Okay, here's an example of what I'm talking about: Can you explain exactly what the mechanics are of how a PHB can "mess up ride height significantly?"
It's a lateral link. It's either in compression (chassis forces towards the driver's side) or tension (chassis forces towards the passenger side). It has no static vertical contribution, which would be needed if the link were to affect ride height at all, let alone "significantly." The ONLY contribution that it could make in terms of vertical load would be from bushing torsion. IE the bushing was "fixed" to the chassis at a higher ride height, and after lowering, the bushing now has potential energy stored up in it in the form of torsional energy. Given how soft those OE bushings are, the amount of energy stored will be minimal, with negligible effect on static ride height. To completely eliminate that as a variable, just loosen (not remove!) the two bolts that hold it to the chassis and axle (and nothing else: one variable at a time!), bounce the rear end a couple of times, then re-torque the bolts. Any bushing preload will be removed at that point. No change in static ride height? Didn't think so. Try looking elsewhere, like LCA bushing preload (MUCH more significant) or swaybar preload.
Honest, I'm not trying to pick on you (or anybody, really), but it drives me bat-shit when a part is blamed for things it couldn't possibly have any effect on. It's like saying that adding a torque arm makes the car corner flatter. It physically can't do that. Other factors (roll steer, %AS, roll center, etc.) certainly can, though.
1) "kicking out the driver's side" Is that a physical offset at static ride height you're describing? Yes significant lowering (and more than 1" or so is significant) can have that effect with a PHB, but it's not nearly as large an effect as people believe. Pythagorean theorem; do the math yourself if you don't believe me. IF you have a situation where tolerances are stacking up against you, then replacing the stock PHB with an adjustable-length piece (prefereably with rod ends for zero bushing compliance) will easily center the axle under the chassis. If you're referring to a dynamic action, where the car exhibits oversteer tendencies to the driver's side, then that is again less an effect of a PHB vs. Watts than it is a rear geometry issue. If your assertion were true, then any PHB car that is lowered significantly becomes essentially undrivable. To refute that, just take a look at any of the Boss302R/Boss302S cars, or the older FR500C/FR500GT/FR500S cars, and explain how they are able to turn laps as quickly as they do if they're so undrivable... See Grand Am Rolex Cup, Continental Tire Sports Car Challenge, and the FIA GT Championships, where these cars are competing against other muscle cars, Porsche GT3's, BMW M3s, etc, and doing it successfully with a Panhard bar.
2) "Upsets the rear in some situations." Again, see above. I will happily grant you that the Watts can potentially show dramatic improvement in the handling characteristics in slalom-type situations, but for anything else, the root cause of the change is open for debate. Is it "Because Watts," or is it from the relocation in roll center, or the virtual elimination in bushing compliance vs. a stock PHB? For it to be a true test, you'd need to install the Watts with the same roll center location and net bushing compliance as the PHB under test, and as far as I could find, there isn't a Watts kit on the planet that offers those options. Going to a Watts will change a BUNCH of factors, some of which may mask other problems.
3) "Significantly messes up ride height." Again, it simply can't do that. The mechanics and geometry just won't allow that to happen.
Now, one could argue that relpacing the stock PHB with a Watts will simply cure all the ills, and they may be right, but that's kind of like throwing the baby out with the bathwater. If it's a bushing issue, then fix the bushings. If it's a geometry issue, fix the geometry. Don't just throw a large, heavy, complex piece of kit at it simply because it fixes those issues, AND fixes a bunch of stuff that isn't an issue. Do it because you understand how the rear suspension works, what causes the problems you're experiencing, and have made the rational decision that a Watts is the right way to go.
Example: If your AS% is screwed up, which leads to massive roll-steer, and all you do is replace the PHB with a Watts, the changed roll-center may effectively mask the roll-steer issue, but it doesn't fix it. Instead of adding $99 LCA relocation brackets, you've added a $900 hunk of machinery instead. The net effect (Car's on rails, yo!) may be the same at a given level of lateral load, but once you start to push the car harder, that damned roll-steer starts to rear it's ugly head again. But... But... But... I have a Watts! That can't happen! Well, it did. Why? Not because a Watts sucks, and not because a PHB sucks, but because you lowered the car and induced a geometry problem that has gone uncorrected.
It's the age-old saw: Treat the problem, not the symptom. But, to treat the problem, you need to correctly identify it, and to do that requires knowledge and understanding of the rear suspension operating as a system. Then, and only then, you can intelligently make decisions to change one or two factors that may be giving you the sub-optimal performance that bugs you in the first place. Using a Watts to cover up geometry or bushing issues is akin to replacing the front suspension with an SLA kit to cure bump-steer. Yeah, it'll do it, but there are better, simpler ways of accomplishing the same thing. Oh, and yes, an SLA has huge advantages over a McStrut suspension, but you don't see a mass migration to Griggs, do you? I wonder why that is. ;-)
Again, I'm not trying to bust your balls, I'm trying to get you (and anybody reading this) to think, and to learn. That's all. It's actually pretty coincidental that the Watts vs. PHB has become the soap-box on which that's happening.
