Mike Kojima posted on December 29, 2008 04:00
The caster angle, which when more positive, helps improve straight line stability, gives more on center steering feel and gives negative camber gain when the wheels are turned, looks to be reasonable, at around positive 6 degrees or so. Eyeballing the kingpin inclination angle indicated that the scrub radius is close to zero with the Dave point being close to the centerline of the tires tread. The relatively steep looking kingpin inclination angle is also good for steering self centering and off center steering feel. There is only a little anti dive in the geometry, which means that trail braking should not cause a non-linear build up of understeer due to wheel rate rise caused by bind induced by brake torque. The upper control arm is angled backwards slightly which gives a small degree of anti dive and a slight increase in positive caster under roll. This caster increase also means an additional gain in negative camber on the outside wheel under roll and a slight firming of the steering feel and a gain in self centering as the car heels over in a turn. In plain English, this is good!
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| The steering rack bolts to the subframe in the vertical plane with stiff bushings. This hold the rack much more firmly than the 350Z's large lateral mounted bushings. The lateraly orriented bushings allowed the rack to slip back and forth, not good. The smaller vertical bushings live where the green arrow points. The change in bushings and rack mounting greatly improves steering feel and precision. |
We also noted that the front suspension and steering rack was bolted to a ridged aluminum subframe that is bolted solidly to the chassis. An interesting note is that the 370Z uses an elaborate lightweight aluminum subframe while the exotic GT-R has a subfame made of plain old steel. Maybe the much anticipated V-Spec R35 will use aluminum to get the GT-Rs might mass down.
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| The same mounting is used on both the drivers and passengers side of the steering rack. The green arrow indicates the bushing location |
The steering rack and upper and lower control arms bushing are small diameter low compliance parts. This is a welcome change from the 350Z which had a lot of gushy rubber in the front end, particularly in the lower control arm and the steering rack. In the development of the M-Workz time attack 350Z, the outer lower control arm bushing would fail and steering rack bushing deflection movement of up to 0.600 inches were observed under load. That's nearly two thirds of an inch of bump steer inducing, sloppy feeling, camber killing mush! The 370Z won't have these issues. The steering rack in addition to being more solidly mounted is in a nearly perfect position with the inner tie rod planer to the lower control arm pivots and outer tie rod in line with the outer lower ball joint. This positioning nearly eliminates bump steer.
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| The 370Z has a nearly perfect tie rod angle for minimal bumpsteer. The inner tie rod pivot is in line and on the same plain with the green line drawn through both lower control arm inner pivot points. This green line is in the same plane and paralle to the second plainar green line drawn through the tie rod and ball joint. The red lines are both plainar and paralle and are drawn through the steering tie rod and the pivot axis of the lower control arm. What does is mean in few words? That the lower control arm and steering tie rod travel in nearly the same arc as the suspension strokes thus having minimal bump steer. Great design Nissan! |