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Thread: Pcars 2 Aerodynamic Model

  1. #81
    Superkart Pilot Zeratall's Avatar
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    Oct 2017
    Quote Originally Posted by Jussi Karjalainen View Post
    To be fair cpcdem's example was a valid point, and the answers aren't as obvious as you might think. I did a bit of testing on vintage Mulsanne as well as some analysis on a special test track, and here are some of the reasons why what he saw happens:

    1. The Daytona oval isn't exactly the best place for these kinds of tests due to the corners, banking, etc. Ideally if you really wanted to accurately see what the aero is doing you'd use a pure straight, and one that's as flat as possible. Vintage Mulsanne isn't exactly the flattest, but averaging across a few runs with different settings I lost about 5 km/h on max negative rake and about 3 km/h on max positive rake compared to running stock (consistency can at times be a bit tough, gotta be careful that the wind isn't changing directions etc.).

    2. The maximum negative rake (max height front, min height rear) doesn't just purely cause more drag, it also reduces downforce. Reducing downforce tends to reduce drag in itself, so if your DF goes down a lot with adjustments like this the actual drag might not change quite as much. On our test track and reading the exact corner forces I saw the drag increase by about 6% when running max negative rake vs. the default settings, but downforce wen't down by over 17%, losing about 100 kg of total DF. Losing this much DF would have a big effect on drag. And less downforce also means less rolling resistance, since the tyres are sitting light on the road. It just happens that in this car (and probably a fair few GT3 cars) running max negative rake doesn't add a humongous amount of extra total drag, but it does cost you a huge amount of DF. The total aero efficiency in the tests went from something like 1.85:1 L/D to about 1.44:1 L/D with the rake change.

    3. Don't underestimate how significant the loss of a few km/h is at these speeds. After I got the ~5 km/h slower speed on Mulsanne with max negative rake, I put the default setup back and started reducing power (via air restrictor) until I got the same loss of ~5 km/h, and ended up going down by over 20 hp. So a speed difference of just a few km/h isn't an insignificant thing when you're going that fast.
    Thats the difference between parasitic drag and induced drag, and why it's not always good to relate downforce directly with drag ( you have to know where you live in the drag bucket) which is what I think people were trying to point out in cpcdem simplistic analysis, as well as the test methodology. : Owner
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    The following 2 users likes this Post: bmanic, Jussi Karjalainen

  2. #82
    Kart Driver alonsomoslie's Avatar
    Join Date
    Jul 2018
    This conversations between you two are quite instructive for me, I love reading these high level discussions.
    The following 4 users likes this Post: bmanic, Konan, Reiche, Zeratall

  3. #83
    Kart Driver Markspeed's Avatar
    Join Date
    Oct 2017
    Quote Originally Posted by hkraft300 View Post
    Some Aero behaviour can, to the untrained mind, seem bugged because it's so extreme. What they don't realise is the scale of forces involved and how strong they can be at race track speeds. I think we're all old enough to remember Webber back flipping the Merc CLK at le Mans. 30 odd feet in the air.
    Vividly! That was back when I could watch all 24 hour's of it without a wink of sleep. That was a good race brewing up till the moment Dumbreck went over the armco before Indy. Then the race settled into cruise mode till about 5:30 am when Kayama's TS020 found thunderous god of sunrise speed! But then all was lost when the left rear exploded at about 190 halfway towards Indy. For some strange reason Indy hated speed that year. All the drama during that race happened on the way to Indy. I believe one of the Rook Racing Porsche's got tripped over by a Viper on the way into Indy as well. If memory serves.
    The following user likes this Post: hkraft300

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