Fw = force due to the mass of the vehicle. This force tends to act directly along the line of the control arm. There is some weight acting on the top of the strut tower, but this is so complex to analyze that it has to be neglected for sanity reasons. The vast majority of the weight of the car is acting on the steering knuckle (or spindle in the rear wheel). The bar i nthe middle between the control arms is there to represent the frame of the car. It is rigid making each of the control arms, either front or rear, act as a "2 force member".
A "2 force member" is one which is usually pinned at both ends and must, by definition, be in pure commpression or pure tension. A 2 force member cannot generate any other reaction. The strut bar is also a 2 force member.
N = the "Normal" force. This is the force due to gravity. Gravity always acts straight down, however more of the weight of the vehicle is acting on the outside wheel when cornering so there are 2 values for N.
Ff = the force due to Friction. The force due to friction is directly proportionate to the Normal force and the coefficient of friction between the rubber and road surface. Ff = (Mu) * N, where Mu = ~0.7 for dry road.
Ma = the "Moment" about the point A. Moment is the fancy name for torque. The total Moment about A is equal to the sum of the forces multipied by their perpendicular distance to that point. Because "Fw" acts directly through the points A and B, it has a perpendicular distance of zero and so creates no moment. But the friction force does and because N1 is greater than N2, Ff1 is greater than Ff2 and the subsequent Moment or torque about A is greater than at B. That means that the deflection of the top of the strut at A is greater than at B as well. This is implied by the size of the arrows at the top of each strut.
Because strut A experiences greater torque and the top of the strut deflects more than the top of strut B, the bar is in tension.
94' RS/GS/MS/CF Monster Turbo...coming soon.
93' GS SE, the Black Beast, the former love of my life...soon to be gutted and crushed.
94' GS, black on black, now in several small pieces...and one large crushed piece.
2007 Mazda3 GT Sport --- super fun
2004 Honda RC51 --- Lost forever to some theavin' bastard
My Worklog
My feedback thread
Never attribute to malice that which can be adequately explained by stupidity.