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Power & Coast

Discussion in 'R3E Setups' started by 2scoops, Jan 20, 2016.

  1. 2scoops

    Premium Member

    Can someone explain briefly what they are please?
  2. Lars Hansen

    Lars Hansen
    RDs Ion-Engine....0-60 in six days. Staff Premium Member

    No. :D

    (Note that I'm not a petrol-head, so there's every chance I've gotten this wrong.....)
    (Also note that this applies to RWD only. I have very little experience with FWD)

    Okay, so the basis of the whole discussion is that when you enter a turn your left and right wheel will have to rotate at different rates.
    The outside wheel has further to travel, and the wheels are the same size, so it'll have to rotate faster to travel the same distance, right?

    The differential lock controls how much torque (power) is transferred to each wheel, and how freely each wheel is allowed to spin.
    Fully open (0%) means each wheel gets 50% torque no how at which speed it spins, fully locked (100&) means both wheels spin equally fast and the torque gets distributed to make this happen.
    Easiest way to picture this is to imagine a car with the left wheel on dry tarmac, and the right on a patch of ice.
    With a fully open diff, both wheels gets 50% torque, but there's no traction on the right wheel so you're not going anywhere.
    A locked diff means that the torque gets transferred to the left wheel (since it's spinning slower), so you get more power to the wheel with traction.
    With me so far?

    So what does this mean to our race-car?
    Well, first of all our race-car has two diff-settings, power and coast.
    These control the differential when you're ON the throttle (power-setting) or OFF the throttle (coast-setting).
    So the power-setting will control behaviour EXITING a turn (since you're on the power) and the coast-setting controls behaviour ENTERING a turn (when you're off the power).

    Okay, so we're mid-turn in a right-hander and we're getting back on power.
    Since we're turning right, the weight is shifting left and thus we have more weight (and thus more grip) on the left hand tires, right?
    If you have a power-diff of 100% all the torque would go to your outside (left) wheel to try and get it to spin as fast as the inside wheel. And since we have lots of traction there due to the weight-shift, the rear of the car would snap around, and off the track we go.
    If you have a power-diff of 0%, the torque would get evenly distributed to both wheels, but since that means we only get half the torque to the wheel that actually has traction, the read end won't come around, we under-steer and off the track we go again.
    Power-diff: High values=over-steer behaviour, Low values=under-steer behaviour.

    It's vice-versa for the coast.
    We're turning into the right-hander, and the weight is still transferring to the left, but this time we're using the engine to brake the wheels as we down-shift.
    A 100% diff-lock means more torque (and thus engine-braking) goes to the outside wheel. dragging us to the left (under-steer).
    0% diff-lock means means more torque goes to the inside wheel, dragging us right and over-steering.
    Coast-diff: High values=Under-steer behaviour, Low values=Over-steer behaviour.

    The pre-load setting dictates how much lock is built-in at neutral throttle.
    It controls the TRANSITION between acceleration and braking.
    If the car is 'skittish' when switching from braking to accelerating, lower the pre-load.
    On the other hand, if it's too slow to react, increase the pre-load.

    Having said all that, the best way to figure it out is to experiment.
    Do some laps on a track you know well, and then try changing ONE of the values and see what changes that results in. Once you have that setting to your liking, move to the next one, but only ever change one at a time.
    And as always, there's no magic number. The trick is to find a balance between control and power.
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  3. Caramidaru Andrei Bogdan

    Caramidaru Andrei Bogdan
    Mr. C Premium Member

    What Mr. Lars said but if you want the easy way out (like me) use setup engineer :) and if I get in trouble I read again Rd setup guide.
  4. 2scoops

    Premium Member

    Lars, thats an excellent report, thank you very much :)
  5. 4 8 15 16 23 42 108

    4 8 15 16 23 42 108
    Only the 5th-most famous race driver from Kerpen

    I can only second that, especially pre-load was something I could feel but never describe to myself yet.
  6. Brian Greenwood

    Brian Greenwood
    "Brian the Snail" Premium Member

  7. Jriv012

    Riverside Premium Member

    + 1. Thanks, Mr.!
  8. Jopamir

    Premium Member

    @Lars Hansen

    Really helpful!
    Thank you very much.
  9. Keith Dixon

    Keith Dixon
    Premium Member

    Although this is a vid for Pcars it explains it and shows it quite well, I found the setup changes made in Pcars to be a lot more prominent, you could feel every change you made so it was quite useful in teaching my youngest

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  10. Jopamir

    Premium Member

    Fantastic video Keith!
    I suppose you have other videos and I sure will watch them :geek:
    Thanks for sharing
    J Paulo Miranda