Tech Article: Tuning Your Z's Suspension For Best Handling

by Ben Pila Jr.

Developing suspension systems and tuning them is one area on Zs I like discussing with others whenever I can. I know that making a car go faster in a straight line returns immediate fun but if you come up to a corner and can't put the power to the ground, you are in for a surprise. If you improve the engine and the brakes, then the suspension needs to be improved resulting in a nice, balanced package.

I like to included the following items all together as all these items effect one another in various ways. Tires, springs, shocks/struts, anti-sway bars, bushings, and camber/caster adjusters along with proper alignment settings make up the total suspension package.

The tires are the first and most significant improvement in the suspension chain. Getting more rubber in contact with the ground nets improved cornering speed. Wider is usually better but other things need to be taken into consideration too. The tire and wheel combination needs to be of the correct width, size and offset. The tires need to fit into the wheel wells and not rub anything during any normal driving condition. Normally a "0" offset wheel with a 6"-8" width works and tires from 195mm to 225mm width can work on Zs '89 and older. The width of tire used all depends on whether you use a 14", 15", 16", or 17" diameter wheel. My experience has shown me that the 15" and 16" wheels in widths between 6"-7" offer the best fit and availability of tires for the 1983 and older Zs. Good tire sizes are 215/60/14, 205/60/15, 225/50/15, 225/50/16. The later Zs from 1984 and up can use the 16" or 17" without problems. If your Z came with 16" and you wish to upgrade, opt for the 17" with a lower profile tire to improve steering response. But on the other hand, 17" tires are quite costly so I suppose it's really a matter of preference on the 1990 and up 300s.

In selecting springs, shocks/struts, and sway bars for your Z, you have to do some research to figure out what is best for you. There are many suspension component companies out there making kits from a street driven Z to a fully prepared road racing Z.

Bushings are usually made from urethane these days but other materials like Delrin and aluminum still get used. Changing from rubber to the harder urethane type bushings helps keep the suspension parts from deflecting during hard cornering resulting in a more precise feel and more stable alignment settings. The trade off for the hard bushings is more road noise and generally a stiffer ride all around. Some bushings like tension rod bushings and sway bar bushings make an improvement and don't change the ride quality noticeably.

Camber/caster adjusters allow suspension alignment settings to be changed that previously couldn't be done. Increasing the front and rear camber to a more negative setting than stock can improve overall cornering and turn in. Changing and adding in more caster allow the steering wheel to turn back faster after a turn but there are other things that come into play with that.

With all the changes that can be done, the first and simplest thing is getting wider tires and wheels. Note, just wider tires alone aren't enough. For the best handling, get lighter aluminum wheels and a name brand high performance tire. We are driving sports cars aren't we so why buy cheap, no name tires? To save from confusion, buy a suspension system upgrade with Tokico gas shocks (regular or adjustable,) or KYB gas shocks, a matched set of springs and a matched set of sway bars. All those items combined, make your Z the most fun and safer to drive. The other things I mentioned are for those who want to "dial" in your suspension to get the ultimate handling. There are a lot of good books out there on suspension so I won't elaborate any more on this subject. If you really want to know, buy some of those books like "How to Make Your Car Handle" by Fred Puhn and other more recent books.

For the benefit of suspension tuning, see the accompanying chart that shows how changes within the suspension system causes changes in the overall handling characteristics. Ultimately, neutral or neutral steer is the most desirable effect to achieve while taking a corner. If your Z had this then you could have the most control of the car by being able to induce oversteer with a little throttle lift (weight transfers to the front while rear gets light and loose,) or induce understeer with a little more throttle (weight transfers to the rear and the front gets lighter and pushes.)

So for more discussion let's see some questions come back to the editor and we can publish them for everyone to benefit. Happy motoring.

If you have any questions, comments or suggestions on this or other tech articles feel free to e-mail me at zcartech@juno.com or write to the Z Club attention Tech writer.

POCKET GUIDE TO HIGH PERFORMANCE HANDLING.

The keys to high performance handling are a top quality suspension system, proper chassis adjustments and properly balanced tire pressures.
Aim for the theoretical ideal with a Neutral steer: matched front and rear traction.
1. Understeer is a plowing or pushing effect when cornering.
2. Oversteer is the rear sliding outward on turns.
Adjustments to increase Understeer Oversteer
Front tire pressure Lower Higher
Rear tire pressure Higher Lower
Front tire section Smaller Larger
Rear tire section Larger Smaller
Front wheel camber More positive More negative
Rear wheel camber More negative More positive
Front springs Stiffer Softer
Rear springs Softer Stiffer
Front anti-sway bar Thicker (stiffer) Thinner (softer)
Rear anti-sway bar Thinner (softer) Thicker (stiffer)
Weight distribution More forward More rearward

Chart provided by Dave Turner Motorsports