GT6 Top Speeds Are Not Realistic, Please Fix PD!

Discussion in 'Gran Turismo 6' started by jlmcmillan1978, Jan 16, 2014.

  1. TurismoBad

    TurismoBad

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    Yeah no problem:

    F40 - 323 km/h

    458 - 326 km/h

    Abarth 500 SS - 211 km/h

    KTM X-Bow R - 253 km/h

    MP4-12C - 329 km/h

    Lotus Evora S - 280 km/h

    Huayra - 370 km/h

    Mercedes SLS - 321 km/h

    BMW M3 E92 - 289 km/h

    Ok then...

    lloyd-300x300.jpg

    But yeah - if that's the case then ok - might still happen.
     
    Last edited: May 8, 2015
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  2. YZF

    YZF

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    Actually it's a mix: some cars have wrong gear ratios (too short), others have them correct. Wrong ratios is another issue that plagues GT6.

    In some aspect yes, but look at GT5 - they made it more or less accurate. And Asseto Corsa or Project Cars or a bunch of other sim-racing games - all have proper top speeds. So while it may require some effort, it's definitely possible to get it right and it's not space science.
     
  3. eran0004

    eran0004

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    If you just want realistic top speed it's a fairly straightforward process. All you need to know is the surface area of the car and the drag coefficient. Or you can simply reverese-engineer those values from the top speed of the real car.

    The complex stuff is what happens when you drive in the slipstream of another car, or when you adjust or add wings and other aero parts. That stuff is pretty much rocket science.
     
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  4. YZF

    YZF

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    With higher top speeds, higher acceleration comes. So this issue in GT6 is much larger: cars have unrealistic top speeds AND they accelerate too fast.

    [​IMG]



    No it's not. Look at all the other games, some of them even 15 years+ old.
     
  5. eran0004

    eran0004

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    It's the same thing. Lower wind resistance gives better acceleration and better top speed.



    Yes it is. Unless you can test the settings on a real car, or are comfortable with guesstimating the values, it's very much rocket science to calculate the values.

    Rocket science doesn't mean it's impossible though. Mankind have been flying rockets with some precision for more than 70 years.
     
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  6. YZF

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    But there can be different curve of the acceleration graph, and it may be not accurate. This must be modeled properly too. For example, durations: 250-280 ; 300-320 ; 330-360, etc. In other words, you may achieve the same top speed with different acceleration rates. So even if they fix top speed, that's not enough. They must check that acceleration from 0 all the way to top speed is correct too.



    If they make acceleration and top speed the same as in other sim-racing games (even if it's not perfectly accurate to the 0.001sec or km/h) this will be more than enough. No need for scientific perfectness here.

    I'll be even happy with GT5 1:1 implementation
     
  7. eran0004

    eran0004

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    You don't model an acceleration curve. What you do is that you calculate the net force of all the forces acting on the car and that in turn decides the acceleration. The physics are the same at 100 kph as they are at 300 kph, there's no change there.

    Sure, close enough is close enough.
     
  8. YZF

    YZF

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    I don't care about implementation, what I need is correct (or almost correct) final output: acceleration curve and top speed. If there is a bug somewhere, acceleration curve can be correct at first and then wrong later. That is the case with GT6: 0-200km/h acceleration is fine! But 200-350km/h is not.

    At the same time, tuned GT5 has the same top speed as stock GT6, but tuned GT5 has different acceleration 0-250 km/h than GT6. Although they both have the same top speed. So the fact that you get top speed 'right' does not necessary mean that full acceleration curve is right as well.
     
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  9. eran0004

    eran0004

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    Force of drag is proportional to the velocity squared, so a flaw in the aerodynamics model have a bigger impact the faster you go. At low speeds it has almost no impact at all.

    Here's a generic car I created in Excel (5-speed gearbox, 450 Nm @ 4000 rpm, drag area roughly equal to a Porsche 911). I let it accelerate from 0-300 km/h for two runs. The first run was in an atmosphere with an air density of 1.293 kg/m^3 (a realistic value), the second run was in an atmosphere with an air density of 1.0 kg/m^3 (an unrealistic value).

    The solid lines shows the force of aerodynamic drag acting against the car. The dotted lines shows the rate of acceleration.

    accelerationvsdrag.jpg

    From 0-100 the acceleration is virtually identical. At 150 km/h there's a visual difference, but it's really tiny. At 200 km/h the gap is wider and it keeps expanding. The blue line almost hits an acceleration of 0 m/s^2 at the 300 km/h mark, indicating that the top speed for that car is just above 300 km/h. The red line, however, still have quite a bit to go and will probably have a top speed at somewhere between 320 and 330 km/h (if the gearbox allows it, I think it will run out of gears first though).

    This shows that a too low drag value would mean that acceleration below 200 km/h can be more or less okay, while it has a much bigger impact on high speed acceleration and top speed.
     
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  10. YZF

    YZF

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    This was my first idea that came to my mind after 5mins of testing GT6 back in 2013 december. Something is wrong with aerodynamic resistance calculation. You can even visually notice how much faster car accelerates at each straight on every track (if you have good enough eyes and memory to notice and observe acceleration rate, watching dashboard live)
     
  11. eran0004

    eran0004

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    @YZF Do you have that picture where you compared top speeds of cars in GT6 and GT5 somewhere? The stock cars, I mean. I'm thinking I could run them through my Excel sheet and see what the outcome is.

    Edit: Found it!

    Here's the first car I fed Excel with, the Mercedez-Benz SL55 AMG '02. I zoomed in to the interesting bit, the part from 220 to 370 km/h.

    SL55.jpg

    I set the blue air density to 1.225, which is the air density at sea level and 15 °C. Then I set the drag area of the car so that the blue acceleration curve would hit 0 at about 332 km/h (which is the top speed in GT5). The final step was to adjust the red air density, so that the acceleration curve hit 0 at about 362 km/h (top speed in GT6). That gave an air density of 0.9.

    Next step: Run some more cars through the Excel sheet and see how they compare.
     
    Last edited: May 13, 2015
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  12. YZF

    YZF

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  13. eran0004

    eran0004

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    Ford GT:

    GT.jpg

    Drag area: 0.7 (which sounds like a lot, considering the SL55 got 0.68)
    Air density: 0.82
     
    Last edited: May 14, 2015
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  14. YZF

    YZF

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    0.82 is similar to 0.9 ...
     
  15. eran0004

    eran0004

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    Adjusting for tyre slip, the difference is a little smaller (0.84 and 0.91).

    SL55_slip.jpg


    GT_slip.jpg

    @YZF It seems like the other cars in that list has custom gear ratios. Would you mind setting the ratios for the cars in GT5 to the same ratios as the cars in GT6? It's a lot easier to compare them if they have the same gear ratios, and I uninstalled GT5 from my PS3 so I can't do that myself...
     
    Last edited: May 14, 2015
  16. YZF

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    If I set GT6 gear ratios (for those other cars) to default (stock) values - I won't be able to reach those top speeds, because I will run out of gears and the car will start bouncing of rev limiter in top gear. It's the same as if I would try to reach top speed in.... 1st gear

    Car designers didn't think their cars will be affected by GT6 bug and be able to go 40-50km/h faster, so they didn't build long enough gears :)

    BTW, where did you get drag coeficient data for each car? To calculate resistance you need coef. of car shape and size of frontal area?
     
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  17. eran0004

    eran0004

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    I meant the other way around, you adjust the gear ratios of the GT5 cars so that they have the same gear ratios as the cars you were testing in GT6.

    Instead of using stock gearbox in GT5 and custom gearbox in GT6, you'd use a custom gearbox in both games, and use the same ratios. That way they can more easily be compared.

    To calculate resistance I only need to know the amount of force produced by the engine when acceleration reaches 0, because then I know that the opposing force is equal. Solve the drag equation and the only missing values are drag area and air density. Assign air density to a realistic value, and the only value remaining is drag area.

    And what's interesting here is not to find out the exact values of air density or drag area, but rather to see if the cars are off by the same proportions, and as such it doesn't really matter what the exact values for drag area and air density are, because if either of them are off by a certain factor, the product will be off by the same factor as well. That factor would be the factor that drag values in GT6 would need to be multiplied with to give the same top speed as in GT5.
     
  18. YZF

    YZF

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    But different cars have different aerodynamic properties, one car might be more slippery while another - not.

    For example, CarX might achieve 320 kph -> 350 kph difference and CarY might achieve 320 kph -> 370 kph difference. But that can be because CarY might have better aerodynamic shape.

    OR it might be that aerodynamic shape is the same, but some other factor in the game affects top speed for that particular car.... so you don't know what is the real cause
     
    Last edited: May 14, 2015
  19. YZF

    YZF

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    Hello...

    I have a feeling...I have a feeling...

    ..there might be something...just maybe...

    we'll have to wait and see...

    can't say more at the moment...

    fingers crossed
     
  20. eran0004

    eran0004

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    Late reply, but I didn't see it until now.

    All cars have different aerodynamic properties, but they're travelling through the same air. So if something is wrong with the air density, then all cars will be off by the same factor.

    If the cars are off by different factors, then the problem is something else.
     
  21. Thomas__633

    Thomas__633 (Banned)

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    Looking through this thread...
    1. The Ariel Atom V8 is a genuine road car in a road car only game, and achieves a top speed of over 200mph.
    2. Can't you just do the tranny so that it is accurate?
     
  22. YZF

    YZF

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    Where? in GT6? And in real life?

    I think it is possible to adjust it manually, when installing fully customized tranny...but I am not sure if the number of gears won't change after such customization
     
  23. Johnnypenso

    Johnnypenso Premium

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    2. Meaning what? That you adjust final gear so that the car tops out at the actual top speed? This will make the top speed correct but will alter the rate of acceleration.
     
  24. Thomas__633

    Thomas__633 (Banned)

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    With tranny tuning the Ariel does it in FH2.
     
  25. Atomsforpeace

    Atomsforpeace

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    [​IMG]





    None of those real times are correct. 0-100 is nearer 4s in real life, 0-200 is about 14s and 0-300 is about 55s given perfect shifts etc. So gt5 was pretty close tbh. In gt6 seems to be a problem with air resistance that ruins it the faster you go. This is a serious bug as it ruins everything about these cars. So i would say gt6 is actually spot on in terms of how car is mapped. Is something wrong with the way the air works in game.
     
  26. YZF

    YZF

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    Real Life numbers were taken from here:


    [​IMG]
     
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  27. Voodoovaj

    Voodoovaj

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    All this talk of aero is nice, but probably the wrong place to look for issues. The give away is the difference between GT5 and GT6.

    GT6 got the new tire model AND the tires are FAR AND AWAY too grippy. A great 550 time on RS tires in GT5 was 8:20. In GT6, that same set up is 8:00. The tires have two grip properties, lateral and longitudinal. That second one not only helps acceleration, but it also affects top speed.

    I did a tire test not long ago with the M3 to replicate the Stig's time around Ascari. I had to use CH tires to go SLOW enough to even come close to his time. GT6 is most definitely skewed for more straight line speed and grip. Personally, I would love to see an update where all that was clawed WAAAAAAAAAY back. As those who race on the Sports and Comforts will attest to, those tires offer a more balanced game experience and more cars are competitive. I think lateral grip can be brought down 1 step (so SS would grip like SM, etc.) and longitudinal grip (at least on acceleration) should come down 2 steps if not 3.

    THEN, I think drag should be increased.
     
  28. Johnnypenso

    Johnnypenso Premium

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    You're going to have a problem with longitudinal and lateral grip and lap times in general, so long as GT goes with a generic tire, chassis and gearbox model among other things. It makes no sense that 71' Ferrari Dino would corner and accelerate like a 2003 Mazda RX-8 when the Dino would have it's door blown off by a modern Hot Hatch on the track.
     
  29. BrodieBoi94

    BrodieBoi94

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    I'm not an expert, and I don't know many equations about physics and such but I have a theory.

    We all know the games can't perfectly replicate natural conditions, there will be imperfections.

    PD has an engine for each element needed for a racing game(just stating the foundation).

    With that said whatever their aerodynamics simulation engine allows is what they go with.

    They don't put a code (or whatever) in place to make the cars go a specific speed but instead let the A.S.E (Aerodynamics Simulation Engine) be the sole influence on the cars, so that they really can say the game is a simulating.

    They haven't got it down pat yet and have to continue working on their formula to get the most realistic results, therefore we have innacuracies.

    Just a summary of an average joe's theory, feel free to debate.
     
  30. Johnnypenso

    Johnnypenso Premium

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    How do you explain GT5 was more accurate than GT6? Is the game devolving?