Suspension

Without question, the best way to make your Porsche faster is to learn to drive it at its fullest potential. As delivered, Porsche automobiles are capable of performing far in excess of most owners’ ability. Investing in Driver Education events and formal racing instruction is much more cost effective than any piece of hardware that you can install on your Porsche. Driver Education and track time will make you a better driver than purchasing springs, shocks, or swaybars.

That said, the main goal in improving your Porsche’s handling is making it easier, more predictable, and more controllable when driven near or at the limit of your ability. The factory suspension components are a compromise between handling and ride quality so any upgrades will change the handling to one specifically tailored to the way you use and drive your car. Some of these components have a negligible effect upon ride quality, while others may transform your car into a race car with the attendant degradation in ride quality. We will indicate which items provide the most cost-effective handling improvements while maintaining a streetable ride.

All 911’s, 914’s, 930’s, 964’s, 993’s, 996′s, 997’s, and Boxster/Caymans all have different components, suspension design and handling differences. We will discuss the various parts that may be upgraded with specific recommendations for each model for street and occasional track use. Full racing specifications are available by e-mail for each car and application.

There are six main suspension components that can be changed for higher performance:

Other items that are usually considered are Front Shock Tower BracesBump Steer kits, Spring Plate kits, and complete suspension systems for racers. This last item usually consists of replacing torsion bars with coil-over suspension pieces. There are some specialty parts such as ERP Products that replace the entire front and rear suspension with custom made pieces that are derived from the Porsche 935. These are very high quality components that save weight and make suspension adjustments much easier and more precise.

Torsion Bars & Springs

These two items perform the same function respectively, for the 911/930 as well as the 964/993/996/997/986/987-series of Porsche automobiles. Porsche used torsion bars of varying sizes on the 911 from introduction in 1964 to 1989. The 930 also used torsion bars from 1975 to 1989. In 1989 the Carrera 4 (964) was equipped with coil springs and the rest of the Carreras followed suit. All of the 964-993-996-997, Boxster/Caymans use coil springs.

Torsion Bar sizes can be upgraded to larger bars in both solid bar and hollow versions. The hollow ones help to alleviate the added weight penalty of using larger, stiffer torsion bars. Some of the aftermarket bars have not been of particularly high quality and have exhibited fitment issues and sagging as well as not being the same spring rate as the factory offerings.

There are some excellent torsion bars available in various sizes that are manufactured here in the USA. Installing larger torsion bars has a small effect on ride quality up to a point. You can install bars that are 25% stiffer without a serious degradation, unless you live where the roads are really terrible. Removal and installation require just basic tools and some have features that allow fast changes.

Coil springs can also be upgraded to shorter, stiffer versions that reduce the lateral weight transfer and sway of the 964-993-996-997, Boxster/Cayman series Porsches. They also enhance the appearance by closing the gap between the fender and the tire. The progressive type springs used by Eibach and H & R minimize the effect upon ride quality. The Porsche Cup suspension system used by the factory for the various European racing series are too stiff for street use unless you have masochistic tendencies,….this stuff is really stiff!

964’s-993′s-996′s-997’s, Boxster/Caymans gain the greatest handling improvements with the installation of aftermarket coil-over struts & shocks. This permits ride height adjustments from 0-2″, precise corner-weighting, and the fitment of some larger, adjustable swaybars.

Dampers (Shock Absorbers)

Shock absorbers, correctly called dampers, perform a multitude of tasks that are critical to optimum handling especially on bumpy surfaces and tracks that have many changes in direction.

Dampers MUST be matched to the springs for the suspension to function properly. This is accomplished by selecting components from a manufacturer with a great deal of experience. The manufacturer must offer several choices that are very close to optimal, or adjustable dampers that will allow a range of adjustments but these may not accommodate a very wide range of spring rates. You may need to choose the type of dampers, specifically for street, sport or racing, to get the range of adjustment that you need.

Dampers that are properly selected and valved, actually dampen spring oscillations and keep the tires in contact with the pavement. They also manage lateral, longitudinal, and diagonal weight transfer during cornering and braking. Dampers control both the amount of weight transfer and the rate at which this happens.

Basically, this means that all weight transfer transients, such as when entering and leaving a corner or changing direction, are controlled by the damper settings. The rate of weight transfer caused by braking and acceleration is also affected by damper valving. Dampers come in different valving combinations depending upon whether they are for street use or track. The damping rates are expressed in two numbers, rebound over compression. These number are expressed in kilograms or pounds at a certain velocity, depending upon the maker. For example, an RSR shock for the 73-89 911 has 180/170; rebound/compression damping rates. The rear Turbo(930) dampers are 136/65 for comparison.

Some dampers are adjustable (Koni-JRZ-Motion Control-Von) and some are not (Boge-Bilstein). Either way, the object is to ba able to adjust the compression and rebound settings to match the spring rates,  street/track surfaces, and sprung/unsprung weight of the car.

A common mistake in setting up a street 911 is to have too much compression damping in the front end. Many people install sport-type dampers on the front needlessly, and suffer the consequences of an insensitive and skittery front end. Another common mistake is to have the ride height too low in the rear. When the rear dampers bottom in a corner due to surface changes or weight transfer, the effective spring rate leaps to infinity and the car can spin quite quickly without much warning; this can be quite exciting! Using dampers that are shorter than the stock ones will really help.

There are three ways to set the dampers correctly. First, install double adjustable types, such as Motion Control or JRZ,  and either experiment with settings until the car feels better and the lap times confirm this or follow the guidelines provided by the vendor. Second, use off-the-shelf components that have been hopefully optimized by the manufacturer. Third, use those same parts that have been re-valved with a custom setting optimized for your car by someone with experience and knowledge in this area.

All three are acceptable methods and vary only in the time required to set the car up.

The MacPherson struts used on the front suspension present a different set of challenges. Porsche has used Bilstein, Boge, Koni, Fichtel & Sachs, and Woodhead struts on the front of these cars since 1965.

Many shock manufacturers have painted their products in their proprietary colors to make identification much easier. Bilstein’s are mostly either Green or YellowKoni’s are Reddish Orange or YellowBoge’sare usually Black, and Woodhead’s are usually Blue.

All but the Bilstein struts share the same basic configuration and design. The High-pressure DeCarbon design used by Bilstein allows the damper to be operated in any position. To lower unsprung weight, these attach to the body at the top of the strut so that the unit ‘s heavy end is bolted to the car instead of the suspension arm. Bilsteins basically operate in the “upside down” position, compared to the other brands of dampers and many H&R struts employ the same technology.

Bilstein’s design has another advantage for the 911/930 owner, the ability to place the spindle in a more optimum location on the strut tube for better geometry and handling. Since the damper cartridge is “upside down”, the tube body is a uniform diameter with no hydraulics inside the support tube. This allows one to relocate the spindle upward to restore lost suspension travel after lowering the car. This also raises the front roll center back up where it belongs to reduce lateral weight transfer and the propensity for lifting the inside front wheel in a corner. Final spindle heights are determined by the wheel diameters: 15″ wheels allow no more than 18mm change in spindle height due to ball joint interference with the inside rim. Using larger wheels will allow higher spindle heights up to 30mm.

When the spindle is raised, the steering arms must be reshaped to correct the inherent bump steer and this is carefully done in a jig made for this purpose. There are also bump steer kits ranging from simple steering rack spacers to special tie-rod ends that allow fine tuning of the bump steer curves. Fox front struts feature height-adjustable spindles to permit fine tuning of front roll centers.

Anti-Sway Bars

Anti-roll bars, commonly called “sway bars”, are transverse torsion bars that attach to each side of the suspension arms. These function by offering varying degrees of resistance to body lean and lateral weight transfer. Changing the position of the attachment point or the length of the moment arm that the torsion bar acts on, allows you make adjustments in the effective stiffness of a given bar diameter.

Some bars offer sliding adjusters, spaced mounting holes, or rotating blades to allow you to fine tune the stiffness. There are even some bars that feature cockpit adjustable units that allow you to adjust the chassis balance for fuel load and track conditions. These are for racing only since the adjustment tower is placed where the passenger’s feet are. Installing bars of larger diameter will also increase the lateral stiffness.

Using the swaybars as part of the overall suspension system is necessary for chassis balance. There are several opinions on this, but we feel that the vehicles’ springs should carry the majority of the desired roll stiffness, not the anti-roll bars. These should be used as tuning tools to adjust the understeer/oversteer balance of the car, not as primary roll stiffness components.

To that end there are several factors to consider when selecting and using swaybars to make your 911/930/964/993/996/997 and Boxster/Cayman handle better. One is swaybar mounting design and the other is chassis stiffness.

Mounting methods vary most with the 911/930 series. The Porsche factory offered two types of front mounts, the through-the-body style used from 1965 to 1973 /Turbo 75-76, and the bottom (under body) style, used from 1974 to 1989. The rear bars also varied slightly where the droplink attached to the suspension. The early front through-the-body design is superior, and in fact necessary if you wish to install an adjustable front bar. The factory bottom-mount bars have no provision for adjustment and have unfavorable geometry for doing so.

The earlier, or through-the-body swaybar must be mounted correctly to prevent damage to the body. Also, the rear swaybar mounts need replacement with an aftermarket design when large sticky tires are utilized, otherwise they are liable to be torn off due to stress.

Several manufacturers provide different adjustable anti-roll bars for the Porsche aftermarket such as Smart Racing and Tarett, Porsche Motorsports makes excellent ones for the late 964-993-996-997 based cars.

Generally speaking, these should be installed in pairs so that you can adjust the roll stiffness and roll couple of the car at each end. These are available in sizes from 20mm to 31mm. Custom sizes are also available at extra cost from the various vendors.

Adjustable droplinks are extremely important for removing swaybar preload. Pre-load is caused by the car not sitting perfectly level on its suspension and pre-stressing the swaybars so that the bar is loaded more on one side of the car. This can be adjusted away by using spherical-bearing adjustable length links between the swaybar end and the suspension part that it attaches to. Adjustable droplinks are available for the front and rear and allow the swaybars to be adjusted to function uniformly in right or left turns. This also removes any cross-weight that has occurred as a result of pre-loading.

The performance of any aftermarket swaybar is dependent upon chassis stiffness. Targas, Cabriolets, and 914s may not respond the same way as a Coupe when using large swaybars, due to chassis flex. These cars will require additional chassis reinforcement to take full advantage of suspension upgrades. The 996/997 Cabriolet’s are far stiffer than their predecessors and do respond very nicely to suspension upgrades.

Suspension Bushings

Porsche installs rubber bushings in the suspension pivots and swaybar mounting points and these are an excellent solution for a car that is used mostly for street purposes. Good aftermarket ones are available that mimic the factory’s design.

For maximum performance however, the natural flexibility of the rubber introduces a certain degree of imprecision when driving close to the limit. Eliminating some or all of the rubber bushings can make the car handle and turn more crisply, with a small increase in noise, depending on which type is used.  Replacing the rubber swaybar bushings with hard plastic ones will make the bar function quicker due to less squirm in the bushing which delays the load into the bar until the bushing has compressed.

Most bushings in use today are either made from some type of urethane, rubber, or urethane-wrapped bronze/steel bushing (ER’s Poly-bronze) that allows external lubrication. These latter ones do not appreciably affect the ride or noise levels, however they are not as quiet as rubber ones. These do rider very smoothly due to reduces suspension friction.

Replacing the bushings with spherical bearings, also called monoballs or uniballs, can virtually eliminate all friction and binding that always occurs with rubber or plastic bushings. This is not for a street-driven vehicle, however the handling difference has to be experienced to be believed!

This is not an inexpensive modification, but overall is very worthwhile and cost effective for track-only cars due to the overall improvement in handling and response. Having little or no friction in the suspension also permits very accurate corner-weighting.

Chassis Strut Braces

Strut braces are installed to tie the front strut towers together to eliminate flex and thus reduce camber loss under cornering loads. These bars attach to the top of the upper strut mounting plates or hardware and maintain the installed camber setting in a corner when the chassis is under load. These are available in steel, aluminum, and carbon fiber. All Porsches except the 914, 996, 997 and Boxster/Caymans truly benefit from the installation of these bars.

Other Suspension Modifications

Three of the most important things, beside what has been discussed above, that make a really good handling 911 are fine tuning the bump steer, corner weight, and alignment.

Tuning the bump steer inherent in every 911 can be as simple as installing a rack spacer kit, all the way to using adjustable spherical rod ends, replacing the OEM tie rod ends (ERP’s or Elephant Racing’s), to precisely position each steering arm heights. This is mostly necessary when the car has been lowered more than 1 inch from the stock ride height. The rack spacer kits are comprised of two steering rack spacers and longer bolts to reposition the rack and level the tie-rods. The spherical bearings that replace the OEM tie rod ends offer a much greater range of adjustment to really minimize bump steer and make the steering less twitchy at speed.

Corner weights must be set precisely so that the car handles the same in left and right hand turns as well as settling correctly over sharp rises that unload the chassis. Accurate corner weights also affect braking since unequal wheels weights create erratic braking characteristics. Anytime the car is lowered from the stock height, you must place the car on 4 equal scales and adjust the springs or torsion bars so that the diagonal weight distributions are correct. Using computerized racing scales makes this much easier to optimize since the scales’ computer will display the desired wheel percentages and diagonal weights so necessary for a well-behaved 911. The front ride height on the ‘65-‘89 cars is quite easy to adjust using an 11mm socket. The rear suspension is more challenging since the spring plates must be re-indexed on the torsion bar splines and this is done using either standard or adjustable OEM spring plates.

Aftermarket adjustable spring plates makes this task far easier to dial-in. One can use either the Carrera two-piece plates or the Elephant Racing adjustable spring plates that allow changes with a ¼” Allen wrench. The later 964- 993-996-997, and Boxster/Caymans require threaded-body dampers front and rear to allow changing wheel weights.

Alignment settings are critical, as are tire pressures, in the final chassis tuning to optimize your car for the street or each track you drive it on. Tire choices and sizing also determine the optimal alignment due to variations in tire construction techniques.

Camber, Toe, and Caster are all adjusted for your specific use by a qualified alignment technician. Be absolutely certain that the person doing your alignment knows Porsches and understands the way you intend to use the car. 993-996 also have a kinematic toe adjustment that is critical for proper handling. Your alignment shop and personnel must be equipped and experienced to align these cars correctly. Adjustable rear suspension links are also available to extend the range of adjustment for camber & toe on lowered cars.

Once again, we have just barely touched on these subjects. We would recommend reading,”How to Make your Car Handle” by Fred Puhn and “Prepare to Win” by Carroll Smith as a good beginning to understanding chassis dynamics and how you car behaves. Bruce Anderson’s Porsche Performance Handbook also has some really good information.

As always, you may direct any further questions to us at Rennsport Systems. We will be happy to help people as time permits.