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Physics Suspension & Understeer

Discussion in 'Assetto Corsa Modding Discussions' started by Grabarz, Mar 30, 2017.

  1. Grabarz

    Grabarz

    Messages:
    64
    Ratings:
    +11
    Hello well I'm a fanboy of Nissan Skyline R34, not so long ago i decided to create Z-tune version of that car,
    i found real data of that version, the engine specs etc...
    so I changed engine power, changed the tyre size, then i encountered problem with tyre temperature rising like hell under cornering - i solved it with help of some Cool guys, to be honest to real data I increased the weight of the car from 1560 to 1600 kg's

    but now i decided to minimize the understeer - don't take me wrong thanks to all those modifications i was able to trim my time at Mugello to 2:09 and Nordschleife to 7:56

    the problem Is I just don't know what should I do to minimize the understeer i tried to make ARB stiffer
    Original:
    FRONT=26500
    REAR=13000

    Upgraded: (NISSAN NISMO R35)
    FRONT=29214
    REAR=13200

    but the suspension .... no matter what i do it has opposite effect of my intentions...
    If someone can guide me how to make the car less understeer would be nice

    Here are suspension values:

    TYPE=DWB
    BASEY=-0.200 ; Distance of CG from the center of the wheel in meters. Rear Wheel Radius+BASEY=Rear CoG Actual CG height =(FWR+FBasey)+(RWR+Rbasey))/CG_LOCATION%
    TRACK=1.480
    ROD_LENGTH=0.120
    HUB_MASS=57.5
    RIM_OFFSET=0.030
    WBCAR_TOP_FRONT=0.38995, 0.3845, 0.09135
    WBCAR_TOP_REAR=0.39595, 0.3885, -0.13765
    WBCAR_BOTTOM_FRONT=0.44595, -0.1435, 0.01435
    WBCAR_BOTTOM_REAR=0.44995, -0.1435, -0.34965
    WBTYRE_TOP=0.2005, 0.41825, -0.043160
    WBTYRE_BOTTOM=0.11121, -0.11753, 0.01839
    WBCAR_STEER=0.42095, -0.11127, -0.1468
    WBTYRE_STEER=0.13095, -0.08929, -0.1315
    TOE_OUT=0.00030 ; Toe-out expressed as the length of the steering arm in meters
    STATIC_CAMBER=-0.60 ; Static Camber in degrees. Actual camber relative to suspension geometry and movement, check values in game
    SPRING_RATE=40000 ; Wheel rate stiffness in Nm. Do not use spring value but calculate wheel rate
    PROGRESSIVE_SPRING_RATE=0 ; progressive spring rate in N/m/m
    BUMP_STOP_RATE=80000 ; bump stop spring rate
    BUMPSTOP_UP=0.060 ; meters to upper bumpstop from the 0 design of the suspension
    BUMPSTOP_DN=0.050 ; meters to bottom bumpstop from the 0 design of the suspension
    PACKER_RANGE=0.120 ; Total suspension movement range, before hitting packers
    DAMP_BUMP=3597 ; Damper wheel rate stiffness in N sec/m in slow speed compression
    DAMP_FAST_BUMP=1978.4 ; Damper wheel rate stiffness in N sec/m in fast speed compression
    DAMP_FAST_BUMPTHRESHOLD=0.080 ; Damper bump slow/fast threshold in seconds
    DAMP_REBOUND=8730.9 ; Damper wheel rate stiffness in N sec/m in slow speed rebound
    DAMP_FAST_REBOUND=4452.8 ; Damper wheel rate stiffness in N sec/m in fast speed rebound
    DAMP_FAST_REBOUNDTHRESHOLD=0.110 ; Damper rebound slow/fast threshold in seconds


    [REAR]
    TYPE=DWB
    BASEY=-0.236 ; Distance of CG from the center of the wheel in meters. Rear Wheel Radius+BASEY=Rear CoG Actual CG height =(FWR+FBasey)+(RWR+Rbasey))/CG_LOCATION%
    TRACK=1.490
    ROD_LENGTH=0.015
    HUB_MASS=55.5
    RIM_OFFSET=0.030
    WBCAR_TOP_FRONT=0.3056, 0.1197, 0.170
    WBCAR_TOP_REAR=0.40223, 0.13956, -0.050
    WBCAR_BOTTOM_FRONT=0.3050, -0.0768, 0.370
    WBCAR_BOTTOM_REAR=0.4302, -0.04995, 0.010
    WBTYRE_TOP=0.1015, 0.1325, 0.005
    WBTYRE_BOTTOM=0.1223, -0.100, 0.00
    WBCAR_STEER=0.5496, -0.005, -0.180
    WBTYRE_STEER=0.2112, -0.04995, -0.180 ; Steering rod tyre side attach point
    TOE_OUT=0.0000 ; Toe-out expressed as the length of the steering arm in meters
    STATIC_CAMBER=1.0 ; Static Camber in degrees. Actual camber relative to suspension geometry and movement, check values in game
    SPRING_RATE=45000 ; Wheel rate stiffness in Nm. Do not use spring value but calculate wheel rate
    PROGRESSIVE_SPRING_RATE=0 ; progressive spring rate in N/m/m
    BUMP_STOP_RATE=100000 ; bump stop spring rate
    BUMPSTOP_UP=0.075 ; meters to upper bumpstop from the 0 design of the suspension
    BUMPSTOP_DN=0.060 ; meters to bottom bumpstop from the 0 design of the suspension
    PACKER_RANGE=0.110 ; Total suspension movement range, before hitting packers
    DAMP_BUMP=2517.9 ; Damper wheel rate stiffness in N sec/m in slow speed compression
    DAMP_FAST_BUMP=1510.7 ; Damper wheel rate stiffness in N sec/m in fast speed compression
    DAMP_FAST_BUMPTHRESHOLD=0.080 ; Damper bump slow/fast threshold in seconds
    DAMP_REBOUND=4087.5 ; Damper wheel rate stiffness in N sec/m in slow speed rebound
    DAMP_FAST_REBOUND=2656.9 ; Damper wheel rate stiffness in N sec/m in fast speed rebound
    DAMP_FAST_REBOUNDTHRESHOLD=0.110


    and feel free to correct all my mistakes, I know that my English is terrible
     
  2. Turismo08

    Turismo08

    Messages:
    12
    Ratings:
    +29
    Stiffer ARB front = Understeer
    Stiffer ARB rear = Oversteer
     
  3. Grabarz

    Grabarz

    Messages:
    64
    Ratings:
    +11
    i knew that from AC setup Guide :)
    and that's why i changed my ARB's

    I'm more interested into Springs, dampers etc stuff :D
     
  4. David Dominguez

    David Dominguez
    Premium

    Messages:
    2,568
    Ratings:
    +1,558
    Well you stiffened up the front ARB more than the rear, so you added more understeer...
     
    • Agree Agree x 1
  5. Grabarz

    Grabarz

    Messages:
    64
    Ratings:
    +11
    exactly :) clever idea from me

    now its about
    FRONT=29214
    REAR=15200

    car is tricky to control in corners, it goes into understeer at low speed and oversteer at med/high speed ...

    still no idea how to setup springs and dampers
     
  6. JackCY

    JackCY

    Messages:
    96
    Ratings:
    +58
    Hi, I've stumbled upon your posts looking at progressive springs, anyway, I've made my own R34 recently as well.
    What data did you find and where? Can you link, share?

    As far as understeer goes and the crappy Kunos R34, it has non existent aero in AC, I think it actually has a lift up to 6kg. The Kunos AWD2 system is torsen central differential with low max torque but immediate ramp up.
    Personally I made my own AWD2 controller, Kunos didn't even bother to make one, used data from wiki, youtube, etc. as to how the default and some custom ATTESSA controllers work. Allowing me to reduce front axle torque at low rear speed ratios but ramp it up when rear starts to go much faster than front. With high power (400+ wbhp) I've actually had to make the front axle torque higher.

    The Kunos R34 needs proper aero, I very much doubt that it is hovering around zero or with slight lift, it has front spoiler and all, it should have a bit of downforce like most cars. Or not?

    The Kunos R34 AWD needs to be ditched altogether, it is what ruins the R34 in AC :( It is just a dumb torsen central diff with no logic. You can remake the AWD2 torsen with logic but I would rather go all the way and do it proper with AWD not AWD2, regulate the torque split completely via a controller and not have the AC torsen logic mixed into it. The real central diff is pressure controlled from what I remember, you set pressure and that defines how much torque is put on front wheels. Where as with AWD2/torsen controller you are only setting the maximum torsen torque and the live torque is done by AC. With AWD you should be setting the torque via controller yourself all the time and AC shouldn't mess with it.

    With the Kunos R34, v7 tyres and optimum surface my time on Nord T. was 7:34.509, yeah I've had plenty Japanese pack WRs on RSRlivetiming before the 10 millions of wipes.

    With v10 I do not know but it should be similar. The updated AWD system helps a lot with making the car more responsive and less FWD like. The rest enable in setup adjustable springs, dampers, camber, toe and play with it, but yeah this requires a lot of knowledge and experience and time to tune it for a specific combo.

    Overall the civilian Kunos R34 is very soft, the front lip makes it bottom out all the time even with stronger springs and dampers. Plus you need the AWD system done first, aero at best too before you start messing much with springs, you can set some suspension you want/like/prefer and then tune the AWD to it and after that fine tune the suspension.

    It all also depends on what your target engine power is, what tyres.

    For an easy fix implement at least some ATTESSA logic, cannot make PRO though, AC cannot do controlled rear differential when AWD2 is used, I think with AWD neither :( And the EDL is broken as well, it hurts performance too, tried it just for the heck of it to have electronic rear diff, no chance.
    Harder suspension. And stiffer front ARB doesn't always mean less oversteer, it can also mean more oversteer, the guides are rough, very rough, they do not go into the fine details and conditions needed to be met for what they say. Take them with a grain of salt. It's all about balance and roll, these vary with different speeds etc.

    For my AWD2 controller I've used REAR_SPEED_RATIO, SPEED_KMH, LATG, BRAKE and change the max allowed central torsen diff force according to what I was able to find about how the ATTESSA behaves and how the R34 handles in reality vs in AC.
    I would use AWD not AWD2 when doing/revisiting R34 again though, similar controller.
     
    Last edited: Apr 2, 2017
  7. JackCY

    JackCY

    Messages:
    96
    Ratings:
    +58
    I can attest to that, as I have made mine for the stock power and suspension, then using nearly 500 wbhp the central diff just couldn't keep up.

    Speedhunters has the Mine's version article, very old but not many details, faster diff, wider track due to wheel offset but that I have to test if AC finally supports it now, it may after all the years with the latest suspension version.

    500 bhp is a good figure for the ST/SM tyres, 500 wbhp is stretching it.

    No matter what the car remains front heavy, 57% to the front is a lot, dunno how these lighter carbon rich versions do, try finding a weight balance of them, but one would need to remove a lot of front weight to even get close to just 56% while keeping the rear stock heavy.
    With a lot of power a rear wing and well balanced AWD should give it enough traction but stock the rear gets very light and doesn't have the grip to deliver 450+ wbhp with a weak AWD.

    The whole car needs to be redone.

    Otherwise it turns into a mess like Kunos did with the T/A Supra that is very hard to drive, fast but not a pleasure to drive.

    I'm not going to revisit the R34 for a long while, working on the Caterhams now and finding R34 mod open servers is hard. Will save the links for later, thanks.

    1) AWD
    2) springs, dampers, ARBs
    3) aero
    4) more power and readjust the above to fit the power level

    Tyres are tyres, all cars turn into supercars with supercar tyres in AC. I use the stock ST/SM so far. I've tested NSX that had supposedly Porsche 918 tyres, unreal. Put them on my moded R34, it was like driving on slicks or glue, so much grip and mainly crazy more cornering grip and G forces allowed. Was about 8-9% faster compared to SMs, a lot.

    Hence beware of tyres. Most mods go nuts and make unreal tyres that are like slicks yet are named as street tyres. Try reuse the stock Kunos tyres if you plan to compare the car to some other similar existing in AC.