Dave, yep, your 2 point sum it up mostly. The hard bit is to find out why it happens and what is causing it. I used to have some confidence in assessing the problem but really nowadays I must confess I'm just guessing..

I also find that braking is difficult as locked tyres (infinite slip ratio!) don't make braking that much worse, although I would mostly like to HEAR that better. I guess much of the curves dropping at higher slip ratios might be due to the effect of quickly heating rubber.. When you bench the tyre it will heat up of course.

I saw the LFS tyre grip vs temp curves that I think AndroidXP made? It seemed that even road tyres have a 'peak' optimum temperature whereas I heard (I don't know, I just heard) that most tyres have a pretty 'flat' grip vs temp curve, until you're really really heating them. I don't know how LFS does tyre heat. Obviously braking a long distance with locked tyres produces a 'hot spot', and if tyre outer surface temperature changes quickly, the moment that slip occurs, the effects of a temperature/grip curve that is peaky, would make the tyre have less grip almost from the moment it starts slipping and thus heating. GPL had this program that made tyre temperatures visible and the rubber temperature changed pretty quickly. If a similar thing happens in LFS, then a more realistic (again, if what I heard is correct!) 'flat' grip vs temperature curve would probably improve handling.

What I don't quite understand is how LFS, when sliding, is so often oversteer. Over the limit of grip is fine, but why does that tend to be oversteer? I'm clueless as to why this happens. I'm setting up the cars with at least the springs based on weight distribution; but often a slightly stiffer front. Rollbars on the front are at least 2x more than at the rear and I don't think I'm doing extreme things with dampers. I often set them based on the springs so I get nice and even damping when dropping the car. I tend to run LSDs in LFS with about 20..40% power lock and often more than that (50+) coast lock. Springs are fairly soft and ride height is not very low. I can't blame the car setup for the easy oversteer as weight transfer is on the slow side and the parameters are between understeer and neutral.

What is also weird, although probably just a 'threshold' setting, is that at speed x, you take a turn, and at speed x + tiny bit, you leave skidmarks yet the supposed increase of friction doesn't really seem to show up; the car tends to keep its speed. I really do not understand the complexities of a physics model. But a tyre leaving skidmarks, i.e. operating at too high slip, would indicate to me that it has a relatively large amount of force NOT in the rolling direction. In LFS it seems that, even beyond optimal slip, the cars cary too much speed instead of loosing speed due to a lot of force NOT being in the driving direction.. I might be talking out of my bottom but its tricky to put it into words!

Quote from DaveWS :

Could this be a setup issue, perhaps if you try moving to brake bias more to the front wheels?

I understand that. But I mean in general, so with all cars and all different setups. I think the issue is maybe the tyres having to much grip with more weight on them or either (more likely to me) too little grip when having less weight on them.

I definately feel this is a huge difference between driving in real life and in LFS. But I have never seen anyone mention it before.

This oversteering in LFS, I don't know if it is still but in older versions if you used LFS tweak to create lot of torque rear of rwd car did loose lot of grip, it felt like torque would remove lateral grip from tires too much, now of course this could mean issue with longitude grip, but I think it has some more into it and my brain is not enough to understand all of it

Yeah, engine braking is pretty evil in LFS. Make a neutral FZ50 set, corner with the clutch in and it's stable. Let the clutch up and it swaps ends.

Niels - don't forget that front/rear tyre pressures effect grip balance as much, if not more so, than spring and arb settings. It made a huge difference back in patch P but was toned done a lot for patch S. i.e. the tyres are more pressure sensitive than load sensitive

Also locked wheels is -100% slip ratio, not infinite. -200% would be the wheels spinning backwards at the same speed you're travelling forwards - rather than twice infinity .

I think that rubber laid to surface is not modeled yet? that might have some influence to grip too as part of contact patch is having rubber/rubber contact instead of rubber/tarmac, surely that is not huge area, but perhaps 10%? I really can only guess

Quote from axus :

Another big thing is the combination of lateral and longitudinal forces. Ie, if your slip ratio is 0.4 and your slip angle is 20deg, the lateral force isn't the same with slip ratio of 0 and slip angle of 20deg. This is something you can't tweak in ISI sims either (to my knowledge). Its important for how snappy the rear is for instance, with oversteer. Most ISI sims tend to do a pretty piss poor job of it, I find, with the whole grip, grip, grip... no grip at all. There's no progression, its way too snappy. LFS is pretty good there, I think.

Yeah it's almost as if LFS and ISI sims are total opposites (no I don't mean that one is crap... well :razz. ISI like you say is too snappy. The transition between grip and no grip is almost instant. In LFS the exact opposite occurs, everything seems too calm at the limit.

(Yes I know it's a sim, and that it's going to be less frantic than real life, but just looking at some real life videos...)

Quote from MillerM :

I understand that. But I mean in general, so with all cars and all different setups. I think the issue is maybe the tyres having to much grip with more weight on them or either (more likely to me) too little grip when having less weight on them.

I definately feel this is a huge difference between driving in real life and in LFS. But I have never seen anyone mention it before.

Don't forget IRL people are blipping the throttle as they change down (on a racetrack at least), so the rear tyres don't lock up. Have you tried auto blip on?

Quote from Niels Heusinkveld :

...

Yes I too find that all cars in LFS seem to be very oversteery for what you would expect the setups to be like.

The problem is that it's all good and well finding out these "problems", but it's darn annoying not knowing why or how.

Edit: Please try multi-quoting posts - Bob

Quote from DaveWS :

Yeah it's almost as if LFS and ISI sims are total opposites (no I don't mean that one is crap... well :razz. ISI like you say is too snappy. The transition between grip and no grip is almost instant. In LFS the exact opposite occurs, everything seems too calm at the limit.

(Yes I know it's a sim, and that it's going to be less frantic than real life, but just looking at some real life videos...)

That is what I'm thinking too and reason why I try to get rfactor's engine to bend to half way

I think I did not post video from one of my tests, far from what I seek, but far from stock ISI. Something over 200hp in that car with welded diff.

But one big thing is how wheel is set, real car wheel turns much more than 720 degrees, 2,5 turns is really fast, normal is between 3-4 turns and it does make feeling totally different if you use 900 degrees or 720 already, grip feels very different, over easy becomes challenging etc.

Quote from Bob Smith :

Also locked wheels is -100% slip ratio, not infinite. -200% would be the wheels spinning backwards at the same speed you're travelling forwards - rather than twice infinity .

Are you sure about that? I thought that -100% slip ratio would be if you were travelling at 60 mph, and the tyres were travelling at the equivalent of 30 mph? Like if you were going 30 mph and the tyres were going 60 mph? I have a feeling I may be wrong here though.

Quote from JTbo :

think I did not post video from one of my tests, far from what I seek, but far from stock ISI. Something over 200hp in that car with welded diff

Just watched the video. Wow that actually looks like very convincing handling in an ISI sim - You can actually drift!! The suspension looks far too soft though IMO. But you may become the creator of the best ISI mod ever!!

Edit: Sorry Bob about the posting. I thought multiquoting was for one post only. Oh well wrong again. Jesus I can be an idiot sometimes.

I'm not talking about any shifts. Just when braking in gear or even when releasing throttle the rear wheels become way to loose in general.

Quote from DaveWS :

Just watched the video. Wow that actually looks like very convincing handling in an ISI sim - You can actually drift!! The suspension looks far too soft though IMO. But you may become the creator of the best ISI mod ever!!

Thx from comments, but I don't think that I will ever be best, just maybe I can make something new as I don't have narrow view which sim is right which wrong, all of them are wrong at some places, but that is rather irrelevant when making mod, you just try to create best that is possible.

But that I have got even this far with these tires is all thanks to Dave Purdy as my tires are very much based to his work and help.

Car has really soft suspension really, front spring are rated to around 26kN/m that is something like 180lbf/in, however I have not yet started to check and adjust suspension to final level as need to learn this tire stuff first and maybe then. Have been working with this only a year, it was meant to be ready for Christmas, but I have been lazy

I have other car, that has real world counterpart (Actually there is many), same model and so, but less power and same mods/spec as real world counterpart has, it is used for drift learning in reallife and friend who drives this real drift car is testing that for me, should come up nicely.

Anyway I think that there is perhaps possibility to learn and perhaps help LFS to evolve too with these projects, I really would like to be making this car to LFS, but we must look that in future

Quote from DaveWS :

Best explanation yet IMO: http://insideracingtechnology.com/tirebkexerpt2.htm

I had dinner with the author of that book, Paul Haney, and Doug Milliken not too long ago, and Mr. Haney attended our tire presentation at the Motorsports Engineering Conference at the beginning of December (granted, this was just on our RC tire research, somewhat intended as comic relief in comparison to some of the other things going on ). Not everything in the book, including what is on that page, is entirely correct, however. Even Caroll Smith got graphs like this wrong in his "... To Win" series. (Tangent: One of the things that came up was how one might go about modelling loose surfaces for rallying and the like. Just having to do games, I got off easy with my reply )

In another post I commented :

Quote :

"Some curves you see in books or online under tractive, positive slip ratio (acceleration rather than braking) show a curve that climbs up to a peak, then suddenly and very quickly swoops down to 60-70% of the peak value and flattens out. You'll see something similar in some sims and folks will emphatically insist that that's how the tires really work. They don't. Real curves look a lot more like the LFS ones than some of these other ones floating around."

Figure 6.7 from the link above is exactly the one I had in mind when writing the above. A quick search didn't turn up that graph, so I didn't include a link to a copy of it. Anyway, I haven't seen a real force curve that looks remotely like that, ever, in any direction. Both curves there are artist's renditions rather than actual data and are the same ones shown in many vehicle dynamics texts aside from Mr. Haney's (a lot of these graphs come from old papers and you see the same ones reprinted with author's permission in all the books). The braking curves are much closer to reality (I've posted real (yet very old) data here on braking curves), but the tractive one is nonsense, at least compared to anything I've seen.

i almost made a thread on this stuff. Well hey i just wanted to let you know, Forza 3 had a new revolutionary engine for the tire physics in one of the press conferences they said how they managed to do it, basically what it implies is that when a car at any velocity makes a turn the center of gravity shifts, but knowing physics you understand before i even tell what happens, as you begin to turn (as in a circle you turn but you move straight) therefore the weight of the car is pushed forward even when you turn creating the long displacement, but the interesting thing is what happens to the tire, since the weight is shifting the outside tire wall is pushed in and the tire "thins" where it makes contact with the floor, while the side of the car facing the inside of the turn experience little force and loose some traction.


Just adding some info since i know you guys where working on that (main page). As there are infinite mechanics on how this works maybe you could have missed something idk, hope it helps.

thanks for bumping it...i just voted for his anyways