Front End Unsprung Weight
I'm all for lowering the Roll Center but not when the LCA can barely move more than 1.5" before crashing into the frame. Not on a street car with sane wheel rates & a Stock LCA.
Several years ago, Firm feel adapted 73 B-Body LCA to
FIX the pot hole = bent arm scenario but keep the lower RC. It adds a good 2.5" of travel over a stock LCA.
A more readily available & intermediate step would be a QA1 LCA, with its smaller dimensions offers ~3/4" of added travel over stock
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I guess in all of your modeling you didn't actually check what the LCA to frame distance was on a car at factory spec ride height?
I'll help you out, it's about 2 1/4" for an A-body. That's hard parts to hard parts, no bumpstop, using the factory manual " A - B " measurement set at 1 7/8” to establish the factory ride height. Now, the 2.25” isn’t the travel at the wheel, it’s the frame to LCA distance at the bumpstop mount, so you need to do some trigonometry to get the wheel travel. With a 12.875” long LCA (middle of the torsion bar socket to the middle of the ball joint), and about 5.75” to the middle of the bump stop, wheel travel on compression at that ride height ends up at ~5”. Which means with a factory wheel rate of 100 lb/in (.85" bars) it would take ~500 lbs to bottom out a factory LCA on the
frame from the factory ride height (ignoring the bump stop). Now the factory bump stop is actually about 1 1/8" tall so you'll
never get that much travel at the wheel, but that's another issue and a separate discussion.
So let’s say you set your frame to LCA distance at 1.5" as you said, and installed a
very reasonable 1.03" torsion bar (230 lb/in). The wheel travel works out to be ~3.36”, and so it would take 772 lbs of force to bottom the LCA on the frame. That's a pretty big
improvement from stock, so less likely to damage the LCA than the factory configuration. Now we ignored the bump stops entirely again and I wouldn't run without one of some kind, but even with a 230 lb/in bar you can run a shorter than factory bump stop and lower the car somewhat significantly from stock without any worries.
On my Duster I have about 1 3/8" from frame to LCA. I currently run QA1 LCA's, but I also ran my Duster with stock LCA's using the same LCA to frame distance, it's about the minimum I need with my torsion bars. At that frame to LCA distance the wheel travel is ~3.08”, and I run a 300 lb/in torsion bar (1.12"), so that's ~924 lbs to bottom out on the frame. So my LCA isn't "crashing" into my frame. And I personally don't think that 300 lb/in is an "insane" wheel rate for a street car like mine. If it were a track only car with softer compound tires I'd need to run an even higher rate than that. I'll give you that not everyone will enjoy the ride quality you get with a 300 lb/in wheel rate, but with the Hotchkis Fox shocks I use it's really not all that different a ride quality than a modern performance car straight off the dealer lot. I put ~70k street miles on my Challenger while it had a 270 lb/in rate wheel rate, it worked great, which is why I didn't hesitate to go to 300 lb/in on my Duster.
As for the modified LCA's to increase travel, they have the one of the same problems as using a drop spindle. The LCA to frame distance isn't the only limiting factor. On my Duster I have 13" from the spindle to the bottom of the inner fender when the LCA is on the frame. That means a 26" tall front tire would hit the inner fender at max compression travel (assuming no bump stop). So, using a 2" drop spindle, or an LCA modified to add much more than the 3/4" or so of travel the QA1's give, is pretty pointless unless you
also raise the inner fenders (or run a pretty short front tire). All you do is trade LCA to frame interference for tire to inner fender interference, and you don't pick up much (if any) travel in the trade.
If excessive stock Anti-Dive is unwarranted on upgraded B & E bodies, its certainly unneeded on an A-body. My modeling supports it and its #1 on list to test.
You totally missed my point. B&E bodies had
MORE anti-dive built in from the factory because of the heavy station wagons that were also on those platforms. A-bodies had less anti-dive built in from the factory. It's not an even comparison.
Like I said, Hotchkis did all of that modeling too, that's why they changed the suspension points for their B/E body UCA's to reduce the anti-dive numbers. I know, I have a set of Hotchkis UCA's on my Challenger for exactly that reason. If it had been needed for the A-bodies I'd be willing to bet Hotchkis would have done it. Instead, they decided it wasn't worth it (for whatever reason), and the A-body Hotchkis UCA's still use the factory suspension mounts. I'm sure there's still some improvement to be had, but, I can guarantee it won't as much as the B/E bodies because they didn't have the same amount of anti-dive built in to begin with.
