Suspension Information and Upgrades

Suspension Dynamics

To optimize suspension performance it is essential to understand oversteer and understeer and what causes them.

Weight Transfer and Grip

During hard cornering, weight shifts from inside to outside wheels. The softer the suspension, the more weight transfers. A perfectly neutral setup transfers equal proportional weight to both front and rear outside tires so both lose traction simultaneously at the limit.

Understeer

If more weight shifts to the outside rear tire than to the outside front tire during cornering, the rear has more grip and the front loses traction first. The car steers a wider arc than intended — this is understeer (also called "push"). The driver feels the rear trying to push the car off its intended line.

Oversteer

If more weight shifts to the outside front tire, the front has more grip and the rear loses traction first. The car rotates more than intended into a tighter arc — this is oversteer (also called "loose"). This is a self-reinforcing condition: more oversteer increases cornering force on the outside wheels, which pushes the rear closer to breakaway. Without correction, the situation escalates until the rear loses grip completely and the car spins.

The 944, like most production cars, is designed with a degree of understeer because a car that understeers remains stable in a panic while a car that oversteers escalates toward a spin.

Slip Angle

Slip angle is the angular difference between the direction a tire's contact patch is pointed and the direction the wheel is steered. Heavier loading on a tire increases its slip angle. When rear tire slip angles exceed front slip angles, the result is oversteer; when front exceeds rear, understeer.

Acceleration and Braking Effects

• Acceleration (RWD): Tractive force at the rear tires increases rear slip angle, inducing oversteer from a neutral setup.
• Braking: Weight shifts forward, increasing front slip angles, which induces oversteer (rear steps out). Sudden lift-off in a corner has a similar effect.

Handling Corrections

Understeer Corrections — Front	Understeer Corrections — Rear
Softer front springs	Stiffer rear springs
Thinner or no front sway bar	Rear sway bar or thicker one
Raise front tire pressure	Lower rear tire pressure
Softer front shocks	Stiffer rear shocks
More negative front camber	More positive rear camber
Remove weight from front	Add weight to rear
More downforce in front	Less downforce in rear
Wider tires in front	Narrower tires in rear
More positive caster	Limited slip rear differential or stiffer rear diff

Oversteer Corrections — Front	Oversteer Corrections — Rear
Stiffer front springs	Softer rear springs
Front sway bar or thicker one	Thinner or no rear sway bar
Lower front tire pressure	Higher rear tire pressure
More positive front camber	More negative rear camber
Add weight to front	Remove weight from rear
Less downforce in front	More downforce in rear
Narrower tires in front	Wider tires in rear
Stiffer front shocks	Softer rear shocks

Stock Suspension Specifications

The following table lists factory spring, sway bar, and torsion bar specifications by model year. The M030 sport suspension package is noted separately where applicable. Data sourced from an Excellence magazine suspension article by Jim Pasha, supplemented with torsion bar spring rate information.

Year/Model	Front Spring	Front Sway Bar	Rear Torsion Bar	Torsion Bar Rate	Rear Sway Bar
1976–1977 924	140 lb	21 mm	22 mm	97 lb/in	18 mm
(note: sway bars were optional these years; standard models had none)
1978 924	140 lb	22 mm	22 mm	97 lb/in	14 mm (opt)
1979 924	140 lb	23 mm	22 mm / 23.5 w/r sway bar	97 lb/in / 126 lb/in	14 mm (opt)
1980 924/Turbo	140 lb	21 mm	22 mm / 23.5 w/r sway bar	97 lb/in / 126 lb/in	14 mm (opt)
1981 924/Turbo	140 lb / 160 lb w/M471	21 mm / 23 mm w/M471	23.5 mm	126 lb/in	14 mm (opt)
1982–1985 924 (from Sept 1981)	140 lb	20 mm / 21.5 opt	23.5 mm	126 lb/in	14 mm (opt)
1982–1984 944	160 lb	20 mm / 21.5 opt	23.5 mm	126 lb/in	14 mm (opt)
1985–1986 944/924S	2946 N	20 mm	23.5 mm	126 lb/in	14 mm (opt)
(M030 opt)	2698 N	21.5 solid or 23×3.5 tubular
1987–1989 944/924S	2946 N	21.5 mm	23.5 mm	126 lb/in	18 mm (opt)
(M030 opt)	3050 N	25.5×4 tubular
1987–1988 944S	3535 N	21.5 mm	23.5 mm	126 lb/in	18 mm
(M030 opt)	3286 N	23 mm tubular	25.5 mm / 25.5 tubular	175 lb/in / 149 lb/in	20 mm (opt)
1985–1991 944T	3286 N	22.5 mm	23.5 mm	126 lb/in	18 mm
(M030 opt)	3250 N	24 mm tubular	25.5 mm	175 lb/in	18 mm
1987+ 944T (M030 opt)		25.5 mm tubular	26.8 mm tubular	175 lb/in	16 mm
1989–1991 944S2	3250 N	26.8 mm tubular	24 mm	137 lb/in	16 mm
(M030 opt)	3120 N	25.5 mm			16 mm
968	3250 N	26.8 mm tubular	24 mm	137 lb/in	16 mm
968 (M030)		30 mm tubular			19 mm (3-way adj)

Note on spring rate units: Rates given in lbs are uncompressed spring rates; rates given in Newtons are for springs compressed to normal operating height. These are useful for comparing one vehicle to another but not for absolute spring stiffness comparison without a common reference point.

Torsion Bar Spring Rates by Diameter

The following applies to solid torsion bars. For hollow bars, obtain the spring rate from the manufacturer.

Diameter (mm)	Spring Rate (lb/in)
22.0	97
22.5	106
23.0	116
23.5	126
24.0	137
24.5	149
25.0	161
25.5	175
26.0	189
27.0	220
28.0	254
29.0	292
30.0	335
31.0	382
32.0	434
33.0	490

Suspension Setup Guidelines

Principles

Changing to higher spring rates for the front springs, torsion bars, and sway bars reduces body roll, improves tire contact during cornering, reduces squat under acceleration, and reduces dive under hard braking.

The maximum stock front spring rate across the 924/944/968 range is approximately 175 lb/in. A spring above 175 lb/in improves over-stock handling.

• Street driving: spring rates from 200–220 lb/in provide good improvement
• Street with occasional track use: 250–275 lb/in is an excellent choice
• Track-only (944 Turbo Cup reference): 375–410 lb/in progressive rate springs — too harsh for street use

Example Setups

Sport Street Suspension

A good starting point for a primarily street-driven car:

• Front springs: 220 lb/in
• Rear torsion bar: 27 mm (neutral steering)
  • 26 mm for more understeer
  • 28 mm for more oversteer (use caution — oversteering cars are more demanding to control in emergency situations)
• Front sway bar: 30 mm
• Rear sway bar: 19 mm (the 968 M030 3-way adjustable bar is an excellent choice as it provides additional tuning range)

High Performance Street/Track Suspension

• Front springs: 260 lb/in
• Rear torsion bar: 28 mm (neutral)
  • 27 mm for more understeer
  • 29 mm for more oversteer
• Front sway bar: 30 mm
• Rear sway bar: 19 mm

Full Race Suspension

Not recommended for street use:

• Front springs: 400 lb/in
• Rear torsion bar: 31 mm
• Front sway bar: 30 mm
• Rear sway bar: 19 mm

Additional Notes

• Indexing torsion bars to change ride height is tedious and may require multiple attempts over several days to allow the suspension to settle (see SUSP-06).
• An alternative is to convert to coil-over shocks in the rear, eliminating the torsion bars entirely. This is more expensive but avoids reindexing.
• A hybrid approach uses existing torsion bars combined with rear coil-over shocks to achieve a specific spring rate balance. This requires coil-overs with adjustable spring perches for ride height control.
• Adjustable shocks and struts are a worthwhile upgrade even for street use. For track use, a full four-corner coil-over setup is the most flexible option.

Realize that no two cars will respond identically to the same component changes, and no two drivers will have the same feel preferences. The setups above serve as starting points for a roughly neutral-handling configuration. Fine-tuning via shock stiffness adjustment, camber, caster, and tire pressure can dial in the exact feel desired.