Tyres behaviour

Discussion in 'General Discussion' started by Slip_Angel, Jul 6, 2019.

  1. Slip_Angel

    Slip_Angel Registered

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    I have been playing the porsche RSR(Endurance DLC)and currently it's easily one of favourite car.
    But the behaviour of car or rather its tyre model doesn't quite seem logical to me.
    Here's my problem,
    (Surface preset on saturated and 27+ Temp & 30-60 humidity;standard aero tune and default setup with rear wing at level 5/7 which is default ; Softest tyre compound )
    On mid-high speed turns like example last turn on zandvroot
    where speeds are easily above 185KM/H the car can be oversteered by adding more wheel lock or putting more angle on wheel than needed.
    This is what is bothering me here the car feels to have exceptional front end grip and that is good BUT these cars have so much downforce and relatively low HP appox 510HP;I don't understand why it doesn't just understeer.
    I must clear one thing that i'm NOT afraid or hate oversteer,Infact i hate understeer so handling oversteer is not a driving issue but a rather a physics issue that is bothering me.
    Yes i can add more rear wing but that will just put LOT of drag on already heavy aero car beside adding more rear wing will feel like artificial solution rather than fix the actual tyre behaviour.
    So has anyone noticed this ? or is this natural behaviour of any GT cars?
     
  2. Korva7

    Korva7 Registered

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    I don't know how the real car behaves, but i don't think high amounts of down force necessarily mean that the car should be understeery, since that depends on the aero balance.
     
  3. Slip_Angel

    Slip_Angel Registered

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    But it shouldn't be sliding on throttle at that speed.Key word is "on throttle" meaning aero balance is at rear ALSO it was already at rear to begin with as my rear wing was at 5 and maximum level is 7.
    Also the slides are way to easy to catch at that speed and i've not seen any racing car slide that predictably at such a speed.
     
  4. Lazza

    Lazza Registered

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    On throttle at that speed doesn't mean a lot in terms of aero balance. The rate of acceleration is so small you don't get a lot of pitch change whether on throttle or coasting.

    You need a real life comparison, footage showing understeer at comparable speed, and allowing for any difference in conditions, rubber, setup, etc.

    At the moment what you have is something that doesn't seem right to you, vs the S397 team building a car using manufacturer data and presumably some performance metrics to check that things are ok. Nothing's ever 100%, and mistakes do happen, but you could also be mistaken.
     
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  5. Slip_Angel

    Slip_Angel Registered

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    I want to be mistaken because it is more satisfying to get oversteer instead of understeer while car is running stable setup.
    What i'm trying to say is that car should understeer ONLY if i push hard enough on high speed turns.
    I want to believe in s397 but this behaviour doesn't seem that logical to me and infact it feels like a physics exploit as i can just add slightly more wheel lock to get rid of understeer or just adjust my line at speeds above 190KM/H.
    Before anyone is mistaken i'm not talking about big drift or anything by saying slides i mean small amounts of slip angle.
     
  6. Lazza

    Lazza Registered

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    Taking that last turn at Zandvoort as an example, it's not a very sharp turn. The entry speed is also limited by the previous corner exit. It seems possible that on the softest tyres, on a fully rubbered track (saturated in game, so fully rubbered racing line or close enough to it), you simply can't go fast enough to reach the limit of grip on the front tyres. I just had a few goes at it and didn't feel like I was maximising the previous turn, but then understeered off there a couple of times as well, so I'm not being very consistent and probably aren't getting out of there at the best speed. Still, on the last attempt I got slightly off the rubbered line in the last turn and understeered straight off into the fence, so I don't think the limit is that far away.

    Also noticed the speed is stalling when keeping it on the line with full throttle, which would suggest the traction control is kicking in as the rear starts to lose grip. That may not feel right to you, but it might just be how the car is. I gather from quick googling that the engine is pushed forward in the GTE spec Porsche, which should reduce oversteer at speed (rear tyres have less weight to push sideways than they otherwise would) but that doesn't mean it should understeer at any given speed either.

    So in summary, what I'm saying is what you're expecting might not be reality. If the car is doing what it can do in real life, that's not broken physics or an exploit.
     
  7. Korva7

    Korva7 Registered

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    One thing relevant to this is that under more load (under down force) the maximum force from the tires should come at higher slip angles. So if you are in high speed corner having same amount of slip in the front as what's optimal in slower corners, you still have room to add steering lock, and make the car turn tighter.
     
  8. Slip_Angel

    Slip_Angel Registered

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    I
    ll try to add a video of it
     
  9. Slip_Angel

    Slip_Angel Registered

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    Yes that is understandable but still...
    I don't know what's real but after driving several other sims RF2 cars seems to much better front end grip at mid to high speed (150-210KM/H)
    I'm saying that it MIGHT be unrealistic as aero balance on static car is already at rear and at higher speeds ON THROTTLE it has no reason to generate more aero at front than rear(that to in a mid engine car with only 500HP)especially at my rear wing setup which at level 5 out of level 7.
    The major problem is there are no proper videos of porsche RSR onboard where the driver is pushing hard and we can see the steering wheel.
     
  10. Slip_Angel

    Slip_Angel Registered

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    Also thank you guys for listening to my issue(thought) without any fanboy attacks :)
     
  11. Lazza

    Lazza Registered

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    Is it? By how much?

    Which is how much? What does 7 mean at a given speed? What is 1? How does that compare to the front downforce?

    My point is only that there are many unknowns. I'm not saying it's right or not.
     
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  12. Bernd

    Bernd Registered

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    That is a very important point at settings that don't show values.
    It all depends on the basic and step values in the hdv.
    For example a setting of 20 on the front wing and a 8 on the rear wing, can nevertheless result in a lower downforce on the front than on the rear.
    You can only compare it when you calculate it with the hdv values.
     
  13. mantasisg

    mantasisg Registered

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    Zandwoort last turn is uphill so it also has an effect on weight distribution. What comes to mind is tire load sensitivity, traction eclipse ... Interesting to try now. Also perhaps diffuser is stalling. Also driving style... Perhaps try causing more understeer earlier in the turn. But in general yeah you would wish not to have oversteery car at high speed. Will try the combo today, also in saturated conditions it is important to stay on racing line.
     
  14. Lazza

    Lazza Registered

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    After more laps, in another GTE car, and a few in a GT3 car, I think the GTE also has slower steering, which can easily seem like understeer. So when you feel like you're 'overturning' the wheel, you're actually just getting to the sweet spot. I used to get that all the time swapping setups with my teammate - I'd occasionally forget to change the steering lock to my preferred setting (rF1) and think his setup had too much understeer. Then I'd realise I simply wasn't turning enough, put the ratio to my normal setting, and all was good again :)
     
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  15. mantasisg

    mantasisg Registered

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    Maybe it could be so that OP is just too gentle with front slip angles, than he thinks he is.

    By the way what is good pace with 911 RSR GTE there ? I know in WSG even aliens were doing 1'34 with GT3 cars. I suppose GTE would be faster.

    I have managed to do mid 1'37 so far, with default setup (including default fuel load), soft tires, but also with TC on 2, I was half a second slower with default TC, but that also could be because I learned to be faster as I drove more, not only low TC setting making me faster.

    I just did 14 laps, mega fun. 7 with default TC and 7 with TC on 2. The difference was little, just little more oversteer at slowish corners, just as expected, though expected a little difference at high speed corners.

    I wasn't experiencing what OP described, at first I was intuitively lifting off slightly, but I did fight that later, and stayed almost or completely flat on throttle a couple of times. I was experiencing very neutral car, it would either understeer slightly, or oversteer slightly, sometimes switching from understeer to oversteer. I was mostly getting slight understeer though. Left tires wore evenly, car would become more playful as tires go down and bellow 95. Right tires wore unevenly, front much more, due to lockups while braking.

    Lastly as I drove with low TC and my tires were around 95 I started doing less rational steering inputs, especially at last turn. It did felt like tires would slide at front, then soon after grip up, turn in more, and cause rear tires to slide. I repeated it for couple of laps in a row. It didn't feel like a quick way to go around the corner by turning in obviously too much and abruptly, but I also had no problems to recover from that oversteerish moment that happened. It wasn't a dorifto indeed, it was like understeer to neutral steer to oversteer back to neutral steer and then back to normal grip. I did feel quite safe doing that, which was weird (I consantly feel stuff being strangely too easy, or strangely too hard with particular same cars :D). I guess it is a sign to go faster.
     
  16. Korva7

    Korva7 Registered

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    Do you mean by this that he would have less tyre wear at the front compared to the back and because of that having more oversteery car?
     
  17. mantasisg

    mantasisg Registered

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    Well it is chicken and an egg thing...

    Car can be oversteery if rear tires are worn out more, but it also could have rear tires worn out more because it was oversteering a lot.

    In my case tires was wearing evenly, except right front wearing more because it was locking up.

    Driving style could also have an effect. As I wrote, I found similar things when I used to turn in abruptly, perhaps same thing that OP described as "turning in more than necessary". I would also add that turning in more quickly than necessary, the intensity of the input seems to have a difference, as sudden strong steer input seems to be able to cause snap oversteer - fronts understeer slighlty, then grip up and steers suddenly provoking sudden increase of slip angle at the rear, which should be scary.

    right for the topic
     
    Last edited: Jul 7, 2019
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  18. Slip_Angel

    Slip_Angel Registered

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    You misunderstood there by saying"turning in more than necessary" by that i mean i was turning the wheel smoothly as i normally would.Also i'm not experiencing snap oversteer but rather good progressive oversteer.
    One more thing don't take oversteer as in big drift it is slight loss of traction at rear which is used to rotate the car to make my line tighter.
     
  19. Slip_Angel

    Slip_Angel Registered

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    I don't know the exact number of aero variation or bias to rear axle it is not given in game (ACC has it :) )BUT it is common to have more aero bias towards rear as it only makes sense.
    Also front splitter has no adjustment available so it at standard(with no actual values written)
     
  20. Slip_Angel

    Slip_Angel Registered

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    To me overall the car is way to forgiving and slides are not only easy to catch but are quite manageable (even without TC).
    IMO this has definitely something to do with how tyres behaves in this sim.Here i can drive gt cars quite aggressively and they don't lose control and as far as what i've seen and heard on YT what pros says it doesn't quite match here.
    I also play ACC and there the cars are much more scary which is what i would expect from proper race cars with tyres that ONLY allow under 10 degrees of slip angles.
     
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