Road normals and normal realistic road car setup, wheel set to 900 degrees, tire pressures same as those would be IRL and it is much more like what many have experienced with super tires and weird setups etc.

Of course there is always room for improvement and luckily we do have developer that is always working towards better model and removes oddities as they are pinpointed and found what is causing problem and what will be the fix.

Bit more sharpness sure is what some cars could use, but in it's current state surely gives best illusion of driving a car and not moving some photo realistic 3d model in game.

High speed stability is too good, imo, probably because of aerodynamics not being complete, also tire stuff that Scawen did mention too, I think quite lot of exploits might be solved when he does find and fixes what causes tires to forgive so much, maybe something like that.

But still only sim where I get feeling of driving a car and not moving 3d model with wheel and pedals, for some reason that is how it is why for me LFS is better than else and why I drive it most, even I play with others those never seem to give similar enjoyment of driving and not that thrill of trying to get corners always better as it is me that limits, not how game transforms my inputs to movement of 3d model.

Personaly I felt LFS was very close to reality when I was driving my little truck around on its not so sporty tires. Then I picked up a miata and my opinion changed some what. The tires and the way the react to the ground in LFS is still better then I have found in any other sim but is still not right. I have mentioned it in other threads and I thing the issue is that there is more overall grip then we have in reality but the tires overall regidity is too low. The best way I can describe this is that they feel more like they are zero pressure tires bolted to the rims then presurised tires held on to the rim. That is ofcourse also only part of the issue.

Running an autocross in my miata and doing the same in the XRG which is the cloest thing to the miata feel completely different even with nearly identicle setups. The tires are where this difference is. The way they load and unload through the solom feels weak, they seem to lack some springy-ness and they don't feel as if their grip is affected by loading in the least.

Quote from ENS Wiseman(USNJROTC) :

This game is also the only true simulation racing game available. The difference between LFS and all other games is that, it isn't actually a game. There is no final Objective to work to, No strict storyline, No "players" or characters. this all gives the player a full control over what he can and can't do. There's no game I know of like this and it gives us all the extra edge

I second that, and I think that's the real reason.

Quote from Gimpster :

Personaly I felt LFS was very close to reality when I was driving my little truck around on its not so sporty tires. Then I picked up a miata and my opinion changed some what. The tires and the way the react to the ground in LFS is still better then I have found in any other sim but is still not right. I have mentioned it in other threads and I thing the issue is that there is more overall grip then we have in reality but the tires overall regidity is too low. The best way I can describe this is that they feel more like they are zero pressure tires bolted to the rims then presurised tires held on to the rim. That is ofcourse also only part of the issue.

Running an autocross in my miata and doing the same in the XRG which is the cloest thing to the miata feel completely different even with nearly identicle setups. The tires are where this difference is. The way they load and unload through the solom feels weak, they seem to lack some springy-ness and they don't feel as if their grip is affected by loading in the least.

Something like that, as g-forces seem to be rather ok, it is not grip but modifiers of grip, something that only man himself is able to know and adjust

I'm waiting what will be next physic changes as there is going to be some good changes to tires I believe.

Quote from Ball Bearing Turbo :

Do you mean in a relatively straight line or during a turn - and what phase of a turn, and how loaded is the car laterally?

During a turn, fairly heavy lateral load.

Quote :

I understand what you're saying but I've only had that happen under very specific circumstances in a real car - VERY heavy throttle while cornering nowhere even close to the limit of the car.

I find these circumstances to be quite easy to replicate in a real car, and have done it in my car many times, trying to train myself NOT to let off the gas too quickly, specifically to prevent this from happening. In fact, you see it quite often, even on shows like Top Gear, Dream Car Garage, etc. A car is coming through the turn and the rear tires are spinning (just a bit, not burning them off drift-style). The car either gains momentum or the driver lets off the throttle and the tires quickly regain their grip. When this happens, the rear of the car snaps back into line. Depending on the circumstances, the car could snap past straight and continue in the opposite direction that it was in. If you watch shows like Fifth Gear (the ep with Jason Plato in the Shelby GT-500 comes to mind) you'll see this happen. The car has it's tail out going around the corner, then it comes back, giving those lovely S-shaped skid marks at the exit of the corner.

This rarely happens in LFS. Traction is regained more gradually and the rear end never snaps back. It almost never snaps back quickly or violently, even if you clutch in while the tires are spinning (which should cause grip to be regained almost instantly).

Quote from Cue-Ball :

During a turn, fairly heavy lateral load.
....
giving those lovely S-shaped skid marks at the exit of the corner.

Well, which one is it?

The "exit" of a corner is like the situation I've described and experienced myself whereas I cannot say I've had a car do that "during" a corner (the latter would be supernatural because what you're referring to as "regaining grip" would not move a car against the fake centrifugal force it's under during a corner).

In my ignorance of being only a "sim-racer" (and not real racer) and not graduated into mathematical or engineerings degrees, i think that the "unrealistically curbs" are caused by 2 things:

- suspension damage
It is modelled into lfs, but still susps can take much more damage it should take into real life.

I remember and interview to Ron Dennis where he said that Ferrari needed to build a Tank for Raikkonen because he never drives for "saving" the car.
Now, i have never seen Raikkonen smashing jumping into curbs or things like this, so probably suspensions in real life are much less "damage forgiving" then in LFS, and that costrict drivers to take care of their cars and dont risk of break them around, because one curb taken bad could cost them many moneys.


- material used for building the curbs
from what i know (readed on books, newspapers, net, etc, never raced on real track), curbs are usually builded with the material called in Italian "cemento" or "calcestruzzo".
Finding these terms on google it says that should be translated into "concrete" or "piling" (i hope these are correct).
This material has much different grip then asfalt (u can feel it when u walk on a surface done with this material too), and is that difference in grip value that cause problems in real life if you try to brake with half wheels on asfalt and half on curb.
Instead, i feel that in LFS curbs are made of asfalt, so, whatever height or dimension they have, they have the same grip of a normal LFS flat track, and that thing, added to high capability of lfs cars of sustain suspension damages, allow racers to use curbs pratically as the rest of the asfalt track.


If we add to these the fact that LFS does not simulate the differences between more used traiectories of the track (with more rubber, so more grip on it) and less used/more dirty trajectories, and that LFS tyres does not suffer of real life flatspotting effects (like unregular susps frequencies/vibrations, less grip for the rest of tyre life and not related only to overheating, etc...) which can be encountered during braking (so during braking on curbs too) we have said it all.

Imho obviously =)


I hope devs will fix these problems soon.

"fix these problems"...nah Improve what is already very very good.

funny LFS is light years better than almost any sim it is ridiculous.
When comparing my own car (US spec s14 Nissan)
the XRG drive a lot like it, when i set up the suspension the same...the lack of G force in SIM is where the big difference is.
I feel the Nissan's tyres claw and grip and then start to go..
where the XRG just starts to slide (thanks for the audible warnings and FFB) I can drive it liek this.
There is a slight disconnect in loading the tires, but it is better than any other sim for sure, and it is so simliar to my Nissan it is ridiculous. I set up a copy of the auto cross i did locally, and when we did it again, i shave 4 tenths off my time! Huge!
is it track familiarity or car predicatability or a good sim givining me all the clues for my real car?

Quote from GT Touring :

I set up a copy of the auto cross i did locally, and when we did it again, i shave 4 tenths off my time! Huge!
is it track familiarity or car predicatability or a good sim givining me all the clues for my real car?

All of the above

Quote from Ball Bearing Turbo :

Well, which one is it?

Sorry. I was under the impression that the exit of a corner still counted as part of the corner.

Quote from Cue-Ball :

Sorry. I was under the impression that the exit of a corner still counted as part of the corner.

:doh:

My anal semantics finally bite me in the ass, although I guess visually this is questionable, since many refer post-apex as "exit", which is still an area that the car would be trying to change direction as opposed to straightening out, or lining up for a connected turn.

Nonetheless, I think you understand what I attempted to say - which is that you wanted to cease turning, not continue turning.

Quote from Ball Bearing Turbo :

Perfectly said. I cringe when I see cars flying over chicanes on two wheels. You might get away with that once or twice, but it should beat the crap out of the car far more than it does right now.

As for the BF1 flight; it has nothing to do with car handling, and everyone knows the collision model hasn't been done, ever. The oversteer video is a combination of silly hand movement speed (somehow I doubt that was done with a comparable amount of wheel rotation, unless he has bionic arms) and poor downforce modelling under yaw.

It may have more to do with the way lat/long grip is combined then, since the faulty longitudinal slip alone probably wouldn't be a problem. Slow motion tire footage from drag races shows considerable longitudinal slip before the tire loses any bite, and in fact it's necessary for a proper launch. LFSs problem seems to be with extreme situations. I doubt the longitudinal behaviour alone is responsible since the amount of slip we're talking about is pretty minimal whilt turning with a locked diff - in which case probably no longitudinal grip should be lost, so possibly the way it's combined is still to blame? (waits for Todd to give a dissertation)

[Takes podium]

I haven't run the FWD cars in LFS very much until quite recently thanks to STCC forcing me to in the quest for virtual stardom. (Becky and Tristan, you guys rock!)

I definitely see what you're talking about now with on-throttle oversteer increasing as you increase differential locking, and getting really quite extreme with the locked diff. With the curiousity piqued I decided to try an FWD in my system to see how it reacted.

The car is not the same as anything in LFS of course and I removed camber effects in order to eliminate camber changes as a variable. The test car was 3280 lb with a bit under 450HP at the wheels. It is pretty stiffly sprung and slung very low with a CG height of only about 15 inches, so weight transfer effects are lower than in most race cars, probably. The weight distribution is 51.9% front and 48.1% rear. Again, this may be very far off from the LFS cars. I don't recall off hand what they are like, but it seemed they were much more front heavy than this.

My anti-rollbars were 300lb/inch front and 100lb/inch rear. The LFS cars IIRC have the split biased toward the rear. I'm not sure if that effected the results much. I wouldn't expect it to, but without testing that I can't say definitively. Front spring rates were a bit higher than the rear too.

I tried two sets of tires, both with rather high cornering stiffness. The first set had grip comparable to a performance street tire at about 1g, but with quite a bit higher cornering stiffness (peak force slip angle was around 6-7 degrees). Something along the lines of some really low profile tires. The second set was a nice set of racing slicks that pull about 1.4-1.5g and peak at around 8-9 degrees. These are pretty typical of road racing slicks in many series.

The basic results were largely the same with both sets. With an open diff plus 150 lb-ft of preload (so not totally open) laying in to the throttle even a little bit in a corner just spins up the inside wheel with both sets of tires, not surprisingly. Cranking the preload up to 1500 lb-ft improved turn in on light throttle a fair amount and acceleration out of the corners considerably. Completely locking the diff (15000 lb-ft preload) was similar to this (1500 lb-ft was nearly locked anyway).

Right. On to the infinite flat expanse of green background color for some skidpad-like testing

Here the car was driven at a constant speed of around 40-60mph or so and steered just to the point where the front tires had peaked (7-9 degrees depending on the tire). The understeer gradient, a numerical description of the SAE definition of the amount of understeer or oversteer, is shown on screen. Because of this the results were not subjective (based on my feel or impression) at all.

With both sets of tires, any amount of throttle increase at all caused the understeer gradient to climb. Even just a tiny increase in throttle resulted in this 100% of the time. As throttle increased further the understeer climbed right along with it. Flooring the throttle of course caused it to skyrocket as the front wheels spun.

The test was repeated by steering the front tires way past the peaks up to 20 degrees slip angle. Perhaps the tires pulling "forward" towards the inside of the turn might cause it to oversteer, right?

Nope. The results were the same. Any increase in throttle at all increased understeer.

It should be noted that as the CG is raised the effect would be even more pronounced. I suspect rather strongly that the front/rear weight distribution would not change this tendency at all.

In LFS, my guess is this is most likely a combined slip thing causing it. Regardless of the slip angle, any traction (throttle) increase should reduce the lateral force which would wind up with greater front slip angles, whether the diff is locked or not. The forward traction vector's lateral component does not make up the difference and cause oversteer or any decrease in understeer at all, at least not out to 20 degrees slip angle at the fronts which is twice as much steering as needed to maintain the circle.

Regarding the Formula cars at high slip angles being too easy to catch: I'm a data person of course so would prefer to see numbers, but if something is wrong here I strongly suspect it's due to a lack of variation in downforce with yaw rather than any slight problem with combined forces in the tire model (as this is improved, drifting has always become easier rather than harder in my experience). I.e., as you increase yaw angle the downforce can increase a little bit out to a few degrees slip angle (that's right, it can increase; That's one of the things those little vertical fins on the front wing do. I'm not sure about the rears though.) Going beyond some point likely causes a decrease in downforce which is probably missing, or not pronounced enough.


[Steps down from podium]

I don't think it's just due to the diff IMO (in LFS), it's the whole combination of the setup. Judging from your description, that's quite an understeery setup. FWD sets in LFS are often really weird in order to obtain this weird behaviour. With a sensible set like you used, I'm pretty sure FWDs in LFS behave properly.

I'm not sure how much difference it would make, but lightening the car and reducing the power, while very unlikely to change the direction of the results, would still make for a fairer test. The CoG height issue is interesting, the FWD cars in LFS all seem to have reasonably high CoGs, and narrow track widths, hence their willingness to roll.

Ok, here's my little dissertation on why combined slip might be responsible for what's happening with the front wheel drive cars.

http://performancesimulations.com/files/combined.JPG

Here we have three brilliantly illustrated pictures of a car travelling forward toward the top of the page. The car is in a left hand turn and we're looking at the forces and components thereof at the right front tire.

Picture A is cornering with some throttle. The black line is the traction force due to slip ratio which is pointing in the same direction the tire is pointing. Steered a bit to the left. The green line is the lateral force that's pointed in the same direction as the spin axis of the tire. The red line is the sum of both forces. I.e., the red force is identical to the black and green lines acting together as separate forces. (The grey lines at the tip of the red line are supposed to be parallel to the black and green lines, but I'm not coordinated enough to do that perfectly by eye Coders often make lousy artists )

Now, what we'll do is increase the throttle (traction force) while keeping the steering the same. Two things can happen depending on how the tire model handles combined slip. These are represented by pictures B and C which are supposed to have the same traction force and direction (black line)

In picture B the lateral force does not change when you increase the throttle. This is the most frequent screw up that new sim developers do and is often the main reason why when you get a new guy on the sim dev block there is just something wrong with the handling that you can't quite put your finger on. With front wheel drive it becomes much more obvious, but with rear wheel drive it's a bit more subtle.

With rear wheel drive you end up with handling such that subtle changes in throttle don't change the attitude of the car in the way you'd expect, if at all. Increasing throttle increases rear weight transfer and therefore lateral force at the same time, which causes a reduction in rear slip angles (the car tends to understeer when you're under the limit). This is because the lateral force is not being reduced as the traction force is increasing as it does in a real tire.

With this type of approach, the lateral force doesn't begin dropping until, and this is very important, the combined force (the red line) hits the edge of the friction circle. Then, one or both forces are modified in order to fit friction circle theory, which says that the red line can only be so long. So if you calculate the length of the black line by using slip ratio, then calculate the length of the green line by using slip angle, the resultant (the red line, the "combined force") can be too long.

There are at least three main ways to deal with this in a Pacejka type or other strictly empirical model (which I think LFS does not use, correct?). One of them is fairly complex and I'm not entirely sure how it works, but is quite good and gives proper results. The other two are the more obvious things to try and kept me up thinking many nights in the early days

One way is to let the longitudinal force stay right where it was and then scale back the lateral force in order to bring the combined force back inside the traction circle. There's a very serious drawback to this method though and many of the sims you've driven over the years worked precisely this way. If your slip ratio hits 0.1 or so, which might be the peak of the traction force, the lateral force completely disappears no matter what the slip angle is. Yikes..

Ok, let's rewind just a little bit to illustrate what this does to the handling of the car. Imagine you're in the turn (still RWD, I've gone off on a tangent here). You're nowhere near the limit of traction. You're well inside the friction circle. Now, you start increasing throttle slowly towards full. If your tire model is calculating the length of the green line (lateral force) strictly as a function of slip angle, it will not change length at all. The lateral force at the rear of the car stays the same in the absence of any rear weight transfer. With the weight transfer the lateral force increases and the slip angle reduces. I.e., as you begin feeding in the throttle you get more and more understeer.

At some point the combined force (the red line again) finally hits the traction circle and you rather suddenly begin scaling back the lateral force. Suddenly, you are getting oversteer and even a little bit more throttle might put the traction force right over the limit. The lateral force plummets to near 0 very quickly.

Sudden, uncontrollable, snap oversteer with no warning whatsoever. Sound familiar?

This is precisely to me how LFS felt until last April's patch (Q?) and is what I was going on about with the combined forces being way, way wrong. After that it was *drastically* improved and as a result the cars felt much easier to drive. And of course, many people cried "arcade" when in actuality LFS had taken a massive leap forward in the realism department.

On to the second of the three main ways to deal with combined forces in an empirical type of model: Instead of leaving the longitudinal force right where it was and scaling back the combined force (red line) to fit the traction circle, you just scale the combined force back. The direction of the force doesn't change then, but the size of it does. The traction and lateral force (black and green) simply scale back and remain proportional to each other.

EDIT: The above paragraph should read:
On to the second of the three main ways to deal with combined forces in an empirical type of model: Instead of leaving the longitudinal force right where it was and scaling back the lateral force (green line) to make the combined force (red line) fit the traction circle, you just scale the combined force back. The direction of the force doesn't change then, but the size of it does. The traction and lateral force (black and green) simply scale back and remain proportional to each other.


This produces much nicer results without the sudden snap oversteer following understeer with slowly increasing throttle in a RWD car. This is precisely how Virtual RC Racing's combined slip model works (the public version that is, the new version in development is totally different). This is wrong too, however. Again, you have a situation where the lateral force is not changing as you feed in more traction force at all until you hit the friction circle. Then, it suddenly begins scaling back, but it does it more subtly and in combination with the traction force.

Both approaches are wrong at the friction circle limit and even more so when operating below the limit, as increasing traction force in that area does not change the lateral force at all. You get increased rear weight transfer which reduces the rear slip angles (increasing understeer), then suddenly at the limit the tires let go as the lateral force suddenly begins plummeting. You can't really steer with the throttle properly by coaxing the rear end out when under the limit like you can in reality in many cars.

When it's done properly, the lateral force will drop with increasing traction regardless of the slip angle. Even when you're way under the limit. As you approach the limit it winds up very smoothly transitioning into limit behavior. As such, you can steer with the throttle quite nicely. It's all very predictable and drifting actually becomes quite a lot easier. Suddenly you find yourself steering as much or more with the throttle than the steering wheel, even when you're below the traction limit. I've yet to see that anywhere except in Gregor Veble's model for Racing Legends and my own.

Ok, back to the FWD (that was a long tangent):

Starting at figure A, we are cornering pretty hard, a bit under the limit of the front tires, with some throttle. We then increase throttle. If our combined slip model works as either method described above, we can easily find ourselves in situation B. The lateral force stays the same and the combined force (red line) gets bigger and changes direction.

The blue line: This is the yaw component on the car that is trying to twist it to the left. If that gets longer we tend to get oversteer. See picture B? We increase throttle, the blue line gets longer, and we go away from understeer or might even get oversteer if it's long enough.

With a proper combined slip model, we should wind up with something more like figure C. We increase forward tractive force, the lateral force (green) drops, and the combined (red) force grows and changes direction. My illustration shows the combined force being shorter, but really I meant it to grow instead. However, the result is that the blue line gets shorter, meaning less lateral force or yaw torque in the car's coordinate system, and we get understeer instead of oversteer.

The combined slip model in LFS seems quite good to me. At least as good if not better than any other sim I've tried. Before patch Q it was, umm.., not so good, but now it's quite super. However, there is probably room for improvement here and what we see with the front wheel drives is likely proof that something is just a little bit amiss there still.

It's still my favorite sim to drive though, aside from my own of course The new sounds are just fantastic and now that I've got a G25 wheel I can finally use FFB without getting all the rocking of the wheel around the center. The FFB is very good in LFS. FFB has kind of ruined some of the other sims for me in comparison, quite frankly

Quote from Bob Smith :

I don't think it's just due to the diff IMO (in LFS), it's the whole combination of the setup. Judging from your description, that's quite an understeery setup. FWD sets in LFS are often really weird in order to obtain this weird behaviour. With a sensible set like you used, I'm pretty sure FWDs in LFS behave properly.

Perhaps. I should probably try a stiff rear ARB like the LFS cars use. The default set ups have the same tendency, however. Locked or very stiff front diff increases oversteer with throttle rather than reducing it. I'll have to give that a go and see if I can get it to happen at all in mine.

Quote :

I'm not sure how much difference it would make, but lightening the car and reducing the power, while very unlikely to change the direction of the results, would still make for a fairer test. The CoG height issue is interesting, the FWD cars in LFS all seem to have reasonably high CoGs, and narrow track widths, hence their willingness to roll.

Weight should have no effect at all. Power is irrelevant too as during the testing as I used all throttle positions. Even just a very, very slight increase in throttle caused understeer.

Interesting and informative post as usual, Todd.

Thanks Todd, for making brainy stuff consumable for cretins like myself. Very informative.

Good stuff!

phew lots of info interesting bit about the combined slip modeling and im a bit surprised that anybody would actually use the constant long force approach
mind to go on a bit about why the lat force is depending on the long force in sub limit situations ?

and about your experiment ... first of all "My car gets forty rods to the hogshead, and that's the way I likes it!"
and i have to agree with bob you have a whole bunch of understeer in your arb and spring setup
to really make a comparison you should try a car that represents an xfg with a throttle oversteer setup a bit more

Quote from jtw62074 :

FFB has kind of ruined some of the other sims for me in comparison, quite frankly

youre turning into a true lfs fanboy

Good that we keep Todd in that closet so we can get clear and informative posts about tire issues

But he just did spoil all the fun from my car building (realised how impossible it is to get proper handling) so now I need to get some other platform where to work I guess and there seem to be only LFS and Todd's sim, but both impossible

Maybe I just wait then undetermined time, that has worked before too

Quote from Bob Smith :

I don't think it's just due to the diff IMO (in LFS), it's the whole combination of the setup. Judging from your description, that's quite an understeery setup.

Understeer gradient at the limit was about 3 deg/g, which is about the same as the most oversteery production sports cars.

Whoops, I stand corrected. Turns out this is a bit more towards oversteer than most production cars, but by racing standards it is indeed quite understeery, especially in comparison to some of what you guys like to run

Very nice. Is Racing Legends done yet?

Quote from Shotglass :

youre turning into a true lfs fanboy

That's because he's very brilliant! :hide:

Quote from Ball Bearing Turbo :

Very nice. Is Racing Legends done yet?

Not just yet