[Sam Strano]

I'm now happy to announce we can take pre-orders on a Watts Link for all 82-02 F-bodies with stock diamter axle tubes. There is a version for bigger axle tubes (suck as 12-bolts, etc.) in the works.

They should be ready to ship in approximately 2-3 weeks. The unit is made by Fays2 who has been doing these for Mustangs for more than a few years. I not only trust the unit and have had all my questions answered, but will be putting one on my car as soon as possible. Jim and I have had a few discussions about the design and I'm happy to say he addressed my main concerns regarding approximate roll-center height. I wanted to make sure we could start @ stock height and adjust down as the owner sees fit. That has been done and implimented in this unit.

Details, specs and a photo on a 4th gen can be seen here:
http://www.stranoparts.com/partdetails.php...7&ModelID=7

(IMG:http://www.stranoparts.com/data/images/p30617181655.jpg)


Price is $650 Plus shipping. Shipping costs will normally not exceed $30 in most cases.

Fays2 own website has the pricing set lower, but after a discussion with Jim Fay, he informed me the prices are incorrect and will be changed.

[sgarnett]

I suspect Sam is busily preparing for Nats, or already on the road by now.

This is an attempt at an unbiased overview. I'm not trying to put words into Sam's (or Jason's) mouth, but if you want his full opinion on the matter (in his own words), it's already out there to search for.

Sam has said that it is a fruitless venture to lower the roll center, and as recently as a few weeks ago (a page or so back in this thread) his opinion hadn't changed. The Watts link does allow lowering the roll center easily, but that's not the reason Sam is promoting it. In fact, he asked Fay to ensure that there was enough range of adjustment to avoid lowering the roll center.

Sam's objection (ie the drawback of lowering the roll center) is primarily that lowering the roll center requires stiffening the rear springs and/or swaybar. This reduces "mechanical grip" (the static ability of the car to maintain the weight distribution between tires on pavement that isn't perfectly flat). The stiffer suspension (all else being equal) also causes the axle to skip around more when crossing bumps, potentially reducing even straight-line traction.

Jason contends that he can address the bump handling with different shock valving.

The advantage of lowering the roll center is that it keeps the handling balance more consistent through the turn, and reduces jacking (which is a bigger issues with swing arm suspensions, but still applies somewhat to live axles). Weight transfers much faster through the PHR (or Watts) than through the shocks and springs. Lowering the rear roll center lowers the PHR/Watts contribution to the total weight transfer, which reduces it's ability to dynamically change the handling.

The advantage of the Watts link setup is also that it helps keep the handling more consistent (though not in the same way), even at the original "approximate" roll center height, because it keeps the roll center from moving around as much relative the chassis center of gravity.

The Watts link does reduce lateral movement of the chassis. Besides any effect on handling, lateral movement increases tire rubbing issues.

Lowering the rear roll center, whether by lowering the PHR or lowering the Watts pivot, will increase lateral movement and rubbing, though the Watts link is starting with an advantage in that regard.

So, Sam's argument against lowering PHR (or Watts pivot) has never had anything to do with "the insignificant amount that the rear shifted from side to side" because lowering the PHR does not reduce lateral movement at all. He has argued that lowering the PHR (specifically on the fbody) will increase lateral movement even more than is inherent to lowering the roll center anyway due to increased flexing of the long brackets.

Outside the context of PHR lowering, Sam has also argued for the importance of using a very strong, rigid PHR with rod ends to minimize lateral movement. So, I don't think he has ever meant to downplay the significance of controlling lateral movement.

Sam has argued that the transitional handling balance changes due to the relatively high roll center in the stock-like configuration do not cause a significant driving problem. In other words, he is arguing that he can adequately address transitional stability with his setups.

As I said, this is just intended to be a summary (OK, a verbose "summary") of the different issues and points of view, not an argument for any particular point of view. I don't think anyone disagrees on the physics/geometry involved with the various topics. I think all the disagreement lies in how much importance to assign to each topic.

Now, the fact remains that if you lower the roll center significantly, you will need to buy a new set of (at least) a new rear bar and springs. Sam sells any springs you may want, and up to at least a 25mm solid rear bar (ST). While he certainly doesn't recommend them, he does sell most of the parts you need if you want to try it.

The Watts link will make it fairly painless to experiment a little. Springs and bars are relatively cheap, and if you change your mind before they get too rusty and scraped up, they are fairly easy to resell. If you lower the roll center enough to need custom shocks, that does complicate the situation a bit, though.

The Watts also allows movement of the roll center by as little as half an inch. That opens the possibility of small tweaks for tuning, even if you aren't going to completely overhaul your suspension package for a large change..

For example, lowering the roll center with no other changes will increase the understeer tendency of the car. Aging tires or a slick surface tend to increase the oversteer tendency of the car. So, lowering the Watts pivot by 1/2" or so as your tires get old or when heading to a notoriously slick site could be a very convenient option. Heck, it should only take a few minutes to move the pivot using ramps (with no further adjustment needed if it was set up properly to begin with), so even a quick adjustment for weather change is feasible.

This post has been edited by sgarnett: Sep 8 2008, 12:50 PM

[shortbus]

Sean, that was a most excellent reply. Kudos to you.