I need exactly this sort of knowledge myself to allow me to design a proper double wish bone set up for my AC Peel trident front end. So I am hoping a magic genie will pop out of a bottle, and help me understand how to choose A arm lengths, and inboard/ outboard positioning of their pivot axis, and how to choose a proper minimum height dimension for the king pin, as well as what values of castor and camber to shoot for at varying amounts of spring compression (bump/ jounce), and rebound, and how to best design the upper A arm for a suspension with a given wide based lower A arm dimension and location. I want to know this because I intend to use the stock single A arm/ wish bone that comes on Peel Tridents as a lower link for my intended better functioning set up.
The problem with the single swing arm set up on the Peel is that like a swing axle rear suspension, it produces far too much camber change with wheel travel. An often observed example of this effect would be if an old VW Beetle would become airborne after cresting a hill at speed- you could then observe the rear wheels tuck in at the end of their rebound travel. Innocent enough in a straight line, but could contribute to a roll over if occurring around a corner at speed, as the Bug would in effect be tending to trip over its too tucked in rear wheel, that was not maintaining a large enough contact patch with the road, and would be leaning too far over, thereby acting more as if you hit a curb whilst sliding sideways around a corner- as a pivot point to in effect trip a lateral roll over. The Peels, and some other minimalist designs attempt to compensate for this effect by utilizing tires with rounded tread surfaces, so that even though the wheel is tilting at too much of an angle, the actual contact surface remains closer to parallel to the road surface. However for performance applications, this narrows the contact patch too drastically for any where near optimal road adhesion during cornering.
Your Pfiel's suspension has made the right first step by utilizing a double wish bone design , so as to enable the road wheels to remain perpendicular during vertical wheel travel, hence allowing theoretically good maintenance of a proper contact patch with the road, when considering just this single variable of suspension design. But, truth be told, cars corner better if their tires tilt in a bit at the top when their road springs are being compressed by lateral cornering forces, as it allows the corresponding wheel to maintain greater perpendicularity with the force that it is resisting the car's tendency to roll between its front springs, and the force that makes it want to drift out wards in a corner. For this reason, non parallel upper to lower A arm/ shorter upper A Arm/ more inboard location of upper A arm pivot point have been proven helpful in achieving this effect. The Pfiel's designer does not appear to have considered this factor, as the twin A arms appear to be of equal length, parallel, and to be utilizing pivot axis located in a directly plumb orientation.
The length of the Pfiel's A arms also appears inadequate to provide for enough wheel travel for absorbing deflections induced by road irregularities. Then there are antidive/ squat concerns that are induced by braking, and acceleration forces causing forward and rearward weight transfer, respectively, that can be addressed by pivoting the horizontal axis of the inner arms front and rear pivot bushings,
whether it is best to use stiffer spring rates or an antiroll bar that partially negates the advantages of independent front suspensions, varying weight loads, your aforementioned Ackerman effect, and who knows what else to complicate matters.
The Ackerman effect refers to the need to consider the fact that the tire closer to the inside of a corner needs to transit a shorter radius path than the outer wheel going through the same corner, and is some how handled by choosing proper location of the steering arms mounted to the hubs, and is effected by length of wheel base. Unfortunately, I do not see the steering arms for your Pfiel in this view, and wouldn't know how to assess their correctness in regard to this concern if I could.
Can anybody else help Richard or myself in these regards?
