Features - Technical
AUGUST 28, 1995
Overtaking in Formula 1
BY PETER WRIGHT
It is ironic that as TV has provided millions with the means to view the action, overtaking in Formula 1 has declined from a perceived high level, in the days when almost no one actually saw it happen. Back in the "golden days" of the Ô60's, prior to ground effect aerodynamics, even the track-side enthusiast saw very little, and had to depend on the scribes of the day for a vision of the wheel-to-wheel battles that took place. Today almost everyone watches every inch of an overtaking manoeuvre, from numerous angles and in slow motion and it does not compare with our memories of past racing, immortalised in the written word.
Yet some of the races that stand out in my memory were of nail-biting, lap-after-lap, five-car strategic battles, fought out at Monza in the Ô60's. And those amazing final, wheel-banging laps as Villeneuve and Arnoux fought for second place in the 1979 French GP at Dijon.
Has overtaking diminished? Or is it our perception, influenced by new technologies? Is it a technical issue, or down to driver psychology? To understand the problem it is necessary to look at the physics of the manoeuvre, and what effect changes to the cars and tracks have had. We must also look at the factors that influence the drivers' approach to racing.
Current Formula 1 cars are just under 5 metres from nose to tail, and so in order to complete an overtaking manoeuvre, from a position just behind another car to just in front, requires gaining 10 metres. A 1 second per lap speed advantage is equivalent to just over 1% on the average circuit. If the speed difference is 1% everywhere around the circuit, the distance travelled during the overtaking manoeuvre would be 1 km, with the two cars on different lines. There are not many circuits nowadays where there is more than one line for that distance. This in a nutshell is why it is so difficult to overtake, and why various techniques have been developed to make it possible on tracks that do not have very long straights.
The distance can be halved if the overtaking driver can persuade (intimidate?) his opponent into backing off when he is alongside. This is the basis of most overtaking manoeuvres today. When neither concedes (Senna/Mansell and Schumacher/Hill) it usually ends in tears.
In reality, bigger speed differences exist between cars and drivers in the various regimes of cornering, braking, accelerating and top speed, even if the average is the same. Set-up changes are exploited to facilitate overtaking, depending on the characteristics of the circuit. In general, given similar performance between the cars, there are three overtaking techniques: slipstreaming, outbraking and outcornering. Each has a set of fixed physical principles that determine the outcome. Let us go back to the late Ô60's, when 3-litre Formula 1 cars used to overtake each other, and see how they did it.
If two cars have equal power and are set up to have the same top speed (i.e. the same drag), it is impossible for one to overtake the other on the straight without slipstreaming. Watching a slipstreaming battle, it often appears that the two cars are travelling at the same speed nose-to-tail, and that the one behind pops out of the slipstream of the one in front, and overtakes it. This is far from what actually happens, for if both cars were travelling at the same speed, when the one behind pulled out to overtake, losing the slipstream, it would be unable to accelerate to a higher speed to enable passing. The manoeuvre starts much further back.
For some distance behind a high drag car, such as an open wheeled Formula car, the drag of a following car is reduced. This can be of the order of 30% reduction at 25 metres distance, and depends on the aerodynamic details of the two cars. This reduction in drag means that less power is needed to maintain the top speed and enables the car to accelerate (around 0.2g for a 450bhp car of the late Ô60's), even though it may be travelling at it's clean air top speed. If the driver accelerates from some 50 metres back behind the car in front, while in it's slipstream (drivers claim that they can feel the effect up to 100 metres behind), he will be travelling around 5 kph faster when he comes right up behind it. Popping out of the slipstream now enables him to use this speed advantage to overtake, but he will still use over 0.25 km to draw alongside and hopefully claim the next corner. Fast corners leading onto long straights were ideal for this manoeuvre.
Selection of the right top-gear ratio is critical, as the engine torque falls off sharply beyond peak power, which must be matched to attaining the top speed when not in another car's slipstream.
Monza achieved it's mythical reputation from the multi-lap, multi-car slipstreaming battles, the drivers vying not to be first onto the straight for the last time whilst, using the others' slipstreams at the same time as trying to avoid others using their's!
Today the great engine-straining straights are gone - Kylami, Monza, Spa, Ricard, even Hockenheim - and what is left cannot be utilised because the reduction in drag behind another car comes with a reduction and unbalancing of the delicately set-up aerodynamic downforce. Getting close enough in the preceding corner to take advantage of another's slipstream is out of the question, due to the inevitable aerodynamic understeer.
Getting alongside at the end of the straight is no advantage if the other driver outbrakes you into the next corner. Let us analyse an example, again for a late Ô60's car initially. Two cars, neck and neck at their top speed on the straight: 280kph. Apex speed of the corner: 80kph. The corner must be won by the time the cars turn-in at around 115kph. Braking at a mean 1.25g takes 3.67 seconds and 201 metres. If one driver can brake 5% harder, he will take 3.49 seconds and 191.5 metres. This means he can leave his braking for 9.5 metres, continuing to travel at 280kph for that distance. The time saving over the full 201 metres is 0.06 seconds, giving him a lead of 1.8 metres - less than half a car's length, but a reasonable claim to the corner. See Figure: 1.
The 1995 car has more of a problem: Same top speed: 280kph; the 80 kph corner is now 120kph, and the turn-in speed: 160kph. Mean braking is 2.5g. The braking distance is 81 metres, covered in 1.33 seconds; and 5% harder braking reduces these figures to 77.1 metres in 1.27 seconds. The latter allows an extra 3.9 metres to be travelled at the top speed. The net time saving over the full 81 metres is just 0.013 seconds, giving a lead of 0.6 metres (less than a front tyre diameter) - arguable as to who won the corner. See Figure:2.
The third opportunity is when the trailing car is able to corner faster than the one ahead. Entering the corner on the tail of the leading car does not allow the potential to be used. The technique is to exit the corner right on the tail of the other car, travelling at the higher cornering speed, the difference being maintained all the way down the following straight - hopefully long enough to complete the passing manoeuvre. This requires hanging back on entry, and catching up exactly by the time it is possible to pull off the cornering line and go past.
That is how it used to be done. The current cars are now so sensitive to front wing performance that they are unable to maintain cornering performance within several car lengths behind another car. It is not possible in any but the slowest corners to come out close enough to exploit any superior cornering speed.
Nor is it possible to drive around the outside of another car. The mixture of tyre rubber, brake dust, oil, track grit and gravel that empties from radiator ducts under braking and lies outside the line, is known by drivers as the "marbles". Go off line and let sticky tyres pick it up and the grip is gone until the debris is scrubbed off again. This can take two or more laps and explains why slower drivers are sometimes so reluctant to move over and let the leaders pass. There is just one line through most corners and if everyone uses it, the rest of the track is effectively "mined". Whether this problem has become worse is debatable, but tyres are softer and stickier since treads disappeared and carbon brakes certainly produce a lot of dust. Also gravel traps are recent additions to circuits.
Based on the above it would appear that it is almost impossible for a current Formula 1 car to pass another if it's performance is only slightly superior. Whilst this is patently not so, it is true that such attempted manoeuvres between cars of similar performance, more and more often end up with an accident. With so little potential to execute a clean pass, it comes down to intimidating the other driver into giving way or making a mistake. The cars and circuits are now so safe that fear of injury is a small disincentive, which certainly was not so in the 1960's. Under certain circumstances, such as when World Championship significant points are at stake, it may actually be the best strategy for the Championship leader to crash both cars out of the race rather than allow himself to be overtaken. Not a good situation, but what can be done about it?
Reducing the performance of the cars is one option, but not a very satisfying or effective one. However slow the cars are, a 1% speed advantage will still need 1km to overtake. Extended braking distances and slower cornering speeds would give more opportunity to pass, as the calculations show, but it would require a return to 1960's levels of grip to do so. The often suggested substitution of cast iron brake discs, in the place of carbon, would not achieve any significant reduction in braking performance. Recent tests by Williams, using F3000 discs and carbon-metallic pads, have shown that braking distances are just about the same. Technology refuses to stand still!
Of far greater benefit would be to enable the cars to maintain their cornering performance whilst close up behind the car in front. This would make it possible to get close enough on exiting a corner to exploit either a greater cornering speed, better traction, more power or less drag on the ensuing straight. For some years now Formula 1 cars have become highly dependent upon the performance of the front wing and the way in which it interacts with the underside of the car. Anything that disturbs it's aerodynamic functioning results in understeer, even in second gear corners. The turbulence and upwash behind another car constitutes a big disturbance, forcing the follower to keep his distance. A return to aerodynamics that are insensitive to following close behind another car is the single most effective way to increase overtaking opportunities. The teams' aerodynamicists are best placed to suggest the route forward.
Given cars that can race through corners, track design should provide the stage. A long, fast, opening out corner, leading onto a decently long straight and finally a slow corner provides the ideal overtaking arrangement. Zandvoort had it just right. The folding of 3.5km (the minimum GP circuit length) into the smallest possible space was a backward step, driven by economics and creating a rash of circuits denying overtaking opportunities.
Another intriguing possibility is being developed by Californian architect/racing driver, David Christian. Involved in track design, he is looking at the feasibility of extending the short-track oval principle of multi-line corners to road courses. The 1/4 and 1/2-mile ovals were built with three lanes, banked at around 6¼, 9¼ and 12¼ from inner lane to outer. The theory was that the longer path in the outer lane was compensated for by the higher speed possible with the increased bank angle. Anyone who has watched the short oval cars will know that they overtake each other! Whether this principle can be applied to road courses, by varying the camber across the track width, remains to be seen. If it can, and there becomes more than one line through any corner, not only will it be possible to overtake round the outside (or down the inside), but by regular use of all the lines, the full width of the corners will be kept clean of "marbles". This is certainly worth investigating for potential application to future tracks.
Even if far reaching changes are made to car and track design, the effects would be a long time in coming. Situations, where drivers struggle to get their car fully or partially alongside another as they both approach a corner, would still occur and will do so in the short term. Both cars crashing out may be momentarily exciting, but does not leave the spectator with the lasting satisfaction of having watched a real race, well won. It is too easy to block an opponent and squeeze him off the track, or if strategically beneficial, to take him off into the gravel trap with you.
In the distant past there have been contact "sports", such as duelling and unarmed combat, where the winner was established as the one who was still alive. There was not much need for rules or judges. These "sports" matured into fencing, boxing, judo etc. with clearly defined Rules of Engagement, and criteria by which the winner could be identified without a corpse. The FIA's International Sporting Code, Appendix L, Chapter 4.1 lays down the do's and don'ts of driving behaviour. Not everyone agrees on the interpretation of Chapter 4, nor how to apply it in practice. In light of the current difficulties in overtaking, and the inability's of certain drivers to participate in the manoeuvre without physical contact, it might be time to thoroughly re-examine that text and re-write it in a way that everyone understands and that can be fairly and firmly policed.