You have a budget for one suspension change. Springs or sway bars? It is the most common question we get, and the answer is not the one most people expect.
What do lowering springs actually change?
Springs control two things: ride height and how the car responds to vertical inputs. Lower the car and you lower its centre of gravity, which reduces how much weight transfers laterally in a corner. Raise the spring rate and you reduce squat under acceleration, dive under braking, and roll everywhere else.
Eibach PRO-KIT springs are progressive-rate, which means the coils are wound so the effective rate rises as they compress. Soft at small inputs so the car still rides properly on a broken road, stiffer as load builds so it stays flat when you lean on it.
What springs do not do is change the balance of the car much. Lower both ends by a similar amount and you get a lower, flatter version of the same handling character.
What do sway bars change instead?
A sway bar only does anything when the two wheels on an axle move differently — which is to say, in roll. Drive over a speed bump square-on and the bar is irrelevant. Turn into a corner and it is doing all its work.
That makes bars a balance tool rather than a ride height tool. Stiffen the rear bar and you reduce rear grip in roll, so the car rotates more readily. Stiffen the front and you do the opposite. Change one end and you have changed how the car behaves at the limit without touching how it rides in a straight line.
Most Eibach ANTI-ROLL-KIT bars are adjustable, with multiple mounting holes at the end link. That is the point of them: one purchase gives you a range of settings you can work through rather than a single fixed answer.
So which comes first?
If the car understeers or feels lazy turning in, buy bars. They target that directly and they do not touch ride quality or geometry. On a rear-engined 911 in particular, roll stiffness distribution is the single most effective lever you have.
If the car sits too high, wallows, or dives badly under braking, buy springs. No amount of bar adjustment will fix a car that is riding on tired springs at factory ride height with four inches of fender gap.
If the dampers are original and the car has covered serious miles, buy neither yet. Springs and bars both rely on the dampers to control the energy they manage. Fitting stiffer springs to twenty-year-old dampers gives you a car that is lower, harsher and still poorly controlled. Sort the dampers first — it is unglamorous and it is almost always the right call.
What about buying both together?
This is what the Eibach PRO-PLUS Kit exists for. It pairs PRO-KIT springs with matched ANTI-ROLL-KIT bars, developed and tested together on the same chassis rather than left to you to guess whether a given spring rate and bar diameter will get along.
Springs and bars interact. Raise spring rate and you have already increased roll stiffness at both ends, which changes what a given bar setting does. Buying them as a system removes that variable, and it is cheaper than buying them separately.
What order should I install them in?
If you are fitting both, do it in one go and get one alignment. If you are staging the work over months, springs first — they change ride height, which changes camber and toe, which means an alignment either way. Fit the bars afterwards and you can tune balance against a geometry that is already settled.
Then change one thing at a time. Move the rear bar one hole, drive the same road, and form an opinion before touching anything else. Changing two variables at once tells you nothing.
Frequently asked questions
Will lowering springs ruin my ride quality?
Progressive-rate springs on healthy dampers usually ride better than tired stock springs, because the car settles in one movement instead of floating. Lowering on worn dampers is what ruins ride quality.
Do I need an alignment after fitting sway bars?
Bars alone do not change geometry, so strictly no. But if the car has not been aligned recently, do it anyway — you are about to start judging handling changes, and a crooked baseline makes that impossible.
Can I fit sway bars to a car with PDCC?
Not without an adapter kit. Porsche's active anti-roll system uses different hardware and most aftermarket bars will not physically mount. We stock the adapters in PASM & Active Suspension.
Can I fit only a rear bar?
Yes, and it is a legitimate strategy if you specifically want more rotation. Many of our ANTI-ROLL-KIT listings are sold as front-only or rear-only for exactly that reason. On a 911, be conservative and go one setting at a time.
Start from your car in the Suspension menu — every listing states the years, drivetrain, transmission and suspension options it fits.