exx1976

Norm - Thank you for the objective response. I especially like when people detail the "bad" things that can happen from a particular mod. Too often guys will glaze over the "possible bad" so that they can spend all day telling you about the "good".

One thing I'm not too certain on (and I'm probably going to have to get some books, if you could recommend a good one or two), is "roll center".. I did a LOT of reading online, and this is one thing that is mentioned time and again. Regardless of the "clamping" method of attachment, the Fays2 seems to be superior to the Lakewood in that it allows for adjustment of roll center. While I can only conclude that ANY type of additional adjustment capability is a good thing (allows for finer tuning), I do not understand exactly what is being adjusted. I've seen many references to having the roll center "below the ground plane", and also that it is bad for the roll center to be both above AND below the ground plane (I guess it changes at suspension travel extremes??)..

If you could clarify any of the above points, it would be most appreciated.

As for my driving style - my previous car was a 97 Grand Prix.. First of the "wide track" Grand Prixs. I did tires, wheels, brakes, Strut Tower Braces, Koni Struts, Eibach Springs, replaced the rear control arms.. I could take a cloverleaf expressway ramp at 45-50 miles an hour without the tires even squealing (Firestone Firehawk SZ-50 EPs). I miss that fun in the twisties. While the straight-line acceleration of the Mustang is FAR superior to the old GP, it's frustrating that when it comes time to turn I have to damn near come toa stop in order to feel as though I have some control over the vehicle, or in order for it to be predictable (well, desirably predictable, anyway).

Thanks!!

Norm Peterson

About the best "first book" on chassis & suspensions is Fred Puhn's "How To Make Your Car Handle". Around $20 these days (I got mine when it was $5 and still refer to it from time to time). It's a fairly broad overview with just enough of the math included to get you started.

With respect to those SZ-50EP's, that goes back to priority #2 in my previous post. I had a set of four on mythumbnail car, but had to swap out the rears for something else due to a road debris incident. Physical replacement, yes, but nowhere near equal performance (BFG g-Force-Sport, if it matters any).

Understand that roll centers are really just a convenient means to an end - it simplifies the computations and allows you to determine more or less how things change during transients. They are NOT points or an axis about which the car rolls, except possibly by coincidence. Roll center heights are part of the tuning process, which includes your spring, sta-bar, and shock selections. All taken together, rather than individually (though you do have to start somewhere). Very generally, unless you're starting from scratch, a lower RC height means that you'll need stiffer springs/bars/shocks, which comes around to what you and any frequent passengers will tolerate given whatever the pavement quality in your area looks like. Things like above grade vs below grade for the RC or just having different front vs rear RC heights has to do with what you want the lateral load transfer to be doing in the middle of a turn when you're as close to "steady-state" cornering as you're likely to get in anything that gets you anywhere but in circles.

Adjustability is nice, but not if you don't know what to do with it. And having too many things that can be adjusted can get you lost.

It may also alter the "feel" as you enter a turn, and either a "loose" or "too-tight" feeling here is pretty good discouragement to hard driving. This can come about due only to the roll center height changes (aka "migration") or possibly due to changes in axle roll steer that frequently accompany roll center height changes. Don't underestimate the importance of this "feel" - it's what tells you that you're pushing some limit or other even though the potential remains for more [performance].

To start with, there's a difference between pushinga FWD carand a RWD carthrough the twisties, and that you'll need to "recalibrate" your right foot. Too much throttle too abruptly with a powerful RWD car can equal tailhappiness, though with a more refined use of your right foot you can start squeezing down a little earlier on corner exit. Unwinding a little of your steering input *may* help, but that's a rather advanced technique. Mechanically, I think shocks really belong at the top of your suspension shopping list, keeping in mind any spring/bar upgrade.

About here I'm going to suggest that you give Sam Strano a call. I've known Sam for about 5years through SCCA Solo (autocross), and he has some pretty impressive credentials as both a driver and a tuner with a fair bit of practical experience(who won't try to oversell you with parts you don't need for what you're trying to accomplish, even though Stranoparts is his business). He knows shocks. He's a relatively new member on this site, so you should be able to find him on either the members list or as a participant in some of the threads in "4.6L Handling" or "Other Professional Racing". Just as a note, Sam drove an F-Stock '07 Shelby to a time that would have earned him a trophy in C-Prepared (a class for pretty much fully-developed non-street-legal V8 race cars on real race tires and 10" - 12" wide wheels all around) at the 2007 Solo Nationals.


Norm

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exx1976

Cool, thanks Norm!!

exx1976

The Fays2 unit is also an axle-tube-clamp style... Go back to working on your loctite'd oil drain plug.

SlideWRX

The Fays2 has much better clamps that distribute the load better. which won't damage the axletube. Personally when I go watts, it'll be the saleen, because I'm not worried about spherical end exactness. This is my year-round car, including snow, and my auto-x car.

The watts also has advantages of less rear end movement over bumps, for a smoother street ride.

exx1976

Please elaborate.. Sherical end exactness?

Also, for the quality that everone says Griggs is, I might just go with that. It's not TOO out of the question, $800 plus the cost of the whatever the girdle is that it mounts to.. Probably <$150 if I had to guess (couldn't find it on the site, not quickly anyway).

But first, I'm going to do LOTS of reading on suspension geometry. I ordered the book that was recommended by Norm, as well as another one. I have until April to figure out what I want to do, so there's no rush. No way this thing sees snow or salt...

Norm Peterson

Be careful. If you don't install the lateral links in a particular relation with each other, that may not be true.

From a chassis dynamics point of view, general consensus is that chassis-mounting the central "football" is preferable to axle-mounting it.


Norm

exx1976

So if I'm understanding correctly, Norm, you're saying then that the Fays2 or the Lakewood is actually better than the Griggs or the Saleen? The central "football" is chassis mounted on the former, and diff mounted on the latter (or so I hear about the Saleen - haven't researched it). I'm also working ont he assumption that when you say "football" you mean the pivot, correct?

??

SlideWRX

Poly bushings have give, which means they aren't race-car exact in locating the suspension. Spherical bushings basically don't deflect. The saleen has poly-bushings on the arms, so there's a bit of flex. It's still stiffer than stock, though.

Norm Peterson

Yes. The "middle" link that has the central pivot which is generally taken to be the roll center. (Not strictly true, but it's a close enough approximation for most practical purposes.)

The thinking is that it is better tokeep the magnitude of the roll moment relatively constant as the suspensions move than it is to maintain the rear roll center height itself. And when the rate of front roll center vertical migration is somewhere around twice the change in front ride height(most strut suspensions), it's argued that it's better for the rear to work in opposite fashion, roll moment-wise. Don't forget that in hard driving you'll be on the brakes (nose down, tail up) as you approach and enter a turn, and on the throttle on exit. Those activities affect the front and rear ride heights. I suspect that it lets you tune things a little closer to 'neutral'.

Not that a fixed rear roll center height can't be made to work well, just that it works better for cars other than relatively heavy and softly-sprung, high-CG cars like these. IIRC, one or two of the very early Lotuses (Loti?) used a low and fixed rear (stick axle) roll center heightto advantage. Low, less than 1500 lbs including driver, and quite frankly, running on tires with less grip than what's available today in fully street-legal form. It's also viable for low, lightened, very stiffly sprung race cars, where you aren't going to get as much suspension movement. I can think of one or two individual efforts on this latter - for pretty much pure track-duty cars that may retain just enough to be technically street legal. Think street-identifiable sheetmetal draped over a tube-frame race car chassis, not heavily modified street car.


Norm