This effort took a lot of research. Enjoy!

My Current Suspension Setup plan:

This a review of my entire suspension setup, which modifications I did, and why. Every non factory modification to a car always affects something else. Even more so with suspension mods, it can really domino like a stack of cards. Every suspension setup is a compromise. I spent 18 years polishing the suspension of my wallowing turd of a 70 Z28 until it was a nationally competitive autocross terror at 1.3Gs. This time around with my dream car BBC C3 I would like to get the initial setup pretty close the first time. Reading, testing and models helped me a lot over the years.

My Suspension goal:

(1st) Great cruise comfort (2nd) Great autocross level handling (but not trying to be competitive, this time.) (3rd) This high HP car needs rear traction. (With different goals, I would make different decisions.)

I’ll rank my mods in my priority preferred order:

Tires first!

Tires:

Michelin Pilot Sports, 275/40-18 or 285/35-18 (final fitment TBD)


Wheels:

18”x 9.5”, possibly 10”, custom Rallys, BSP T.B.D. (max width wheels reduces required camber, a lot)



Shocks:

Viking Berserker, Double Adjustable, GB “Cruiser” Valving, front semi-coil over (double adjustable allows the best fine tuning) (cruiser valving favors street bumps for smooth handling response at 1-3 in/sec vs quickest handling response) (semi coilover was required to get my desired spring rates)



Ride Frequency:

1.43 FR / 1.68 Rr (stock BB is 1.2/1.4) (desired to firm up handling response 20%) (moderate autocross / sports car ride quality) (I ran 2.1 before to be super competitive) (will require good shocks to tune best ride quality aka: double adjustables)



Flat ride:

+11% Ride Freq in Reart = smooth ride @ 80mph (for best ride quality pitching motions)



Spring Rates:

450# Fr / 330# Rr (hit desired reide frequency targets) (can still lower car some and not hit bump stops at 1G)



Front spring;

QA-1 semi-coilover 450#, 9” length (for desired rate for ride frequency) (no others available)



Rear Spring:

330#, VBP (fiberglass rear for less friction) (min. rear spring rate required to keep off bump stop at BBC WOT) (stronger rear spring would reduce travel, but would hurt ride quality)



PS Box:

Borgeson Box (quicker 12.7 box ratio vs 16:1 stock) (doesn’t leak)



Steering Arm Ratio:

Standard Steering hole. Gives 16.0:1 overall ratio vs 20:1 stock on standard or 17.6 on fast. (Borgeson box on fast ratio would give 14.0:1 too quick for comfort) (2017 Z06 has 17:1) (lock to lock is 2.7 turns vs 3.4/2.9 stock, or 2.5 Z06) ( Caroll Smith recommends 16:1 as optimum even for race cars)



PS valving:

Turn One blueprinted box, “race” torsion bar mod, 45in-lb or 6.5# at wheel rim. ( ZR1 level or 60% more than a manual C3 or Min Van) (I ran similar in my Pro-Solo car and it was one of the best mods I ever did to the car)



Steering Wheel:

14” Leather, 1980 thick rim, re-covered (vs 15” skinny rim stock)



Front Bump Steer:

0.006” toe-out @ 1” bump (vs .185” stock) (reduces twitching wheel on bumps, or bumps in curves, even at street speeds) (stable steering wheel is very confidence inspiring)



Front bump stud:

.42” shims Rt, .62” shims L (solves bump steer)

(bump blocks caused a severe bump curve) (linear line overruled) (bump blocks may come back into play for wheel clearance) (will need .35” more shims and taller bump stud if custom arm is not used)



Steering arm:

0.35” drop, custom billet, aluminum (allows shorter bump stud)



Front roll rate:

73% (stock level understeer) (may need less) (adjust with sway bars, not RCH, for one change at a time)



Sway Bars:

1-1/8” Fr / 9/16” Rr (or Possibly ľ” rear) (could also soften front bar or use spring links) (This balance depends on how much power “oversteer” I want to use coming out of a turn)



Alignment:

7* pos caster (straight line stability, adds .9* neg camber on 10* turn)

0.5* neg camber (compromise between tire wear, handling, WOT traction and braking traction)



Upper a-arms:

SPC Adjustable, delrin bushings, oem height ball joint (delrin eliminate friction) (1/2” taller B/J helped camber by .25*, but hurt bump curve by .045” and raised RCH) (RCH & bump steer overrules) (Stock a-arms with offset shafts and slotted holes gave max 5.5* Caster, but no room left on studs for a camber brace) (desired 6-7* caster and brace over ruled)



Adj rear strut bracket:

Lowers rear bump steer by 60% from .123” toe-out stock to .053” (at 1” bump) set on high position. But decreases camber gain (per inch bump) from -.55* to -.33*. Hurts lateral traction but tire stays more upright for improved rear WOT traction. (Bracket set on high is 0.6” lower than C3 pivot.) (Improvement over C3 bracket) (favor bump steer and WOT traction over corenering camber) (going lower helps WOT traction but hurts tire pos camber even more)



Lower a arms:

Ridetech Delrin Bushings, spring cup plate reinforcement to allow coil-overs (Aldan American) (less friction) (no need for tubular lowers)



Front camber tower brace:

custom for BBC with stock fan (stiffens front end) (none available) (tight fit)



Ride Height:

1.0” drop in front, stock rear (for looks and aero)

Fr Z= 1.43” w/ 2 pass vs 2.10” stock; Rr D= 1.34” w/ 2 pass same as stock

Lower F41 ride height increases camber gain curve (at 1.0” bump) from .9* stock to 1.1* No effect on bump steer. May lower rear another ˝” for fender gaps if bump travel permits.



Vertical wheel movement at 1G (corner):

0.74” (half of stock 1.6”) (higher roll resistance) (springs & bars)

Vertical wheel movement (on 1G brakes):

0.9” (stock was 1.5”) (stronger springs)

Front wheel bump travel:

3.0” (with Bump Stop trimmed to 0.6”) (need max of 0.9” travel on brakes)

Rear wheel Bump Travel:

3.0” (with bump stops cut to 0.6”) (need minimum 1.8-2.0” travel at WOT



Front RCH:

2.5” w/ oem height B/J (taller ball joint hurts bump steer) (taller b/j raises RCH 1”, prefer low)



Rear RCH:

3.6” with adj strut bracket on high (going lower lessens weight transfer on corenering, but increases tire pos camber) (Roll axis biased just slightly to front, with slightly lower front RCH, for neutral f/r tire weight transfer) (Adjust rest with sway bar balance)



Results:
Static camber:

-0.5* (Ideal for tire wear )

Camber gain due to 0.7” body roll (in 1.0 G turn) :

+1.3* (greatly reduced from 1.6” body roll stock with +3.1* camber gain)

Fr Camber Curve:

-1.2* (Degree per 1” bump) F41 lowered vs Stock -0.9* (improved for cornering)

-0.8* @ 0.7”drop on turn

Camber Gain due to 7* Caster @ 4* turn (1G @ 60 mph):

-0.36* vs stock 0.1* (greatly improved for corering traction)

Dynamic Front Camber (at 1G, 60 mph, 4* steering, 4-7” at steering wheel rim):

-0.36* Front: (pretty ideal for max cornering)

(Could tune front dynamic camber with +/- caster)

(tall upper ball joint not needed for extra camber curve, but may be desired for autocross)

Camber Curve due to .9” Bump on 1G Braking:

-1.1* (drop was 1.6” stock) (lowered 1” helps camber curve)

Dynamic Front Camber on 1G Braking:

-1.6* (not ideal it’s a compromise)( I favor tire wear, cornering, and ride quality)

Rear Camber Curve:

-.33* Brkt vs -.55* Stock (Degree per 1” bump) (tire more vertical for WOT traction)

-.23* @ 0.7” turn drop

Dynamic Rear Camber on 1G Acceleration:

-.73* (vs -1.05* Stock) (strut bracket) (Rear tire more upright for improved forward traction)

Dynamic Rear Camber on 1G Cornering:

+.57* (edge of acceptable) (Carroll Smith says ideal front camber is more important)

 

Some Backup Info:


Courtesy of Zora Arkus Duntov and his 1962 SAE Engineering Paper

 

A few quotes by famous authors:Very Good Website on Suspension Tuning & Shock Tuning:

By SCCA National Champion, Book Author, Engineer, and SAE Formula Car Advisor:

Dennis Grant

https://farnorthracing.com/autocross_secrets16.html



Various Published Authors comments on suspension theory:

[“In the old days (‘50s/60s) it was common to use roll-center height as an adjustment to tune the chassis. The theory is, by raising the roll-center height at one end of the car, you get more weight transfer at that end. There are two problems with this method and it is no longer used.

First, raising the roll center decreases the weight transfer due to body roll. This introduces complications into the chassis tuning process that are hard to figure out.

The second and by far the worst problem is the almost impossible task of changing roll-center height without changing the suspension geometry radically. People used to move the upper A-arm of the double A-arm suspension, thinking it would only alter the roll-center height, but they were changing the camber characteristics and bump-steer of the suspension at the same time. These multiple changes make adjusting roll center a very risky and confusing guessing game with independent suspension. To me it seems so much easier to use adjustable anti-roll bars. They are not only easier to adjust, but the anti-roll bars give you an infinitely fine adjustment.”] “How to make your car handle” by Fred Puhn

Modern high perfromance cars use a very low roll center height, as it allows for much better bump steer control, which is better for modern wide radial tires. (Herb Adams)(SWDuke)

Most rear wheel drive cars handle pretty well with around a 72% Front Roll Rate. Further adjustments should be based on feel. (Fred Puhn)

(Carroll Smith quotes – Tune To WIn):

Old school suspension theory was used with skinny bias ply tires, they used high RCH to limit body roll, and the tires tolerated the resulting camber & bump steer changes. Modern wide radial tires are much more sensitive to camber & bump steer changes. So suspension theory has evolved to very low roll center heights that allow improved camber and bump control. The narrower tires will tolerate a fair bit of camber.

There are four methods to reduce chassis roll: (1) High Roll Centers (RCH) – these result in poor camber curves and high jacking forces. (2) Stiff springs – results in too much spring for braking, or too much body roll. (3) Anti-roll bars – we can tune the springs for droop on brake and the bars for droop on turns, and use the bars to balance the car (4) Longer suspension links – reduces the bump steer but also the camber change on roll.

The front RCH should always be lower than the rear. If too much lower –But to much lower will make a car not enter corners well and could exit on three wheels.

We cannot achieve Utopia in suspension geometry, it becomes necessary to compromise. A low HP car needs a different compromise than a high HP one.

It is more important to keep the front loaded tire more upright than the rear one. It is very important to get the rate of generation of the front & rear lateral load transfers somewhat equal, for balanced handling.

Ackerman steering is not very critical in a racing car. Some is desired. It reduces understeer only during corner entry. The same effect can be achieved by static toe-out or bump-steer that toes out, and those are much more easily adjusted.

Too stiff of roll resistance (by any means) and the car gets very stiff and slidy and loses its sensitivity. The car darts and follow the bumps.

Minimum liveable front wheel travel is 2-1/2”, and 3.0” is a lot better.

We can use deliberate amounts of bump steer to alter the response of the car in cornering. A minute amount of toe-out in bump can reduce corner entry understeer. If we put in too much, the vehicle becomes dynamically unstable over bumps and under the brakes. I have seldom run over .030” of bump steer over 2” of bump. (Same as .015” over 1” bump).

With a high HP car, there is a lot of torque to squat the chassis out of low and medium speed corners. The key to lap times with these cars lies in acceleration out of the corners. We need to ensure that the camber does not vary too much with squat. We are willing to sacrifice keeping the rear tire vertical in roll, and accept less than ultimate cornering power at the rear, vs the front. Larger diameter rear tires tolerate more camber change than shorter front ones.

A front engine car, requires that the outside front tire be kept as upright as possible, even at the cost of heavy bump camber change , but that can be reduced by anti-dive.

I believe it is a hell of a lot more important to get the roll center locations and movements happy with each other, than it is to get the camber curves perfect – which we can’t do anyway. (Carroll Smith)



(Herb Adams)

The F41 Corvette comes with very high rate springs. (550 #/in) The ride can be greatly improved by installing softer springs, with no effect on the handling capabilities. I recommend to buy the standard springs (300 #/in) and cut ~1/2 coil off for the proper ride height.

If the front RCH is raised, the front suspension roll stiffness is increased. The outer tire carries more lateral weight transfer, and the understeer is increased. It also reduces the camber gain, which causes even more understeer.

On springs, the first thing you should do is calculate how much spring rate or load is required to keep the front end off the bump stops, in a 1.0G braking. This is usually equal to normal irregularities on the street. This provides full suspension travel, and is considered soft by many. Further spring rate/load increases beyond this are used to allow for no bottoming on big bumps on a track, quicker handling transitions, etc.

A car with a 98 inch wheelbase, and a 58” track width, it requires much stiffer roll resistance than spring rate, because of the large leverage difference.To keep the motions (in inches) during a 1G turn the same as that during braking at 1G. The car will feel the most consistent to the driver if it moves the same ~1” during braking and/or turning, and/or acceleration. (Leigh Smith adapted from Jackie Stewart)

You should be able to tape a punch bowl on the hood, and roll a tennis ball around the upper rim, during all these manuvers and especially hold the tennis ball high at the rim during transistions. Do that and you are very smooth, and have optimized your tire traction in every direction on the “circle of traction.” (Jackie Stewart)

On a C3 this only requires 280# front springs and stock bars to get 1.4” of movement in both directions at 1G. And the car is still well off the front bump stops. 550# front springs and 1-1/8” & 9/16” sway bars cut both numbers to 0.7” at 1G. (Leigh Smith) But the 550# spring hurts ride quality as noted above.

 

I wish I would have installed a 330# spring vs a 360# spring. Handles great but the ride quality definitely suffers.

 

You -> "but tire stays more upright for improved rear WOT traction"

Probably worth a discussion somewhere, I'm not in agreement. The Hoosier recommendation I followed back in my day was somewhere around 2 degrees camber for maximum cornering. I had lots of power induced oversteer whenever I wanted it.

A lot of similar numbers for me (spring rates etc) but yours have a lot more insight

I have always puzzled (but not very hard) about how to determine "ride frequency"

One more parameter you may want on your side is corner balancing. There's a rule of some sort for cross axis weight balance. Something like that I would have to look up the terminology.

Doesn't matter much, I don't do this any more, I am more interested in riding comfort these days.

Many will thank you for putting this out there. No matter how I strived the C5's and C6's were always just a hair faster. I used to hope they would not show up.

 

Thanks Ignatz.

I agree the C5s have a few technology advances that we just can not hope to match: (Short of an SRIII frame upgrade)( even with that our cars are skinnier with a thinner track and more weight transfer - the price we pay for better style):

Like a lower roll center height, better camber and bump curves, wider track, more rear antisquat - those will let it put down more WOT power or more Gs to the tires, and more consistently. With less traction hick-ups.
They also have a stiffer frame, and less usprung weight with aluminum a-arms - those will make the quick transitions that much quicker and more stable. It can put down G force more quickly after a change.
Most of the rest we can update to pretty equal performance levels.

So with equal drivers, technically they should win.
But we can stay pretty darn close. And if they were "just a hair faster" you may have been the better driver!

A "very good" driver can almost always put a sec or so on a "pretty good" driver.

The weakest nut in the car is almost always the one behind the wheel!

I think Cargotzman or 69427 might have something to say about how close they can stay to those newer C6s.

I would hope that GM put 30 years worth of computer modeling and field testing to some advantage in their newer suspensions.
Ours were designed on a slide rule and graph paper! I'd say they are still pretty good regardless.
Close enough that a good driver can just about close the gap.

Most of the time I would "run with" or beat the corvettes, back in the '80s & '90s, even tho my solid axle '70 Z28 was in a different class, and "supposed" to be ~1.0 sec slower according to the PAX index. (AS, BS, ASP, BSP & ESP) But when I found a national caliber driver in a '90 ish corvette, yeah 1.0 sec was about right! I was much closer to the C3s, and only 1 or 2 guys could take me, Like GreenDot in his white LT-1 or LS6, he ran both, who used to be here. Tires were key. BFG-R1s or Yoko 008Rs were so much better than the bias ply Hoosiers back then! At treadwear 0 to 50 rated they felt like slicks, but with lightning quick turning response! I tried the old bias ply Hoosiers, they were were a throw it and wait and pray kind of tire. There was not enough "extra traction" to make up for the sloppy turning response. I lost 1-1/2 seconds. Later Hoosier finally went to radials, but they still weren't good enough, for a few years, anyway.

I am currently reading Dennis Grant's free Amazon Prime book "Autocross to Win". From Far North Racing.
It is excellent!
I thought I did a lot of testing, but I used stopwatches, a G-Analyst, built my own suspension spreadsheet models, etc. This guy used a lot of relatively less expensive instrumentation that became available in the 2000 era. Shock testers, real-time suspension movement and real-time IR tire testers, etc.
Great reading!
Still learning at 70! LOL

 

I resemble that remark

 

Just remembered these remarks:(Duntov Racing) – Classic Corvette Racing Experience for 60 years – With Eight National Championships

>These cars want a lot of caster – as much as you can handle. The more caster, the harder it is to turn the wheel, so anything more than >about 3 degrees becomes a problem after a long stint. With our power steering system, you can run 7 degrees of caster, which the car >really likes.

>Shown at the left is our adjustable bump steer blocks, an absolute necessity to calm down that vintage Corvette.

In analyzing pictures of their car setup, it looks like they are running a stock C3 rear strut bracket, not the lower one, oem height upper ball joints, not extended, 7* caster, and a 3/4" drop on the bump steer block. That is the same drop I came up with at 7* to calm down the bump steer.


Interesting brakes! 3/4" high bump block.

BTW they only run 450/300# springs Fr/Rr on their 800 HP 200 mph race cars!!!
Let that suspension work.

 

Holy cow, this was like reading the encyclopedia collection.
Nice work Leigh!

 

I kept it "short & sweet" just for you OCB! LOL

I saw no need to go into shock valving or tire temperatures.
I didn't want you to fall asleep!

But it took that much effort, and more, to run in the top 3 at a Pro Solo event.
At least it kept me out of the bars at night and away from the girls!

 

And that's a good thing???

 

Big money.I had most of those parts and more on my old 81, I went with the steeroids r/p and offset trailing arms. While the car handled well, my 89 C4 still was better on the track.

 

One thing I would also address is the wheel hubs ? C3 in general work very well many years ago.

Now in 2026 the rear hubs are a problem in finding good replacement parts. Rear spindles are no longer made by anyone ? (Post if you have a good source) Duntov corvette used to resell great parts.

Front spindles I believe there are good sources.

For the year Have you looked at the C7 hub options from ridetech ? while this requires a change to rear coilovers. I have converted to rear coilovers many rears ago, and using triple adjustable shocks.

Many spring weight options + adjustability makes it great for street track events. With Offset arms to allow wider wheels another plus. Also allows to install factory C5/C6 brakes as well.

Front options also available.

I am looking at Ridetech front system using my SPC Upper arms + Flaming river steering. Upgrade to C6 brakes. Everything is bolt on install. Using C7 hubs front & Rear.

Getting the C3 like my C6 Grandsport is not possible. C6 suspension is much better overall. Better street driving (smoother) and faster on the track.

My C3 comparison:

1978 corvette: Engine LS3/480, T56 6 Speed, 3.36 Rear gear does a 1:30.6 best lap at my local track.
2010 Grandsport. Engine LS3/436, 6 speed auto , 2.73 Rear gear does a 1:27.98 best lap.

The biggest difference is the brakes. C3 I need to brake early. Rotors are too small to get the same brake feel overall.

For street driving it overall doesn't matter. C3 is a noisy chassis compared to a C6, seats much better in the C6, steering setup is much much better.

But the C3 upgraded suspension is much better than any factory setup. Worth doing.

 

I think getting within 2 seconds on a 1-1/2 min track with a 40 year old chassis sounds like a great job to me!

And you have to admit it looks good doing it.

Honestly even with a full fledged SRIII C7 chassis it could get closer, but it would still be slower than a C7.
Too many technology advancements over 40+ years.
The chassis will never be as stiff, it will always have a skinnier track, no computer nannies, etc. etc.

But if I wanted a C7 I would just go buy one.
I have driven several. They are great cars. Just not for me.

This one has old-school soul.
And it can handle "pretty-close" to a newer one, with the correct mods.

 

The Achilles heal of the C-3 is the rear suspension. Bump causes tow out because compression pulls the hub inboard with respect to the front trailing arm mount point. The result is a loose condition. There are crutches, but they will never be on par with a double wishbone or multilink rear suspension. Long story short - I bought a '56 Corvette in 1975. In 1976 I welded in a C-3 front crossmember with all C3 suspension components, JFZ disk brakes, and C-3 rear suspension. It was better than the John Deere suspension I took out, but it handled like a C-3. Next, in about 1986, I swapped in a modified version of the C-4 rear suspension retaining the C-3 differential, C-4 hubs, and custom forward links. Much better. Then I added C-4 front control arms, ATS (now Speedtech) spindles, and a front steer Woodward rack. I left the C-3 front crossmember but modified it to accept the C-4 control arms. Then, about 3 years ago, I ripped it all out and built custom control arms, Speedtech spindles with C6 hubs/bearings, and a Sweet Manufacturing front steer rack. In the rear I modified a Detroit Speed Decalink suspension designed for a C-2/3 with longer forward links and Detroit Speed's 12-bolt Hammerhead differential. The C3 differential will also work with the Decalink. I still have the car. I also now have an old 1960 Corvette vintage race car that I am swapping out the front suspension for a modern front steer set-up of my own design using C-3 control arm geometry and a Van Steel C-3 spindle. C-3 stuff can be made to work on the front as Leigh has demonstrated. The only issue is the downward pointing lower ball joint's height above ground that makes it difficult to position the inner pickup points of the lower control arm high enough for a reasonable roll center (on a lowered car) and proper camber gain profile. A dropped spindle is almost a must. I don't have as much hope for the C-3 rear. If you really want the car to handle, you are probably better off swapping the rear for a C4 package or the Detroit Speed Decalink. Both require a little fabrication, not nothing massive. It also doesn't hurt to get rid of 5-600 pounds and move the motor back a little for CG. Below are a couple of photos of the modified C-4 rear suspension mounted to a C-3 crossmember with a C-3 differential (just happens to be in a C-1 chassis), and the Decalink which is built for the C-2/3.


C-4 Rear Suspension modified for C-1 application

C-2/3 Detroit Speed Decalink modified to fit C-1

 

Amazing work Mfain!

You are pretty close to what I would consider my ultimate pro-touring C3.
A full SRIII chassis, hammerhead diff, port efi BB, 6 spd and stock fenders.
If I had started this project 20 years earlier I just might have!
Sorta like one of these... well maybe some small flares...



The blue one nails the stance....but the gold one has the best wheels

 

So, any idea on what happened to the Hotchkis 6 link project? Did they just give up?

https://www.corvetteforum.com/forums...-a-6-link.html

 

No idea really. The guy quit returning my calls, and I just haven't bothered calling direct.
They added a lot of cool features in there, and I am sure that ran the price up.
They were waiting on two forged pieces to be produced. Then silence.

 

I think that they figured that the market was not there at a workable price point. High dollar cars are going to go Detroit Speed or SRIII chassis. Mid-range already has Van Steel and Ridetech options. Market is honestly not that big.

 

Yep.
I think there was room in the lower end of the market. For some quality feature improvements.

But they threw so many features into it that they ran the cost up, and were up against DSE, and I do not think there is any advantage to challenging somebody like that, who is much bigger, and has been in the market longer, with a product that is not cheaper, and can't be any better.

Not unless they were 20-30% less expensive. (With similar features)

My 2 cents.