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Tire physics
(88 posts, started )

### Poll : Which curve is more realistic?

LFS current curve (in red)
48
My attempted curve (in black)
26
#1
Tire physics
Please don't vote if you don't know what I am talking about.

Ok basically I'd like you to look at the (rubbish) graphs I have tried to do, and vote for which one you think would be more realistic.

Or just discuss it.
Attached images
lol i didnt understand the graph, but i know how lfs is it needs to change so i voted for yours lol
I think you'll need to consider racing slicks and road tires separately, as their applications are completely different. Besides, I remember reading on the forums that the lateral roll-off is actually quite small in some cases. Longitudinal curve definitely needs some improvement in LFS. Did not vote..
#4 - axus
I've seen proof of the accuracy of the current lateral curve. Your one is shockingly far off and what ISI sims have been doing for years. Its just plain wrong. As for longitudinal curves, I don't know much, but I'm not really convinced by LFS' current behaviour. I however voted for the LFS curves, because LFS' lateral behaviour superiority is what gives it the edge physics-wise over other sims currently.

(Yeah, I know I've said a lot as if it were fact - that's because I've seen proof [which I can't share]).
#5 - JTbo
What does mean that slip angle of 1 degrees there is only half of grip in lateral graph?

Now I'm not very good with this stuff, but grip is not doubled with slipping, it may increase perhaps 10% maybe more maybe less, I don't know exact numbers, but it is not changing 50% from 0-7%

This is what I think I know:
There is grip even there is no slip, loads of it, it increases depending from tire to slip angles of 3-10 degrees, modern racing tires do like less slip angle than older tires, racing slicks don't have such dramatic drop off as street tires do have.

Surely I don't know half enough from these, just bits here and there, but I hope I'm still learning

Yes, I did not vote as I'm not enough familiar with this stuff yet.
#6
Quote from JTbo :What does mean that slip angle of 1 degrees there is only half of grip in lateral graph?

Now I'm not very good with this stuff, but grip is not doubled with slipping, it may increase perhaps 10% maybe more maybe less, I don't know exact numbers, but it is not changing 50% from 0-7%

This is what I think I know:
There is grip even there is no slip, loads of it, it increases depending from tire to slip angles of 3-10 degrees, modern racing tires do like less slip angle than older tires, racing slicks don't have such dramatic drop off as street tires do have.

Surely I don't know half enough from these, just bits here and there, but I hope I'm still learning

Yes, I did not vote as I'm not enough familiar with this stuff yet.

Ahh, but when there is 0 slip angle, the tyres are heading in the direction of travel and so there is going to be 0 lateral force isn't there.
I agree with Axus. In the real world lateral grip doesn't fall off after the peak, it just levels out. Your curve looks like you drew how you think it should look instead of how science tells us it should look.
#8
Ok, but I remember Tristan talking about the steering torque reducing a lot when he turned the wheel too much for the corner in his F3 car. And that this doesn't really happen in LFS.

Surely, assuming Tristan is correct, this would mean the lateral force DOES actually does drop off after the peak?
Btw if you have 100% slip, you can't have grip anymore, afaik.
the lateral curves of lfs are correct .... the longitudinal ones are rather far off so probably yours is more correct
#11 - axus
Quote from Cue-Ball :I agree with Axus. In the real world lateral grip doesn't fall off after the peak, it just levels out. Your curve looks like you drew how you think it should look instead of how science tells us it should look.

Actually, it does fall off rather steeply after some insane slip angle (ie. 50 or more degrees). Before that its basically flat. Todd explained lateral behaviour beautifully in a post in the GTR2 forum at one point (and hopefully he won't bite my head off for pasting a link as he felt he gave out a bit too much there ):

http://forum.rscnet.org/showpo ... 3228551&postcount=120
#12 - axus
Quote from DaveWS :Ok, but I remember Tristan talking about the steering torque reducing a lot when he turned the wheel too much for the corner in his F3 car. And that this doesn't really happen in LFS.

Surely, assuming Tristan is correct, this would mean the lateral force DOES actually does drop off after the peak?

Force feedback is a complicated matter - the reason for force feedback is because the force centeroid (ie. if you were to take all the tiny forces created by each tiny bit of tyre and combine them into a pair of perpendicular forces applied at one point, this point would be the force centeroid) is not in the same place as the point where the steering axis meets the ground. Therefore, the lateral and longitudinal forces create a torque around the steering axis. What you feel is this torque. You should know how torque works, so I won't explain it. Basically, the FF can be affected by both the location of the force centeroid and the lateral and longitudinal forces. Therefore, the problem may be the force centeroid movement simulation, not the forces.
#13 - Vain
Quote from DaveWS :Ok, but I remember Tristan talking about the steering torque reducing a lot when he turned the wheel too much for the corner in his F3 car. And that this doesn't really happen in LFS.

Surely, assuming Tristan is correct, this would mean the lateral force DOES actually does drop off after the peak?

That depends on the type of tyre and it's inner construction.
Milliken/Milliken "Race Car Vehicle Dynamics" has some nice tyre data (slightly aged, but I haven't seen better). The more road-like tyres have a very small drop off at excessive slip angles while the very soft champ car tyres downright invert the aligning torque.

So if you post slip angle/force-diagrams then please say what kind of tyre your graph is supposed to simulate.

Vain
The dropping off of steering torque is probably more to do with the self-aligning force of the tyres, rather than the actual grip of the tyres. I was just turning the wheel to much, which with camber and castor would (I think) reduce the contact patch and thus reduce the steering torque required, thus the wheel goes light and fluffy. If you don't steer 'too much' then you still have the understeer (in my case) but the wheel is still 'heavy'.

It only happened once, which isn't enough for me to draw too many conclusions from. It could have just been mud or something on the track at that point for all I know. Hopefully with a bit more testing (March hopefully, depending on how many evenings I spend on the car) I'll be able to either reproduce it or discard it as misinformation.
Quote from Ger Roady :Btw if you have 100% slip, you can't have grip anymore, afaik.

If the tire is in contact with the road there is friction, always. 100% slip (slip ratio = 1) means that if the tire's free rolling speed was 30kph, it's rotational speed is 60kph. I.e., it's spinning at twice the speed of free rolling. There is most certainly plenty of force being produced. It doesn't vanish to 0 in any case except when it is no longer in contact with the ground.

LFS tire force curves are much closer to everything I've seen in reality than the OP's suggested curves, which as axus pointed out, look very much like Simbin/Blimey's curves. LFS curves are the closest thing to reality I've seen in a sim. Granted, I haven't seen what Papy's curves looked like with their Nascar stuff, but in the rFactor/GTR/GTR2 vs LFS debate, LFS wins hands down. Their curves actually look like somebody bothered to do some research into tire operation
What are these curves based on as far as car setup?

In real life these "curves" change every lap, and with every tire pressure change, and with every chassis adjustment, so only knowing this part with out the other parts and their effects on these curves, it seems moot.
Quote from Mister2zx3 :What are these curves based on as far as car setup?

In real life these "curves" change every lap, and with every tire pressure change, and with every chassis adjustment, so only knowing this part with out the other parts and their effects on these curves, it seems moot.

They don't change with chassis adjustments other than camber. When you change the springs or something like that you change the loads on the tires, but the 1000 lb load 0 camber curve still looks the same. Only now maybe you're at 750 lb load instead of 1000 because the ARB has been tweaked.

In reality, yes, they change with tire pressure. They do in LFS too, although I don't know exactly how they do so. In general it seems to be in the right direction. Increasing pressure seems to increase cornering stiffness (the curves rise more quickly at the beginning and peak at a lower slip angle), at least that's how it seems to me to work in LFS.

They'll change a bit from lap to lap too, yes, but my point was the curves in LFS look much, much more like real tire curves than in any other sim I've seen curves plotted from.
#19 - JTbo
Quote from DaveWS :Ahh, but when there is 0 slip angle, the tyres are heading in the direction of travel and so there is going to be 0 lateral force isn't there.

Well that was part that I did miss again, thx

I'm actually making tire curves for one rfactor mod, so all information I can find is useful, also this
Damn it felt good with new curve, just need quite amount of adjusting, but I can tell you this, it is not that far away from LFS with LFS curves, so there is truth behind those words that point tire curves of ISI and saying they are wrong, it felt much more like a real car as I could do same things, cone slalom, linked chicane drifting controlling angle with throttle etc.

I have only edited lateral curve now, original was much like that one drawn with black, now I made curve that looks more like LFS (ish) curve, but added big drop off to greater angles, very rough it is still. I wonder how big that drop off should be after 50 or so degrees? 20% from 50-70 degrees?
Todd Wasson, I understand now what you have been saying about the sliding of the tyres in your post which axus pointed out.

However. Say that a car is driving around a roundabout at a constant speed. The front wheels are turned to the slip angle which will provides the most lateral grip. Then the front wheels are turned in to say 45 degrees slip angle. Surely then the lateral (in relation to the car) force is going to drop a lot? I have drawn I diagram to explain what I mean.

Edit: Ok, I now believe that the lateral curve I did is wrong. There should be be no "sudden drop" after the peak, but it should drop of linearly (spelling?) after the peak?

Also, any more opinions on the longitudinal curve?
Attached images
The lateral force generated will of course go down, but more because the steering geometry reduces the contact patch. If you could maintain the tyre camber in relation to the road you'd find it doesn't drop all that much.

The simplistic view of 'too much steering gives a lot less lateral grip' is one of the reasons ISI sims are so rubbish. Don't believe them!
#22 - JTbo
Quote from tristancliffe :The lateral force generated will of course go down, but more because the steering geometry reduces the contact patch. If you could maintain the tyre camber in relation to the road you'd find it doesn't drop all that much.

The simplistic view of 'too much steering gives a lot less lateral grip' is one of the reasons ISI sims are so rubbish. Don't believe them!

I think this is because how tire curves are made to them, they are just like black curves in first post pics.

Drift cars do use lot of caster, intention is keeping more negative camber when wheels are steered, I think?

I think that when I get my work done with this mod, it will be huge shock to ISI sim lovers, I already hear comments how all tire curves are wrong etc.

I think that ISI's engine is not so badly flawed, only how it is used is, I could try to create full LFS tires and suspension of course to see how different it will be, just bit lot of work to do and does it serve as platform to test how different tire curves would affect / benefit handling in LFS as it is still ISI engine, I don't know
Quote from DaveWS :Todd Wasson, I understand now what you have been saying about the sliding of the tyres in your post which axus pointed out.

However. Say that a car is driving around a roundabout at a constant speed. The front wheels are turned to the slip angle which will provides the most lateral grip. Then the front wheels are turned in to say 45 degrees slip angle. Surely then the lateral (in relation to the car) force is going to drop a lot? I have drawn I diagram to explain what I mean.

youre mixing lateral forces on the tyres with lateral forces on the whole car
the plots for lateral vs slip angle are always the tyres individual slip angle not the angle of the entire car
Right, I am wondering if this curve is more realistic? NOTE that the scale goes right up to 90 degrees.

Edit: Hmmm, this graph is for the lateral force acting on the car. I wonder if LFS uses the lateral force on the car, or on the tyre? If on the tyre (which makes sence) then LFS latural curves must be right.
Attached images
Why can't that tyre generate friction (and therefore force) at 90°

It's complete rubbish after about 12°

Tire physics
(88 posts, started )

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