How Audi chased per­fect equi­lib­rium

Take that, grav­ity! Audi’s new Pre­dic­tive Ac­tive Sus­pen­sion says ‘not to­day’ to the laws of physics.

- By Jake Groves Audi · Audi S8

Ac­tive sus­pen­sion isn’t a new con­cept – car brands have been ex­per­i­ment­ing with the idea for decades, us­ing hy­drop­neu­mat­ics, air sus­pen­sion and road-scan­ning tech­nol­ogy to iso­late bumps and in­crease com­fort. How­ever, af­ter our first drive of the new Audi S8 limou­sine, we think In­gol­stadt has re­ally cracked it with the su­per-limo’s as­stan­dard ‘Pre­dic­tive Ac­tive Sus­pen­sion.’

Based on an air-sus­pen­sion set-up, PAS has fa­mil­iar air-sprung tricks up its sleeve, in­clud­ing a quick 50mm ride-height in­crease when you grab the door han­dle, min­imis­ing chances of celebri­ties mak­ing undig­ni­fied ar­rivals or get­aways from red­car­pet events.

But it also uses an electro­mechan­i­cal ac­tu­a­tor on each sus­pen­sion arm, with all four con­trolled by a cen­tral com­puter. This, in turn, is fed in­for­ma­tion from a cam­era em­bed­ded in the wind­screen that keeps an eye on road con­di­tions ahead.

The idea is to min­imise body roll and there­fore sub­ject oc­cu­pants to lower g-forces, keep­ing them al­most in an ar­ti­fi­cial equi­lib­rium. Given the kind of well-heeled folk who’ll sit in the back of this brawny V8 limou­sine, com­fort and the elim­i­na­tion of jar­ring ex­ter­nal forces is a top pri­or­ity – Audi has even up­graded the nor­mal Com­fort set­ting in the Drive Se­lect con­troller to Com­fort+ to stress its ex­tra stress-re­duc­ing abil­i­ties.

Most no­table is how PAS re­acts to speed bumps; the ride height swiftly raises by 50mm when the cam­era sys­tem ‘sees’ one com­ing. The in­crease in ride height al­lows each sus­pen­sion cham­ber to com­press while min­imis­ing the ef­fects of the bump for those in­side, al­most like it’s zapped large lane-span­ning speed bumps with a shrink ray. It’s not in­fal­li­ble, though, as the cam­era needs a set dis­tance to see the speed bump in the first place.

Brak­ing and ac­cel­er­a­tion forces are also coun­ter­acted and, be­tween speeds of 50 and 80mph, the S8 will lean into bends by three de­grees like a Pen­dolino train.

It’s not all about com­fort: go full sporty in Dy­namic mode and PAS halves the max­i­mum roll an­gle of a nor­mal A8 (five de­grees down to 2.5) with a fo­cus on the front axle un­der hard cor­ner­ing. That, along with the stan­dard rear­wheel steer­ing, means your five me­tre-long limo steers like some­thing much smaller.

Does it work?

Def­i­nitely. The road scan­ning works best when you’re not tail­gat­ing, and the tilt func­tion can feel un­nat­u­ral at first, but Audi has man­aged to bring to mar­ket a clever sus­pen­sion sys­tem ca­pa­ble of lit­er­ally de­fy­ing the laws of physics, all in the name of keep­ing its oc­cu­pants com­fort­able. Quite the feat of en­gi­neer­ing.

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