When should you upgrade torsion bars?
IM upgrading my rear springs to Espo’s 6peaf +1’s and I have been reading a lot of the guys that go with 1” torsion bars. Is that only for big blocks or is that wise for a guy like me who has a build 360? 73 dart swinger... let me know what your thoughts are. Wondering if it is worth it to upgrade while I’m doing the rears or if it will just make it super stiff and undrivable.
I wouldn’t build a Mopar without using 1” or larger torsion bars.
Here’s the deal. The factory cars came with bias ply tires. Even compared to a BFG T/A or Cooper Cobra radial the traction those stock bias ply’s had was marginal. So if you run radials, you already need much stiffer torsion bars.
And that’s even before you consider the factory set these cars up to understeer, or that they undersprung the front end even well beyond that because that was the trend at the time- smooth, floaty suspension and abysmal handling.
How do the different manufacturers's 1 inch bars ccompare?
Which would be softer and which may be stiffer?
Very little way to know that without actually testing the bars themselves. You’d have to know the spring constant of the metal used to forge the torsion bars. Most of the wheel rates are actually calculated with a somewhat generic spring constant.
You can look at the published specs, Firm Feel advertises their 1” bars as being 195 lb/in. Last I checked Just Suspension didn’t advertise their actual spring rate, but I ran a set of those on my Duster for a bit and they were still fairly soft, definitely less than 195 lb/in. Too soft for me to use again, and I have a small block car with a decent amount of aluminum parts and manual everything. PST’s 1.03” bars are around 230 lb/in, and I wouldn’t run anything smaller than that for a street car.
Realistically for the same diameter most of the metals that would be used would provide a wheel rate within 10-20 lb/in. You could probably do something custom that would vary more than that but the off the shelf stuff will usually be in that window. And unless you specifically test the bars you receive that’s the ballpark you’re working in anyway.
