Bill Verburg

yes, the chassis ignoring twist has a single CoM but there is is a a different CoM for the transverse slice of the chassis that the suspension is acting through, connect the front and rear versions and you have the notionary mass axis.

The 2 components of roll are geometric and elastic, the geometric comes from the roll axis height variation front and rear, elastic from the springs, tires, roll bars etc.
The following from Mark Ortiz
the geometric component is determined by the roll center relation to the CoM, higher roll center at the front implies more geometric roll resistance at the front, hence more load transfer at the front, other things being equal.
In steady-state cornering (constant speed, on a constant radius), on an unbanked road surface, the total load transfer from the inside wheels to the outside wheels depends entirely on the height of the whole vehicle’s center of mass (center of gravity, or c.g.) and the track width at the c.g.
Suspension design and tuning have almost no effect on the magnitude of the total load transfer. What we mainly do with suspension design and tuning is control the distribution of that total, between the front and rear wheel pairs.
We customarily consider the car to be a rigid object, supported by a single compliant structure at each end. The sprung structure is the rigid object; the front and rear suspension systems are the compliant structures.
There are portions of the load transfer that come from the unsprung components, and there are portions that come from the dampers if the car is rolling upon corner entry or de-rolling on exit. However, for simplicity in answering the present question let’s look just at the components of the load transfer that come from the inertia force (centrifugal force) of the sprung mass acting through the suspension, in steady-state cornering. There are only two such components: elastic load transfer and geometric load transfer. Elastic load transfer comes from elastic roll resistance: the roll resistance supplied by the springs and anti-roll bars. Geometric load transfer comes from the properties of the structural components attaching the wheels to the sprung mass, which can be arranged to generate forces opposing roll, or geometric roll resistance.
With independent suspension, these two components influence each other more than is commonly recognized. The load distribution on an independently suspended wheel pair affects how much geometric roll resistance the wheel pair has, for any given suspension geometry. To illustrate with an extreme case, if the inside wheel is off the ground, the geometry of its suspension linkage is irrelevant and only the geometry of the outside wheel has any effect on the car.
When we speak of roll center height, we are speaking of an imaginary point whose height represents the amount of geometric roll resistance for the front or rear wheel pair. If this point is assigned properly, we can closely approximate the geometric load transfer at one end of the car as: roll center height times sprung mass centrifugal force at that end of the car, divided by track width at that end of the car.
When the suspension is symmetrical, the point you generally see in the chassis books – the force line intersection – is a good approximation. When the suspension is not symmetrical, using the force line intersection as the roll center can lead to major mis-predictions of car behavior. Sometimes the force lines may be parallel, in which case there is no intersection.
We may define a line connecting the front and rear roll centers, called the roll axis. The car doesn’t really roll about this line, but as a crude approximation we can reasonably think of it as doing so.
If we raise the roll axis at both ends, the geometric roll resistance is greater at both ends. If we raise one end of the roll axis and lower the other, leaving its height at the c.g. unchanged, the total geometric roll resistance is unchanged, but we increase the geometric roll resistance at one end and lower it at the other. The elastic elements – the springs and anti-roll bars – are not affected by this.
So the end where we lowered the roll center has less geometric load transfer and the same elastic load transfer as before – hence less load transfer overall. This will make that tire pair grip better, because they will be sharing the work more equally. At the opposite end, the elastic component will likewise be unchanged, but the geometric component will be increased – hence more load transfer overall.

Bill Verburg

I agree w/ Tosi here, choose the components for you r ride height and use

for street use at RS height or a little lower the RS are fine, at the extremes, down around RSR height, you may gain some advantage from the geometry imparted by the alternatives

Peteinjp

I haven’t compared the erp and bib units but I’m pretty sure that the both raise the spindle about the same amount- a 10 or so mm higher than the RS units that said at the moment I’m discussing a fitment issue with Tarett regarding the ERP units. The bolts the hold the wheel bearing retainer in place at literally thousandths of an inch from interfering with the hub. I’ll update my thread with some photos.

Pete

nk993

Thanks for pointing it out. Looked at your pics in the 964 thread. Definitely needs to be replaced IMO, even if the force is "good enough". part needs a revision for sure