Bump steer kit

[A John In NJ]

So if you install Boss S front control arms, you should install a bump-steer kit too? Ugh, I might go back to buying the FRPP arms since I don't really want to spend more money or time to replace my blown ball joints.

So the Watts Link didnt help with the bumpsteer?

 

[tigercrazy718]

So the Watts Link didnt help with the bumpsteer?

I mean the rear end doesn't dance around as much when hitting bumps in turns anymore, so I think it did. In its current set up, it doesn't really bother me much anyways, but that might be me being used to how the car is, and I don't know any better.

 

[Norm Peterson]

So the Watts Link didnt help with the bumpsteer?

Bumpsteer is strictly a front steering & suspension matter. Whether you've got a stick axle out back, IRS, or just a single wheel like a backwards tricycle does not matter.


Norm

 

[tigercrazy718]

Bumpsteer is strictly a front steering & suspension matter. Whether you've got a stick axle out back, IRS, or just a single wheel like a backwards tricycle does not matter.


Norm

What do you call the LRA bouncing around when in a turn, which the Watt's link settles down? Just instability?

 

[TheKurgan]

If you had blown ball joints that will definitely make it bounce around.

 

[tigercrazy718]

If you had blown ball joints that will definitely make it bounce around.

Ha well when your steering wheel starts shaking on a straight, you notice somethings wrong.

 

[Whiskey11]

What do you call the LRA bouncing around when in a turn, which the Watt's link settles down? Just instability?

Yes.

At most roll steer.

 

[tigercrazy718]

Gotcha. Wasn't sure of the exact definition of bump steer besides for the obvious haha

 

[Whiskey11]

Gotcha. Wasn't sure of the exact definition of bump steer besides for the obvious haha

Well Bumpsteer is the change in front toe when the car goes over a bump. This change of toe can be looked at either individual sides or both together (total toe) but it's usually pretty bad.

The S197 chassis' bumpsteer doesn't get bad until you tweak the LCA geometry out of stock relative to the tie rods. I was lowered nearly 2.25" up front and never experienced violent jerking of the wheel with stock geometry lowered 2.25".

 

[tigercrazy718]

Yea I've had no problems that I can tell. I'm mildly lowered and haven't touched the LCA's.

 

[SoundGuyDave]

What do you call the LRA bouncing around when in a turn, which the Watt's link settles down? Just instability?

Oversprung? Blown shocks? Placebo effect? Do the math with the amount of axle deflection with a rod-ended PHB (not one with pencil-eraser bushings) and you'll see it's pretty minimal through the bulk of the normal range of motion.

Lets get some definitions and concepts out on the table.

BUMP-STEER can be defined as change in toe-angle as a direct result of vertical suspension motion. Ideally, you want the toe angle to remain constant as the suspension cycles up and down, which is "zero bump-steer." The leading culprit for bump steer is the different arcs described by the tie rod and the lower control arm as the suspension moves around, but to be honest, with stock components, Ford pretty much got it right for the overwhelming majority of the usable suspension travel on the car. IF, however, you introduce a change in the geometry, either by installing taller ball joints, or relocating the pickup points for the inboard side of the LCA, you introduce a pretty dramatic arc-length difference, and that creates bump-steer.

So, why do we go there in the first place? Because racecar. We want to (at least on this forum, anyway) go faster around the corners than Henry Ford ever intended us to, and in stock form, the Mustang is a wallowing, marshmallow-y, understeering mess. Light years better than previous platforms, but still hardly optimal in stock trim. So what do we do? First thing we do is lower the ride height down from the stock 4x4 spec (lower CG, slight decrease in aero lift at speed). Hopefully, we've also increased the spring rates and have installed dampers that are up to the task of controlling the masses involved. HOWEVER, under the universal law of TANSTAAFL, that creates almost as many problems as it solves. Of prime importance to us here is the inclination of the LCAs that it induces. By lowering the chassis, we also lower the inboard side of the LCAs, causing them to slope downward. This does two really bad things. First, our front roll center is now somewhere underground, and second, it puts the front suspension in a REALLY bad place in the camber-gain curve. What's that, you ask? Well, Virginia, when you compress the suspension, like you would going into a corner somewhere between light-speed and ludicrous-speed, the outside tire moves vertically upward. The LCA pivot points are fixed relative to the chassis, as is the strut top, at the upper strut mount. Additionally, the knuckle is fixed in angle relative to the strut body. So what else happens when the wheel moves up? The LCA, which started with an upward slope looking from inside to outside, gets even more inclined, which necessarily shortens the distance between the vertical plane passing through the LCA inner pivot points and the ball-joint centerline. That means that the wheel is moving up, AND in. But wait, since you acted now, for no additional cost, we'll make it worse. If the KNUCKLE is moving inward, but the strut top isn't, that means that the whole thing is also pivoting, losing all that beautiful negative camber we dialed in, and we're now abusing the outside edges of the tires... Sigh. Here's the rub. The greater the angle of inclination of the LCA, the greater the rate of positive camber gain. That means that if the arms are close to flat to start with, "X" amount of vertical motion at the ball joint produces less positive camber change than if the arm started with a heapin' helpin' of inclination. A LOT less.

So, what are we to do? Geometry correction. We want to lower the car for all the goodness that brings, BUT we don't want to pay the price. So, we can install ball joints with a taller stud, which pushes the LCA downward at the outside, getting us close(er) to flat again, OR we can relocate the pickup points on the inboard side of the LCA, raising the inboard end and again getting us close(er) to flat. Or both! The roll center can see daylight, and the camber-gain is minimized. Awesome, right? Not exactly. Remember how Ford had gotten the bump-steer curve pretty much right with stock geometry in the first place? Remember how we had no real problems even after dropping the front end 2" or so? Well, now that we did the roll-center relocation, the arcs described by the tie rod (canted upward at static ride height) and the newly re-angled LCA (flat-ish at static ride height) aren't even in the same zip code, and what does that mean, Virginia? Exactly! Bump-steer. In this particular case, as the suspension moves upward, the toe changes (aggressively) inward. Can you say "darty front end?" I knew you could!!

Simple enough solution, really. Either install tie rods with an extended-length stud (Whiteline, FRPP from the FR500 program), or a bump-steer kit (the rest of the world, like Steeda, MM, Griggs, et al) which does the same thing, but can be fine-tuned. A bit of time, some aggravation, a little swearing, and you're done. Now, you have a properly lowered car, with appropriate spring rates and damper curves, along with minimal impact to the front roll-center and camber gain curves. More grip, crisp turn-in, and it won't eat the tires alive, either!

A bump-steer kit is a supporting mod, used to correct geometry that has been altered from factory-spec. Nothing more. It's not going to "supercharge your suspension" like a Watts link will ! Oh, and in case you missed it, the last sentence was pure sarcasm.

 

[tigercrazy718]

Thanks for the great explanation, really informative. Btw, I know the Watt's link isn't a fix all mod, but it did help with the rear end over bumps as compared to the pan hard. Made it a lot more predictable IMO.

 

[SoundGuyDave]

It's a pet peeve of mine... the BULK of the issues with a Panhard (it's a guy's name) bar is in the bushings. Minimize the deflection from those bushings, and it tightens right the hell up. Stock pencil-eraser to poly is a night and day difference, and my preferred bushing material, steel (rod ends!!), is night and day again. Is there a difference in feel? Yes, there is, I won't deny it. Is a GOOD Watts easier to tune, in terms of roll center? Yes. HOWEVER, there are some folks on this forum that have used that exact phrase ("Supercharger for your suspension"), and frankly that, it ain't. My personal car has a rod-ended everything in back, and is nice and predictable. I've also driven several Watts-equipped S197s (Fays2 and TechCo, but not the Whiteline) and was frankly underwhelmed. At three times the cost, and up to five times the weight, I'll pass, thanks. I would never bag on somebody putting one on their car (after all, it is their car!), but when I hear stories about how somebody went from a stock PHB to a rod-ended Watts and "suddenly it was like I had IRS, dude!" I just want to.


In the end, both a PHB and a Watts do the same job, that of lateral axle location. Yes, the Watts does it better over a wide range of motion, but if you do the math, a rod-ended PHB only allows something like .080" of lateral deflection with a nominal 1" bump...

 

[Whiskey11]

It's a pet peeve of mine... the BULK of the issues with a Panhard (it's a guy's name) bar is in the bushings. Minimize the deflection from those bushings, and it tightens right the hell up. Stock pencil-eraser to poly is a night and day difference, and my preferred bushing material, steel (rod ends!!), is night and day again. Is there a difference in feel? Yes, there is, I won't deny it. Is a GOOD Watts easier to tune, in terms of roll center? Yes. HOWEVER, there are some folks on this forum that have used that exact phrase ("Supercharger for your suspension"), and frankly that, it ain't. My personal car has a rod-ended everything in back, and is nice and predictable. I've also driven several Watts-equipped S197s (Fays2 and TechCo, but not the Whiteline) and was frankly underwhelmed. At three times the cost, and up to five times the weight, I'll pass, thanks. I would never bag on somebody putting one on their car (after all, it is their car!), but when I hear stories about how somebody went from a stock PHB to a rod-ended Watts and "suddenly it was like I had IRS, dude!" I just want to.


In the end, both a PHB and a Watts do the same job, that of lateral axle location. Yes, the Watts does it better over a wide range of motion, but if you do the math, a rod-ended PHB only allows something like .080" of lateral deflection with a nominal 1" bump...

The advantage to a Watts is in quick transitions. A PHB will plant and unplant tires in quick transitions because of how the weight of the chassis pulls on the suspension through the PHB:


Do it quick enough and you'll upset the car much easier in one direction than the other.

A watts doesn't do that.

 

[csamsh]

On track, I agree with Dave's watts opinions....couldn't really tell much of a difference.

It's really a big upgrade for autocross though, especially in a slalom. Much more consistent, and reacts the same to left or right transitions.


......aaaaaaand this thread had turned into our 3272nd watt vs Panhard thread

 

[claudermilk]

Agreed, I don't notice the back end getting as upset on track vs autocross. Like Whiskey said, in the rapid, violent transitions of an autocross you do notice the rear end getting moved around.

BTW, dammit, Dave got in the Space Balls reference before I could.

What's that, you ask? Well, Virginia, when you compress the suspension, like you would going into a corner somewhere between light-speed and ludicrous-speed,

I'll put in mine anyway...

Ha well when your steering wheel starts shaking on a straight, you notice somethings wrong.

That's the car saying "We're already going ludicrous speed, I don't wanna go to plaid..."

 

[tigercrazy718]

Agreed, I don't notice the back end getting as upset on track vs autocross. Like Whiskey said, in the rapid, violent transitions of an autocross you do notice the rear end getting moved around.

BTW, dammit, Dave got in the Space Balls reference before I could.


I'll put in mine anyway...

That's the car saying "We're already going ludicrous speed, I don't wanna go to plaid..."

Haha, with just 220ish WHP, I don't believe I am approaching Spaceball level speeds just yet.

 

[TheKurgan]

......aaaaaaand this thread had turned into our 3272nd watt vs Panhard thread

Not sure why that happened either. The OP was asking if a bump steer kit is required just because you are lowered and the answer is no.

 

[tigercrazy718]

Because I was randomly asked about my Watt's link for some reason haha

 

[Pentalab]

Do you have taller ball joints on the car, or OEM height?

Entire front end is oem. Front is lowered 1" with roush suspension package. (1.2" rear). Eng is lowered .25" via steeda eng mounts.