Announcement

Collapse
No announcement yet.

The effects of motion ratio on IFS valving

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • The effects of motion ratio on IFS valving

    Hey all,

    There’s plenty of good discussion around about the effect of the IFS motion ratio (MR) on the relationship between strut shaft travel and wheel travel, and the effect of changing coil height or coil preload on ride height. However, many are not aware of the effect it has on damper valving. The schematic below shows the mechanics of the motion ratio at work on the IFS lower control arm;



    Once you know the simple relationship between motion ratio and Force and velocity, you can then understand how the valving changes from the strut position to the wheel position. The most important equations are;



    You can see from these simple equations that an increasing motion ratio (moving the coilover towards the end of the lever arm) increases the Force at the end of the lever arm, and will decrease the velocity. The plot below shows the scaling effect of the Force and velocity equations;



    This plot shows the effect of motion ratio scaling for the Bilstein BE5-D563-M2 strut. As you can see, the lower the motion ratio becomes, the softer the valving ends up at the wheel position. You can also understand why struts with soft compression valving (such as TRD with 1500N) can end up with very little compression valving at the wheel, leaving the IFS exposed to hard bump outs. A motion ratio of 0.75 is what the Ford Raptor has, with a strut that is located well outboard near the ball joint, as shown in the photo below on the left, compared with a Prado on the right;



    As you can see the Prado strut is located further back along the arm, roughly at the mid-point. As such, the low ca. 0.53 motion ratio on the Prado IFS has a very strong effect on scaling the valving, and out at the wheel position it is quite soft.

    Another feature that becomes clear from this scaling is the maximum amount of critical damping (how quickly roll, pitch heave etc. can be cycled out) that can be achieved at the wheel position. The amount of critical damping you can achieve is strongly dependent upon the knee velocity in the low velocity part of the damping curve, and the motion ratio can change this dramatically. The plot below shows the maximum critical damping that can be achieved at the wheel position for a 100% critical strut;



    While this plot demonstrates that the maximum amount of critical damping is around 27% (0.5291x0.5291 = 0.27) for the Prado IFS, in practice you will be limited by the bleed shim and how thin the bleed circuit can be made. In practice a knee of around 50mm/s is feasible, giving around 17% at the wheel.

    This lack of critical damping at the wheel position for the Prado indicates that Toyota designed the front of the Prado for comfort as opposed to handling ability. The rear OEM shock has critical damping of ca. 63%, considerably higher, and this is really where the kinematic control of the Prado comes from. Without that high critical damping in the rear shocks, the Prado would be a very sloppy boat, with pitch and roll motions being extremely difficult to cycle out.

    Even so, it is still possible to maximise the kinematic response of the Prado IFS by shortening the knee velocities. Anything over 150mm/s is kinematically inactive, and will not work against body roll, pitch etc. Around 50-100mm/s at the wheel position is what makes a big difference on a heavy 4wd. As such, to make the front struts kinematically active requires shortening the knee at the strut position to around 50-60mm/s, so that at the wheel position it is around 100mm/s (50x1.89=95mm/s).

    I’ve designed a new valving curve for the front of the Prado on this basis, and the new valve stack is being built into Ironman Pro hydraulic struts. Shortening the knee will produce around 500N more rebound at 100mm/s, which will help minimise squat and heave under low speed driving conditions, something the Prado is unfortunately quite susceptible to.

    Hope you are all getting the best you can out of the Prado IFS!

    Best

    Mark
    Whitey
    Shockie Maker of the Month Award
    Last edited by Whitey; 20-09-2017, 03:18 PM.
    2006 GXL petrol auto. ARB deluxe bar x3 HID IPF's, ARB alloy roofrack, ARB awning, BFG A/T, Safari snorkel, Piranha breathers, Pacemaker extractors, custom Ironman 45710FE 436-569mm with Dobinsons 350, custom Ironman 45682FE 383-618mm with Dobinsons 487, Firestone kevlar 60psi airbags, 30mm extended Roadsafe links, AMTS bashplate and recovery points, ABR Flyer with Powersonic AGM.
canli bahis siteleri bahis siteleri ecebet.net
mencisport.com
antalya escort
tsyd.org deneme bonusu veren siteler
deneme bonusu veren siteler
gaziantep escort
gaziantep escort
asyabahis maltcasino olabahis olabahis
erotik film izle Rus escort gaziantep rus escort
atasehir escort tuzla escort
sikis sex hatti
en iyi casino siteleri
deneme bonusu veren siteler
casibom
deneme bonusu veren siteler
deneme bonusu veren siteler
betticket istanbulbahis
Working...
X