mustangdebt

I'm not horribly knowledgeable on cars, though I'm getting there (slowly).. and in an effort to speed that along I was hoping some people here could help me out. I've read over and over that UCA/LCA help reduce wheel hop and what not, but what exactly are they doing to do that? What is the point of their existence (if they were having an existential dilemma)?

Thanks!

UberHax0r

from: http://www.globalwest.net/Mustang_rear_control_arms.htm

"When a car leans in a curve, one end of the rear axle is moving upward relative to the body while the other moves downward and both ends are moving in arcs. The Mustang’s lower control arms govern the rear axles up and down movement, as well as keeping it located fore and aft. The upper control arms serve to locate the axle and allow it to move in the aforementioned arcs."

Norm Peterson

I think debt wants to know how LCAs/UCA affect traction and wheel hop, not how they locate the axle during cornering. You need to look closer up.

It's not the links (meaning just the steel thingies) themselves.

Mostly it's the use of firmer bushings (typically polyurethane) or bearings (rod ends) installed in the ends of aftermarket(and apparently the OE GT500)LCAs/UCA that kills (or at least reduces)wheel hop. OE rubber is somewhat more flexible (compliant is the more precise term) so they can effectively sell this car to a wider range of buyers and locations. Most of the time, the softer bushing works OK, but as it "squishes" under the initial launch 'hit'it stores energy that can be suddenly released. The tire slips a little, grabs again, squishes the bushings again,and the cycle continues. OE bushings are intended to act a little like springs, and just like coil springs or valve springs they aren't going to remain well-behaved when any energy stored in them is suddenly and uncontrollably released.


Norm

mustangdebt

Ah. That helps quite a bit, thanks guys.

shooter23

hes correct, the stock LCA have quite a bit of flex in them, mainly from the weak bushings.

this is done, becuase they are then quieter. The stronger the bushings for traction, the louder they are.

itchy5

I think this is for the 4 link rear on the previous mustangs. It seems like the LCA's on our cars locate the axle longitudinally and allow it to move along the arcs.

F1Fan

Hi itchy5,

Exactly! The lower LCA's formthe arc that the axle's lower mointing points can move inwith the other halfof the arc defined bythe UCA andthe axle's upper mounting point. Between the two arcs defined by the control arms,chassis mounting points andaxle mounting points the arc the axlemoves in and the axis it rotates aboutare defined. The softer the busingsat the ends ofthese control arms the more or higher the level of isolation from road noises transmitted by the control armsto the body side mounting points. Additionally just as Norm describes the softerrubber O.E. bushings allow more freedom for the axleto move inunintended waysallowing the axle to move, and store upthe small but incredibly bothersome bit of energy used to compress the bushing and release it at the most inopportune times causing wheel hop. OBTW, wheel hop can occur under accelleration AND braking and is also strongly influenced by the suspension geometry of the rear axle.

So as you can see ideally we would use bushings that are just firm enough to fully control the unintended axle movements.This would give us the maximum isolation fromNVH and justenough axle control to elminate wheel hop caused by the unintended oscillations that happen between the bushings and the tires (wheel hop). Unfortunately the level of bushing firmness we need to eliminate wheel hop caused by the bushings is also just firm enough toadd NVH to the cabin of the car. It's a small but noticable change and is dependent on the bushing hardness and LCA/UCA design.

HTH!