Physics thread

Discussion in 'Project CARS 1' started by LVracerGT, Feb 28, 2014.

  1. NightHawkFur

    NightHawkFur

    Messages:
    494
  2. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    Does this game simulate less brake cooling when your following someone and less downforce in braking zones when your behind someone?

    What about different downforce levels at different altitudes?
     
  3. NLxAROSA

    NLxAROSA Premium

    Messages:
    7,847
    Location:
    Netherlands
    Drafting and dirty air is there.
     
    ebelen92 and Mike_grpA like this.
  4. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Not sure about brake cooling, as I haven't tested that, but that's a great question, so now you've sparked my interest I'll have to test it lol.

    As for the second part, yes the "dirty air" effect is well modelled. The aero model is actually really good, and since air density is modeled, I would imagine it does affect aero, though this would be very subtle.

    The aero model is good enough that you can stall the diffuser in a Formula A car by running too much rake, and I haven't experienced that in any other game.

    Edit: Ninja'd on the dirty air
     
  5. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    How much rake are we talking about?
     
  6. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    A lot, I can't remember the numbers off the top of my head, but I was testing to see how the car would react to different settings, testing extremes in geometry, wings, and suspension.

    I decided to test out how rake affected the handling, and was pleasantly surprised how planted the car felt with added rake. It didn't just give it a higher tendency to oversteer, as you'd expect in a low downforce car or a road car, it gave the rear a lot more high speed stability, making me think rake was also modeled aerodynamically in cars like the FA with floors and diffusers designed to produce downforce.

    I wanted to see just how much grip I could get out of the floor with extra rake, and kept adding more and testing. I have only done this with the FA, which has 2011 style F1 EBD to aid the diffuser. In case you don't know the basic principles of this system, they placed the exhaust outlets on either side of the diffuser, at the throat end, to use the exhaust plume as a "fluid skirt" to seal the sides, preventing the turbulent air from the spinning rear tyres "tyre squirt" from entering the diffuser and messing with it's flows.

    Unlike early EBD concepts, which had exhaust gasses inserted directly into the diffuser itself, in order to energise the flow, this newer design was a way of replicating the old ground effect era skirts, which not only prevented tyre squirt getting into the diffuser, but also prevented the high pressure air above the floor from spilling over into the low pressure side at the diffuser end. All of this allowed much higher rake to be run before the diffuser would stall.

    Running higher rake has two main benefits aerodynamically.

    1) It gives the entire floor an angle, similar to the old GE cars venturi tunnels, with the leading edge very close to the ground, and the diffuser throat and trailling edge much higher. This gives a significantly larger expansion ratio which in turn increases rear downforce, or more accurately, increases the downforce produced at the diffuser throat, which is forward of the rear wing, so kind of rear-mid downforce.

    2) It enables you to get the front wing closer to the ground, which will allow it a better interaction with the ground. In essense, the front wing runs in ground effect too, so getting it closer to the ground will drive it harder.

    This of course is highly dependent on the diffuser being capable of being driven at such high angles without stalling. Turbulent air entering the diffuser will reduce the amount of laminar air flow inside it, leading to flow separation, or stalling. To prevent this, the front wing and barge boards are constructed so as to create and direct vortices to the edge of the floor, to help seal edges of the floor. The exhaust plume is much more powerful at doing this, but is more useful at the edge of the diffuser throat, where it can keep tyre squirt out, and seal the diffuser, where the floor edge will be at it's highest.

    Of course, there will always be a point where the angle will be too steep for the laminar flow inside the diffuser to stay connected at speed, which will stall it too, even with perfectly sealed sides.

    Sorry about the massive explanation if you already know all of this, but I'm sure it will help some people to understand how and why it works.

    Back to my testing. I kept increasing the rake angle to see how much grip I could get out of it, iirc adding 5mm increments at the rear after the front was as low as I was willing to put it (to avoid bottoming out the front wing). I reached a point where one 5mm increase in rear ride height turned the car from feeling like it was on rails, to having massive oversteer at high speed. I lost a lot of rear downforce, which made the car horrible to drive. It was still ok at low speeds, but once I was moving at a decent speed, the rear end would break away as though I'd turned the rear wing all the way down, or enabled DRS before turning in.

    Due to the EBD on the FA, I reckon the rake angle it can run will be significantly higher than the FB, as that doesn't have the same amount of sealing of the diffuser. I haven't tested it with the FB though, so I'm not sure how much it can handle.

    Edit: There are also a number of other factors that need testing to find the optimum rake angle for the FA. As the likelihood of flow separation increases with air flow speed, the optimum rake at low to mid speed will be higher than at high speed, so that brings spring stiffness into the equation as something that could allow a higher rake at low speed, and less at high speed as the downforce forces the rear ride down. Fuel load will also change the rake angle if the springs aren't stiff enough, which would mean your quali rake angle won't be the same as the race start. Obviously the flows won't be as accurate as real life, so it'll be interesting to find out how complex this effect is. I remember Doug from SMS talking about ride height affecting drag due to the diffuser's interaction with the rear wing.
     
    Last edited: Oct 31, 2015
  7. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    No need to apologies for enlightening people. :)

    I wonder if GT3 cars can utilize additional rake. They certainly don't corner at the speeds of open wheelers, so I'm guessing the aero effect would have to be substantial to overcome the loss in mechanical grip at the rear. Maybe there is a benefit with more rake and less rear wing for a higher top speed? Time to test.
     
    LVracerGT and Mike_grpA like this.
  8. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Yeah I read a conversation at the official forum about increasing floor downforce with rake to reduce rear wing angle and hence lower drag, but positive rake will also increase drag, so it depends how much drag you can take out of the rear wing, whether it'll simply cancel each other out, or slightly reduce overall drag. A good thing to test out!

    As for GT3 cars benefiting from rake, I believe they will. Positive rake will give the chassis an oversteering tendency, but this can be overcome with other changes to your set up to give you a more neutral mechanical grip balance. Damper settings can be altered to give the car a softer attitude on corner entry and exit or over bumps, which will make it more drivable over kerbs and under late braking, but increase understeer. Positive rake will counter this, making the car easier to drive, but still balanced.

    The aero benefits won't be anywhere near as big though, as the diffusers aren't as good, usually having simple convex throats, and lacking the complex vortices and flow structures to seal them, not to mention the lack of F1 style ebd. However, a small amount of rake will still increase the expansion ratio, and hence downforce, and due to the simpler nature of the diffuser on a GT3 car, the pressure drop should occur further forward in the floor, giving you a more central downforce increase. So while it may only give a subtle increase in downforce, it should be pretty well balanced front to rear, instead of simply giving more rear downforce. In this case, the rear wing can be used to adjust the high speed aero balance of the car, to give you better turn-in for high speed corners, for example.

    So to conclude, I reckon you will definitely find gains from your tests, but it will require many changes to work together. The diffuser won't handle too much positive rake, which could end up making the car a mess to drive, but a small amount of rake, combined with adjustments to dampers to balance mechanical grip somewhat, could yield a neutral and easy car in low to mid speed corners, and a bit higher downforce from the floor for high speed corners. Coupled with rear wing changes this could enable you to find the right balance for you in both low and high speed corners independently, instead of sacrificing one area to benefit another.

    Good luck with your testing! Trying out these kinds of things is one of my favourite things with Pcars, and the improvements in tyre model accuracy and fixes to camber that are coming will only make the game even more realistic. :cheers:
     
  9. svenvangent

    svenvangent

    Messages:
    1,467
    Location:
    Belgium
    Can someone give this man double/triple beer please :tup::cheers:
     
  10. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Haha. I am a car nerd that's for sure! I've said it a couple of times here that I spend quite a bit of time over at F1technical.net, because auto engineering and aerodynamics are hugely interesting to me.

    I drive my Mrs nuts with my obsession. I'll say "I'm just going out to check something on my car", next thing it's four hours later and she's coming out for the fifth time to moan at me "what the hell's taking you so long, I thought you were just checking something". Meanwhile, I'm sitting there covered in grease with the whole front end of my car apart lol.

    Oh, and as an Aussie I absolutely love beer, so thanks for the suggestion! :D
     
  11. svenvangent

    svenvangent

    Messages:
    1,467
    Location:
    Belgium
    Give's me a big smile on my face when someone has that kind off passion for his hobby love it .
    It go's you well Mike :tup:

    Greets
     
    LVracerGT and Mike_grpA like this.
  12. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Thanks mate :tup:. Life's nothing without passion :cheers:
     
    LVracerGT likes this.
  13. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    Did some basic testing with GT3 diffusers and I got some surprising results. I only tested the Z4 and had a friend be a guinny pig with the R8. There is definitely a noticeable increase in rear doenforce and overall stability. In the Z4 I needed about 20-25mm of positive rake to get a noticable gain. Anything less than that and the car went into oversteer on entry and exit. There was a lot of drag though and I was 2mph down at Monza. There must also be a decent amount of weight shifted forward with that much rake because the car is a lot more stable on entry as if the static weight distribution was moved forward.

    The R8 only needed about 8mm to produce more downforce. There was also less drag with the R8 than the Z4. I don't know if the R8 diffuser is simply a lot more efficient than the Z4's or there is something else going on. I'll test at Silverstone or some other downforce dependent track.
     
  14. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Excellent work mate. I'm surprised the Z4 handles so much rake, but remember to check your telemetry hud while driving, as depending on spring rates, your ride height may drop more at the rear than at the front at speed, making the rake less at high speed, which would make more sense to me. Like I said, the higher the speed, the lower the optimal rake angle will be. Perhaps the R8 runs stiffer suspension to the Z4, and therefore the rake doesn't change as much with speed. Just a guess, but it's good to see you're finding positive results with the GT3 cars, as it'll certainly help people with their set ups.

    Another possible explanation for the R8 gaining more with less rake is the diffuser's interaction with the rear wing might be more efficient, so the downforce increase will be larger, without too much rake, so the drag will be less.

    How much rake can the R8 benefit from?
     
    svenvangent likes this.
  15. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    Not sure on the limit of the R8, but now that you mention it the Z4 in question had full soft springs and the R8 had stiff springs. I know the Z4 also has very efficient wings so maybe it relies on them more than the diffuser. I'll try the Z4 again with stiff springs.
     
    svenvangent and Mike_grpA like this.
  16. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Remember to check the telemetry hud when testing, so you can see how the ride height and rake changes dynamically.
     
    svenvangent likes this.
  17. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    Tested more at Brno in Z4 with really stiff springs. Now a 10mm rake produced noticeable df all the way up to about 25mm where you now have a lot of understeer. At 40mm the car still has df, but not any more than at 25mm and the loss of mechanical grip on entry makes the car nearly undriveable. I think that on lower df cars it's more of a fine tuning device rather than a necessity. Although the setups I used were already very good setups that were made with only 5mm rake, so maybe if you made a setup based around a set rake/ride height you would get better results. One thing for sure is like any other setting, adding rake by itself isn't going to make you the fastest driver in the lobby.

    Edit: Looking at the horrible console telemetry, dynamic rake was roughly half of static.
     
    Last edited: Nov 1, 2015
    svenvangent and Mike_grpA like this.
  18. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Yeah, due to the much lower downforce produced by the floor, it won't be as dramatic a loss when you stall it, but you'll still notice it. Also note, with too much rake, you will stall the diffuser at higher speeds, so it shouldn't affect you so much at the lower speed turns, but during turn in on high speed turns you should notice a lack of stability. Your rear wing will still be producing good downforce, but with the diffuser stalled, you're also losing the affect of the diffuser flow interacting with the underside of the rear wing, which means you'll also be losing some downforce from the rear wing.

    I can't be sure, as it depends on a few things, but a high rake angle on a car with a front splitter instead of a front wing, might also ruin the flow far enough forward in the floor when it stalls that the splitter becomes ineffective, as stalling the diffuser will be creating turbulence under the car, you may end up getting lift from the entire floor, which could give you oversteer, understeer, or an unstable combination of the two. This all depends on a lot of factors, and of course one of those is how accurately modeled is the airflow. As I said earlier, Doug has stated that diffuser-wing interactions are modeled in the aero, so it must be significantly complex to achieve that.

    You're spot-on about needing to change a lot of other settings to maximise the gains in downforce from rake, and it's about finding a good middle ground between exploiting rake for aero benefit, keeping the chassis balance neutral, and not sacrificing mechanical grip to do so. Some tracks you might want the downforce, some you might want to exploit the floor to trim the wings for less drag, and some you might want a narrow rake with a very low ride height, in order to go for overall lowest drag (only for tracks like Monza), even lightly bottoming out the splitter at the highest speeds, to completely cut off diffuser flow and stall it that way, for minimum drag.

    Also note that running a decent amount of rake allows softer rear springs, which will aid in low speed traction. In this set up direction, you'll want a static rake much higher than optimal, significantly softer rear springs than usual, but stiffer rear arb, to prevent the back end flopping about under lateral load.
    The stiffer arb and high rake should be counteracted by the really soft springs to avoid making it overly oversteery, coupled with changes to the dampers (depending on the car and how it feels initially with those changes, use dampers to adjust it's attitude to your liking) you should get a decent chassis balance, but the benefits will be the back end will sag under longitudinal acceleration, aiding the rear tyres significantly in traction out of low speed corners, the high rake at low speeds will be beneficial to weight balance and front splitter performance, giving good turn in for tight low speed corners, and the soft rear springs will allow the rake to lessen as the speed increases, getting the angle into the right zone to increase high speed downforce.

    If you try this, you'll definitely need to make the rear damper rebound stiff, and front bump stiff, otherwise you'll get massive dive under brakes, which, in tricky braking zones, could end up causing the car to swap ends dramatically lol.

    Edit: Also, if you try that set up direction, remember small increments at a time. It would be very easy to overdo it and end up ruining the balance completely. This set up (and design) direction is basically what Red Bull Racing does in F1. Next time you watch F1, look at how much rake they run, and note their incredible corner exit traction, and the amount of suspension travel compared to the other top teams.

    The really amazing thing is how they are able to run so much rake without stalling the diffuser. Their front aero surfaces are all so well developed, they are able to use vortices for a better sealing effect than anyone else. Newey is a genius where that's concerned.
     
    Last edited: Nov 1, 2015
  19. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    My current league race is at Monza so there's not much to gain from more downforce since I'm in the Z4 and I already struggle for straight line speed. The next race is Brands Hatch and I'll definitely play with the rake there to see if I can use it.

    In F1 yes it is amazing what Red Bull does chassis wise. Just imagine if they had the Mercedes engine. They'd be on their way to 6 constructor titles in a row.
     
    svenvangent and Mike_grpA like this.
  20. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    As a long-time Ferrari man I sincerely hope that doesn't happen lol.

    As for your league, do some testing with really low ride height, and a bit of static rake. Try to aim for the rake to be close to neutral at high speed on the straights, with the front almost bottoming out. To achieve this, do a very slight version of my "red bull" strategy, with the softer rear springs to allow the rear ride to drop at high speed. The soft rear end will increase traction which is hugely important at Monza, while the small amount of rake will benefit turn in response for the tight chicanes, and the really low ride height will give you low drag on the straights. If you can get the front splitter to come close or slightly bottom out at close to top speed, it'll stall the diffuser near the end of the straights, which should allow an extra few kph top end, even more if you're in a slipstream.

    Set the suspension up to allow squat under power, but not dive under brakes. Use the dampers to achieve this. Even with the reduced downforce, you'll still be producing enough at high speeds to lower the ride height, especially at the rear.

    If you do try this out, let me know how you go. It should be a good set up direction for Monza, but I haven't actually tried this approach with the GT3 cars yet, as I've gone through open wheelers and prototypes in career, and have only spent a small amount of time stuffing around with other cars at Mojave. Therefore, all of this comes from real world tuning knowledge, not in-game, but apart from static camber levels, everything I've tried in-game correlates to my real world knowledge.

    Also, good luck with your race :gtpflag:
     
    F1Racer68 and svenvangent like this.
  21. Cocomoto

    Cocomoto

    Messages:
    696
    Location:
    Brazil
    So guys... what about drift physics in Pcars?


    I find it really anwkward, the front tyres takes grip without any previous warrning and the cars goes from one side to another so fast...

    Small drifts are ok, but long and high speed drifts are so hard to do. I'm it's not only me, some friends thing the same and others guys from youtube videos. I can drift in GT, LFS and even in racerroom. But in Pcars, oh well, it's so hard.
     
  22. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Being able to drift a car easily has a lot to do with the set up and tyres used. In Pcars, some of the road cars tyres are very grippy, and are designed for outright grip. With these road cars, try using the all weather tyres, and you'll find it easier to hold higher slip angles.

    Drifting is definitely possible in the game, without a doubt, but you'll have to set your car up to do it. Trying to drift cars with their stock set ups is a pointless exercise, as they are mostly set up to understeer out of the box, and you'll find yourself just snapping back and forth between oversteer and understeer trying to drift with the stock set up.

    Are you using a wheel or controller?
     
    mister dog and Cocomoto like this.
  23. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    Ended up running minimum ride height at Monza, 60 front 65 rear. These cars don't produce the df or have a low enough ride height to ground the splitter unfortunately. Trying to read the little height numbers on the telemetry while they bouncing up and down is impossible, but at best guess the front was even or a little higher than the rear. I know positive rake is very bad so I raised the rear 3mm and it seemed to be marginally faster down the straights, but the issue was my setup was completely built around the minimum ride height I had before.

    At Brands I'm going for a totally different setup approach and hopefully I can better use the higher ride height.

    The Audi's were unbeatable today though.
     
    svenvangent and Mike_grpA like this.
  24. Cocomoto

    Cocomoto

    Messages:
    696
    Location:
    Brazil

    I'm using a wheel, and you're right, my cars always snap the front and then i lost the car's control. Any tips of how to setup the car?

    I'm participating in a online endurance championship, i'm beginning to understand some aspects of tunning now, never really tried in others games.
     
  25. Mike_grpA

    Mike_grpA

    Messages:
    2,810
    Location:
    Australia
    Good work mate, bad luck about the race, but better luck next time :)

    I'm honestly not that into drifting, so I wouldn't be the best person to ask for set ups in that regard, as I prefer racing, so my knowledge revolves around motorsport like F1, prototypes, and touring cars. But I'll try to help out.

    However, it will depend on the characteristics of the car you're using. If you need the car to oversteer more easily, you'll want a stiffer rear end and a softer front. Also remember camber isn't working properly, so I'd just minimise it for now (0.0 or as close as possible).

    You'll want a lot of caster, but as I'm unsure of how camber gain from caster will affect the car, due to the camber not working properly, I'd probably leave that stock for now until the camber fix comes. So already two very important settings for drift set ups, camber and caster, are compromised by that bug.

    Go for stiffer rear springs than front, but don't overdo it, or you'll find the traction hard to re-gain, and the back end snappy. Very stiff roll bars are also something I'd try here, because roll is the enemy of predictable oversteer, especially when transitioning.

    For the dampers, try setting a hard slow rebound in the rear and softer in the front. This will give your car a tendency to oversteer as you turn in to a corner, especially in combination with a low LSD decel value. Essentially you'll get lots of lift off oversteer on corner entry. I did this with the road c Lancer Evo X in career (Minus the LSD), as it didn't have many adjustable things in the set up, but had horrendous understeer, so I did this to maximise lift off oversteer, and it worked a treat. It would fang out sideways on entry, and it would pull itself out of the oversteer almost by itself lol.

    Add to this maximum accel on the LSD, and maybe a bit higher initial torque, depending on how strong this is stock. This will give you a strong and fast lock of the rear axle when you slam the throttle, giving you more more control of your slide.

    For toe angle, this also will depend on how the car acts with these other changes. If you want extra bite from the front on turn in, add more negative front toe. Negative front toe might also help the transitions.
    If the rear end is too hard to catch, you can add positive rear toe to help the rear end try to pull itself back in line.

    The general idea I guess is to use the settings to produce a large amount of oversteer on corner entry, as quickly as possible, without the rear becoming too unstable, and to have the car sit very flat while sliding, with as much control as possible with the throttle, and a self aligning component to the rear to help straighten the car.

    Hope that helps, and if any drifters are reading, please add your wisdom to this, as this post is all guess work. This is how I would approach it if I were to get into drifting, but I could also be wrong or missing useful tips that only drifters would know. :)

    Edit: If all else fails, use the Lotus 49, I've held some majestic slides in that beast when playing around with it, and that was with a set up designed to maximise it's grip :lol:

    Edit #2: I'd also do initial testing at Mojave on the skidpan. Plenty of space there to test your ability to hold a slide without worrying about going off track.
     
    Last edited: Nov 2, 2015
  26. mister dog

    mister dog (Banned)

    Messages:
    8,396
    Location:
    Belgium
    ^ Archived ;)
     
    Mike_grpA likes this.
  27. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    Why oh why oh why does apex curbing cause instant spins or instant oversteer followed by hitting a wall in some cars? :confused: If you haven't noticed this you can drive the Z4 GT3 on your favorite track and you'll find some apex curbing that when you run over it the car instantly becomes unstable. It's not a bouncy type of unstable where the car may be bottoming out. It like the car is literally having the front end pulled towards the apex like a Bat Man grappling hook. I have no idea why this is happening, so any insight or comments will be appreciated. I have never seen a GT car avoid smooth curbing because it will spin the car, especially on the apex. The Bentley GT3 is probably the best example of how you'd expect a race car to handle apex curbing. It just soaks them up unless you try to run over a sausage curbing. The Z4 is the polar opposite. I don't think it's down to tuning, but I suppose it could be.

    Please help!!
     
  28. bleeder

    bleeder

    Messages:
    3,034
    Location:
    England
    I find that Z4 to be one of the most stable cars to drive, but if you haven't already, I'd recommend looking at your Fast Rebound settings. Stiffen the fronts and soften the rears. This usually helps a lot when a car goes crazy over bumps. It should stop the back end spinning out on you.
     
    F1Racer68 and ebelen92 like this.
  29. ozwheels

    ozwheels

    Messages:
    2,371
    Location:
    United States
    It's not bumps, it's apex curbing. It acts like super glue.
     
  30. bleeder

    bleeder

    Messages:
    3,034
    Location:
    England
    I meant crazy over curbs, not bumps. My bad. If you've tried it to no avail hopefully someone else can suggest something else instead.