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

Total 911 - - Contents - Writ­ten by Kyle for­tune Pho­tog­ra­phy by Porsche ar­chive

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.

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