Torsion bar compliment to 340 XHD Spring

Wvbuzzmaster said
Kind of an interesting question that got me thinking. I had upgraded my rear leaf springs to Espo 6 leaf (340 XHD) which have a spring rate of 130 lb. I understand that Torsion bars should compliment the leaf springs, so on a car such as a V8 Duster, what is the correct compliment torsion bar up front. I already bought the PST 1.03” bars which have a rate of 230 lb in., but figured I would ask the question, it could benefit others going this route, or I could be off in my selection of parts myself. I know the consensus is that 1” minimum bars really should have come from the factory and no one has been sorry they upgraded their torsion bars either. How does one determine how much spring rate they need for just an average well mannered car that is just a street car, and not a full fledged drag or auto cross car?

There are formulas to calculate that kind of stuff, but they require you knowing the corner weights and front/rear bias of your car. Among other things. They're more intended for race cars, and even then they're just a ball park. The wheel rate requirements change on the corner weights, rake, tire width's and compound, brakes, wheel alignment settings, driving style etc. Heck the road race guys will change all of that stuff from one track to the next and depending on the weather and air temperatures.

I run 1.12" torsion bars on the front of my Duster, with a 1.25" hollow Hellwig bar up front and 121 lb/in AFCO rear springs with a 7/8" rear sway bar. I feel the car is pretty well balanced, but I also have a tire stagger with 275/35/18's up front and 295/35/18's out back. And I'm down to a 200 treadwear tire. With a 400+ treadwear tire like you get with most non-race 15" tires my set up is probably a bit too stiff. But it also might be a little soft for 80 treadwear race slicks. All relative.

With 130 lb/in rear springs I would say you should be fine with the 1.03's and sway bars, you may end up "tire limited" with that set up so you may get some oversteer. That would be the thing with stiffer rear springs, you may end up too stiff in the back and get oversteer with the sway bar. The rear Hellwig sway bar is adjustable though. Just as a general recommendation for street use I'd say anything from 1" torsion bars to 1.06" torsion bars would be fine. Clearly I went larger than that, but I have wider and stickier tires too.