Differential Setup.

Discussion in 'General Discussion' started by Simulation_Player, May 7, 2023.

  1. Simulation_Player

    Simulation_Player Registered

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    Hello all,
    I needed some tips, advice on tuning differential, especially the pump setting. Sadly the explanation given in setup menu and Skipbarber HDV file .....i didn't understand both of those.

    the preload , power and coast setting i understand enough (i think)
    so what i know (in short) >>

    Preload : is basically time it takes to reach given diff lock during coast AND power. so it doesn't change the amount of lock itself but how sooner or later it arrives.

    Power : how much power u want to transferred to outside/ loaded driven tyre on throttle application, this is "easy" to set by looking at tyre HUD and seeing the inside tyre getting hot on throttle, i tune it based on that and just general feel.

    Coast : How much wheel speed difference do u want during off throttle condition, more lock means more the 2 wheels spin at same speed , less turning, more understeer turn-in and stabilize braking a bit.

    Pump : NO IDEA ! :confused:

    so this is what i know so far , please feel free to correct me or add anything i don't know.
     
  2. Lazza

    Lazza Registered

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    It would be best to concentrate on the skip barber HDV comments. Bear in mind the way it seems to work when tuning a car can be dependent on how the car maker has set up the diff, and of course the effect of any change depends on what's currently happening.

    Preload for example is a base locking, which might feel like adjusting the timing of engagement but really isn't. High enough preload will give you a spool (solid, locked) diff, not because it's applied with a delay of 1/infinity but because it's an amount of constant locking. More discussion on preload and some of the others here https://forum.studio-397.com/index.php?threads/diff-preload-description-documentation-bug.73497/

    I'm sure these will have been discussed multiple times, from both a setup tuning and modding point of view, and these are perhaps completely unchanged since rF1 so will be lots of historical discussion too. You just have to ignore the subjective stuff people come up with.
     
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  3. Simulation_Player

    Simulation_Player Registered

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    Thanks for commenting , now i understand preload diff much better.
    it is the amount of torque that must be overcome THEN differential works on our setup values of power and coast settings , correct ?
    So there is a base or default amount of power and coast locking before preload is overcome, so do we set this base lock with differential pump ?
     
  4. Lazza

    Lazza Registered

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    No, they're separate things.

    A car with all 4 options makes things more confusing, because you can do several types of diff using less than those 4 options. As doddynco went through in that other thread.

    The main diffs I've done are clutch packs, using preload and then power/coast for the ramps. No viscous (diff pump) at all.

    Preload needs to be overcome before the driven wheels will spin differently, and that means the Nm between the rear wheels. Power and coast lock in accordance with the incoming torque (from the engine), so generally the same 'fraction' will give more power lock, since you get more power than coast torque coming into the diff. Pump is a constant viscous locking, like an auto transmission, with 100% being the full amount set. And then of course a particular car probably won't show you any of the underlying values but just give you setup numbers to play with.

    So 3 different avenues with those settings, they don't all do the same thing.


    *edit: sorry, I said the torque coming from the engine, really it's the torque from the driveshaft. So it'll vary between gears too.
     
    Last edited: May 8, 2023
  5. Simulation_Player

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    So before preload is overcome the diff is locked ? completely or some default value ?

    Tbh i don't know , how auto transmission work. but what i take from this , is that pump basically sets both power and coast lock in 1 setting....on top of individual power and coast setting.
    so in case i want to increase both power and coast same time instead of changing them individually i can just add more pump lock correct ?

    i don't 100% get what all of these is doing , especially the pump but....so far pump setting seems redundant ....since i never run out power , coast and preload values anyways.
    so unless pump does something that power, coast and preload can't do, it seems overkill to me.

    P.S : damn it , i wish they just added e-differential to these F1 cars (like they have IRL ...or so i have heard) where it sorts itself and u can choose different preset maps....and off you go.
     
  6. Cosmo

    Cosmo Registered

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    As I understand it, the "pump" setting is more akin to a viscous (fluid coupling) differential, where as the difference in wheelspeed increases, more torque can be redirected to the slower wheel. Power, Coast and Preload relate to plate-type (Salisbury) differentials.

    The "pump" setting dictates how strong this viscous coupling is, with 100% equalling the value in the DiffPumpTorque line in the [DRIVELINE] section of the HDV, the value of which is in newton-metres per radian wheelspeed difference per second.

    That is to say, with a DiffPumpTorque value of 30, and 100% diff pump, the viscous coupling can redirect 30 nm/rad/sec maximum :)
     
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  7. Lazza

    Lazza Registered

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    From the HDV:

    preload torque that must be overcome to have wheelspeed difference

    That is a complete lock. Look for information on LSDs, specifically preload and ramp angles. There are many sites and example videos.

    Power and coast lock in proportion to the input torque (from the driveshaft).

    The viscous coupling acts between the driven wheels, it's like a soft version of the preload. So the pump acts on both power and coast, yes, but it's doing it differently.
     
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  8. Simulation_Player

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    Thanks both @Lazza and @Cosmo
    I did look up some videos on LSD , it did help me visualize. also did some motec runs on skidpad. So far only did ON THROTTLE/POWER test see how
    A) 0% vs 100% pump diff does
    and
    B) 0% vs 78% power diff does (78% is MAX lock for FPRO)

    so far both did what i expected , 100% pump and 78% power lowered the inside wheel rotation compared to "open" settings.
    problem is they both are doing exactly the same thing , so i don't know which of these 2 (pump or power) to tune , if i wanted to lower inside wheel spin, since both get same job done.
    I will do coasting test later to see if i can draw some conclusion.

    if you have explanation or example , on which scenario it is better to tune pump or power specifically, i would like to hear it.
     
  9. redapg

    redapg Registered

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    @Simulation_Player I have an old rF1 Setup Guide and there i have the following Descriptions, that may be helpful:
    (An important Line is marked in bold)
    Pump:
    at 100%:
    - Stabilizing Power when yawing and better Traction when Accelerating
    - Understeer. Stable in Corner Entry, less stable in Corner Exit
    - Worse Chassis Responsiveness
    at 0 %:
    - When Accelerating, the inner Sides of the Tires lose Stability
    - Oversteer. Unstable in entering Corners, stable in exiting Corners
    Advantages and Disadvantages can be balanced with the Differential Power
    Power:
    at 100%:
    - Good Propulsion but Car understeers when Accelerating
    at 0%:
    - Lack of Propulsion when exiting a Corner, Oversteer possible
     
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  10. Simulation_Player

    Simulation_Player Registered

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    I read about viscous diff on wiki, it says that it offers more smoother transition to locking than mechanical type
    In some viscous couplings when speed is maintained the fluid will accumulate heat due to friction. This heat will cause the fluid to expand, and expand the coupler causing the discs to be pulled together resulting in a non-viscous plate to plate friction and a dramatic drop in speed difference. This is known as the hump phenomenon and it allows the side of the coupler to gently lock. In contrast to the mechanical type, the limiting action is much softer and more proportional to the slip, and so is easier to cope with for the average driver.
    https://en.wikipedia.org/wiki/Limited-slip_differential

    so if it is correctly simulated in rf2 , the conclusion i draw is that i should get most job done via pump diff and tune out remaining problems via power and coast settings
    like @ redapg said " Advantages and Disadvantages can be balanced with the Differential Power "

    one more interesting thing wiki says that
    " Any sustained load which overheats the silicone(the fluid in differential) results in sudden permanent loss of the differential effect "

    do we have differential fluid temp simulated in rf2 ? i didn't see anything like that in HDV file, maybe it is defined somewhere else.
     
  11. Lazza

    Lazza Registered

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    No, it doesn't do that. Again, the HDV is your reference.
     
  12. Simulation_Player

    Simulation_Player Registered

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    Reviving the old thread for a bit,
    i'm doing setup work of diff by looking at wheel speed of both rear wheels. So far i managed to get them spin at similar speed in final portion of cornering. i managed to do this with ~30-35% power lock on 2 different cars (IR18 and FPRO) at monaco.
    i choose monaco because it requires low gearing hence more torque at wheels plus add low speed corners with high HP..... thats a good recipe for inside wheel spin.
    so whats the problem ?
    Why does the power lock can go upto 70-80 % , when even on monaco 30-35 % acts almost like a locked diff ?
    I think i may be missing something here, maybe i'm not looking at other stuff ? so far i only look at wheel speed difference and if that is close enough, i call it a day for diff setup BUT i want to know why such high lock values exist, is there purpose for it.

    more fun thing i found out that indycar uses spool diff at oval , i'm sure there is a reason for it but i can't think of any especially when LSD exist , so why complete spool ? very interesting thing.
     
  13. As far as I understand the comment in the HDV file preload is the amount of power which must be reached before the diff will unlock the wheels (wheel difference can be 100% at a non-locking diff whereas if you have a 100% locked diff wheel speed difference is theoretically 0% - and if there is any amount of power needed to make the diff unlock (to what percentage ever) it is preload settings value (according HDV file)).
     
  14. Simulation_Player

    Simulation_Player Registered

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    I think you may have missed my point from earlier comment, i was focusing on power lock differential.
    but the second line did add some interesting info on preload , more stuff for me to think. Now i wonder what is preload doing in oval spool diff , since it is 100% locked together.
    I don't remember if we even have diff adjustment in oval trim of IR18, will check later . I imagine think all option would be greyed out since its a spool diff.
     
    Last edited: Aug 6, 2023
  15. Simulation_Player

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    To add more info on this topic (if anyone is reading) ,
    i now tested 88% power lock on IR18 around monaco , it certainly drives quite differently and it shed some light on this topic for me
    The high speed section Turn 13 , the car don't want to turn as much on T13 entry compared to my original 32% power lock and rest of the corner , the car wants to go straighter , but i do believe it requires better driver execution with 88% lock ...it is stable only if your inputs are more smooth and precise otherwise it is more punishing than 32% power lock.
     

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