Understanding rear wheels slip influence on steering torque

Discussion in 'General Discussion' started by mantasisg, Dec 30, 2018.

  1. Jihemme

    Jihemme Registered

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    Hey all,

    Actually, the steering wheel shouldn't be the cue you trust when you are over / under steering. Wheels sound shouldn't neither...

    At best, those 2 cues are confirming factors (and FFB should help you to correct it).

    The only cue you should trust 100% of the time is your sight.
     
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  2. mantasisg

    mantasisg Registered

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    I have exact same opinion, it is not too easy to explain it.

    As always most knowledge is in aircraft world:
     
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  3. mantasisg

    mantasisg Registered

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    I wonder about wheelbase length now, am I right to assume that shorter wheelbase will give better/faster oversteer response through the wheel ? As much as it seems it does work like that in rF2. It makes sense because for longer wheel base for same slip angle rear end will be able to step out greater distance. And steering wheel is slower to start spinning into a slide. When you drive cobra, which is shorter you can pretty much let steering wheel lead you when oversteering, Howston G4 for example feels like it needs more of your own initiative.

    In conclusion, seems to me that faster FFB/steering torque response makes it tougher to be smooth and precise, with longer wheelbase it is easier to be smooth responses are slower, but you also have to steer wheel more yourself, rather than expecting commands from FFB. Basically I think that longer wheelbase will require slower reaction than short wheelbase, but also will be less suggestive.

    Maybe thats one of the reasons why modern F1 and FE cars are as long as football field, in addition to trying to imitate jet fighter aircrafts.

    Also I wonder if it is right to assume that the "seat feel" would be more important for short wheelbases, and less important for long wheelbases ? It is tricky to say, in short wheelbase you'd move out in lesser distance when oversteering, but the yaw rotation would be quicker ?

    Also I suppose seat position is also very important, I remember reading or from some documentary that Autounion Type C drivers had a lot of difficulties with controlling oversteer, as they had seats at the very front, and the car was long. That would be totally true for visual cues, and probably the seat feel as well.
     
    Last edited: Jan 14, 2019
  4. Korva7

    Korva7 Registered

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    I think that effect on ffb is mostly caused by different suspension/steering geometries. Higher caster for examble makes the car correct it self more strongly.

    Quote from some random website:
    "Caster really helps a drift car by making it self-steer better. When you start to drift, you can simply let go of the wheel and let if feed through your fingers, and the car will counter faster than if you were steering it yourself. "
    http://www.superstreetonline.com/how-to/chassis-suspension/modp-1201-basic-drift-chassis-setup/
     
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  5. mantasisg

    mantasisg Registered

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    Hmm.. that page is for some reason unavailable for "some EU countries".

    Yes indeed it has to do a lot. It would be interesting to try exactly same vehicle just with different wheelbase lengths. There are multiple reasons for self aligning, seems like it isn't fully understood, as for example from this video



    Of course there is no oversteer there, but just caster stuff.

    Interesting thing is also that caster angle alone is not the whole thing, it also is important where the axis goes in relation to the wheel, as in this video.

     
  6. Nitrometh

    Nitrometh Registered

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    Car dynamic is really interesting. I had some lectures years ago about all that stuff.
    We went to Boxberg to drive on the different test tracks. It was fun as hell :)
     
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  7. Korva7

    Korva7 Registered

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    Wheelbase for sure have somekind of effect on the oversteer behavior of a car.
    But if you imagine two versions of the same car, other with longer wheel base and other with shorter, making the same angular movement (rear end stepping out in same way), i don't think there would be much difference in what you feel in the steering of the car.
     
  8. mantasisg

    mantasisg Registered

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    Maybe... I'm basing my assumption mostly on the logic that for the same angle longer wheelbase will be able to slide bigger difference, thus more time, thus more time to react. On the other hand I speculate that it might not give such obvious response through steering.

    But it might not be more important as tire and geometry properties of steering.

    I had an idea, I don't know if I shared it already, positive mechanical trail for wheel could be something similar like wheelbase is to whole car.
     
    Last edited: Feb 9, 2019
  9. mantasisg

    mantasisg Registered

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    *I have decided to share these thoughts there, I was replying in other thread, and realised that it is major offtopic there.

    -In reply about synchronization of FFB with car.-

    To me it is a shame that the very first release of ACC was labeled as wrong handling, as in my opinion it was very right. My perception is either worse than most, or better lol

    I wish the right path of simulation will win.

    After playing a lot of rF2 and a lot of first build of ACC (I spent 40 hours with lambo in Nurburgring) nor AMS, nor AC doesn't feel right to me. Not bad, but not right.

    I would describe two different typical sensations/handling types of simulation:

    -1st. Don't interfere with FFB too much and just guide the steering. Thats how AC and AMS feels to me.
    -2nd. Don't rely on FFB too much and just let it guide you while you do the steering.

    Probably most effect on that has output time on FFB, naturally faster output requires less input for a driver. It has advantages and disadvantages, it wrecks you if you are not aware to catch the steering in time and countersteer, but it helps to initiate many many corrections if you only don't fight the wheel when it is helping.

    It is difficult to say whats wrong, and what is right, because both could be right or wrong to certain degree, cars have different steering mechanics.

    *Thats where it comes to this topic. Cars have differences. To be completely fair, thats why I like rF2. Cars have bold differences. Sometimes people dislike them, and thinks it is an issue. Like for example understeer feel of Mercedes GT3 car, or torque steer like sensation with Honda Civic. Some cars in rF2 feels more like the type which handling depends more on driver inputs and less on steering outputs, and vice versa.

    Right now I am playing about equal amount rF2 and AC. It is always strange to get from one to other for a couple of laps before getting used. AC is fine if you realize that you simply shouldn't interfere FFB too much, and rF2 is fine if you realize that you have to be more active with a steering.
     
  10. mantasisg

    mantasisg Registered

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    Scratch that, AMS feels very good. I had a problem with settings. For some reason "Auto steering" was enabled. It ruined everything. Also interesting was that with different cars it had different level of "damage", it didn't change Puma road car very much, but completely ruined V8 supercar.
     
  11. mantasisg

    mantasisg Registered

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    As if the thread was not dead enough already :D, can someone explain how pneumatic trail works at the rear wheels ? How it affects handling of the car ?
     
  12. RaceNut

    RaceNut Registered

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    Pneumatic trail
    [​IMG]
    Pneumatic trail or trail of the tire is a trail-like effect generated by compliant tires rolling on a hard surface and subject to side loads, as in a turn. More technically, it is the distance that the resultant force of side-slip occurs behind the geometric center of the contact patch.

    This effect should - in theory, be accounted for in the steering and FFB but, I would not expect it to be very dramatic in most cases and, certainly not at the same level as rear grip-loss effects. We could perhaps, think of it as a "pre grip-loss" sense of over-steer feeling (subtle).

    I suspect AMS does a very good job of simulating this because of the way it communicates grip-loss in very subtle ways.
     
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  13. mantasisg

    mantasisg Registered

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    Well for front tires it obviously has to have a lot of effect, thus steering and ffb. Especially in case of understeer if pneumatic trail is relatively large to mechanical trail then there should be a lot of FFB variation with different load, contact patch shape and slip situations. More trail is also more immediate alignment I suppose. I usually see information that caster angle is responsible for quicker steering response, but I wonder if it is not simply because bigger angle creates longer mechanical trail.

    I don't think anything what happens at rear tires gives direct response through steering, till it affects front tires. So I wonder if it really could possibly change steering response of rear tires changes trail length. I doubt more pneumatic trail would help with more suggestive steering output to rear end grip loss.
     
  14. RaceNut

    RaceNut Registered

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    As suggested, I think any effect would be pretty subtle in steering-effect but, if any sim's go into modeling such detail, I imagine rF2 would be one. rF2 is certainly one of my favorite titles in regard to front-grip feeling near the edge and it's more progressive nature lends itself to anticipating over-steer as the tires hook-up more aggressively. I get some of that feeling in AMS but, rF2 does it better imo.
     
  15. mantasisg

    mantasisg Registered

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    IMO every sim should have details like pneumatic trail nailed down completely, though perhaps it is not easy because tire deformations are involved.

    For front tires it is quite clear, but I am still very puzzled what about pneumatic trail of rear tires, maybe it also helps anticipating oversteer, but how ? Does it produce toe-out effect when cornering on outside wheels, and toe-in on inside wheels ? In that case it would help to rotate the car assuming that it would cause some instantaneous toe change at initial turn when slip angle is small and pneumatic trail is at maximum.
     
  16. RaceNut

    RaceNut Registered

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    I imagine rear pneumatic trail might offer a bit more margin where we might feel a very slight drift but, it's actually a result of tire-flex before grip-loss occurs (?)
     
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  17. mantasisg

    mantasisg Registered

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    Thats good point, maybe more of it could give impression of greater tire flex. I am messing around with physics for a mod car, and once I had trail much too large, it gave an impression of greater flex.
     
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