Features - Technical
JULY 7, 1999
Overtaking in 1999
BY PETER WRIGHT
There is no doubt that the current breed of Formula1 cars, narrow-tracked and under-tyred, with low mechanical grip and high downforce wings, are not ideal for overtaking. The reasons are many and the mechanics of overtaking were described in a previous article:........, particularly the effects of circuit changes over the years and the high-g braking that carbon-carbon brakes have made possible. The last few years have seen regulation changes that set out to control the speed of the cars and may, according to one body of opinion (namely the drivers) have made overtaking harder. It is too soon to tell statistically whether there are actually fewer overtaking attempts but there is no doubt that, under certain conditions, drivers are less inclined to have a go. The reasons for this are complex and to understand them it is necessary to consider the risk/benefit ratio of various passing opportunities, something that certain drivers are very good at analysing, while others often seem to get their sums wrong.
The opportunities for gaining a place in a Formula1 race are many:
1. Qualifying - i.e. grid position
3. First corner
4. Re-start or Safety Car
5. Scheduled pit stops
6. Unscheduled pit stops due to rain
7. Wet track
8. Mistake by driver ahead
9. Passing backmarkers
10. Unreliability of car ahead
11. Being faster than the car ahead and overtaking it
Qualifying, quite apart from the psychological advantage of being ahead for a day, offers the least risky opportunity of gaining places over an opponent. The performance margin necessary to move up a place is only a 0.001secs per lap and there is no need to go "toe-to-toe" with anyone on the track to do so. It has been claimed that extensive testing at GP tracks results in the drivers lining up on the grid in precisely the order of their performance, with the inevitable result that there is little likelihood that any car will be fast enough to overtake the car ahead. The starting grid also positions the cars on the track for the next opportunity, the start. The start is down to the driver alone as car performance has little influence until the speed is such that they are no longer traction limited. One or two places can be gained by a perfect start, and six or seven lost by a botched one. The risk element is there, as jumping the lights carries a 10 second stop-go penalty which will effectively move the offender to the back of the field.
The next opportunity, the first corner, probably offers the greatest chance to gain places and carries with it the greatest risk. The whole field will be so tightly grouped as it brakes and turns into the first corner - while no one will be quite sure how much grip they have got on cold tyres as they brake with cool brakes - that mistakes are frequent. If a driver brakes too early or allows himself to be boxed in, two or three cars will stream past, probably with the inner front tyres smoking. Brake too late and, even if the driver avoids hitting another car or spinning, he will probably run wide and be able to observe slower cars go past around the inside. Some drivers almost always pick up places at the start and first corner; some almost always lose them; one or two often get no further than the first corner.
A race re-start, following a Red Flag incident, or a rolling re-start behind the Safety Car provides similar opportunities and risks. The Safety Car also enables the gaps between cars to be reduced, in the middle of a race, to around 0.25 seconds, saving an awful lot of hard driving. A rolling start is not as unpredictable as a standing start as it is not initiated by lights.
Scheduled pit stops have added a whole extra dimension to Formula1 racing, providing an intellectually, if not visually exciting element to overtaking. They involve almost every member of the team, including the designers who set the size of the fuel tank; the strategists, who working with the driver choose the number and timing of the pit stops; the race engineers who analyse timing and information data available on the bank of pit wall screens and determine where among the other cars the driver will emerge from the Pits, to the pit crew themselves, any one of whom can add seconds to a pit stop and instantly negate any advantage of the chosen strategy. The flexibility of Ferrari pit stop strategies, concocted by Ross Braun and executed by Michael Schumacher, is becoming legendary. With the addition of some luck they have won Schumacher races were he did not have the speed advantage. However, others are learning from them and the battle of minds is intensifying. It has been said that pit stops have replaced straight overtaking as the risks are less, but every visit to the pits carries its own risk and even the best drilled pit crews can have problems.
Unscheduled pit stops to fit rain tyres test the teams' abilities to think on their feet. Information about the state of the track, the performance of other cars that have already changed tyres and weather forecasting, has to be gathered and analysed instantly and decisions relayed to drivers and pit crew. Places can be gained by making the right decision, often as much luck as judgement, and by taking advantage of the wrong decisions of others. The driver plays a big part, especially when conditions change rapidly as they do during a sudden, short, sharp downpour. Jackie Stewart used to state: "A racing driver should drive as fast as the conditions allow at all times - you never know what will happen next." This remark holds particularly true for driving on a wet track. Conditions vary corner-by-corner, lap-by-lap and the potential for a driving error is enormous. To overtake under these conditions requires exploring the grip limit of each metre of the track, without ever exceeding it. It is necessary to stay close to the car in front in spite of the loss of visibility due to the spray. The possibility of a small error by the leading driver is always present and a tiny mistake is all that is required to enable the driver behind to overtake, provided he is close enough.
The likelihood of a driver making a mistake, on a dry track at least, is a function of how hard he is being pressed by another car. Chasing another driver, feinting to pass him and forcing him to take defending positions on the track and lines around corners that are less than ideal, is a big part of the psychology of motorsport. Modern Formula1 cars are so sophisticated that the old opportunities to make driving errors e.g. missed gear-changes, over-revving the engine, fading brakes etc. are no longer there and a cool-headed driver can keep even a significantly faster car at bay for a long time - ask David Coulthard. With the conservative tyres now raced it is not even possible to push a driver to over-cook his tyres, as it used to be. The risks involved in this pressurising tactic are low, provided the chasing driver does not become involved the consequences of the other driver's mistake when it eventually occurs.
When a leading battle comes up to backmarkers to lap them, there is a good chance to induce mistakes. A couple of slower cars, sometimes driven by less experienced drivers, will often position themselves badly on the track and balk one of the battling cars. Under these conditions opportunists can sometimes get passed.
The only no-risk way of passing another car is when the latter has a technical fault that either slows it or causes it to retire. It is not quite zero-risk as, if the fault is an engine failure, following cars may spin-off on oil liberally spread on the track. However, it is the gearbox and its electro-hydraulic control system that most frequently causes retirements these days.
The final opportunity is being faster than the car ahead, at least on part of the track, and being able to overtake it. This opportunity is the one causing all the controversy and discussion and is the one that has undoubtedly deteriorated since the development of high-downforce, flat-bottomed aerodynamics. It even appears to have worsened in the last two or three years. Considering that during that time we have had a tyre war on slicks (1997), a tyre war on grooved tyres (1998) and now have single-supplier, hard compound, grooved tyres, there is not enough statistical evidence to point the blame at tyres. What may have been a significant factor however, is tyre size. Ever since rear tyres were restricted to 15inches width (1993), cars had been under-tyred at the rear and hence marginally stable, especially under braking. Since the loss of the great slipstreaming circuits, braking into a corner has been the main opportunity for overtaking. When a car becomes less stable the later and harder the driver brakes, the less likelihood there is that the driver will risk holding off braking until after his opponent has done so. Carbon-carbon brakes provide such formidable braking performance that even slowing from 300+kph down to a 2nd-gear chicane takes such a short time and is so violent that drivers are fully occupied with controlling their own cars, let alone worrying about an equally busy opponent right alongside them. The risks are often just too great.
However, this is not the whole problem. In order to out-brake an opponent, it is necessary to be alongside or only just behind at the braking point. The straights are the only parts of the track where there are more than one racing line, and so must be used for positioning the car for the first part of the overtaking manoeuvre i.e. getting alongside. The classic way of doing this was best accomplished on that part of the circuit that included a long, fast corner followed by a straight that led into a slow corner, requiring heavy braking. Entering the fast corner some way behind the car ahead, provided space to take the corner at a higher speed, so exiting the corner onto the straight faster and maybe 50m behind. At this distance, the wake of the leading car reduced the drag of the following car, enabling it to accelerate at a greater rate. By the time the following car had caught up the leader it would be travelling at a significantly higher speed and so would be able to pull out of the wake and use its momentum to pull alongside or even complete a passing manoeuvre.
The fact that the drivers are now unable to perform this manoeuvre in a modern Formula1 car, on the circuits in use today, is due to two main factors: the nature of the aerodynamic wakes that the cars generate have changed, and the cars themselves are crucially dependant on the qualities of the air through which they travel. Unfortunately, very little research has been published on the nature of the wake behind a high-downforce, open-wheeled racing car. Whether the top teams have performed this research, but not published the results, is not known, but it is doubtful that many have done so. The wake of a Formula1 car is extremely complex, 3-dimensional, and made up of strong vortices (rotating flows) and turbulence. The effect on a following car is to reduce the energy available to generate downforce and drag, and to change the effective incidence of the car. Effects will vary with both distance behind the car and lateral position. The result is that as a car follows another and the distance changes, downforce and more importantly, the balance will vary significantly. This is a situation that is less than desirable when trying to catch up a car in a fast corner.
Even if the following car can keep up through the corner, it appears that the wake is less suitable for slip-streaming than it used to be. While narrow rear tyres and narrow track may have reduced the cross-section of Formula1 cars, the increases in wing-induced downforce have maintained the drag pretty well constant over the years. However, experience with the Handford Super Oval wing in Champcar racing, which greatly increased slip-streaming, indicates that a high downforce rear wing lifts the wake of a car such that it passes over the following car, and it is thus unable to benefit from a resultant drag reduction. The Handford wing is low downforce/high drag, and following cars are able to pick up the slip-stream 100+m behind another car. High downforce wings also generate strong tip vortices and so the current Formula1 cars have a totally undesirable wake. See Figs 1 & 2. Not only is the turbulent wake unavailable for slip-streaming, but the edges of the wake contain strong rotating flows that can significantly change the effective incidence of the air flow experienced by a following car and change its balance as it passes through it. The net result is that it can neither get close enough to the leading car when cornering, nor benefit from the drag reduction once it does get close enough behind.
The problem of a lack of overtaking in Formula1 is not simple. It is not just that the drivers cannot perform passing manoeuvres in the current cars, it is also that there are other opportunities that are less risky. Involving, as it does, relatively under-researched aerodynamics phenomena, driver psychology and team strategy, it is not surprising that no one has come up with a clear definition of the problem (if there is one), nor an instant and effective fix.