Watts linkage FTW. Forget about rear bump steer forever and you have all the adjustability you need...

 

Hey marcuskeeler,

You may be confused. A Watt's link has nothing to do with bumpsteer or rear axle steering and cannot change the way the rear axle steers. A Watt's link only locates the axle laterally in the chassis, establishes the roll center height of the rear axle and NOTHING ELSE.

Dynamic rear axle steering is unavoidable in the S197's 3-link suspension. Which way the rear axle steers can only be controlled by changing the angle of the LCA's period. This can be used to your advantage if you know what you want the rear axle to do.

HTH!

 

When the axle assembly moves up and down as the suspension compresses etc the whole rear end moves from side to side due to the nature of the panhard bar.
During fierce gear shifting and over sharp bumps the reactive lateral movement manifests itself as rear steer and instability.

We are into semantics here so let me rephrase by saying this is the rear steer 'effect' I refer to and the watts linkage stops that dead.

Yes, unequal LCA angles will create rear steer as the rear of the car rolls too and fro. That can be minimised, to some degree, by a bigger swaybar and firmer springing.

 

I carry the full line of UMI bars, also Steeda, Hotchkis too. And I carry both the Steeda and Fays2 Watt links as well. In short, I've got all the options you could want.

A Watts does settle the back down over bumps. It's not really bump steer, but I can see how one might think that as it moves around less (if they call that "steering") over bumps.

 

Get the POLY Grease Spohn sells it on their web site for poly ends if you go this way other grease may eat up the bushings worth the 10 or 15 bucks and it is enough to last for a long time 11oz tube. I use it on my BMR parts no problems grease every 5000-6000 miles or if driving hard every 3000 miles.

TW

 

Umm, sort of but not really, the axle should not be moving up and down in the chassis. Hopefully your rear tires (and axle) stay on the ground and the chassis moves up and down over the axle.

A Panhard bar moves through an arc which is described by its length. Because the bar is attached to both the chassis and axle the chassis also has to move through that same arc over the rear axle. The S197's Panhard bar is nearly optimized being almost as long as possible which causes the bar to describe a larger arc. The effective length of a Panhard bar on an S197 that has been lowered so the bar is set-up optimally or parallel to the ground is about 40" or so. Let's say our example sport suspension travel is about 4" during sporty driving. This means that the chassis will be moving up and down 2" from the imaginary static parallel midpoint. If you do the math this means the chassis is moving side to side over the axle about 0.1995" during the time the suspension is moving through it's full dynamic travel.

But if you replaced all of your soft O.E. rubber bushings with poly bushings or some form of spherical joints, you installed a nice stiff Panhard bar with a stiff Panhard bar brace and you have sticky tires you can feel the action of a Panhard bar in the way the chassis responds when turning left vs. right. This causes you to feel like the car wants to turn better in one direction than the other and also prevents you from getting on the power as soon when exiting the corners. It also makes the car's ride feel poor because you keep feeling the chassis moving over the rear axle as the chassis goes left right then left again. It is a subtle thing but you can feel it on the freeway if you pay attention and this is perceived as poor ride motion. If you have a Watt's link that is reasonably setup this motion goes away and you think the car rides better, less movement and less jiggle side to side. But of course that doesn't make it ride any better so much as removes that nervousness at the back of the car.

A Watt's link can shrink that amount of side to side movement to nearly zero but only if the geometry is optimized. If the links are not set up to be the same length, set parallel to the ground and the center link is not vertical when static all bets are off as to the exact vertical movement of the axle. In other words the benefits of a Watt's link go out the window if the Watt's link is not well optimized and you are left with a much heavier car and a lot of more unsprung weight for no good reason.

Anyway that is not the point. The point is that no amount of side to side axle movement can cause rear axle steer. Rear axle steer is caused by the S197's solid axle changing thrust angle due to the arcs that the LCAs describe. When the LCAs move in opposite directions one up one down the rear axle is steering the car. When they move up or down together the rear axle steer remains neutral and stable. The trick is to take advantage of this and set the LCAs up using LCA relocation brackets to add a small amount of stability when cornering hard. Obviously a Watt's link has no significant control over the rear axle changing its' left/right direction relative to the axis of the chassis.

So no, you still don't have it quite right.

HTH!

 

Is that your car? If so your LCAs look like they are set to make the rear axle promote stability in corners and makes the car not want to turn at higher speeds. This can be a good thing if you are looking for stability in the middle of a 130mph sweeper. That car needs some Steeda LCA relocation brackets welded in so you can tune out the rear axle understeer and ret your IC so the car can get out of the corners sooner and launch harder off the line. That car is also too low in back and also probably bottoms out a lot unless you are using 250lb/in+ springs in back.

HTH!

 

UMI from Sam here and it was and easy install with a little bump from the rubber mallet

Adjusting it is a freaking breeze.

 

Hey Shane, has the PHB showed up yet?

 

My car had all poly bushings and the stiffer Panhard bar brace and KDW2s and it was the feeling described above, especially on a quck left to right chicane, that made me decide to buy the FAYS2 Watt's link. Since I have installed it everything just feels better and feeling better equates to going faster

If you are intending to track the car then save up until you can get the FAYS2.