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Topic: Comparative stiffness between standard 84 suspension and Z51 85 suspen

in Forum: C4 Handling Components

Comparative stiffness between standard 84 suspension and Z51 85 suspen (1/3)
 6/4/18 7:55pm
Our-83
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Saint Cloud, FL - USA

Vette(s):
1983


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Posts: 7

Ok ... in 1985 the standard suspension was softened up from 1984 by 26% front and 25% rear. The Z51 was softened by 16% front, 25% rear in 1985. So ... does anyone know how non Z51 1984s end up being sprung in comparison to a 1985 Z51s ? I would guess they canít be very far apart. Iím not talking about how they handle or the related difference in roll bar dimensions etc - just the differences in Iím assuming the front and rear transverse spring rates.
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Re: Comparative stiffness between standard 84 suspension and Z51 85 su (2/3)
 7/31/20 6:57pm
Our-83
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1983


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Thx especially for link to specs. I had looked into it but couldn’t come up with anything definitive. 

I have a base 84 and way back when a friend had a Z51 85. Although a bit difficult to compare the ride in his with the 84 I purchased a few years ago - my impression is that they rode / ride exactly the same : VERY firm. Which I like very much. 

In fact i read read somewhere that the 84 Corvette was the most firmly sprung car GM had produced in the modern era. 

The Black Book says to compensate for reduction in 85 Z51 spring rates the diameter of the sway bars was increased.

imagine an 84 Z51 with 85 Z51 sway bars : might give you an idea what it was like riding in a Prarie Schooner. 

 

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Re: Comparative stiffness between standard 84 suspension and Z51 85 su (3/3)
 7/31/20 7:03pm
Our-83
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Saint Cloud, FL - USA

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1983


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Posts: 7


( thanks to several who supplied various links and/or technical data - ive basically summarized it here : )

 

 

83-84 Base Suspension : Subtle Variation of 85 Z51

Quote

I have an '85 Non-Z51 with KYB Shocks and stock OEM Bushings and it rides nice and comfortable. I have no squeaks, squawks, leaks, etc from bouncing the car off of every pebble... I get compliments from people surprised at how comfortable the ride is and how well the car handles.

—————————-

I couldn’t agree more with you. I have a base ‘83

( it was manufactured on 30 March 1983 - Chevrolet decided to call it an 84. Ironically a friend is the original owner of an 84 built in March 1984. Chevrolet says they’re both ‘84’s. Chevrolet can bite me)

Back to our regularly scheduled program :

The interesting ride variations of the 83-84 Corvette and ‘85 Corvette.

Here’s some background from various sources :

Of total 83-84 production 51,547

25,995 came with Z51 suspension

Of total ’85 production 36,729

Only 14,802 ordered Z51 suspension



And this was after the suspension of both base and Z51 were both softened considerably.

“...in 1985 a result of harsh ride criticism springs for the base suspension were softer by 26% in front, 25% in the rear. Springs for RPOZ51 were 16% softer in front and 25% softer in the rear. Z51 stabilizer bars diameter was substantially increased.

So what was the effect on handling, vis-à-vis - the skid pad ? Less than you’d think : “... (1984) ... cars equipped with the Z51 handling option were routinely turning in an astonishing 0.95g lateral acceleration on the skid pad. Even the base suspension provided 0.90g on the pad ...”

“... The effect on the all-important skid pad ( for the 1985) was measurable but not a source for concern. With the base package coming in at .88g and the Z51 package generating .90g,...”

Note : a base suspension 83-84 and 85 Z51 generated the same skid pad number.

This is very interesting when you now look at the spring rate specifications:

83-84
Base FE1
Front 63.5
Rear 72.0

85
Z51
Front 63.5
Rear 57.2

83-84
Z51
Front 102.0
Rear 87.5


Makes a lot of sense a base 83-84 suspension equipped car and a 85 Z51equipped car would generate the same results on the skid pad.
The 83-84 base suspension is essentially the 85 Z51 with a slightly stiffer rear spring but smaller diameter stabilizer bars.

Maybe the 83-84 base car is the ideal compromise among all the 83-85 suspension combinations.

I drive a C5 and the 83 over the same rural hilly twisty road I live on and much prefer the 83. It hugs the road ( vertically) - you feel all the entertaining undulations - kind of like how you feel attached to the vertical undulations of the track riding Space Mountain at Walt Disney World. You don’t sink down, you get pulled down.

The C5 flows up and down.

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