Does sliding the car get punished in Rfactor2

Discussion in 'General Discussion' started by David O'Reilly, Jan 15, 2021.

  1. Bruno Gil

    Bruno Gil Registered

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    That is the reason I suspect it has an open diff. We're talking about the cup car right? Well I am. Haven't touched the gt4
     
  2. John R Denman

    John R Denman Registered

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    I gave the Alpine a whirl the other day, reminded me of an SCCA E-Production Porsche 914 from the late 70's on really hard race tires with about a dozen heat cycles on them. A good learning mod for sure, even with audio clues on power wheelspin etc.

    Rear sway bar lifts the inside tire and with an open diff its going to spin that tire exiting a turn, more or less depending on the setting.
    The Alpine had fixed springs so you can't just dial in heavier rear springs and remove the sway bar to compensate for exiting wheelspin of the inside tire.

    On the other hand if your spinning the car on exit its either going to take more feathering the throttle on exit or even a different line with a tad bit earlier braking to tighten up the entry radius with a wider exit radius. Late breaking into a turn followed by a long straight only works when your defending or passing, as you carry speed all the way down the straight. Food for thought anyway.
     
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  3. Nieubermesch

    Nieubermesch Registered

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    Both actually. Well, maybe that's it. I'm sure the Gt4 in ACC did have a lot more wheel spin and I think I could mess around the locking of the Gt4 with no change.

    It's not only arrongance for sure... I can see now ;)
     
  4. Bruno Gil

    Bruno Gil Registered

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    What I've noticed is some drivers on the CS seem to push the roll center (backward? Make the front stiffer) , which u can see by the car lifting the front wheel on corner exit on certain turns. this seems to keep the two rear wheels touching the ground, preventing wheel spin on power, right? I find I can sometimes put the car on a state where I can put down the power fully, the front seems to be skidding but it's like the rear wheels make the car turn, maybe that's the front wheel on the air? Or maybe it's the exact opposite and it's the less grip on the "levitating" rear tire causing the rotation? So much to learn lol
     
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  5. mantasisg

    mantasisg Registered

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    Yes, big enough roll stiffness difference makes the stiffer end inside wheels unload strongly enough to lift inside up. Haven't tried new alpines race cars yet, but I know at least that Gt4 has aero balance very much rearwards, which is doubtful and makes it very understeery. Also so race video, where two guys were crashing each other repeatedly and both kept steady like tanks.
     
  6. David O'Reilly

    David O'Reilly Registered

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    I'm looking forwards to a setup and test session in the Alpine. It's a car that fascinates me in real life with its dedication to light weight and it's giant killing performance and value/price.
     
  7. Yzangard

    Yzangard Registered

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    Not sure if this is true (have to try) but anyway, what makes you think ACC got it right actually ?
     
  8. mantasisg

    mantasisg Registered

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    Gilles speaking a little about driving at and over the limit, very straight. Simple to understand what he means and it does reflect what has already been said in this thread. Of course it was late 70s, it was a bit easier at over the edge, but still they must have not to overcook it as he says, also he tells that they did get very tired driving like that. Worth to mention that he was possibly most skilled F1 driver ever, when it came to dealing with car at over its limits.
     
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  9. Nieubermesch

    Nieubermesch Registered

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    I tried it yesterday and there's no differential adjustment on the Rfactor2 version other than preload. I actually drove it and felt more wheel spin, so I don't know, maybe it was track related when I couldn't make it lose almost any traction with throttle. I don't know, just found that 300 HP would be enough to get more spin on the car and don't even remember well ACC that well to be fair.
     
  10. Yzangard

    Yzangard Registered

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    You are still dealing with GT4 ? Did you turn the traction control off ?
     
  11. Nieubermesch

    Nieubermesch Registered

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    Yeah, I am and I did.
     
  12. Yzangard

    Yzangard Registered

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    Strange, I had really no problem making it oversteer like crazy...
     
  13. Nieubermesch

    Nieubermesch Registered

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    Yes, as I said I tested it yesterday again and it seemed like the problem wasn't there anymore, so I don't know, maybe it was something on my end.
     
  14. John R Denman

    John R Denman Registered

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    Suspension geometry literally adds new dimensions to tuning. Roll Center (RC) is a somewhat generic term so it helps to understand the moment arm that determines RC at each corner - Virtual Swing Axle Length (VSA). This link gives a bit better explanation of how VSA applies to RC.
    https://www.autospeed.com/cms/a_111163/article.html@populararticle

    Geometry plays a role as both Latitude (corner loads) and Longitude (braking/acceleration loads).

    Keep in mind the linkage connecting to the upright above the wheel center line has a different force load and sometimes than the linkage below the center line. Think of a lever. Through a turn on the outside wheel the lower linkage is the fulcrum point.

    Draw a line through the center of the car front to back, thats the Latitude axis. Think about a right turn load, as the car rolls over on the left side (droop) while the right side unloads it rises. That alters the VSA points left & right so this happens (see link):
    [​IMG]
    By changing the geometry of the suspension linkage its possible to actually induce lift on the loaded side of the suspension rather than droop. Geometry based anti-roll is an instantaneous effect rather than a a sprung & dampened effect; sprung and dampened gives more feedback to the driver as the dampers tend to control the time factor for the delay, and its that delay that adds some time before the tire breaks loose. So you don't want to go overboard with anti-roll geometry, typically about 10-20%. Of course the RC settings in rF2 only provide positions rather than percentages so its a trial & error thing. But thats the effect on corner loads, and they literally change values in the Chassis.ini file when altered.

    Likewise draw a line through the center of each axle of the car side to side for the Longitudinal axis. Longitudinal is a bit more complex because its acting on both longitudinal forces as well as torque forces of the upright. Under braking the upright wants to rotate putting compression forces above the tire centerline and tension forces below the centerline. Again picture it as a lever with the lower linkage as the fulcrum point.

    When the VSA is above and ahead of the center of the wheel it induces dive under braking and anti-squat under acceleration. However when the VSA is behind the and above it does just the opposite. Likewise for below and ahead vs below and behind.

    Most of the time relocating the pickup points for the lower linkage has a more profound effect but it really depends on the moment arm lengths.

    So yeah, its pretty complex. As the VSA changes with ride height the best way to analyze it is with a Geometry Analysis Program and even then with a good knowledge of practices. For example as the rear rises and the front droops its best to keep the VSA's as close to the same distance apart within reason, otherwise as the car rolls into a turn you'll get dramatic changes to handling.

    That's enough for now.
     
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  15. Bruno Gil

    Bruno Gil Registered

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    Well @John R Denman,
    that's quite a read you've dropped me there ahah.
    It's gonna take a while to digest everything, but I will, including the link you posted, as I've read about VSAs in the past, and I feel like if you understand the geometry of the suspension of the particular car you're driving, you can take the most out of your approach. I actually would like there was something with which we could study suspension geometries of cars in rf2. I think you can kind of do this with ptool?

    Ill be back here (a lot) later to comment on my study
     
  16. davehenrie

    davehenrie Registered

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    one would think his talents would have been suffocated in todays whiz-bang tech marvels. Such a joy to watch videos of his driving.
     
  17. davehenrie

    davehenrie Registered

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    There were suspension tools for GT2/rF1. You could take the suspension files BACK to rF1 formats and visualize them, then edit them back to rF2.....maybe????
     
  18. John R Denman

    John R Denman Registered

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    20200429_131040.jpg 20200429_130817.jpg
    Ptool also works for that in rF2, both of them are somewhat crude but do provide a visual image of the suspension at a static ride height. Analysis would be a dynamic number of iterations (normally about 256-512) of the ride heights at all 4 wheels under braking, acceleration and lateral loading conditions, and those points plotted on various graphs.

    The first example is from the original iDT Panoz Indycar after Chris Lesperance converted it to rF2 (which I believe he has altered somewhat since).

    The second is from the 2020 Indycar I gave Yoss a hard time about many moons ago. Both cars used the same tire files. The 2020 IndyCar was just plain undrivable despite being one of the finest graphics found for IndyCars. The geometry simply lifts weight off the rear tires under acceleration, and off the front tires under braking.

    It gets pretty tedious to just swap chassis files out as the dimension to the contact patches need to match the graphical model without having the bizarre component movements you see in most iRacing open wheel cars.
     
    Last edited: Jan 20, 2021
  19. Bruno Gil

    Bruno Gil Registered

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    I'm now watching michi hoyers stream where he tested and did a setup for the alpine @ Portugal, and looks like he shares many of my opinions about the behaviour of the car, and that he also thinks it comes down mostly to the tires. He and other people in the steam chat even did the same comparison to gt3 cars that we were hypothesising. You can check it out if u want. He even tested the "detach arb exploit", with no success
     
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  20. Nieubermesch

    Nieubermesch Registered

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    Well, from my limited testing understeer seems to wash out the car much more then the GT cars from studio 397.
     

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