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Discussion Starter · #1 ·
I have been interested in Tom Frederico's new sway bars and springs. Since the stock Impala springs and most of the after market offerings up to this time have been linear in rate what is the advantage or disadvantage of a progressive rate. My assumption would be that the lower inital rate would make for a better ride on the street and that the higher final rate would help on the track. However, there could be more body roll and different reactions to mid corner bumps. For example what happens mid corner when the car is heeled over and you hit a bump hard enough to double the spring rate momentarily. Seems like that could be unsettling to say the least. Any suspension engineers out there?
 
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Discussion Starter · #2 ·
Progressives are definitely more comfortable than linear in my experiences.

I've had Intrax rear springs and currently run ST in the back. The intrax which was progressive was a much more comfortable ride, and still handled really well.. I think the ST's are a bit better for handling but they are really STIFF... I think I'm going to put the Intrax's back in once I get some different rims
 
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Discussion Starter · #3 ·
Allen,

I have wondered that myself, and have always been afraid of going to a progressive rate for that very reason... the possibility of an immediate change in mid turn.

I'd be interested to hear feedback on this as well.
 
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Discussion Starter · #4 ·
Linear : more predictable, and not subject to rate change (which can upset the car) during compression.

Progressive : more comfortable.

FWIW, GM uses linear springs both front and rear (stock) on the SS.
 
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Discussion Starter · #5 ·
I am switching back to stock SS springs in the rear of my Caprice, because the rear Hotchkis spring rate doesn't feel compatible with my front cut 9C1 spring rate (though I've been running this for 2 years now). I expect the ride will get a lot more comfortable, with a little more understeer at the limit. Worth it to me.
 
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Discussion Starter · #6 ·
I've tried to get response on any B-body Performance parts impressions, but my thread was dead with no responses.

Maybe the bars haven't shipped yet, or maybe no one has had a chance to try them out.

Not sure, but I'd like to hear responses before I make a decision on whether to try a full B-body Performance spring/sway setup or go with the well known, f-body front, HO/HA rear, GW front and ?? rear spring combo.

-PJ
 
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Discussion Starter · #7 ·
PJ

I was told that the first run of bars has shipped. I ran the HO/HA bars with stock springs and shocks and it worked great on the street.T here was still too much understeer for autocrossing so I went to GW front springs and F body bar. That setup worked well on the track but the end links wear the holes oval in the LCA"s.Installing a T2R brought lots of power on over steer so I went back to the HO front bar. Toms bars look to be the ticket for my goals but I am not sure how the springs would act. I re-read one of the suspension books and it basically said softer springs=good ride and stiffer=better cornering.
 
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Discussion Starter · #8 ·
I just took out my rear Hotchkis springs and installed some stock Impala SS take-outs. I was previously using upper and lower isolators with the Hotchkis. I removed the lower isolator for the SS springs (like 9C1s) and the ride height still increased (as I expected).

Also as I expected, the ride improved. The way the car handles bumps is MUCH more civilized. At the very least, the progressive rear springs combined with my front spring rate led to a very untame, uneven feel to the suspension. A full Hotchkis car may not feel as bad, but I've never driven or ridden in one to know.
 
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Discussion Starter · #9 ·
His High Performance Springs have a 1 1/4" drop. If those springs are progressive, does it really make a difference when going around corners?
 
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Discussion Starter · #10 ·
Progressives are used for two reasons:

1. for load carrying to maintain approximately consistent ride frequency whether unloaded or loaded. The ride frequency at the rear is usually 1.1 - 1.2 times the ride frequency of the front - this maintains a "flat ride" - meaning when you go into a ride swell, the front of the car compresses first, and (obviously) the rear lags - the higher rear frequency helps the vehicle come out of the swell flatter and not pitching so much. If you didn't adjust the rear spring rate up to offset the additional rear load, the ass end of the vehicle would start to lag the front motion more and it becomes pitchy which is annoying as hell.

2. The second reason is when a vehicle doesn't have enough ride travel and they need to have a normal spring rate for ride comfort, but need to firm it up substantially to keep from crashing through. Polyurethane jounce bumpers used on almost all cars help significantly for the crash through, but some vehicles have such little ride travel compared to what they are allowed to haul(because low looks cool) that it is necessary to keep from destroying the structure/suspension.

The only problem with progressives is that the spring rate does not increase smoothly - often they have a very non-linear rate changes to them depending on how well the spring design and manufacturer produced them. Sometimes (not always) that can be felt during handling maneuvers. You can see it in the roll and wheel travel response plots during things like lane changes and step steers, but for the most part they aren't that bad and it is not usually much of a problem for an everyday vehicle.

If you are autocrossing or road racing you wouldn't use these because of the non-linearities that can upset the vehicle, but on a street car it isn't that big of a deal.

Actually, I would almost consider the way my 95 RMW (74K miles) felt stock as unsafe for handling because of the horrible steering response and floaty ride. But considering it was tuned for nearly deads, it wasn't as big of a concern that the handling was rather spooky if driven agressivley. The way everyone firms their vehicle up with bars, poly bushings, body bushings, and tires, the handling is so vastly improved, that the strange things that progressives do are mostly insignificant. I would rather have them there for the times when I am hauling big loads or trailering.

Todd
 
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