How to Start in Setting up A Rally Car?

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Formula 1 has it easy. The multi-million-pound superstar teams have to cope with lapping an asphalt road60-odd times with the only likely variation being down to the weather. The rally boys have to cope with ever-changing conditions from the relatively consistent asphalt roads of Corsica and Spain through the gravel tracks of Indonesia, Argentina, Finland and Australia to the snows of Sweden and the destructive rocks of recceing in Kenya.

All of this has to be tamed by one car, perhaps the ultimate compromise in any form of Motorsport. Outright performance is one thing hut driver confidence is just as important. So just how does the World Champion team, Subaru, get the trick right?

David Lapworth, Prodrive’s engineering director, has a wealth of experience in the matter. Some 15 years ago 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 compromise but this week, in Australia, he faces what he admits is the toughest event on the calendar. ‘You get a nasty combination of very unpredictable grip thanks to the ball-hearing surface of the roads in WesternAustralia. The roads are generally very good and pretty fast hut there are some nasty bumps and jumps. On the one hand, you want a really low-riding car to cope with the smooth and fast bits, but also one with lots of suspension travel to extract what grip you can and ride the humps. A difficult one to call. Given a freehand, where does Lapworth start in setting up a car?

‘We nearly always start with an asphalt car with its 6000K h3 led headlight bulb,’ he says. ‘A car is usually more sensitive to changes on asphalt than on any other surface and it also gives us a chance to work on the car without wrecking it by driving on the loose. If the car has a particular weakness it will show up more readily on asphalt. On gravel, there’s so much going on that it can mask small problems. But on a clean surface on nice stiff tires, it’ll show up clearly. ‘Lapworth and Prodrive have enough experience not to end up completely baffled by any new car. Most of the time it will be development – an evolution if you prefer – of an existing 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, will be developed from lessons learned on the Impreza.

But Lapworth still insists that he’d go first to asphalt to try out the design of a completely new concept, a Formula 2 car for example, should Prodrive go that route in future.

‘We are confident that we could take a pretty good stab at ride heights, damper settings and everything else and I’d expect to be within five percent of the optimum first guess. I’d be really disappointed if I wasn’t within10%. Then we’ll work with a driver to fine-tune the camber or spring rates to a particular surface.’

Two words underline the challenge facing a rally engineer; two words that have opposite effects on a car hut 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 surfaces without transferring it to the rest of the car. On the other hand, cornering demands that you try to run the car as low as possible in order to lessen the weight transfer and keep all four wheels on the ground.

‘The more grip you’ve got, the more important it is to run low and the less grip you have mean you need as much suspension travel as possible and to keep the springs soft. More grip equals low and stiff, less grip equals high and soft.’

All of which explains why, when Subaruwent to Safari at Easter, the Imprezas looked to be sitting feet high, while the cars that go to the World Championship finale at Catalunya in November will be low-riding beasts, arguably the ultimate in rally technology.

‘Given those two extremes,’ continues a worth, ‘the detail compromises follow on quite logically. If you get the car low enough to give the kind of grip you want on asphalt you have to run stiff springs as well just to keep the thing level. If you try to run soft springs the car will roll onto the hump stops.

Luckily, the increased grip also increases the car’s responsiveness and that again requires stiff springs and roll bars so it all has a kind of logic as the settings complement each other. ‘Weight transfer on the snow of Sweden, however, is virtually non-existent as there are 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 snow tires used on such events to increase what little grip you can get.Car

Bumps and jumps add their own twists to the set-up game. ‘There’s probably the same grip on the safari as on any other gravel event,’ says Lapworth. ‘However, the humps are so had and the speeds so high that handling becomes less important than ride. New Zealand, by contrast, is so full of twists and turns that you shift the compromise towards handling rather than ride and run the car lower and stiffer.

‘Finland was an awkward challenge for the engineers as the roads are so smooth that a car should be able to run near-asphalt suspension. However, there is no way that such a set up could cope with the huge jumps and hard landings- especially if the car meets an up-slope on landing – so something stiffer is required.

‘What you really need in Finland is a Finn!’ jokes Lapworth. ‘Such a lot of what we try to do is make a car driver-friendly, one to give him loads of confidence.’

Ah, so that’s a big difference.

‘Racing takes place on a fairly stable surface with a lot of predictability. Rallying is ever-changing and 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 changes every time you drive the bloody car down it so you might as well throw the stopwatch in the ditch. You can just about spot a general underlying trend but the driver has to be very good to simulate not knowing the road with every run. As soon as you know the road you can’t help but drive over it faster every time, or at least differently. If there’s a bad bump that nearly causes you to crash you won’t drive over it the same way next time, but I really need them to do just that to try to solve the handling problems.

‘In nearly every case the optimum test set-up is not the one that will prove fastest on a rally. You have 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 come away 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-body protection etc) and guessed the rest. We were probably within that 10% at the start of testing and refined it. We only had one stab at it, we knew we couldn’t get it the right first time, so just gave it our best shot. Mitsubishi did it just that little bit better 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 point at 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 other during the event without too much trouble.’

Lapworth names four factors in any competitive car; drivers, tires, cars and teams. ‘Those four factors have to be right in roughly equal measure if you want a successful event. The cars are becoming more and more equal so it is how we run the cars that affect how well they perform. However, drivers and tires are the biggest variables and hence they can make the biggest difference once the event is underway.

‘We got the tires horribly wrong in Corsica last year because we’d spent too long testing with Pirelli in what turned out to he the wrong conditions. That had an effect on the drivers’ confidence and we were right out of it.’

With everything so close at the head of the championship this year, Lapworth isn’t giving away any of Subaru’s secrets. Tommi Makinen, Mitsubishi and Michelin look set to wrap up the drivers’ title hut Subaru and Pirelli are in the driving seat for the manufacturers’ crown. The titles will go to the engineers who give their drivers the most effective compromise between grip and ride.

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