I was under the impression that different weight and springs of a car will give them different wheel rates...(wheel force vs wheel travel)....or maybe not....one guy has a 63 B body (coil spring?) and one guy has a torsion bar setup for a lighter car. I guess I am confused as to why ordering the same shock is a good idea. especially at that cost. Am I missing something here? No disrespect, you da man.
'63 B body is still a torsion bar suspension. And the Bilstein RCD's for the B-body's are a different part number. I don't know if they're actually valved differently, but they're not just A-body shocks. The other thing is that with higher quality shocks there's typically more valving, which allows the shock to react differently with different inputs (which correspond to different fluid velocities in the shock). Because of that, they can also be used over a wider range of wheel rates with success. Compared to say a cheaper shock, which will react the same over a wider range of inputs.
As for the wheel rate, the weight of the car doesn't matter. Obviously it matters for the shocks and for determining which wheel rate you actually need, but the calculated wheel rate is just a function of the spring constant of the steel used, the diameter of the torsion bar, the length of the torsion bar, and the length of the LCA. And with torsion bars the wheel rate is linear.
Some high end suspension places have shock dynos that can run a series if tests on what your car is weight wise and spring rate, etc. Probably way overkill. Best is to just ask what everyone likes. I dont get why KYBs always get the stink eye, are they just stiff across the board?
KYB's are just cheap shocks, and they're stiff as hell. When used with soft, factory torsion bars that result in the car being undersprung the KYB's can actually mask some of that by overdampening the system. So, lots of guys with factory torsion bars think the KYB's are fine.
But when you combine them with 1" or larger torsion bars the resulting ride quality is awful. An overdampened suspension system with a 200+ lb wheel rate is very stiff and jarring. I ran KYB's on my Challenger with 1.12" bars (270 lb wheel rate) for a really long time. I just attributed the harsh ride to the large bars, because that's what everyone said would happen (because they didn't know better either). When I installed the Bilstein RCD's it was a whole new car. I'd go up on the wheel rate in a heartbeat now, it changed the ride completely. On my Duster I have run both the Bilstein RCD's and the Hotchkis Fox's (non adjustable version). The Hotchkis Fox's handle the 1.12" bars on that car a little better than the RCD's do, but on an A-body the 1.12" bars translate to a 300 lb/in wheel rate. I would wager the RCD's are just getting to the top end of the range with those size bars, the difference between the two would likely be less noticeable in the 1" to 1.06" diameter range. It was a pretty minor difference on my Duster, but it was noticeable.
