizarre frequently. The ones I've seen for tires operating even at 0 slip angle, 0 camber, and free rolling, show a somewhat unusual pattern across the width of the tire. It's often a fairly unpredictable looking wave. Local load sensitivity (imagine the contact patch made up of thousands of little chunks of rubber, each with its own friction coefficient that's varying with load) could very well be having an effect here.

A tire engineer in an engineering thread somewhere said he didn't really believe that rubber's load sensitivity was responsible for this, more or less denying that it exists (lots of sliding rubber research indicates otherwise, however), and that the load sensitivity of the tire as a whole can be attributed to carcass effects. In my mind at least, carcass effects vary the local load distribution and would explain much of what's going on provided the rubber itself is indeed sensitive to load (all rubber data I've seen shows this to be the case). So I'm not quite sure what the tire engineer was on about.

Anyway, when you start dialing in camber, slip angle, and especially slip ratio (braking/acceleration torque), the pressure profile can change dramatically. I'm having a hard time visualizing what might happen to this pressure distribution at slip angles past the peak with a lot of camber, though.

I've played quite a bit with FTire (the simple FEM type of tire model) and it never predicted much of a peak at all with the default tire that comes with it, even with quite a bit of camber. That's using local friction coefficients that vary with load and quite a lot of other stuff. There is probably a mishmash of all sorts of things happening in the rubber.

I hesitate to speculate on a dominate effect, however. A tire engineer with the really serious FEM stuff they're using these days could probably answer that.

Quote from Shotglass :

have you got a intuitive explanation for why this happens ?

Since this is new to me, I really don't know. Friction coefficient in reality is different everywhere in the contact patch. It varies with several things, all of which are not known yet by anybody as far as I know.

One factor is vertical pressure (load sensitivity on a local scale), which again is different at any given spot in the contact patch. Adding camber or braking/accelerative torque alter the vertical pressure distribution throughout the patch (in the case of braking/acceleration it's very significant). Changing slip angle at constant load ought to do this too. The FSAE tire test videos showed the tire moving up and down significantly with slip angle in an attempt to keep the load constant. (Increasing slip angle caused the tire to squat considerably). Add in some camber in combination with that and who knows how the load distribution is effected? If the area under the curve of the entire distribution is changed, then the total friction will too, as will local surface temperatures, which would then modify friction again on top of this.

Again, I don't know exactly what's going on in the patch or why it happens, but it does. This is the realm of FEM modelling by tire companies on supercomputers.

Quote :

and also a rough rule of thumb number of how much it will fall at worst ?

I don't know.

This is the biggest drop I've ever seen in a car tire (thanks BuddhaBing):

http://i11.tinypic.com/4l96wyh.jpg

That's at -9 camber and appears to be an extreme case with a tire that's very stiff in the lateral direction. As I've said before, I haven't seen anything measured in the tire plane until now that showed a drop that was worth noting and was outside of the usual tire noise. I'll have to see more data at high slip angles with a couple of degrees of negative camber to give a useful answer. I'll definitely be keeping an eye out for it

Quote :

ah but gtr2 curves keep dropping without ever flattening so if you dont countersteer faster than the curve drops or run out of lock all youll achieve is making the situation worse ... or on the other hand steering into the slide will be your best option which it really should not

thing is if youre not biggie bawbag niels or peri chances are you wont feel the spin comming until its too late with strictly monotonic decreasing tyre curves

Yes, I agree. I'm beginning to wonder now if perhaps the combined slip modelling might be more at play than I thought previously. I'll have to try some curves that drop off a bit in mine when negative inclination is present and see what it does.

Quote from BuddhaBing :

Todd, it's available -- for a fee -- from the link at the bottom of this page: http://www.mae.buffalo.edu/research/phd-kasprzak.shtml If you want to avoid the fee, you could probably ask him if he has a copy he can forward to you. It's an interesting read and well worth a look for those interested in the subject matter.

Thanks for the link.

Quote :

I too would be very interested to hear Doug Milliken's take on the data shown in those figures and, more generally, on the various approaches used to model tyres in these consumer level simulations.

Doug and I have gone back and forth a bit on this via email the past couple of days. He went through this thread and read some of the posts (ours in particular) and looked at the data. While he's too busy to get involved in a debate right now, he did clear up a couple of things with me.

Essentially, there can indeed be a peak and a slight drop off when enough negative camber is present. When we had discussed peaks in the past, what he had in mind were the book illustrations found all over the place that show lateral force plummeting after the peak over a very small slip angle range, which is wrong. So it seems when he was reinforcing that there wasn't a drop off, it was meant more relative to those sorts of illustrations and wasn't to mean that there never was any measureable drop off after the peak in any situation at all. When there isn't any camber or camber is positive, the curves are indeed flat after the peaks as I've been preaching.

When there's a fair amount of negative camber there can be (but not necessarily always is) somewhat of a drop off in the direction where the tire is leaning into the turn, which normally flattens at a slightly lower value (similar to previous LFS versions). This isn't to mean it drops 10 or 20% or anything like that, just that there can indeed be some measurable drop. Away from the turn or at 0 camber the curves are just flat after the peak.

The picture you showed from Kasprzak's thesis with the really big drop off was at -9 degree inclination, which is some very serious camber and probably not a normal operating condition for that tire and would likely explain what's happening (this is the highest drop I've seen in lateral to date aside from drum test data that often looks similar to that). Note that some of the FSAE tire data showed a slight drop while other data was pancake flat. This can most likely be attributed to camber differences in the tests. I suspect pretty strongly that the 4 pics you showed were all indeed flat belt data since it came from Calspan, so my suggestion that it might have been showing a drop due to being measured on a drum is very likely wrong.

However, the point is, as you said, that there is indeed data out there that shows a drop off. At 0 camber, positive camber, and mild negative camber the curves are quite flat as I've been preaching, but when you start dialing in the negative camber in fairly significant amounts the situation can indeed change. I wasn't aware of this, so I've learned something here and thank you for challenging me over the past few days on this

I must now agree with your earlier statement about the GTR2 curves not being all that bad since they only show a few % drop once you've tripled the slip angle beyond the peak as long as this is in a situation where there's a fair amount of negative camber involved (granted, the inside tires which are now in positive inclination should then be operating quite differently, but since the loads there are much lower in comparison it's not as critical).

The original rFactor curves I posted though are a still way overboard, but perhaps GTR2 curves are not all too bad up to and a fair ways past the peak. I suspect it's still excessive though as the countersteering problems were still there (at least in the demo I tried it was), but the point is that some drop off is allowed as long as it's in negative inclination (essentially camber), which is contrary to the data I've seen up until now and what I've been telling everyone as a result.

Can someone pass the salt? My foot tastes a little bland

Another thing to watch out for when looking at curves, especially if there's any drop off at all, is the axis system it was measured in. If the data is in the tire plane then normally things will be flat after the peak as long as the negative camber isn't up there too high. If it's measured in the vehicle plane then of course there will be a drop off right down to 0 force @ 90 degrees. Just another thing to watch out for...

Something else that was pointed out was that in their business (racing) they aren't interested in what happens after the peak, so when they fit their model to the data they don't care if the modelled force plummets into the abyss afterwards or varies considerably from the measured data. They are only interested in getting a good match below and up to the peak. If the mathmatical formulation that gives the best fit to that winds up causing the force to drop, rise, drop, rise, then shoot off to the moon in either positive or negative direction after the peak, that's perfectly fine with them.

We can't have that luxury in the simulator business though of course since it needs to operate well everywhere

Last edited by jtw62074, Thu, 5 Jul 2007 23:23.

Quote from BuddhaBing :

http://i11.tinypic.com/4l96wyh.jpg
http://i15.tinypic.com/4u2oyzm.jpg
http://i8.tinypic.com/52naku9.jpg
http://i14.tinypic.com/6bu2iyt.jpg

Both data sets were produced at the Calspan Tire Research Facility." - Kasprzak, pp79

Calspan has a flat belt tester. I'm not sure if they have a drum tester (why bother drum testing when you have a belt?) so this might be proper data after all. Looks like I might need to eat my foot here

Here's a good one that goes out quite a bit past the peaks. It's very flat and you can see how much noise is generated (2-3% variation maybe?) http://www.edccorp.com/pdfs/WP2001-4.pdf

Here's one with some F1 tire data. This is even rather flat in slip ratio too: http://www.ee.ic.ac.uk/CAP/Reports/2003/norm_tyr.pdf

Last edited by jtw62074, Wed, 4 Jul 2007 08:01.

Quote from yoyoML :

With 84 parameters I wonder if can still be called Pacejka... You should be able to pick some generic functions to fit all the variables.

It's still a Pacejka model because he either wrote it, or it is an expansion of one of his previous models

Quote :

I like the "physical" approach, too. With all those 84 parameters I don't think they can even model a flatspot, but with LFS's approach it is done quite well. And to model a different tyre you don't need loads of raw data and fit that again, but adjust some easily measurable parameters to get approximate results. This is probably the best way to model a variety of cars at the same time.

My thoughts exactly.

Quote from BuddhaBing :

Here's a screengrab of the GTR2 Michelin M3 GTR tyre file in Dave Purdy's Physics Editor. http://i17.tinypic.com/5ybsgh3.jpg The y-axis is lateral force (normalized to a peak value of 1.0), the x-axis is slip angle (measured in steps where each step is 0.009 radians). The max value along the x-axis is 236 steps which corresponds to 2.124 radians or 121.7°. The peak normalized lateral force occurs at step 11 which corresponds to a slip angle of 0.099 radians or 5.7°. At a slip angle of 45° (0.785 radians, step 87) the normalized lateral force is 92.8% of the peak.

That's the default tire and not a modded one? I don't have rFactor installed right now so can't check it, but this was over at rsc and it seemed to me this was indeed one of the default ones. Perhaps the GTR2 tires are more relaxed.

0.000000 0.174836 0.349483 0.518060 0.668882 0.790665 0.878928 0.936783 0.971287 0.989751
0.997978 0.999999 0.999443 0.997887 0.995458 0.992353 0.988824 0.985156 0.981646 0.978577
0.976196 0.974695 0.974186 0.973741 0.972613 0.970820 0.968385 0.965342 0.961732 0.957600
0.952999 0.947981 0.942602 0.936919 0.930986 0.924856 0.918579 0.912202 0.905768 0.899315
0.892879 0.886489 0.880172 0.873950 0.867841 0.861861 0.856022 0.850333 0.844802 0.839432
0.834228 0.829189 0.824317 0.819610 0.815065 0.810680 0.806452 0.802376 0.798448 0.794663
0.791017 0.787505 0.784121 0.780861 0.777719 0.774691 0.771772 0.768957 0.766242 0.763623
0.761094 0.758652 0.756293 0.754013 0.751809 0.749677 0.747613 0.745615 0.743679 0.741803
0.739983 0.738218 0.736505 0.734840 0.733223 0.731651 0.730121 0.728633 0.727183 0.725771
0.724394 0.723052 0.721742 0.720464 0.719215 0.717995 0.716802 0.715636 0.714495 0.713377
0.712283 0.711211 0.710161 0.709130 0.708120 0.707128 0.706155 0.705199 0.704260 0.703337
0.702429 0.701537 0.700659 0.699796 0.698946 0.698109 0.697285 0.696473 0.695673 0.694885
0.694108 0.693341 0.692586 0.691840 0.691104 0.690379 0.689662 0.688955 0.688257 0.687568
0.686887 0.686214 0.685550 0.684894 0.684245 0.683605 0.682972 0.682346 0.681727 0.681116
0.680512 0.679914 0.679324 0.678740 0.678163 0.677592 0.677028 0.676471 0.675919 0.675374
0.674835 0.674303 0.673776 0.673255 0.672741 0.672232 0.671729 0.671232 0.670741 0.670256
0.669776 0.669303 0.668835 0.668372 0.667916 0.667465 0.667020 0.666580 0.666146 0.665718
0.665295 0.664878 0.664466 0.664060 0.663660 0.663265 0.662876 0.662493 0.662115 0.661743
0.661376 0.661015 0.660659 0.660309 0.659965 0.659627 0.659294 0.658966 0.658645 0.658329
0.658018 0.657714 0.657415 0.657121 0.656834 0.656552 0.656275 0.656005 0.655740 0.655481
0.655228 0.654980 0.654738 0.654502 0.654272 0.654048 0.653829 0.653616 0.653409 0.653208
0.653012 0.652823 0.652639 0.652461 0.652289 0.652123 0.651962 0.651807 0.651659 0.651516
0.651378 0.651247 0.651122 0.651002 0.650888 0.650780 0.650678 0.650582 0.650491 0.650407
0.650328 0.650255 0.650187 0.650126 0.650070 0.650020 0.650000

Interesting points on the curve:

5.6 deg -> 1
15.66 deg -> .953
20 deg -> 0.905
37 deg -> 0.806

So before it even hits 45 degrees it's lost 20% of its grip already. On one real tire there was a 2-3% drop at 35 degrees (most likely within the noise threshold anyway, so I'd deem it insignificant. The transients can likely vary by more than that as pressure/temperature change during the corner), which would put this rFactor one at over 10 times the drop rate you'd get in reality. Yikes... This is what I mean by a cliff.

I know 5% drop at 15 deg doesn't really sound like much, but it's pretty noticeable in countersteering. If you had the wheel straight and all 4 tires at 15 degrees in a slide, say you had a 20:1 steering ratio, you'd more or less have to steer the wheels to a 3 degree slip angle in order to begin slowing the rotation of the car down at all. That's a 12 degree change at the front slip angles (240 degrees opposite lock! Heaven forbid you were steering into the corner at the time) in order to even begin recovering from the spin. If you steer any less than this the car's spin would just accelerate up to 5% rather than stay at a more constant yaw velocity like you'd get with flat curves. There's no room at all to do some mild countersteering when you overcook it just a touch like you'd do in a real car.

Quote :

Incidentally, for a bit of fun I tried using Niels' C6 Corvette tyre files with the M3 GTR in GTR2. It was sliding all over the track - lots of fun!

I saw videos, but haven't tried it. It does look like good fun indeed

Last edited by jtw62074, Wed, 4 Jul 2007 07:42.

Very interesting data there. Do you have a link to his thesis? I haven't seen it yet.

I've seen curves that drop off like this too for car tires, but only when the measurements are done on a drum tester. Once you put it on a flat belt or mobile tester (running on a real road) the curves flatten out in anything I've ever seen within 2-3%, which is pretty much within the range of noise you get throughout each revolution of the tire. Can you verify what machine it was tested on? We don't know if the loads/pressures involved are within the design operating range (talking about figure 12, not the others; maybe you can check on those?) If you pumped it up to double or triple the tire pressure and overloaded it, who knows what might happen?

The FSAE tire test consortium data is from a flat belt tester, so if you find a big drop off there then I'll have to conceed that I didn't know as much as I thought I did. They didn't run them to super high slip angles though, but at the low loads where the tires saturate at just a few degrees of slip angle, the curves are pancake flat. Edward showed rather cool videos of this. The deflections involved are stunning.

EDIT: http://www.millikenresearch.com/TTC_SAE_paper.pdf (See figure 4. No drop at all and there's quite a bit of noise.)

Doug will hopefully take a look at this thread. Maybe he'll have something to say to set one or both of us straight.

One thing to keep in mind with that figure 12 one is that spin can effect the lateral force considerably. In the bottom curve the cyan line has a very visible loop. As slip angle is being increased at a constant rate, the force goes up quite a bit in comparison to what you get when they return the slip angle down toward zero. Still though, the average through the two does indeed show a slight drop. Next up is to find if it was done on a drum or a flat belt. I'd bet it's a drum test...

Last edited by jtw62074, Wed, 4 Jul 2007 07:32.

Quote from Bob Smith :

The Pacejka is outdated now, the most modern sims use a better model.

Pacejka is a magic formula, it has nothing actually to do with tyres (from a physics point af view) but the numbers it produces are very good, given good input data. Note this input data is a bunch of random numbers that makeo the model match a tyre, they are not measurements of the tyre.

More modern sims use a physically based model where the parameters of the tyre are used to model a tyre. Sounds logical but in practise is harder.

I wouldn't say Pacejka's Magic models are outdated, really, although the tendency for sim developers "recently" has appeared to be shifting toward doing physically based ones (brush, string, etc..) If a Pacejka's Magic model does the job well enough then it doesn't really get any more outdated than F=MA. One of the F1 teams this year is using an 84 parameter Pacejka model. If you have the resources to do really extensive tire testing then it's really the way to go, although the Radt/Milliken non-dimensional model is rather choice too and expands on it.

For sim developers it's much nicer (imo) to use a physically based model given the lack of really complete sets of tire data they have access too. They're easier to work with and tend to spit out curves all on their own that are quite reasonable without having lots of crazy coefficients to deal with. It's more of a personal preference thing though, I suppose. I just like the idea of having the tire literally being simulated at the physical component level rather than having a curve fitting function, although they both can produce the same results. In the end, the curves are all that matter as Shotglass pointed out.

Quote from Shotglass :

so we agree after all
i was a little put off by this



which like i said isnt entirely true due to the flat

the thing with the usual isi curves is that the more you swing out the back the harder it becomes to catch it which wasnt the case in lfs
so like you said while for racing on the limit lfs was quite wrong for drifting it was more or less as correct as it is now (discounting the short transit phase which you spent little time in anyway and actually makes entering the slide easier) which explains the popularity or rather the absence of any drifters in any other sim

btw after i saw androids curves back when he first posted them i ran one of these uncatchable slides which were all too common back in p/q through one of the raf analyzers and as expected the car was sliding at ~12°

I see what you mean and agree. My point was more that the LFS curves had quite a drop to them too back in the day, although yes, they flattened out at some point like you said so were not identical to rFactor/etc.. We're in agreement I think

Countersteering worked as long as you did a lot of it, of course. What I mean is using just a little bit when you've got the rear past the peaks. Once your front tires are on the right side of the peak and you countersteer only a few degrees, the force climbs upwards through some slip angle range, accelerating the spin. I remember this happening in LFS too at that time and the curves you just posted show why rather clearly. In order to correct by countersteering, you had to countersteer far enough to lower the force below what the rear tires are putting out, which is the same as you get in any sim with curves that drop off even a little bit. So once the back starts to go out a little, you need a large, very quick correction to get the car rotating back towards straightening up. Then you need to feed in the steering again very quickly as the rear tires gain grip on their way "back down" to the peak which can shoot you into a spin in the opposite direction. There's no slow, easy, back and forth steering action going on as you balance the car on the limit in harmony with the throttle. It's sort of all or nothing, and it doesn't take much of a drop off to make this happen.

Tires in the wet do this (the spinning pickup truck story), but car tires in the dry don't as you know.

Last edited by jtw62074, Mon, 2 Jul 2007 01:32.

Quote from BuddhaBing :

At the end of the day, the initial curves might not be particularly meaningful. For example, as a test, I tried setting one of the slip angle vs lateral force curves to a flat line at 1.00, leaving the other tyre parameters the same; the in-game results were not significantly different than using the original unmodified tyre file. I think parameters like LatPeak, LoadSens, DryLatLong and DropoffFunction are much more important in determining the actual values used by the game than the raw data in the curve table itself.

I've done this too with rFactor and found very different results. This is totally subjective of course, but if you flatten out the curves, suddenly you can countersteer a little bit and it actually slows the rotation of the car down rather than speeding it up. To me this is all the difference in the world. My favorite non-LFS car to drive at the moment is the red Pantera in GTL. However, once I get off my own sim or LFS, I have to retrain myself to stop trying to correct a spin with a mild countersteering input because it only makes things worse. I steer into the spin to correct a slide. Again, everything is just peachy as long as I don't get too happy with the rear end

However, below or on the limit of course it would not make a difference. If you're a perfect driver you could do whatever you wanted to the curves after the peak and not notice a change since you won't operate in that area anyway. Then yes, the other parameters you pointed out completely dominate. The folks that don't particularly like ISI sims routinely complain of the "steering into the spin to correct a slide" (caused by force curves dropping off, even just a few % is enough), as well as it just being generally too difficult to catch a slide any other way. Again, the very same curves are very largely to blame for this, in my opinion.

LFS used to be the same way if you've been around it long enough to remember. There was a major tire update and the force curves were flattened out. People then immediately complained that it was too easy, but after a bit of time that quieted down and they began to notice that a lot of the unpredictable behavior was now gone. Countersteering worked, if you spun out you knew why, etc..

Quote from BuddhaBing :

Ask Pacejka. Better still, ask your colleagues Kasprzak, Milliken, Radt et al why their normalized slip angle vs lateral force curves show a drop below 90% of peak even at low slip angles as shown in this graph from the paper you cited earlier: http://i8.tinypic.com/6frvejn.jpg. Here's the link to the paper again: http://does.eng.buffalo.edu/pu ... ons/Kasprzak.SAE.2006.pdf. The issue is also discussed by Radt in some detail in chapter 14 of Milliken and Milliken and includes similar curves that also display significant drop offs below peak even at low slip angles.

I don't see how you can on the one hand criticize the slip curves in rFactor/GTR2/etc as being nonsensical for showing drop off yet on the other hand point to research which shows slip curves with similar drop offs without criticizing it too.

Support for drop off in lateral slip needs to be in the model to allow for wet conditions where generally there is quite a drop off after the peak. Very much like the rFactor/GTR2/etc curves. (Dr. Radt passed away, btw.) EDIT: Also, truck tires and so on need it.

The data posted for the truck tire was an example of drop off observed in dry conditions. This is common to see in truck tires, but I've been told several times that this is just not observed with car tires in the lateral direction by Doug and have never seen it happen myself. He was on rec.autos.simulators telling us all this back in 2002 or so, actually. Longitudinal, yes, there's often times a significant drop, and often times not.

I'm not trying to bash rFactor/GTR2/etc.. They're quite good up to the peak, so as long as you're driving on the edge and not going over it. I have rFactor and GTL and enjoy both. The original GTR press demo really blew me away and I couldn't get enough of it (the sound, oh dear God the sound!). However, it's a different animal once you go over the limit from my own sim, LFS, and Dr. Veble's model for Racing Legends. There's nothing really all that inherently wrong with the tire model I think, but they're continually giving it shoddy data at best after the peak.

In regards to my comment about 120 and 60 degree slip angles, the answer is they should be the same. The curve ought to mirror itself once you cross the 90 degree point. 170 degree slip angle is the same as -10, right?

Anyway, I assume there's some lateral scaling in slip angle with load there so they probably need the extra space in some situations, and it's pretty unlikely they ever come up with 110 deg slip angle instead of -80, so it really makes no difference either way. That comment wasn't meant to be taken too seriously. It was more of a test to see if anyone would give it some thought and provide an answer

Last edited by jtw62074, Mon, 2 Jul 2007 22:05.

Absolutely

Quote from tristancliffe :

I'm back!!!!!!

Wow, that was amazing really... Lots of hard work, lots of waiting around, lots of dampness, and a smidgen of track time...

As previously mentioned, qualifying was wet. And I mean WET! With a car in front of you it was difficult to see anything other than their rain light, let along braking points or people behind you in the mirrors... But out of about 36 people on track for qualifying, about half spun at some point, and I wasn't one of them. Admittedly I was 11 seconds off the 'pace' but for a first time at the circuit in that car, the first wet track session ever (other than a bit of drizzle in a kart once), and being a bit scared of crashing I think I did okay... A few bit moments, either out of Camp (I wanted full throttle, but the rears didn't), or braking for Quarry (big fishtail, somehow kept it on the track and then whilst running wide had a Formula Ford spin inside me in slow motion...).

I was about half way down the list of qualifiers, but once the classes were split up again it left me 12th out of 14th on the grid - the only novice (i.e. person with less than 6 races) on the grid.

By race time it was dry, so we put the (very old) slicks on, and off I tootled to the grid. The formation lap was very slow, with a bit of pushing and shoving so I didn't weave much or spend time getting heat into brakes - I was too busy making sure I didn't run into someone or do something unpredictable. Formed back up on the grid. Waited for 1 light, 2 lights... 5 lights, GO! Nearly stalled, but a quick whack of the clutch brought the revs up and converted stall into wheelspin. Didn't lose a place at the start, and didn't want to be stupid into T1 so kept back a bit. To start with the two people behind me gave a bit of pressure, but within a lap or two I was pulling away, and going faster each lap!!!!!! At one point I left my braking (I brake like a pansy at the moment) too late, and had to unintentionally trail brake into a chicane, which was scary and exciting at the same time, and showed how good F3 brakes really are. At no point did the car step out of line, despite me braking later and later, getting on the power earlier and earlier (often before the apex towards the end), and carrying more speed through the corner.

My best lap was just three seconds shy of the winners (and he is VERY quick, with a much newer cars, and slicks that aren't 19 years old). I finished 51 seconds behind the winner - over 10 laps (our race was shortened for some reason, and I'm cross about it) that's 5 seconds per lap - sounds a lot, but trust me it's not for a novice!!

Martin, my Dad, reckons if I hadn't been such a girl for the first two laps I'd have caught (and maybe passed!) at least two cars... I finished 10th in the end, only because two cars ahead retired...

I loved it. I want to do it again!

But I have to go and do some work, so I can't talk about it any more. Photos are still on Andrew's camera. The camcorder trackside footage was a bit crap. The onboard camera didn't work - I've got 7 seconds of footage of me in the paddock checking the camera works, but none of the car driving. Bugger!

I'll do a write up on my website after work, and put as many photos online that I can, as well as my datalogging (I got all of qualifying, but forgot to turn it on until half way round the first lap of the race - there's a lot to think about when it's all new)...

To quietus, karl, chris and callous hooper - thanks for coming, thanks for finding me and I hope you liked what you managed to see...

A bit late on this post. Just wanted to say:

:bowdown:

I'm rather jealous