911 tech: Weissach LSA axle
Porsche’s transformational Weissach LSA axle on the 993 was derived from the shelved 989 four-door model. Total 911 explains how it works
How and why did Porsche revitalise the 911's suspension for the 993 generation?
“The 911 for the next 25 years,” is how Heinrich ‘Heinz’ Branitzki, interim CEO, described the 964 Carrera when it was first unveiled. That, ultimately, would prove not to be the case. A cautious man, Branitzki had seen how the 911 had slowly evolved in previous decades, and saw no reason for that to change.
The 964’s run would be short-lived, underlining a change in the mindset within the company. While the 964 was arguably a relatively radical departure from the G model that preceded it, the 993 that replaced it would take that further. For all the 964’s advances, the 993 moved Porsche’s icon into another era.
Harm Lagaay, head of styling, admitted they started work on it as soon as he arrived in 1989, with Ulrich Bez heading up engineering on the new 911. The 993 had to be a car for the modern era, being less expensive to produce, as engaging to drive yet more economical. “I was absolutely convinced it had to change radically,” said Lagaay, and cost-saving axewielding with Porsche’s internal projects would help the 993 do exactly that.
However unambiguous the title of this magazine might be, it’s impossible to ignore the fact that Porsche’s survival isn’t down to its most famous product alone. The SUVS and saloons it now produces alongside the 911 and the 718 Boxster and Cayman sports cars fill the company’s coffers enough to allow it its rear-engined indulgence.
And not for the first time either, as among the most radical changes to the last of the air-cooled
911s was its suspension, specifically on the rear axle, and it’s largely attributable to a stillborn 989 project that would have been Porsche’s first four-door model, preceding the 964.
In a time where the company was in a state of seemingly constant management upheaval, the 993’s development was largely ignored by the executives, though it survived, while the 989 it borrowed from was shelved. The 993 would be introduced under Wendelin Wiedeking’s tenure as CEO, the tenacious executive using Toyota’s expertise to streamline production techniques, allowing the 993 to sell for substantially less than the 964, yet generate more profit at the same time.
Visually the 993 clearly differed, but under that radical new look was a car that was substantially different to its predecessor. The multi-link rear axle, LSA (Lightweight, Stable Agile), was key to that, though it might have been different. Initially Porsche was developing a rear-wheel steer axle for the 993, but two years before it reached production the idea was shelved. The solution would be that raid on that 989 development, the 993 team using its LSA – also referred to as the Weissach axle – the development costs for it having been swallowed up in the 150 million Deutschmarks Porsche reputedly spent developing its stillborn four-door.
Bez was unhappy with the road and suspension noises the 964 generated, and increased stability was a development goal with its 993. Friedrich Bezner, project manager of 911, initially took the rear-wheel steer route before it was axed in favour of that LSA rear-axle geometry. That axle technology itself was borrowed from the 928 and developed further for the 989 before it was pressed into use on the 993.
The benefits of the LSA were improved stability at the rear, with less propensity to oversteer, and less rear-end lift on braking or squat under acceleration. The subframe was constructed of Vacural, a die-cast alloy that featured thin walls with a stiffening web structure. This was supplied in its entirety by outside suppliers, allowing it to be bolted on complete during assembly, helping with Porsche’s production efficiencies.
Porsche’s own archives describe the LSA as being ‘instrumental in finally putting an end to the capriciousness of the rear-engine-powered 911’. That’s quite an admission coming from it’s own archives, Porsche basically suggesting here that the 993’s multi-link rear removed some of the
911’s unpredictability. Certainly the 993’s more sophisticated axle helped with Bez’s goals of improved refinement and comfort, the subframe allowing for the separation of noise insulation and the suspension function. Bernd Kahnau would adapt the LSA for the 993, fitting the subframe to the body via four rubber supports which are flexible in longitudinal direction yet rigid in transverse direction.
That subframe would carry all the suspension, with only the lightweight spring coil struts over aluminium dampers attaching to the 993’s body via rubber mounts. Two upper links pivot on the subframe and join the wheel carrier to create what’s essentially a two-piece upper wishbone. The bottom is a more conventional wishbone mounted to the wheel carrier by a single mount. Fitted to that there’s a track control arm that pivots on the subframe, while an 18mm anti-roll bar is also fitted.
The geometry and mounting bush design is such that lateral forces on the wheel carrier compress the bushes, enabling that track control arm to create toein, the inverted forces on the opposite wheel helping to generate some passive rear steering. All that has benefits on the stability, both in normal cornering or during evasive manoeuvres. Both of these were key drivers in adopting a new rear axle. With the suspension isolated via the subframe the ride could be smoother, as well as quieter. The 993’s multi-link set-up also improved stability under braking where the weight shift to the front of the car creates toe-in at the rear axle, to the benefit of stability. Kahnau suggested such were the benefits to stability that the LSA largely negated the need for all-wheel drive 911s.
The LSA axle also removed the 964’s harsher ride on its semi-trailing arms, with the 993’s LSA allowing some fore and aft compliance to reduce interference from sharper bumps on the road surface, while increasing agility at the same time. The track was significantly wider at 1,444mm, compared to the 1,374mm of the 964, the front suspension too sitting on a wider track of 1,405mm, all covered in that familiar 993 body.
“Porsche’s own archives describe the LSA as being instrumental in ‘finally putting an end to the capriciousness of the rear engine-powered 911’”
Everybody has their own opinion, and there’s arguably no right or wrong here, but my experience of both is exactly as described by Porsche’s goals for the 993 over the 964. The 964’s a car I love driving, but driving it alongside the newer car – relatively speaking here – reveals the 993’s greater sophistication, with it providing greater stability, the rear axle being more predictable and forgiving at higher speeds.
You could argue that it’s less demanding and easier as a result, and certainly you can afford to be a little bit less cautious in a 993, as you might be in a 964. What is clear is the greater ride comfort, the 993 not suffering over poor surfaces where a 964’s suspension might, though again a lot of that is down to perception, a 964 rarely presenting any genuine compromises, particularly in the way they’ll be used today: that being sparingly, for enjoyment.
Back when the 993 replaced the 964 though, when these cars were being used as daily driving transport, the effects would have been more appreciable more of the time. Here the benefits the 993’s suspension brought unquestionably make it the superior car. However, like many debates in the 911 world, be it around manual or automatic transmissions, air- or water-cooled, rear- or fourwheel drive, hydraulic or EPAS steering and many more, that’s down to context and situation, and, as we all know, hard as the facts might be, opinions always differ.