Launching Into The Future

This is the inaugural issue of MaxChevy.com, and I am Gary Heidt, owner of Heidt’s Hot Rods.  I am so glad to be part of a launch of a new, fresh publication. I say publication, as that is what this new Internet offering is going to be. This new venue offers us writers a lot of freedom -- and space -- to really pour out our minds about everything that pertains to Chevy muscle cars.

The Internet has certainly opened a new way to communicate and to publish. It is certainly here to stay. I only hope to be able to use it to service and teach all of you about chassis and suspension concepts in a way that you can actually use the information on your own cars.
     
We have made a commitment at Heidt’s Hot Rods to develop and bring to market products that will serve to enhance and promote the performance and safety of the cars we all love to build and drive.  Recently we unveiled a new product for the first-generation ‘67-69 Camaro, our Rear 4-Link Suspension Kit. Due to Chevy’s overlap of producing cars on like-chassis, the kit also bolts in to second-generation Novas, which your staff at MaxChevy have included in this first issue.  This system is designed as a completely bolt-in kit, with no welding or cutting to the floor or frame rails.

Gary Heidt is one of the aftermarket’s foremost experts on chassis and suspension design.  At Heidt’s Hot Rods, one of the aftermarket’s most respected fabrication companies, Gary is always working to raise the bar on bringing classic muscle cars up to modern handling standards.  Heidt’s roots are firmly planted in the street rod sector, but his move into the muscle car market has been a successful one, with products for tri-fives, Novas, Chevelles and of course, Camaros.  One of Gary’s greatest strengths is his ability to listen to what enthusiasts want, and one of his most popular attributes is his positive attitude toward making it happen.

The main reason to use this type of rear suspension system is the elimination of the leaf springs. We all know about wheel hop, and all the devices through the years people have dreamed up to eliminate this "bouncing" effect. Some work and some don’t.

Leaf springs were never intended to be a great traction device, or a great handling type of suspension, either. They had only two good features: they were simple and they were cheap. Period. Put 300, 400 or even 500 horsepower to a pair of leaf springs and they just wrapped up under the car. The stored energy was released into the tires in such an uncontrolled fashion that the rear wheels hopped so badly that they felt like they were going to tear themselves out from under the car. They would shake the car so much that it felt like it was going to explode.

Adding traction bars calmed them down, but only a certain amount and then you had to deal with the harsh ride and pounding you had when you were just driving the car around.

Then came along performance 4-link. This new concept, which was really not new at all, as it was used by Chevy in a triangulated form on the Chevelles, was designed for use on all-out race chassis. This was a very good system in that it created a characteristic called "anti-squat." This is when the rear of the car tends to lift from the torque applied to the axle housing. The forces applied to the upper and lower bars actually produce an upward force on the chassis during acceleration.

This is very similar to the "anti-dive" characteristic found in the front suspension. You can see the design feature by the rearward tilting of the upper control arms. If you look at a couple of different types of cars you will see different amounts of angle. A pick-up has only a minimal amount of anti-dive angle, as they are just basic vehicles used for regular driving. Look at a Corvette upper arm. It has a huge angle, which indicates that it is intended for maximum stability during hard braking situations (we tend to call this "drive it like I stole it").

Although the rear 4-link on a factory car has basically parallel links as viewed from the side, it is still a true 4-link setup. The fun began when guys figured out that if you angled the two bars in relation to each other that you would induce a complementary characteristic called "anti-squat."

The bottom line to all this lifting and squatting is this; the car on launch wants to lift in the front and settle down in back as the weight transfers from the front to the rear. It is as if the chassis is trying to drive out from under the body. At the same time that the body is trying to squat in the rear, the suspension is trying to push against it as it is trying to hold the rear up. But since the body is above the axle and weighs more, it wins and pushes the suspension down onto the axle.

With, say, leaf springs for example, they just squish down the amount that they are pressed on by the body transfer weight and that is the amount that is then pressed against the street for traction. But with properly designed 4-link with anti-squat the suspension actually creates a true lifting force that can equal or exceed the amount of weight transfer force from the launch. You probably have seen this when a car actually lifts off the line as it launches.

The real bottom line here is this: the tires, which hold up the axle, which holds up the suspension, are pressing against the track to do all this lifting. If the suspension is actually lifting the car and offsetting that transfer weight, all that force is pressing those tires against the track with a much higher force than just the weight of the vehicle. The amount of increased traction resulting from this increased weight is huge. Thus, a great launch!  As you can imagine, then, the tunability of a 4-link has far reaching possibilities.

So much for this installment of suspension theory and design. Next time we may get into the real reason for Dropped Spindles, calculating roll centers and roll axis, Panhard Bars and all kinds of cool suspension stuff.

Till then, happy burnouts! 

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