It did not take many miles to realize that although my creation accelerated like a banshee, it was a real handful in the corners and the brakes (drums) sucked. Back to the junkyard and I made a deal for some discs from a big block Nova donor car – a real safety improvement. Now for the handling issue. Basically, my amateurish efforts were mediocre by today’s standards but the heavy duty shocks, firmer springs and sway bars teamed with some Goodyear radials made a tremendous difference. It felt tight and glued to the road. For the 70’s it was about as good as you could get.
Now, let’s fast forward to today. Let’s say you are building a muscle car street rod like the Nova and you want it to handle as well as scorch the ¼ mile. Here are some ideas about how to improve the suspension without breaking the bank.
First, get the best tires you can afford. That means tires meant to handle so stay away from the semi-race bias ply tires; they look great and really hookup but they aren’t meant for corners. Get a set of slicks for the drags if you are into straight line speed. Four brands of very good summer tires (meaning not intended for near freezing temperatures or driving in snow and ice) are the Continental Extreme Contact DW, Goodyear Eagle F1 Asymmetric, Michelin Pilot Sport PS2 and Pirelli P Zero. All have excellent dry and wet traction and perform well in road course and slalom testing. In testing of 225/45R17 tires for ride comfort, dry and wet traction, lateral grip, steering response and road feel there was very little quantifiable difference in these four tires. The ranking was:
1. Michelin Pilot Sport PS2
2. Goodyear Eagle F1 Asymmetric
3. Continental Extreme Contact DW
4. Pirelli P Zero
The difference between first and last ranking score was 7.48 to 7.45 so any one of these is an excellent street performance tire.
performed this testing in June of 2009 on both a 6.6 loop of expressway, state highway and county roads and a 1/3 mile test track course that includes 90-degree street corners, lane changes and simulated expressway ramps. Run in both dry and wet conditions, the test track allows evaluation of traction, responsiveness, handling and drivability normally only encountered during abrupt emergency avoidance maneuvers or competition events. Check out the full report at: http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=120.
performed this testing in June of 2009 on both a 6.6 loop of expressway, state highway and county roads and a 1/3 mile test track course that includes 90-degree street corners, lane changes and simulated expressway ramps. Run in both dry and wet conditions, the test track allows evaluation of traction, responsiveness, handling and drivability normally only encountered during abrupt emergency avoidance maneuvers or competition events. Check out the full report at: http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=120.Next, shocks. Things have changed since the 70’s when heavy duty was about the best you could do. Shocks determine the rate of weight transfer by damping the motion of the spring and optimizing weight transfer is what good handling is all about. The shocks essentially control how the suspension operates, and you can't achieve the ideal damping for your combo without an adjustable shock. Next to tires, the shocks are the most important components of the entire suspension. Double-adjustable shocks allow independent damping of both compression and rebound. Some single-adjustable shocks change the damping of the compression or rebound, but not both, while others change the compression and rebound action at the same time in equal amounts. Double-adjustable shocks allow very quick adjustments for fine tuning your suspension and are your best choice.
Springs: Springs come in many forms - coils, leaves, torsion bars, or air bags. Springs primarily support the weight of the chassis, but also allow the tires to follow the contours of the road while providing roll stiffness in the corners. Perhaps the most important aspect of spring design is its spring rate, which is different from spring load. Spring rate is simply how much force it takes to compress a spring one inch. For instance, a 200-lb/in coil spring requires 200 pounds of force to compress 1 inch. Spring load, on the other hand, is how much weight a spring can support at a given height. Spring rate does not change as a spring compresses but spring load is reduced. The more a spring is compressed, the less weight it can support. A shorter spring must have a stiffer rate than a taller spring to support the same weight.
Linear-rate springs are found on most production cars and race cars. Some aftermarket springs have a progressive rate, which means that they get stiffer as they compress. This design initially provides a softer rate to improve ride quality, then stiffens up the more it's compressed to limit body roll. The theory is good, but with a variable rate spring, the shock valving must account for a wide range of spring rates, which can adversely affect ride quality and handling. A progressive spring rate can unnecessarily complicate fine-tuning the suspension. When matched with the right shocks, a linear-rate spring can ride and handle better than a variable-rate spring so be wary of the benefits of progressive rate springs.
Most passenger car spring rates are pretty soft so a good rule of thumb is to increase the spring rates about 30%; if the vehicle has the optional “heavy duty” suspension option and a firm ride, try some of the other modifications mentioned in this article before you pop for new springs.
Yep, sway bars. Sway bars help resist body roll by increasing roll stiffness; this is done by attaching the left and right sides of a car's suspension together and anchoring them to the frame. In the front suspension, the sway bar anchors the lower control arms to the frame. In the rear, the sway bar usually attaches from the rearend housing to the frame. As a car's body begins to lean in a corner, cornering loads twist the sway bar. Consequently, it is the bar's torsional stiffness (resistance to twisting) that determines how much the body roll is reduced.
The three primary factors that determine a sway bar's torsional stiffness are (1) its diameter, (2) swing arm length and (3) whether it is of solid or hollow construction. In regards to sway bar diameter, stiffness increases the bigger the diameter. Small increases in diameter substantially increases bar stiffness so be conservative when selecting a bigger bar. A 32 millimeter bar is 70% stiffer than a 28 millimeter bar!
Changes in swing arm length dramatically impact sway bar stiffness as well. The swing arm is the portion of the sway bar that extends from the frame to the control arm or rearend housing. Lengthening the swing arm reduces sway bar stiffness, while shortening it increases stiffness. Shortening the bar’s swing arm from 10 to 5 inches results in a sway bar that's twice as resistant to twisting.
Is a tubular sway bar less stiff than a solid bar? In reality, a tubular sway bar can be just as stiff as a solid bar for any given diameter; the wall thickness is the critical parameter. A tubular sway bar is also lighter than a solid bar and tends to flex back to normal faster when twisted. Less weight and faster response makes the tubular bar a good choice.
Roll Stiffness. Here is a discussion on how to make the springs and sway bars work in harmony. If optimizing handling is all about controlling weight transfer and body roll, then proper roll stiffness is your target. Roll stiffness is simply a suspension's resistance to body roll and is determined by the stiffness of the springs and sway bars. Some prefer using stiffer springs and smaller sway bars, while others prefer softer springs and stiffer bars. There is no clear consensus as to which setup is best. Stiff springs and small sway bars allow the left and right sides of a suspension to perform more independently from each other, but compromises ride quality. Soft springs and stiff sway bars preserve ride quality, yet detract from a suspension's side-to-side independence. A number of suspension experts prefer the soft springs and stiff sway bars approach simply because stiffer springs deteriorate ride quality and are not necessary if you select a good balance with the sway bars and shocks. For good street handling and decent ride quality, the suggestion here is easy on springs rates and very firm on roll bar stiffness.
Another tip. Deflection in the bushings can harm suspension geometry and limit the rear suspension's ability to put the power down. Although they transmit the most noise and require regular lubrication, Heim joints virtually eliminate deflection, and they also enable the differential to articulate from side to side to reduce suspension bind.
What we have discussed here should help you significantly improve your muscle car’s handling. Purposely, there was no attempt to go beyond what can be accomplished with simple hand tools and a reasonable budget. We have assumed your suspension is stock and in good working order as a starting point. Many aftermarket suspension suppliers offer packaged kits of springs, shocks and sway bars that are cost effective and easy to install. Do your research and twist those wrenches, the result in street handling will make your Chevy muscle car even more fun to drive!
Haynes 10345 Suspension, Steering & Driveline Haynes Techbook
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