From leaf springs to ac­tive sus­pen­sion: nine decades of chas­sis de­vel­op­ment


No area of car de­sign has ad­vanced more than this in the past 90 years, and it’s easy to see why. While the in­ter­nal com­bus­tion en­gine was a child of the late 19th cen­tury, the leaf-sprung lad­der chas­sis used by al­most all cars in 1928 dif­fered lit­tle in con­cept from that used by wag­ons dat­ing back to the mid-18th cen­tury. Yet so lit­tle was known about chas­sis de­sign that even in the mid-1930s the Mercedes-benz rac­ing team was shocked to learn that the pri­mary spring­ing medium of its state-of-theart W25 grand prix car was not its sus­pen­sion but f lex in its chas­sis.

There had been cars with what we would recog­nise as mod­ern uni­tary con­struc­tion be­fore the war – notably the 1922 Lancia Lambda – and the Amer­i­cans were far ahead of most of Europe in this re­gard dur­ing the 1930s. But it wasn’t un­til the 1950s that this stiff, light, space­ef­fi­cient form of chas­sis be­came com­mon, along­side the space­frame con­struc­tion that was sim­pler for low-vol­ume man­u­fac­tur­ing.

This was also the time when most man­u­fac­tur­ers re­placed their leaf springs with coils and de­signed truly in­de­pen­dent sus­pen­sion, at the front at least. In­de­pen­dent rear sus­pen­sion took far longer, with de­sign­ers pre­fer­ring to mit­i­gate the worst ef­fects of non-in­de­pen­dent rear axles with de­vices such as the Pan­hard rod, Watt’s link­age and De Dion tube. To this day, al­most all small hatch­backs, and an in­creas­ing num­ber of fam­ily hatch­backs, fea­ture non-in­de­pen­dent tor­sion beam rear axles be­cause they are cheap and easy to pack­age.

But if we’re look­ing for land­marks, there was none more strik­ing than the Lam­borgh­ini Miura that dropped jaws at the 1966 Geneva show, thanks to an en­gine mounted nei­ther in the front nor at the rear, like many small cars of the era and all Porsches. Mi­dengined de­sign was noth­ing new in rac­ing cir­cles, but cen­tral­is­ing the car’s ma­jor mass in a road car was some­thing else (even though, like so many de­vel­op­ments we think of as pi­o­neers in their field, it wasn’t ac­tu­ally the first mid-en­gined road car – take a bow the Ma­tra Djet).

The Miura’s con­fig­u­ra­tion was not with­out is­sues, notably the low po­lar mo­ment of in­er­tia that re­sulted and

Four-wheel drive halved the work­load of each tyre

what then hap­pened once the car started to slide, but the ben­e­fits in grip, re­sponse and steer­ing could not be ig­nored. Two years later, Fer­rari in­tro­duced its Dino and proved that, with a bit more thought and a bit less mass, a mid-en­gined car could be the sweet­est-han­dling de­vice imag­in­able.

But even if by the 1970s man­u­fac­tur­ers had (largely) sorted out sus­pen­sion and con­struc­tion, cars were still be­ing pre­vented from re­al­is­ing their true po­ten­tial in the most fun­da­men­tal way: sim­ply put, those four lit­tle patches of rub­ber that con­nected them to the road sim­ply weren’t fit for pur­pose.

True, tyre tech­nol­ogy hadn’t stood still since the 1920s and Miche­lin’s suc­cess­ful in­tro­duc­tion of the ra­dial tyre as stan­dard equip­ment on, of all things, the 1948 Citroën 2CV was a huge step for­ward, pro­vid­ing as it did a more sta­ble foot­print while ac­tu­ally im­prov­ing ride qual­ity. But even by the mid-1970s, Fer­raris still sat on tyres whose di­men­sions would look wholly in­ad­e­quate on the most mod­est hot hatch to­day. The 308GTB, for in­stance, was fit­ted as stan­dard with a 205/70-sec­tion tyre. But then Pirelli in­tro­duced its new P7 and al­most overnight ev­ery­thing changed. First made avail­able on the Porsche 911 Turbo with a 225/50 rear boot, soon Lam­borgh­i­nis and oth­ers were parad­ing around wear­ing 345/35 sec­tion rub­ber. Th­ese ul­tra­w­ide, ul­tra-low-pro­file tyres were the key to un­lock­ing the per­for­mance of the world’s fastest cars, be­cause not only did they trans­form apex speed but their ef­fect on trac­tion and brak­ing was also no less re­mark­able.

True land­marks in chas­sis de­vel­op­ment have been rarer since, although we should namecheck the 1980 Audi Qu­at­tro as the first car to use four-wheel drive for sport­ing pur­poses: not only did it halve the work­load of each tyre when ac­cel­er­at­ing but it also al­lowed hith­erto front-wheel-drive plat­forms to trans­mit mon­ster amounts of torque with­out the trade­mark tug­ging at the steer­ing wheel.

Carbonfibre tubs still aren’t com­mon­place but they have been around since the 1994 Mclaren F1 (or the 1990 Jaguar XJR-15, if you choose to count that road-go­ing rac­ing car). Such tubs not only keep weight down and mas­sively im­prove crash per­for­mance (the F1 re­put­edly drove away from its own crash test) but, cru­cially, they also pro­vide a level of tor­sional stiff­ness that can­not be achieved by con­ven­tional means.

Prob­a­bly the sin­gle big­gest growth area in re­cent years for more main­stream cars has been the in­flu­ence of elec­tron­ics, from the fit­ment of sim­ple adap­tive damp­ing, past ac­tive roll con­trol to an en­tire suite of sta­bil­ity sys­tems whose acronyms and ini­tialisms when spelled out are of­ten longer than the car’s name. Th­ese sys­tems en­able chas­sis en­gi­neers to set up cars to be far more re­spon­sive than would ever be pru­dent were su­per­cars still re­liant on the driver alone to keep them point­ing in the right di­rec­tion.

As for the fu­ture, it’s in­ter­est­ing to note that tyres are still ad­vanc­ing at an in­cred­i­ble rate and rep­re­sent a size­able chunk of the rea­son that stan­dard road cars now pos­sess the lap speed of the much-vaunted hy­per­cars of five years ago. But the real growth area, par­tic­u­larly among sport­ing cars, will be down­force. So long as it can be achieved with­out an enor­mous drag penalty, down­force is the gift that keeps on giv­ing. It re­quires few mov­ing parts and the faster you go the eas­ier it makes the car to drive. So do I think we’ll see con­ven­tional sports cars sprout­ing enor­mous wings? I do not, but more down­force can be achieved un­der the car than over it, and it is from there I ex­pect the bulk of progress to come.

With Citroën’s 2CV came the ra­dial tyre

Audi in­tro­duced its qu­at­tro four-wheeldrive sys­tem in 1980

The Mclaren F1, road tested in May 1994, had a carbonfibre tub

The Lam­borgh­ini Miura in­tro­duced the po­ten­tial of mi­dengined de­sign but left it to oth­ers to re­alise it in full.

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