Suspension Upgrades

[Invetterate]

Even though the rear suspension of the C3 (and later C2's) dates back to the early/mid 60's for its day the rear end was relatively high tech compared with much else on the market (except perhaps a few really exotic European high end cars) and when thinking about some of the UK and European 'ordinary' front (or rear) engined, rear wheel drive cars that were brought on to the market that had independant rear suspension and how potentially poor they were in extreme handling conditions (Triumph Spitfire/Herald?) it makes you realise that the Corvette IRS (for all its relative simplicity) works quite well.

I thought that, Ross, when Andy was only a couple of seconds slower than me round North Weald in a car that is nearly 25 years older. Mind you, a lack of talent on my part probably didn't help!

 

[Roscobbc]

I thought that, Ross, when Andy was only a couple of seconds slower than me round North Weald in a car that is nearly 25 years older. Mind you, a lack of talent on my part probably didn't help!

There are two manufacturers that come to mind when thinking about simple is best combo's (in terms of suspension/comfort) ....Honda and Lotus. Both generally handle really well with a good balance between handling and comfort........provided you keep with the OEM tyre/wheel combination........deviate from that proven combo usually results in inferior handling. Same with C3 Vette......go 'wide track' with a wider wheel/more wheel 'outset' and create major traction/handling issues.........which is why even with 285 section rubber on the rear of mine the rear wheel at 9" width (and 'inset' a further 1") actually retains the OEM vertical wheel centreline and the designed 'moment arm' measurement of IRS radius arms - theoretically allowing the additional tread width to remain in contact with the road surface.....hopefully even under full suspension deflection.
I can recall back in the days when Grabbers and the like were king. You'd perhaps see a C3 (or IRS C2) with a pair of L60's (285/60/15) or even wider on the rear end with 10" rims and possibly a 2" offset 'hiding' under extended L88 type flares. Look cool didn't it? ('er no.....) untill one looked at the car from behind when it was being 'giving the beans' off the line........and you'd notice when the rear end squatted-down the outer section of the wider tyres wasn't actually contacting the road surface.......

 

[Forrest Gump]

I thought that, Ross, when Andy was only a couple of seconds slower than me round North Weald in a car that is nearly 25 years older. Mind you, a lack of talent on my part probably didn't help!

I guess it comes down to fundamentals that our cars are similar weight, similar power, treaded road tyres with relatively similar grip. Slightly different suspension parts/designs isn’t going to make all that much difference. The huge difference in our times to Dave’s is a complete mystery however

 

[teamzr1]

I‘m trusting that VanSteel have a lot of experience with Corvette suspension! It’s really much the same as GMs Gymkhana option anyway.
Regarding rear weight transfer, the very soft steel spring was allowing so much squat bringing in excessive camber change and loss of grip that way I think. It was like looking over a ships bow at sea when going on and off the power.

Nice set of photos for your ZR1 mods. The C4 suspension is night and day step forward over the C3.
Why was the shock absorber lower mount extended? that looks prone - increasing the leverage on the stud into a casting.
I must admit when working on the C3 suspension and seeing your C4 set-up, you realise there is a lot of potential for binding. The link bolts from the spring to the trailing arms are moving in different arcs. Ditto the sway bar links where pivots or rose joints really would be more more satisfactory than the link bolt and bushes. But it is just a primitive and old road car at the end of the day!

The shop I had do the setup stated this kept the shock travel from binding and wanted the shock to mount straight vertical down due to the coil flexing in hard high speed cornering mounted around the shocks.

As we know what suspension setup works well for some, others do not like as how they rather want an under or over steering vehicle
Myself want a setup that might bias oversteer and I can manage with right foot, where I do not like a car at speed to push/understeer.

 

[teamzr1]

As ever, John, you are at the pinnacle of what is possible with a Corvette and that is both fascinating and stimulating. I think most of us here who are modifying from standard do not have the facilities/resources to test options and are just trying to improve the car overall bearing in mind that the vast majority of the time, we are on the road and not the track. This means researching and picking an option more often than not. Andy [Forrest Gump] is using the GM Gymkhana set-up as the basis for his mods, although the Bilsteins will be far better than the GM shocks of the time, I am sure! As to running at 160mph through the mountains, that is a dream I will never realise I'm afraid - more's the pity!!
Cheers,
Mark

Thanks, Mark
Due to my work as with GM I am a tester and design thinker, so I go about things much differently than others as never happy with just going with the crowd but rather design and then deep test to make sure it is what I feel works the best and to do that I do a lot of testing, analyzing the results and change design until I am happy with the final design

Thinking about Bilstein,
back in my C4 days you could send the shocks to them, and they would re-valve the shocks for the type of driving or racing conditions
Also recall for C4 was the FX3 suspension option
Behind the driver's seat in the cubbyhole where the ABS was there sat the FX3 controller, and we figured out a way to reprogram the tune in the IC chip to change what the 3 shock modes did

 

[Gibbo205]

Hi there

Where did you order the Vansteel leaf spring from please? What year is your car?

I have a 1978 Pace Car, like you I fitted the Bilstein shock and the ride quality was vastly improved over the stock shocks, my car has the gymkhana option.
I want to change the rear spring to composite for the improvement but also because of safety as my rear leaf spring is 43 years old and when they fail they generally destroy the rear of the car.

Where did you buy your Vansteel from please?

 

[Forrest Gump]

Hi Gibbo

VanSteel in Florida are the suppliers. Link below to the composite springs for a C3.

Vansteel

www.vansteel.com

My car is a '75 but I would recommend that you advise VanSteel which year your car is because there are some differences across the years. 78 I think has a wider spring and different clamp plate/bolt sizes.

 

[Gibbo205]

Hi Gibbo

VanSteel in Florida are the suppliers. Link below to the composite springs for a C3.

Vansteel

www.vansteel.com

My car is a '75 but I would recommend that you advise VanSteel which year your car is because there are some differences across the years. 78 I think has a wider spring and different clamp plate/bolt sizes.

Yeah mine is a 78 but has FE7 Ghymkhana factory suspension so is a 2.25" leaf spring I've discovered thanks to Gavin Roe helping me out.

 

[Mad4slalom]

I’ve finally got round to bolting on some new suspension parts to both ends of the car with the aim of sharpening up the handling. All the items are from VanSteel in the US except the shock absorbers. I’m following a street/slalom combination recommended by VanSteel which will be similar to the Gymkhana option.

Out-going stock front coil springs (c~300lb?) replaced with 550lb coils. The new springs are much shorter making them a lot easier to install.
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The stock 7/8” sway bar has come out and replaced with an 1 1/8” bar, only quarter of an inch bigger but looks so much beefier. This should stiffen up the cornering! See the brackets have a grease nipple which is a nice feature. All bushes are poly.

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To the rear, and this is where it is more exciting….The stock 10 leaf steel spring, rated at 196lbs has come out. It still looks okay from when I took it apart and painted it ten years ago, but is way too soft for my liking on corners and allows the car to squat too much under acceleration. They say steel springs get softer over time so it could be considerably less than 196lbs by now.

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In goes a VanSteel 360lb rated low arch composite spring. The composite weighs 7lbs versus the 36lb steel spring. I knocked-up the aluminium plate which shields the composite from the exhausts where they pass under it. Composites don’t like too much heat. The new spring is so straight when unloaded that I didn’t need to do the “dangerous” procedure of jacking up the ends of the spring to get the link bolts in. In fact I had to do the opposite and lift the trailing arm a bit to get the bolts through, the bolts then dangled loose until the car was back on the ground. 8” link bolts and poly bushes.
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My car didn’t have a rear sway bar fitted so I’ve added a 5/8” bar. The tapped holes for the brackets are present in all chassis from the factory but tend to get concealed with paint and crud if not in use. I had to run a tap through to clean the threads. A bracket added to the top of the trailing arms connects the link bolts.

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I’ve fitted Bilstein B6 shock absorbers front and rear to replace KYB Gas-adjust units. The KYBs have been okay, perhaps slightly harsh, but also not suited to controlling the composite rear spring.


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I‘m going to re-jig the brackets before refitting the exhausts so haven’t taken the car out for a drive yet. It should feel totally different with all these changes.

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Nice work , look forward to your road test feedback. Do all the bits come with it to fit the rear sway bar? Is this what gm called “gymkhana” suspension ?

 

[Forrest Gump]

Thanks Mad4.
Yes the sway bar comes with everything you need - brackets, bushes, bolts etc.
The front end coil springs and sway bar sizes are as factory fitted Gymkhana.
It‘s a bit different at the rear. Gymkhana was a steel spring of circa 300lb/in and a 7/16 sway bar.
Following VanSteel’s advice I’ve put on a 360lb composite spring and 5/8” sway. This would seem to be slightly stiffer at the rear than Gymkhana but the composite will behave differently from the steel spring and hoping the front/rear balance will still be good.