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according to Corvette Black Book “Suspension rates were lowered in 1985 ... Springs for RPO Z51 were 16% softer in front and 25% rear....”
( the rates for the base suspension were softened 26% front and 25% rear )
So ... the question is what are the actual spring rates for a base 1984 and a 1985 Z51 ?
Iirc the spring rates for a base 84 are the same as the 85 z51 or so close there is no meaningful difference. The sway bars are different too though I believe. (If equipped, it's been a while.)
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.
I have had two 84s. New one in 1984 and traded it for a 1986 Z51 coupe. The 86 definitely rode a little softer than my 84. I have a 84 now that I purchased in 2011 and completely restored including new poly bushings. It rides harder than the new 84 did back in the day it was new. I like the new feel, it got a lot better after I got some miles on the new bushing install.
Wonder how 84 with base suspension compares against 85 Z51 on track
It was once popular to find a Z51 early C4 for track competition- makes me wonder how many base 84’s, of which there’s a kazillion, were passed over ! Furthermore it would seem the optimal car to build for track use would be an 84 base suspension with 85 roll bars.
And really makes you wonder how an 84 with base suspension performed on a road course vs an 85 with Z51 suspension. Anyone got some old Road & Tracks ?
The 85 z51 would put a hurting the 84 base. The lower spring rate is offset by the larger bars. L98 will out perform the L83. Driver also has alot to do with the outcome.
The 85 z51 would put a hurting the 84 base. The lower spring rate is offset by the larger bars. L98 will out perform the L83. Driver also has alot to do with the outcome.
On top of that the 85 z51 rims are 9.5 all the way around with +38mm offset vs the 8.5 32mm front 9.5 38mm rear of the 84 rims. All he 84 rims are identical iirc. Mine are different widths front and back even though the car is a base model. I have no reason to believe they are swapped as pretty much everything on the car was stock when I bought it. Every little bit helps. Z51 to Z51, the extra 25 horsepower the 85 makes puts it up a notch but honestly it probably would come down to the driver more than anything like you said.
Furthermore it would seem the optimal car to build for track use would be an 84 base suspension with 85 roll bars.
I'm not sure that's the hot ticket in modern times. Especially now that tires have much more grip than they did back then, even the 84 Z51 springs are on the soft side of optimal for anything except the bumpiest tracks. Nobody with an unlimited rule set and access to aftermarket springs would set up a C4 with springs that soft. And for track use, the use of soft springs and really big swaybars (i.e. the Herb Adams approach) is usually not the best way to do things. You end up with a much higher wheel rate in roll than in pitch/heave, and you have to choose the ideal damping for one or the other but not both. It also ignores the fact that the biggest acceleration force on any car is braking, so keeping the car off the bump stops with stiffer spring rates is usually a good thing. In later C4s (88-96), Chevy did this by adding a crap ton of anti-dive geometry, but that's not really ideal for other reasons.
And really makes you wonder how an 84 with base suspension performed on a road course vs an 85 with Z51 suspension. Anyone got some old Road & Tracks ?
Kevova and 84 4+3 gave some good answers to this. On almost any road course, power is really important. The huge disparity in that alone would dictate that the 85 would dust the 84. Maybe in an autocross it would have been a lot close, but...
Originally Posted by 84 4+3
All he 84 rims are identical iirc. Mine are different widths front and back even though the car is a base model. I have no reason to believe they are swapped...
According to two different online sources (Mirrock Corvette and Jonas Byland), the 84 and 85 C4 Base model had 16x8.5 both front and rear, the 84 Z51 had 8.5 front and 9.5 rear, and the 85 Z51 had 9.5 both front and rear. So the 85 Z51 wins on the wheel width as well.
I'm not sure that's the hot ticket in modern times. Especially now that tires have much more grip than they did back then, even the 84 Z51 springs are on the soft side of optimal for anything except the bumpiest tracks. Nobody with an unlimited rule set and access to aftermarket springs would set up a C4 with springs that soft. And for track use, the use of soft springs and really big swaybars (i.e. the Herb Adams approach) is usually not the best way to do things. You end up with a much higher wheel rate in roll than in pitch/heave, and you have to choose the ideal damping for one or the other but not both. It also ignores the fact that the biggest acceleration force on any car is braking, so keeping the car off the bump stops with stiffer spring rates is usually a good thing. In later C4s (88-96), Chevy did this by adding a crap ton of anti-dive geometry, but that's not really ideal for other reasons.[left]
Kevova and 84 4+3 gave some good answers to this. On almost any road course, power is really important. The huge disparity in that alone would dictate that the 85 would dust the 84. Maybe in an autocross it would have been a lot close, but...
According to two different online sources (Mirrock Corvette and Jonas Byland), the 84 and 85 C4 Base model had 16x8.5 both front and rear, the 84 Z51 had 8.5 front and 9.5 rear, and the 85 Z51 had 9.5 both front and rear. So the 85 Z51 wins on the wheel width as well.
I was under the assumption that even though it was noted that 84s had different rims base to Z51, in reality it would seem that they all were the same. Pretty much every 84 I've come across has been the same as mine. However I know mine is a base model, the others may or may not have been Z51 cars.
But agreed, while punishing, the 84 springs are still soft. I'm by no means a suspension expert so I'll take your word for it. However the suspension in my car has no issues trashing my back, I could only imagine a Z51 car... It's fun for the street though. Feels like a big go cart.
I was under the assumption that even though it was noted that 84s had different rims base to Z51, in reality it would seem that they all were the same. Pretty much every 84 I've come across has been the same as mine. However I know mine is a base model, the others may or may not have been Z51 cars.
That could be. I'd defer to those more knowledgeable about this. I do know that the catalog showed a 15x7 base wheel, but it apparently never appeared on a car except maybe for the "1983" prototypes. So that does lend credence to your theory.
But agreed, while punishing, the 84 springs are still soft. I'm by no means a suspension expert so I'll take your word for it. However the suspension in my car has no issues trashing my back, I could only imagine a Z51 car... It's fun for the street though. Feels like a big go cart.
So much of the ride quality of any car really comes from the shocks that it's hard to attribute all the difference between two model years of C4s as just the springs. Bilsteins generally seem to ride harsher than some other premium-brand shocks, for reasons I don't completely understand. And I'm sure the 1984 Z51 shocks in particular were pretty stiff to cope with those spring rates. It's all kind of chicken-and-egg stuff, though, because with stiffer springs you ideally want stiffer shocks, especially in rebound - so they should come as a package. But on my car, which has stiffer springs than the 84 Z51, if I have the Konis installed and backed down to about halfway in their stiffness adjustment, the car gets surprising decent in ride quality. That's even with Banski rod-ends in the rear suspension and poly LCA bushings up front.
That could be. I'd defer to those more knowledgeable about this. I do know that the catalog showed a 15x7 base wheel, but it apparently never appeared on a car except maybe for the "1983" prototypes. So that does lend credence to your theory.
So much of the ride quality of any car really comes from the shocks that it's hard to attribute all the difference between two model years of C4s as just the springs. Bilsteins generally seem to ride harsher than some other premium-brand shocks, for reasons I don't completely understand. And I'm sure the 1984 Z51 shocks in particular were pretty stiff to cope with those spring rates. It's all kind of chicken-and-egg stuff, though, because with stiffer springs you ideally want stiffer shocks, especially in rebound - so they should come as a package. But on my car, which has stiffer springs than the 84 Z51, if I have the Konis installed and backed down to about halfway in their stiffness adjustment, the car gets surprising decent in ride quality. That's even with Banski rod-ends in the rear suspension and poly LCA bushings up front.
See, the bilsteins I put in mine actually felt better than the Gabriel's they replaced. Their dampening is better than the gabriel's but the gabriel's initial hit hurt more, they didn't want to compress as much. But that really shouldn't be the case, so it could also be entirely anecdotal. Basically hitting the bump hurts less with the bilsteins and it settles down faster. The exact opposite happened with the gabriel's...
Theres actually a promo video floating around YouTube of the 15 inch rims. They seem to be inspired by the mid 70s c3 rims. A modernization of them. If someone has a set they're probably worth something because only a few photos of them even exist iirc.
according to Corvette Black Book “Suspension rates were lowered in 1985 ... Springs for RPO Z51 were 16% softer in front and 25% rear....”
( the rates for the base suspension were softened 26% front and 25% rear )
So ... the question is what are the actual spring rates for a base 1984 and a 1985 Z51 ?
my guess is they must be fairly close
anyone shed some light on this ?
I’ve learned way more about early C4 suspension etc than ever imagined
Had to smile when I read this comment:
Feels like a big go cart.
im fortunate to have a 15 mile twisty over hill & Dale NH back road ride to work ( the 84 is a daily driver ) and I’ve hoften thought it’s like driving a big go cart
Sorry to add to a year old thread but I hope this is relevant.
I found this document in the GM Heritage Center archives and it states front spring rate for the 1984 Corvette base model as 75.4 (431) and Z51 110.9 (634)
Can anyone confirm this as I have a 84 with BMA front spring BMF rear spring and small front and rear sway bars (FE1 equipped))
I've searched all over but kept coming up with different answers.
Does anyone have a 1984 Corvette Specifications Manual?
Iirc the spring rates for a base 84 are the same as the 85 z51 or so close there is no meaningful difference. The sway bars are different too though I believe. (If equipped, it's been a while.)
...there's a fairly large difference... the 1984 Spring Rates, especially with RPO Z51, were practically undriveable on regular roads... at the time, there was a lot of chaos from buyers of the Z51 RPO Option for that year... everybody wanted the hyped up "High Performance Suspension" not knowing that translated to "Jaw Breaking Hard As A Rock Suspension". A lot of cars were sold with that option... GM/Chevy Corvette Engineers were Quick to make substantial changes in the Ride of the Corvette for 1985. 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.
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-ŕ-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.
Stay safe
E. W. Sea 4&5
Last edited by Wall-E; 04-25-2020 at 10:10 PM.
Reason: Spring rate chart still confusing
I have a base ‘83. It was manufactured on 30 March 1983 - Chevrolet decided to call it an 84. . Chevrolet says they’re both ‘84’s. Chevrolet can bite me.
What is the tenth digit of your VIN? If it's a "D", you do have an '83!
I'll bet it's an "E".
Every manufacturer builds cars in advance of Jan. 1, XXXX. That doesn't mean they're manufacturing year old cars! Of course, they call them new cars, even though you can buy them before Jan. 1, XXXX! You MUST know the truth about the '84 Corvette, and yet you spout that garbage.
Post a picture of your VIN. If its a "D", I'll send you $20!
12-10-2018, 04:50 PM
Spring Rates Base 1984 vs 1985 Z51
