autocross spring choice?
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 825
Likes: 40
From: Glasgow, Scotland
autocross spring choice?
ive got a 78 vette, which will have high bhp, 335/30/18 rear tyres and 285/35/18 front tires, qa1 double adjust full coilover upfront with 550 spring and have qa1 double adjust shocks at rear, looking to update my rear mono spring, to a new mono spring, what would be the best spring rate for the rear 300, 360, 400, 420 ???
will be used for street and plenty trackdays, autocross
anyone help, thanks
will be used for street and plenty trackdays, autocross
anyone help, thanks
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
First you need to figure out how much squat and body roll you have with your existing springs and go from there. I had people take still and videos of my 79 drag racing and on a road course.
I added a leaf to make it 500 lbs rear and my 550# coils from VB&P on inch shorter. I ran it that way for many years and then decided that adjustability on ride height was needed.
So I installed the QA-1 dual adjust front with 650# springs. I also have 600 and 700#
Then I decided to loose some weight and I went with a rear VB+P 420# mono. and 3/4 rear sway. My first day at the track my slicks were into and rubbing the rear wheel flares. So I cranked up the bolt to lift the rear end to finish out the day. On monday i called VB+P and said that the 420 was no good for me and I needed about 500# so they made me a 520# and that really works nice. with my rear dual adjust
I added a leaf to make it 500 lbs rear and my 550# coils from VB&P on inch shorter. I ran it that way for many years and then decided that adjustability on ride height was needed.
So I installed the QA-1 dual adjust front with 650# springs. I also have 600 and 700#
Then I decided to loose some weight and I went with a rear VB+P 420# mono. and 3/4 rear sway. My first day at the track my slicks were into and rubbing the rear wheel flares. So I cranked up the bolt to lift the rear end to finish out the day. On monday i called VB+P and said that the 420 was no good for me and I needed about 500# so they made me a 520# and that really works nice. with my rear dual adjust
Last edited by gkull; Sep 16, 2016 at 06:42 PM.
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 825
Likes: 40
From: Glasgow, Scotland
First you need to figure out how much squat and body roll you have with your existing springs and go from there. I had people take still and videos of my 79 drag racing and on a road course.
I added a leaf to make it 500 lbs rear and my 550# coils from VB&P on inch shorter.
I installed the QA-1 dual adjust front with 650# springs. I also have 600 and 700#
Then I decided to loose some weight and I went with a rear VB+P 420# mono. and 3/4 rear sway. My first day at the track my slicks were into and rubbing the rear wheel flares. So I cranked up the bolt to lift the rear end to finish out the day. On monday i called VB+P and said that the 420 was no good for me and I needed about 500# so they made me a 520# and that really works nice. with my rear dual adjust
I added a leaf to make it 500 lbs rear and my 550# coils from VB&P on inch shorter.
I installed the QA-1 dual adjust front with 650# springs. I also have 600 and 700#
Then I decided to loose some weight and I went with a rear VB+P 420# mono. and 3/4 rear sway. My first day at the track my slicks were into and rubbing the rear wheel flares. So I cranked up the bolt to lift the rear end to finish out the day. On monday i called VB+P and said that the 420 was no good for me and I needed about 500# so they made me a 520# and that really works nice. with my rear dual adjust
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
I think the reason George had to go up on spring rate in the rear is steel springs are progressive and fiberglass springs tend to be linear. If he would have had a 420 pound steel spring, it's resistance to the forces would have progressed as a rear corner was pushed down stopping it from reaching the point of tire rub. It's why some racers prefer steel. Going up on spring rate fixed his problem though so they both work, just differently.
Car weight, traction, balance (weight distribution), power, overall setup and driving style can all affect what is needed for springs and shock adjustment. You'll have to experiment.
Car weight, traction, balance (weight distribution), power, overall setup and driving style can all affect what is needed for springs and shock adjustment. You'll have to experiment.
Tech Contributor
Joined: Jun 2004
Posts: 20,841
Likes: 959
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I started with a 360# composite rear spring a bunch of years ago (but removed the rear bar to reduce the snap oversteer that C3s are prone to on occasion), but after a couple years of autocross and track days I changed to a 420# piece. I liked the feel and handling of the car better with the 420# spring.
I've since put a C4 suspension under the car, and am running the (500# IIRC) Z51 rear spring.
I've since put a C4 suspension under the car, and am running the (500# IIRC) Z51 rear spring.
Safety Car
Joined: Nov 2008
Posts: 3,713
Likes: 550
From: Seattle Washington
I started with a 360# composite rear spring a bunch of years ago (but removed the rear bar to reduce the snap oversteer that C3s are prone to on occasion), but after a couple years of autocross and track days I changed to a 420# piece. I liked the feel and handling of the car better with the 420# spring.
I've since put a C4 suspension under the car, and am running the (500# IIRC) Z51 rear spring.
I've since put a C4 suspension under the car, and am running the (500# IIRC) Z51 rear spring.
Tech Contributor
Joined: Jun 2004
Posts: 20,841
Likes: 959
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Not yet. I've kicked it around a few times putting a rear bar on it to see if I like it better with more rear roll stiffness, but it's a complete nightmare trying to figure out some bar shape/configuration that will work on my car. The combination of narrowed suspension, wide knuckle pieces, and stock C3 frame width/shape just doesn't leave much room to snake the bar arms through and also allow some end link lengths.
Hopefully one of these times I'll have an a-ha moment and find a workable solution.
Hopefully one of these times I'll have an a-ha moment and find a workable solution.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Safety Car
Joined: Nov 2008
Posts: 3,713
Likes: 550
From: Seattle Washington
I'm currently looking for that A-Ha moment. The C4 Bar has way to long radius bends. The C3 bar is much better but I think a very special Spring Bolt will need to be created to attach the Sway Bar.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Not yet. I've kicked it around a few times putting a rear bar on it to see if I like it better with more rear roll stiffness, but it's a complete nightmare trying to figure out some bar shape/configuration that will work on my car. The combination of narrowed suspension, wide knuckle pieces, and stock C3 frame width/shape just doesn't leave much room to snake the bar arms through and also allow some end link lengths.
Hopefully one of these times I'll have an a-ha moment and find a workable solution.
Hopefully one of these times I'll have an a-ha moment and find a workable solution.
The attachment point to the HD trailing arms and spring ends are all from VB&P. But I had to bend the bar in the middle to get a perfect 90 degree attachment.
Back when I had Koni rear shocks and the rear tires are off the ground. 3/4 inch bar, but the spring end links make it not come into play until you have a certain amount of vertical wheel movement. So it is like no bar and then body roll can bring it in
