Tom Wilson
August 1, 2002

Horse Sense: Though it is best known for offering springs and suspension kits for improved handling, Eibach also offers springs for drag racing. The company's Drag Launch kit for Mustangs includes four springs with rates designed for quarter-mile work, as well as an airbag for the passenger-side rear spring. The bag allows you to preload the spring to fight the chassis twist common on Mustangs launching at the dragstrip.

Of all the things we've said about lowering springs, performance shocks, and the like, we haven't said they improve a Mustang's ride-until now. Difficult as it is to believe, Eibach's Pro System Plus does improve the ride 95 percent of the time, all while building grip, tightening the steering, and doing the lowering thing. Definitely cool.

Notice we said an Eibach system, not just lowering springs. While Eibach has great name recognition when it comes to springs, the company has added sway bars and shocks to its repertoire. Don't be surprised if you didn't know Eibach is building its own shocks and struts. While the wound and bent wire technology in coil springs and sway bars is expected from Eibach, its in-house shock development department is relatively new.

The fact is, Eibach has added an entire damper department to its Irvine, California, plant. Therefore, its dampers are developed in-house, alongside the spring and sway bar production and engineering. This obviously helps Eibach get precisely the ride and handling compromise it wants, a point the company was eager for us to experience firsthand.

To make that comparison, we bothered Ford for a stock '02 Mustang GT five-speed, while Eibach provided a customer's similarly equipped '01 GT with the Pro System Plus kit on board. Because the installation of the shocks, struts, sway bars, and springs follow standard Mustang practice, we bypassed the installation process and went straight to testing.

While the Pro System Plus is most definitely a street-oriented kit for daily driver Mustangs, Eibach agreed that a session at a road-racing track would provide the gung-ho driving that would fully show the difference between stock and the Pro System Plus suspenders. That opportunity came at Buttonwillow Raceway Park, which gave us 227 street miles in each Mustang just getting to the track and back, and as many laps as we needed to feel the difference between the two cars. Having thus sampled surface streets, miles and miles of freeway, country roads, and a road-racing track offering a combination of sweepers and tight sections, we're confident in our calibrated-Levi's evaluation.

We won't bore you with details of the stock Mustang's street manners, other than to say it is plush in a loose sort of way. The rear axle flops around over sharp edges (in case you've been driving an IRS Cobra the last three years), the steering is vague, the rear waggles uncomfortably through minor culverts, and-hey-it's a Mustang. In the best factory tradition, the Mustang's ride is cloudy enough to never insult, but that also means it's never direct enough to clearly communicate, either.

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On the street, the Eibach car is definitely improved compared to the stocker. The ride is supportive and confident without making itself known, the steering is much tighter, and overall vehicle response is considerably faster. It feels the way a factory sports coupe should.

If this sounds as though the Eibach kit is plush enough to make it as a factory suspension tune, that's the idea nine-tenths of the time. On smooth pavement, it's dead smooth, of course. Rough up the pavement and you can tell things are more controlled, but it takes sharp upheavals to make this noticeable in a negative way. That's the part the factory would not allow.

The occasional curveball is possible. We felt some funny vibrations or buzzing from the front end due to a short section of unusual freeway surface. We figured this is because the tonier shocks and springs can set up harmonics the dead-soft stock stuff just marshmallows over. But that's an oddball, and not necessarily unpleasant.

Turn-in is hugely improved due to reduced body roll, such that the steering feels twice as tight. In fact, on the freeway the steering will go where it's pointed, something the stocker doesn't do. The Eibach suspension follows your lead and responds to the road without being nervous. It's especially well done this way, feeling like a car that wants to be driven rather than one that can be.

Let's not forget the car looks a million bucks better as well. That stock high-water-pants look is wrong after all.

Before we leave the ride business, we have to say the Pro System Plus is a major improvement over a simple set of lowering springs. By tuning the shock valving, the bump-stop firmness, and the sway-bar and spring rates, Eibach's engineers really have had the opportunity to completely redesign the Mustang's road manners. The target they aimed for, and bull's-eyed, is the tightest control possible without telegraphing anything has been done. Take your mom for a ride and she won't be able to tell the difference-unless you warp speed over a major frost heave or clobber that old railroad crossing the gravel trucks have pounded into a moonscape.

On Track
Interestingly, at the track we were quite impressed with both the stock and Eibach-modified cars. Why be impressed with a stock Mustang? It was the first time in ages we had gotten a plain, old GT on the track for some hot laps, and it did much better than we thought. For old Fox-Mustang hands, the current-generation Mustang is two-edged. It's quieter, more powerful when revved, has much better brakes, less nose dive (but still too much), and is definitely better screwed together. On the other hand, it's heavier, softer on its springs and shocks, and combined with the still-numb and over-boosted steering-not to mention the still-with-us Bind-O-Matic rear suspension-it feels bloated and unresponsive when pushed.

So, we were expecting a cornering disaster, and-surprise-once we settled down and learned to caress the big girl in and out of the turns, the stock car did surprisingly well. It takes a butterfly's touch, and there's sparse room for midcorner corrections. But given a gentle hand, the stocker heels over and mechanically plants its outside tires deeper than a potato farmer's spuds. Transitions are still essentially hopeless, but the red stocker at least wasn't laughed off the track when mixing it up with race-prepped Porsches and the like during the Buttonwillow test day.

It seems some of the problem going into the test can be attributed to us. We hadn't realized just how much grip was hiding in that soft suspension. Put another way, the Mustang has decent grip, but it takes smooth discipline to use it. Also, the stock Mustang's limit is "soft." That is, the steering and grip gradually break down. You can try harder and harder, but it only understeers more. All the while the tires are yelling that the end is near.

The Eibach car went much faster, of course. It did everything better, from less dive at the brake application, to a sharper turn-in, to a changeable midcorner composure and more predictable corner exit. Where the stocker was a bit white-knuckled over Magic Mountain-a rise and turn combination at Buttonwillow that results in satisfying tail-out slides down the backside-the Eibach-equipped car was predictably steerable with the throttle. Great fun and much faster.

Where the Eibach gear had the least advantage over stock was on corner exit. There the soft stocker had so much weight transfer, it could really plant the tires. And, it was going slower, so what extra jiggly motions it had were less troublesome.

The Eibach rear suspension travel was limited when cornering and accelerating hard at the same time (an inevi-table consequence of lowering the ride height). Thus, when really hammering away, the rearend started to go away first. This brought on the quick, unexpected yaws and waggles that characterize the Mustang's schizophrenic four-link rear suspension. The major difference is, with the Eibach kit the limit is much higher than stock. Also, the limit is harder edged. Everything is fine, then the rearend starts acting up. Nothing dangerously sudden, mind you, just better defined.

Some rear-axle nervousness also showed up during heavy braking over rough braking stutters in Buttonwillow's Turn 1 pavement. You rarely find these on the street, and we hope you never brake this hard on public roads anyway. This would be a limitation for aggressive track drivers, however.

Also, the front tires were working harder, and were thus easier to abuse than on the stocker. Again, this is because you are going faster and because with the car lowered there isn't that much camber left to work with. We'd guess more caster to increase the camber-while-turning might help.

In short, the Eibach kit makes the car definitely faster, and much easier to drive up to eight- or nine-tenths. Then the rear becomes too excited and brings on the white-knuckle feeling.

Final Thoughts
What Eibach has done is tune the Mustang suspension as highly as possible for daily driver duty, while putting in track-ready levels of precision and grip. So, the bottom line is, the civilized Eibach kit is fine for daily driver Mustangs. For the enthusiast looking for great street performance or the guy wanting a daily driver and the occasional open-track thrill, it seems ideal. And that's 95 percent of Mustang enthusiasts.

The Eibach kit is not for the crazed hard charger, the guy who comes home from his daily commute with brake dust on his chin, or who's dedicated hobby is open tracking, slaloming, or road racing. That fellow needs to double the money for the complete reengineering approach available in more comprehensive kits. Those suspensions are also superb daily driver fare-make no mistake-and they get everything the tire has to offer at the track. But, they do cost more.

Kits, Systems, and Plus
In Eibach-speak, a Pro Kit is a set of springs. Among these are the familiar Mustang lowering springs. Next up is a Pro System. This is the lowering springs and sway bars. The advantage here is more roll resistance is added by the large sway bars without having to increase the spring rate. The Pro System Plus includes springs, sway bars (front and rear), and dampers (shocks and struts). This allows the most precise ride and control tuning possible.