Torsion bars for better handling; your experience?
you guys are in a much more advanced league than me,but here's what i did and found.
My changes were .920 torsion bars, Bilstein shocks and expo 6 leaf rear springs with the
stock sway bar,disc brakes and 70 series tires...sm blk '69 Dart.
the car has a much more modern feel, is firmer and the ride is nice on good roads. The
problem is that most of our roads are not good and the ride is harsh and uncomfortable
because of them.I am going to do some more experimenting.My new vehicles including my truck,ride,handle
and stop on these same roads with exceptional comfort...i think i am just spoiled.
I found that even with 1.12" torsion bars and the hotchkis shocks that the ride quality of my Duster was about the same as my wife's 2013 Mustang with the factory premium suspension option. Now, she always had the thing is sport mode, so maybe that had something to do with it. When I was running 1" Just Suspension torsion bars in it I found the car to still be quite a bit softer than most modern vehicles, I think I still had the old blue gabriel shocks on it at that point though. I mean it handled better than stock, but it still had a lot of body roll with corners.
Suspension has to be matched, it's a system. If you run 70 series hockey puck tires, you don't have a ton of grip. That limits your handling, your braking,
everything.
The other thing is ride height- If you only have .920" torsion bars, and you've lowered the car
any from stock, you're probably still bottoming out the suspension onto the bump stops on rough roads. And that is going to give you a harsh ride, even with the factory progressive bump stops. I hear that a lot, people that increase the size of the bars slightly and complain of a harsh ride. Well, you have a higher wheel rate, but you're still bottoming out. The ride with the 1" bars on my duster was anything but harsh. It was still almost plush. But I hadn't done much if anything to the ride height at that point. The bars aren't stiff enough to make up for a big loss of suspension travel from lowering the car. You can get away with a little, but not much. A .92" torsion bar is only like a 150 lb/in wheel rate. That's not much more than most of the stock .87" V8 A/C bars, which are 120 lb/in. That's stock, and that's undersprung. Most 1" bars are around 200 lb/in, the 1.12" bars I run are 300 lb/in. And that's how I can lower my car, because my suspension is 250% stiffer than stock and uses a lot less suspension travel.
And, ride quality is subjective. What you expect from an old car and what you expect from your new car can change your mindset too. And what I think is "harsh and uncomfortable" may be totally different from what you think.
i've read stiffening the front or rear will cause understeer, also that the front suspension should be much stiffer than the rear and to be careful with rear sway bars...how do you decide which components to use when you start making these changes...especially shocks.
i feel i gained in some areas and lost at others?
Again, everything has to be matched and it depends on your set up. If you run narrow, hard tires you can make the front too stiff and you'll get understeer pretty quickly. If you make the rear too stiff you'll get oversteer. And if you're running 70 series tires you don't have a ton of grip, so you don't want your suspension to be super stiff. The tires will just give up before the suspension starts to work.
The front suspension should be quite a bit stiffer than the rear, you just have to look at the weight balance of the car. These cars are nose heavy to begin with, so, the front suspension carries more load. The front suspension also deals with steering, so again, more load. And any time you brake, you shift even more load to the front.
So, it's all physics, and it's trial and error. I based a lot of my suspension choices on what guys were already running at autoX's and on the road courses, autoxcuda and gmachinedartgt (peter bergman) had a lot to do with what I chose for suspension. And I still missed a few times and have made changes. Even looking at what the aftermarket companies are offering helps. Hotchkis does a ton of research, and their cars handle really well. So, you can look at the wheel rates they run to help make decisions. But it also depends on your individual set up. The tire compounds and sizes you run make a big difference. In the back your power levels make a difference too. If you run a stagger in width from front to rear it makes a difference. My front suspension has a wheel rate of 300 lb/in just off my torsion bars, and I have a 1 1/8" sway bar on top of that. Meanwhile in the back I have 121 lb/in leaf springs, so I run a 7/8" sway bar. But I also have 295's back there, and they're hard to break loose. I know both Peter Bergman (gmachinedartGT) and hotchkis were selling springs that were 130 lb/in for A-bodies. But both Peter and Steve (autoxcuda) had remarked their cars were getting a little tail happy in certain situations with a rear bar, so I went with 120 lb/in springs. Both of those guys still use a rear sway bar though, just not on certain tracks.
Shocks have to be matched to the wheel rates, but better shocks have a wider range where they'll be good than cheap shocks. More valving and tuning. I was running Bilstein's on my Duster because that was one of the few shocks being made specifically for handling mopars, but I got a chance to buy a set of Hotchkis Fox non-adjustables second hand and mildly used so that was how I found out they worked a little better with my 1.12" bars than the Bilsteins did. That was just straight up trial and error. I ran KYB's on my Challenger for a long time, and although I knew they were a bit harsh I didn't know how truly awful those shocks are until I started running Bilsteins on my Duster. My Duster had a far better ride than my Challenger, even though the Duster had stiffer torsion bars by 30 lb/in. I swapped to Bilsteins on the Challenger and it was a whole new car. Which is why I now tell everyone to toss their KYB's in the garbage if they're going to run a larger torsion bar. Because they're awful.
You basically have to start from the capabilities of your tires, and work in from there. Tire grip sets the wheel rate needs, the wheel rate determines the level of shocks you need, the total grip and wheel rates determine how much chassis stiffening you'll need, etc, etc. The more grip you've got the higher your wheel rates need to be, the better the shocks need to be, and the more stiffening you'll need to keep the chassis from flexing.
