Panhard Bar vs. Watts Link

Norm Peterson

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.......and I still ask, what about the guys who drag race, or even the street guys who drive their car "with spirit" on the street?

If lowering the rear body causes the panhard bar to push the body sideways, I believe to the right? What happens when the car rises in the front and dips (lowers) in the rear (normal weight transfer) with spirited acceleration which I would guess is very common with these cars, especially with a manual transmission? Does the rear body push to the right upon every shift as the car lifts in the front and dips (lowers) in the rear? It may not be much, but isn't that a "side effect" (no pun intended) of the panhard bar? and the Watts Link keeps the axle moving up and down only, with no side effect except added weight of a Watts Link structure?

R
SCGallo has basically described the PHB's geometric behavior as the rear suspension rises and squats - it really is minimal. OE PHB bushing compliance very likely involves greater lateral axle movement during cornering than the geometric arc can when you launch, shift, or brake hard.

There's still a few things in those links that I haven't spent much time with.


Norm
 
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me32

BEASTLY SHELBY GT500 TVS
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No, it is the Shelby/Fays2 alum. version, but it is still in the box........I have not tackled that project yet......too many other things going......

Remember this picture of alloy Shelby Fays2's.....which were only available through Shelby Perf. Parts?

View attachment 1663006
View attachment 1663007

R

I do remember them, but have never seen on personally installed. Interested in seeing what cleances there are.
 

Norm Peterson

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No way to make this short . . .

Seems neither one of those articles ever mentions 'rear axle roll steer'. This is where the axle actually steers slightly as the body rolls. This is not the same effect described as the rear of the chassis moving sideways relative to the rear tire footprints. With the possible exception of autocross (where nimble handling is a plus and speeds are low so the risk of poo happening is minimal), you really want this effect to be minimally understeerish rather than oversteerish. This is not an either understeerish or oversteerish concept; it can be quantified with numbers as to how much (of either) exists with any given stick-axle suspension linkage arrangement.

I think it's important to realize that axle steer is generally just a little bit out of step with your steering wheel inputs unless you're particularly smooth with your steering inputs. That's because roll steer has to wait for the roll to actually happen, which takes up to a few hundred milliseconds after you've done some steering to get the cornering started. Has to, and while this may be on a subliminal level it is something a driver can pick up on, especially on the oversteerish side when the rear axle is actually steering itself toward the outside of a corner and the car is basically giving him more steering than he asked for. At autocross, that can be fast, as long as you can keep up with it. At higher speeds too much oversteerish roll steer can be spooky to downright scary, and on the street, risky because you do need to stay on top of it. People who have aggressively lowered their LCAs without lowering their cars may understand this, because of pushing the rear axle suspension into roll oversteer that way.


They both missed the matter of bushing compliance, and even polyurethane has some, whether we're talking about a PHB or a poly-bushed Watts. At 2° of roll, this component of lateral axle shift could be on the same order of magnitude as the shift due to the PHB arc at 1". While this is more of a street driving concern, it's still something to think about. After all, if you're building up a street driver, you probably want at least a little NVH isolation in your suspension. And if you're actually racing, the rules for your racing class may dictate what you can and cannot use (like NASCAR not allowing the Watts link). Autocross and wheel-to-wheel road course racing generally aren't "run what you brung, and hope you brung enough" like drag racing tends to be.


On the matter of differential mount vs axle mounted Watts link 'propeller', missing entirely is any mention of whether you want to hold the amount of lateral load transfer carried through the roll centers constant and let the amount of roll vary slightly with ride height (diff-mount Watts), or hold the amount of roll constant with ride height and let the geometric (roll center) load transfer do the varying (chassis-mount Watts). I'm not convinced that either way is better than the other, only that they're slightly different.



A lot of the rest reads like nitpicking between proponents of the different methods of locating an axle, with each side obviously having their own agenda.

Yeah, the geometric rear roll center for the Fox/SN95 chassis is way up there at about where the upper links attach to the pumpkin, and in the S197 it's closer to axle height. MM's writer apparently dropped the ball on that one, but it's not the clear indication of MM not understanding the problem that Griggs would have you believe it is.

And while Griggs makes a point about it being possible to locate the Watts link geo roll center down really low (almost as low as front suspension geo-roll centers tend to be), the solution they described for the Trans-Am racers is not something that anybody makes for public consumption. As far as bolt-on solutions for a street-ish car go, the Trans-Am solution is basically a unicorn.


Norm
 

Norm Peterson

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So long story short, just buy a corvette
Sometimes that's the right answer, sometimes it isn't. Just #becauseCorvette doesn't necessarily eliminate the tinkering . . .

Truth is, I've found it kind of fun trying to understand what's going on here, with suspensions in general, and in extracting more cornering & handling performance out of various cars than those cars' OEMs provided them with in production-stock form.


Norm
 

01yellercobra

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No way to make this short . . .

Seems neither one of those articles ever mentions 'rear axle roll steer'. This is where the axle actually steers slightly as the body rolls. This is not the same effect described as the rear of the chassis moving sideways relative to the rear tire footprints. With the possible exception of autocross (where nimble handling is a plus and speeds are low so the risk of poo happening is minimal), you really want this effect to be minimally understeerish rather than oversteerish. This is not an either understeerish or oversteerish concept; it can be quantified with numbers as to how much (of either) exists with any given stick-axle suspension linkage arrangement.

I think it's important to realize that axle steer is generally just a little bit out of step with your steering wheel inputs unless you're particularly smooth with your steering inputs. That's because roll steer has to wait for the roll to actually happen, which takes up to a few hundred milliseconds after you've done some steering to get the cornering started. Has to, and while this may be on a subliminal level it is something a driver can pick up on, especially on the oversteerish side when the rear axle is actually steering itself toward the outside of a corner and the car is basically giving him more steering than he asked for. At autocross, that can be fast, as long as you can keep up with it. At higher speeds too much oversteerish roll steer can be spooky to downright scary, and on the street, risky because you do need to stay on top of it. People who have aggressively lowered their LCAs without lowering their cars may understand this, because of pushing the rear axle suspension into roll oversteer that way.


They both missed the matter of bushing compliance, and even polyurethane has some, whether we're talking about a PHB or a poly-bushed Watts. At 2° of roll, this component of lateral axle shift could be on the same order of magnitude as the shift due to the PHB arc at 1". While this is more of a street driving concern, it's still something to think about. After all, if you're building up a street driver, you probably want at least a little NVH isolation in your suspension. And if you're actually racing, the rules for your racing class may dictate what you can and cannot use (like NASCAR not allowing the Watts link). Autocross and wheel-to-wheel road course racing generally aren't "run what you brung, and hope you brung enough" like drag racing tends to be.


On the matter of differential mount vs axle mounted Watts link 'propeller', missing entirely is any mention of whether you want to hold the amount of lateral load transfer carried through the roll centers constant and let the amount of roll vary slightly with ride height (diff-mount Watts), or hold the amount of roll constant with ride height and let the geometric (roll center) load transfer do the varying (chassis-mount Watts). I'm not convinced that either way is better than the other, only that they're slightly different.



A lot of the rest reads like nitpicking between proponents of the different methods of locating an axle, with each side obviously having their own agenda.

Yeah, the geometric rear roll center for the Fox/SN95 chassis is way up there at about where the upper links attach to the pumpkin, and in the S197 it's closer to axle height. MM's writer apparently dropped the ball on that one, but it's not the clear indication of MM not understanding the problem that Griggs would have you believe it is.

And while Griggs makes a point about it being possible to locate the Watts link geo roll center down really low (almost as low as front suspension geo-roll centers tend to be), the solution they described for the Trans-Am racers is not something that anybody makes for public consumption. As far as bolt-on solutions for a street-ish car go, the Trans-Am solution is basically a unicorn.


Norm
But would you drop 2 seconds per lap like if you installed an X brace? :D
 

Norm Peterson

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But would you drop 2 seconds per lap like if you installed an X brace? :D
Can't tell for sure whether you're joking or if you know of a certain large thread elsewhere where the value of another kind of S197 chassis bracing was under discussion with the same 2 second lap time claim from having added it. (different vendor from either of the two so far in this thread, with his own thoughts on how to work with PHBs).

The Cliff's Notes version is that the S197 chassis is stiff enough to where added stiffening can't improve the car's performance by that much. But it is possible for additional bracing to improve driver confidence by making the car feel "more solid" without making it much stiffer. It's a perception thing that can make it easier to drive the car harder than you might in its absence.

I even made a few chassis twist measurements of my own, and saw for myself that there just isn't that much chassis torsional 'flex' for added stiffeners to take out, no matter how much stiffness they might add.

FWIW, even the early S197 Mustangs are about 50% stiffer in torsion than the C7 Corvette, and well over twice as stiff as the C5 Corvette . . .


Norm
 
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01yellercobra

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Can't tell for sure whether you're joking or if you know of a certain large thread elsewhere where the value of another kind of S197 chassis bracing was under discussion with the same 2 second lap time claim from having added it. (different vendor from either of the two so far in this thread, with his own thoughts on how to work with PHBs).

The Cliff's Notes version is that the S197 chassis is stiff enough to where added stiffening can't improve the car's performance by that much. But it is possible for additional bracing to improve driver confidence by making the car feel "more solid" without making it much stiffer. It's a perception thing that can make it easier to drive the car harder than you might in its absence.

I even made a few chassis twist measurements of my own, and saw for myself that there just isn't that much chassis torsional 'flex' for added stiffeners to take out, no matter how much stiffness they might add.

FWIW, even the early S197 Mustangs are about 50% stiffer in torsion than the C7 Corvette, and well over twice as stiff as the C5 Corvette . . .


Norm
It was a joke because of that thread. I used to be on s197.
 

Black Cobra '99

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I'm not convinced that either way is better than the other, only that they're slightly different.

Norm

This really sums it up, both companies took an idea and refined it as much as they can and only they know the limitations of their product and under what circumstance it would perform best.
If one product was superior we'd know right away, and this thread wouldn't exist.
 

Robert M

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What was the Ford engineer purpose when they lengthened the 2011-2014 upper control arm vs. the original short version used from 2005-2010? They were apparently trying to improve something?

Sorry, the only picture I have also includes the 2011-up "Roush Anti-Hop" arm shown in the middle and it is the same shorter length as the 2005-2010 oem Ford with only the under seat bolt upsize as was also included on the 2011-up oem Ford......2005-2010 UCA/UCM on left - 2011-2014 UCA/UCM on right......

007-2-zpsba6d8d52.jpg


^^^^^^^Note under seat bolt hole upsize/upgrade for the 2011-2014 shown on the Roush and oem Ford UCM's (center and right).

R
 

Norm Peterson

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I think they were tweaking how fast the SVIC migrated and how fast the anti-squat varied as the car's rear ride height varied. Any difference in the height from the ground to the chassis-side pivot would also be involved, and there's no reason to expect that this was left alone either.


Norm
 

Robert M

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I think they were tweaking how fast the SVIC migrated and how fast the anti-squat varied as the car's rear ride height varied. Any difference in the height from the ground to the chassis-side pivot would also be involved, and there's no reason to expect that this was left alone either.


Norm

I was thinking, for a chassis that was only going to be run for 4 more model years, they were still tweaking well into production. This longer arm revision also included a fuel tank revision just ahead of the UCA/UCM, however, the longer arm and mount can be installed in the earlier cars without the fuel tank change.

R
 

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