Suspension Shock Length

Discussion in 'Car Modding' started by kermit, Jun 2, 2016.

  1. kermit

    kermit Registered

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    Hi Guys,

    I am struggling to understand how the following line in my HDV work.

    BumpStopTravels=(-0.122,-0.16)

    My understanding is the first value is my compression but the second i do not understand i gather its rebound?

    does this value define the overall damper travel length?

    the real life specifications of the damper is as follows

    Length free =496.80mm
    Compressed = 372.87mm
    Stroke = 122.93mm

    so what i have is -0.122 for as is the stroke of the damper. and the second value i have put the vehicles right height.

    can anyone shed some light if this is correct?

    i have seen a thread about this but it went way over my head.

    Cheers.
     
  2. Jokeri

    Jokeri Registered

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    Bumbtravel = (dampercompressedlenght - damperlenght) / motionratio
    Reboundtravel = (damperextendedlenght - damperlenght) / motionratio

    Bumpstoptravel = -(design ride height + bumptravel)
    Reboundstoptravel = -(design ride height + reboundtravel)
     
  3. kermit

    kermit Registered

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    Thanks for the reply.

    but my HDV is based on the NSX and it does not use bump travel or rebound travel values anywhere in the HDV.

    having said that i gather i can still calculate that without defining them in the HDV and it will use bumpstoptravel instead?

    also what is the difference between damperextendedlength and damperlength?
     
  4. Raintyre

    Raintyre Registered

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    I am not sure whether new 'BumpStopTravels' works in the same way as old 'BumpTravel' and 'reboundtravel', but the numbers in skipbarber.hdv are the same:

    [FRONTLEFT]
    BumpTravel=-0.000 // suspension travel upwards
    ReboundTravel=-0.120 // suspension travel downwards
    BumpStopTravels=(-0.0,-0.12) // suspension travel (upwards, downwards)

    I think you should take 'Bumptravel' value as the minimum ride height before bumpstop is hit, and 'Reboundtravel' value as the maximum ride height before rebound stop is hit. So it is a ride height reference but with reversed sign!!

    Example 1:

    BumpTravel=-0.12 /// Ride height for bump stop= 0.12
    ReboundTravel=-0.30 /// Ride height for rebound stop = 0.30
    ...
    RideHeightRange=(0.20, 0, 0) /// Static ride height = 0.20

    At this case, your suspension can oscilate freely between ride height 0.12 and 0.30. That would be 0.08 travel downwards (0.20-0.12) and 0.10 travel upwards (0.30-0.20).


    Example 2:

    BumpTravel=-0.0 /// Ride height for bump stop= 0.0
    ReboundTravel=-0.082 /// Ride height for rebound stop= 0.082
    ...
    RideHeightRange=(0.034, 0, 0) /// Static ride height = 0.034

    At this case, your suspension can oscilate freely between ride height 0.0 and 0.082. That would mean a 0.034 travel downwards (0.034-0.0) and 0.048 travel upwards (0.082-0.034).


    I think it worked like this on RF1, i hope it is the same on RF2...
     
  5. lordpantsington

    lordpantsington Registered

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    The other way to think of this is as the distance the wheel moves to hit the respective bump stop when at 0 ride height. In your Example 1, the bumpstop is already being compressed 12mm @ ride height 0mm. So 12mm of downward wheel movement (hence negative sign) before the bump rubber spring rate is nullified, and there is 30mm before it is 'fully extended' (aka rebound stop, also down/negative).
     
  6. Jokeri

    Jokeri Registered

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    What is the lenght of the damper when its installed to the car? ( that doesnt actually make any difference)

    When the car is stationary, how much can the damper move down before it hits the bumbstop? How much can it move up before it hits the rebound bumbstop?
     
  7. kermit

    kermit Registered

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    ahhh, i think i may understand.

    So with my current setting

    i have Bump stop travel -0.122 basically gives me 0.04cm compression, instead of the actually 0.10cm compression that i need, and this is the difference as my static ride height is 0.16cm. so really i should be setting my bump stops to 0.06 to give me that full range.

    when it comes to rebound i have it at my ride height of -0.16 which means there is no rebound? but how much would a road car rebound?
     
  8. lordpantsington

    lordpantsington Registered

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    Rebound is always determined by spring rate and load.

    Assuming MR of 1.0, a 100N/mm spring will compress 20mm under a load of 2000N. If 2000N is your static load, the rebound travel is 20 mm. Springs in their natural state are extended, thus the damper is also extended fully when not loaded.
     
  9. Raintyre

    Raintyre Registered

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    I am not sure i understand your wish and i think you are mixing cm and m units (it should be expressed in m) but if your total travel is 0.122m and you want a 0.100m of compression after static load i guess then you have 0.022m left for the rebound.

    I would use this:

    BumpTravel=-0.06 /// Ride height for bump stop= 0.06
    ReboundTravel=-0.182 /// Ride height for rebound limit= 0.182
    ...
    RideHeightRange=(0.16, 0, 0)


    Travel downwards = 0.16-0.06 = 0.1m
    Travel upwards = 0.182-0.16= 0.022m
    Total travel = 0.182-0.060 = 0.122m

    Is this what you are looking for?



    What i ask is:
    Why we can set a bump stop stiffness and not a rebound "stop" stiffness? How rfactor handles the rebound limit behavior? :confused:
     
  10. lordpantsington

    lordpantsington Registered

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    The stop spring rate is set at both extremes (think of it as a soft limit to travel). If you run data logging, you can, under certain circumstances, see a negative value for damper position (indicating you are indeed on the rebound stop).
     
  11. kermit

    kermit Registered

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    sorry i did mix up the units when writing my reply, just noticed now.

    what i was after was 0.122 compression expressed in meters.

    so the values i ended up with were BumpStopTravels=(-0.038,-0.170 with my ride height being 0.160 giving me the difference for compression.

    however rebound i have just added the 0.10 on top of ride as a guesstimate.

    i do notice the values i'm using above my tyres tend to go through the body frame when hitting a good size curb or bump.

    my next question is how does RF measure the ride height, is it indeed ground clearance?

    Cheers.
     
  12. lordpantsington

    lordpantsington Registered

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    For the 3d Model the ride height is assumed to be zero, the up/down axis origin sits on the bottom of the chassis.
    For the Physics Model Ride height has been assumed to be measured at each of the first 4 undertray locations (LF, RF, LR, RR). They might just be measured at the axle locations.
     

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