11 FRONT SUSPENSION TYPES
The F308 car has two different options for its front suspension.
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WMP [Wishbone Mounted Pushrod]: This is a conventional suspension with the pushrod
mounted on top of the lower wishbone. This suspension is only in detail different from the
front suspension on our previous F3 car.
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UMP [Upright Mounted Pushrod]: In this suspension the pushrod is mounted on the upright.
The pushrod position is adjustable in longitudinal sense. Extra load is transferred to the
corner front inner wheel, potentially reducing understeer thanks to a more equal vertical load
between front inner and outer wheels.
Between both suspensions the following parts are different:
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Lower wishbone
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Ackermann arm
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Lower part of the pushrod
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Additional bracket for UMP
For the UMP suspension we have foreseen 4 different positions [in longitudinal sense] to increase or
decrease the effect typical of this suspension lay-out. Two different brackets give a total of four
positions. We call these positions according the distance they are set behind the front axle line.
Positions:
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P -5(mm) [on standard bracket]
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P -10 [on optional bracket]
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P -15 [on standard bracket]
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P -20 [on optional bracket]
There are various ways to express the difference between the 4 positions, we choose one that clearly
shows the level of effect.
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P -5 transfers ‘X’ load to the corner inner front wheel
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P -10 transfers 70% more compared P -5mm
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P -15 transfers 130% more compared P -5mm
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P -20 transfers 170% more compared P -5mm
Further information:
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The effect on load transfer [by turning steering wheel] of the standard geometry with ‘typical’
caster is near identical to the effect on load transfer on the UMP P -5
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In a straight line the UMP behaves identical compared to a conventional WMP front
suspension. UMP’s effect increases with steering angle. Therefore the effect is most
noticeable in slow corners.
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All 4 positions cause an increase of steering force, P -20 being the heaviest of the 4 positions.
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All positions cause an increased load transfer on the rear axle opposite in direction compared
to what occurs on the front axle. This will decrease traction capacity, P -20 causes the
largest load difference between rear inner and outer wheel.
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Roll centre height, camber, camber change, steering ratio, damper ratio, ARB ratio,
Ackermann, off-set and trail do not vary between the 4 positions. When changing the
pushrod position always check the front ride height, the only [other]feature that varies
between different positions.
