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Subaru Rally Car Setup by Dave Lapworth |  |
AUTOSPORT 12 September 1996 Formula 1 has it easy. The multi-millionpound superstar teams have to cope with lapping an asphalt road60-odd times with the only likely variation being down to theweather. The rally boys have to cope with ever-changing conditionsfrom the relatively consistent asphalt roads of Corsica and Spainthrough the gravel tracks of Indonesia, Argentina, Finland andAustralia to the snows of Sweden and the destructive rocks ofrecceing in Kenya. All of this has to he tamed by one car,perhaps the ultimate compromise in any form of Motorsport. Outrightperformance is one thing hut driver confidence is just as important.So just how does the World Champion team, Subaru, get the trickright? David Lapworth, Prodrive's engineeringdirector, has a wealth of experience in the matter. Some 15 yearsago he was tuning the Talbot Sunbeams that won the 1981 manufacturers'title before joining Prodrive to work with BMW and, latterly,Subaru. Every event involves some form of compromisebut this week, in Australia, he faces what he admits is the toughestevent on the calendar. 'You get a nasty combination of very unpredictablegrip thanks to the ball-hearing surface of the roads in WesternAustralia. The roads are generally very good and pretty fast hutthere are some nasty bumps and jumps. On the one hand you wanta really low-riding car to cope with the smooth and fast bits,but also one with lots of suspension travel to extract what gripyou can and ride the humps. Difficult one to call. Given a freehand, where does Lapworth start in setting up a car? 'We nearly always start with an asphaltcar,' he says. 'A car is usually more sensitive to changes onasphalt than on any other surface and it also gives us a chanceto work on the car without wrecking it by driving on the loose.If the car has a particular weakness it will show up more readilyon asphalt. On gravel there's so much going on that it can masksmall problems. But on a clean surface on nice stiff tyres it'llshow up clearly. 'Lapworth, and Prodrive, have enough experiencenot to end up completely baffled by any new car. Most of the timeit will be a development - an evolution if you prefer - of anexisting machine. The current Subaru Impreza 555, for example,owes a lot to the Legacy that preceded it and the new World RallyCar, currently hidden away within Prodrive's Banbury base, willbe developed from lessons learned on the Impreza. But Lapworth still insists that he'dgo first to asphalt to try out the design of a completely newconcept, a Formula 2 car for example, should Prodrive go thatroute in future. 'We are confident that we could takea pretty good stab at ride heights, damper settings and everythingelse and I'd expect to he within five per cent of the optimumat first guess. I'd be really disappointed if I wasn't within10%. Then we'll work with a driver to tine tune the camber orspring rates to a particular surface.' Two words underline the challenge facinga rally engineer; two words that have opposite effects on a carhut which need to be married together to produce the right compromise.'Grip and ride,' insists Lapworth. 'That's what we have to balance.For the best ride you run the car with plenty of suspension travel,especially bump travel so that the wheels can absorb rough surfaceswithout transferring it to the rest of the car. On the other hand,cornering demands that you try to run the car as low as possiblein order to lessen the weight transfer and keep all four wheelson the ground. 'The more grip you've got, the moreimportant it is to run low and the less grip you have means youneed as much suspension travel as possible and to keep the springssoft. More grip equals low and stiff, less grip equals high andsoft.' All of which explains why, when Subaruwent to Safari at Easter, the Imprezas looked to be sitting feethigh, while the cars that go to the World Championship finaleat Catalunya in November will be low-riding beasts, arguably theultimate in rally technology. 'Given those two extremes,' continuesLapworth, 'the detail compromises follow on quite logically. Ifyou get the car low enough to give the kind of grip you want onasphalt you have to run stiff springs as well just to keep thething level. If you try to run soft springs the car will rollonto the hump stops. Luckily, increased grip also increasesthe car's responsiveness and that again requires stiff springsand roll bars so it all has a kind of logic as the settings complementeach other. 'Weight transfer on the snow of Sweden, however, isvirtually non-existent as there is so little grip and response.Lapworth explains that here you can run the car on softer springs,raise the ride height and also take advantage of the skinny snowtyres used on such events to increase what little grip you canget. Bumps and jumps add their own twiststo the set-up game. 'There's probably the same grip on the safarias on any other gravel event,' says Lapworth. 'However the humpsare so had and the speeds so high that handling becomes less importantthan ride. New Zealand, by contrast, is so full of twists andturns that you shift the compromise towards handling rather thanride and run the car lower and stiffer. 'Finland was an awkward challenge forthe engineers as the roads are so smooth that a car should beable to run near-asphalt suspension. However, there is no waythat such a set up could cope with the huge jumps and hard landings- especially if the car meets an up-slope on landing - so somethingstiffer is required. 'What you really need in Finland isa Finn!' jokes Lapworth. 'Such a lot of what we try to do is makea car driver friendly, one to give him loads of confidence.' Ah, so that's the big difference. 'Racing takes place on fairly stablesurfaces with a lot of predictability. Rallying is ever-changingand so a driver needs to have loads of confidence in the car.That's the hardest thing to create, especially on gravel. There'svirtually no such thing as a representative test. 'On gravel the road surface changesevery time you drive the bloody car down it so you might as wellthrow the stopwatch in the ditch. You can just about spot a generalunderlying trend but the driver has to be very good to simulatenot knowing the road with every run. As soon as you know the roadyou can't help but drive over it faster every time, or at leastdifferently. If there's a bad bump that nearly causes you to crashyou won't drive over it the same way next time, hut I really needthem to do just that to try to solve the handling problems. 'In nearly every case the optimum testset-up is not the one that will prove fastest on a rally. Youhave to give the driver the one that gives him the greatest confidence.' The Safari was a new venture; the first time that Prodrive Subarus had gone to Kenya, so the set up was less than the optimum. But Lapworth consciously chose a fast,safe car with good ride and durability and was delighted to comeaway with three cars in the top five and a sackful of manufacturers'series points. 'We more or less started with an Acropolis car,fitted the essential Safari bits (snorkel, bull bars, under-bodyprotection etc) and guessed the rest. We were probably withinthat 10% at the start of testing and refined it. We only had onestab at it, we knew we couldn't get it right first time, so justgave it our best shot. Mitsubishi did it just that little bitbetter but, if you'd told me at Christmas that we'd finish second,fourth and fifth on our first Safari I'd have settled for that,no problem.' If Australia is the toughest event forset-up, and Catalunya the easiest, the gravel/asphalt mix of SanRemo poses an interesting challenge. However, the service pointat the end of the road section between Tuscany's gravel and SanRemo's asphalt gives the team enough time to make a complete switch.'With a minimum weight limit we don't build lightweight cars anymore. Our gravel car is more or less the same as our asphalt car,underbody protection aside. So we can swap from one to the otherduring the event without too much trouble.' Lapworth names four factors in any competitivecar; drivers, tyres, cars and teams. 'Those four factors haveto be right in roughly equal measure if you want a successfulevent. The cars are becoming more and more equal so it is howwe run the cars that affects how well they perform. However, driversand tyres are the biggest variables and hence they can make thebiggest difference once the event is under way. 'We got the tyres horribly wrong inCorsica last year because we'd spent too long testing with Pirelliin what turned out to he the wrong conditions. That had an effecton the drivers' confidence and we were right out of it.' With everything so close at the headof the championship this year, Lapworth isn't giving away anyof Subaru's secrets. Tommi Makinen, Mitsubishi and Michelin lookset to wrap up the drivers' title hut Subaru and Pirelli are inthe driving seat for the manufacturers' crown. The titles willgo to the engineers who give their drivers the most effectivecompromise between grip and ride. | |
