How should my duster handle
I actually do agree...people who turn the steering wheel without the car rolling are poor drivers. These are the same people who have cars that break and/or require repairs....my cars never, ever break. I've also never worn out a set of brake pads in under 100K miles.
As for the idea that if you upgrade the tires, you must 'upgrade' the rest of the suspension....that is 'magazine talk' which is founded in the need for their advertisers to sell more stuff.
I have had many old Mopars with 100% stock suspension and modern radials. They drove very well. Sure, you can make other changes but they're not necessary and are often 'downgrades' as much as upgrades. Human nature- along with magazine talk - is to assume any change must be an 'upgrade' if it's shiny and has clever stickers on it. Companies spend more money than you and I have together in studying how to appeal to that side of our brains.
Many parts sold for suspension are pure garbage...polyurethane bushings are at the top of that list but so are a lot of the fancy shocks and springs and sway bars. Too many guys buy a bunch of expensive parts and never bother sorting them out or even finding out if they work well.
I am all for modifying cars....but the mods have to work and work well. If you have an A Body that has mods that actually perform, that's what it's all about. But for every car like that I see 10 that are bolt-on specials.
The 'Gold Standard' of any Mopar suspension is to be 100% fresh and 100% stock. That is the starting point from which all mods are judged. It's a good starting point because, unlike other cars of the era, Mopars rolled out the door with a suspension that still holds its own 60 years later.
Stock suspension maybe holds its own compared to a dump truck. Even after rebuilding the front end of my Duster with stock parts and getting a better alignment I wasn't comfortable just cruising on the freeway at 75 mph since the body roll was soo bad with factory torsion bars and no sway bars, any curves or turns were sketchy. Put in 1" bars with poly LCA bushings, VAST improvement. And they don't squeak because I lube them every year or so. UCAs are stock with offset rubber bushings for more caster. Adjustable strut rods also went in shortly after, that made it feel much more stable under hard braking especially when turning.
First time I went to a track day it was somewhat balanced but of course, some understeer. I put on front and rear sway bars; roll reduced and it understeered less but the lame fat-sidewall tires had no grip.
Upgraded to actual modern performance low-profile tires on 18" wheels and much wider in front. Grip massively improved but then it was overpowering the springs and I'd hit the bump stops in hard cornering. Upgraded torsion bars to fatty 1.14" ones, holy cow now it feels like a slot car. Understeer came back a bit so I changed the alignment to go from 0 static camber to 2 degrees negative. Now it's pretty damn balanced and reacts great but the stock-replacement shocks basically do nothing now so I'm looking at a set of those "fancy shocks" (adjustable Foxes or equivalent) along with aftermarket UCA's that are more rigid and have more adjustability with beefier bushings.
What's the point of me outlining all this? It's to show that while the
design of the factory suspension is very good, the factory spring rates, shocks, and tiny or non-existent sway bars are a joke and borderline dangerous with modern tires on modern roads with modern traffic. Every person who comes in here asking for advice on parts to upgrade or even just rebuild their suspension for even a street-only car my first recommendation is always 1.03-1.08" torsion bars, and if they can afford it adjustable strut rods and poly or delrin LCA bushings. Because I've been there and done that the whole way from stock to heavily modified for more cornering ability. It wasn't all at once either, there were years between each major upgrade so I had plenty of time to get a feel for my car in that configuration.
The people who aren't doing themselves favors are the ones dumping $3,000+ on a front coilover conversion thinking it'll make their car handle better. It won't, not any better than properly modified factory front suspension.