Mark Hales on Technique: Shifting the weight about
In the first of a new column, Mark Hales discusses weight management in pre-aero race cars
Having mentioned weight, the driver of an older - i.e. non-downforce-equipped car - is still in a position to influence its effective weight distribution simply by using the steering, accelerator and brakes. An accessible instance of this done to perfection was (and still is) available most weekends of the season in the Formula Ford 1600 category, which for so many years was the training ground for anybody and everybody that aspired to any kind of professional career on the circuits. Formula Ford was a basic racing car, with a Cortina engine and Hewland gearbox in the back, the driver lying down in the middle and skinny wheels and tyres at each corner. It was where Ayrton Senna and Emerson Fittipaldi, Nigel Mansell and all the greats began their careers. Formula Ford dates from the 1960s so it is also a blueprint for a great many historic racers.
Formula Ford has always been fantastically competitive and picking apart the optimum technique could take a whole book, but let's just study how a driver uses the brakes - which results in the largest amount of weight transfer - and how the car is designed to let them optimise that. The power is relatively limited (and in theory, everybody has a similar 105hp or thereabouts) and there is no limited-slip differential to prevent the wheels spinning. If a driver encounters even a tiny bit of wheel spin, the loss of drive is akin to backing off the accelerator and three people will tow past down the next straight. So the car designers would engineer as much grip into the back end as possible.
The weight distribution would also be arranged to favour this as far as the regulations would allow (although there is only so much you can rearrange with a gearbox, engine and driver inside a certain length), the camber and castor, anti squat and anti dive would all be configured to keep the tyres in as much contact with the road as possible and to do whatever made them work most effectively. The springs and dampers would be as supple as possible to do likewise while still controlling the body.
There would then be a trade off with the front end. It would need to be firm enough in order to stop the car rolling (and affecting the back end) but not so much that the car pushes wide (or understeers) whatever the driver does. Invariably though, the designer would accept some understeer, because it allowed a good guy to keep his foot in it. When the tail slides, you can control it so far, but eventually, you have to lift off.
The same good guys then developed a technique which was to take a load of speed deep into the turn and squeeze the brakes very firmly, then ease the wheel gently towards the apex. As the weight shifted forwards the front tyres gained some extra grip, the car lost its tendency to understeer and pitched around its nose. The trick was to thump the accelerator to the floor at exactly the right moment, sit the weight back on the rear wheels while catching the incipient slide with the slightest dab of opposite lock - before straightening up the steering and letting the drift carry them around the turn. As always, it is the timing that is the key and in this instance, it was beautiful to watch at the top level.
The Sennas of the world would approach, say, Paddock Hill Bend, in a line, sweeping up and across the gradient to the crest, then one by one in a kind of synchronised dance, the cars would appear not to turn so much as perform a corkscrew motion about their axis. The nose would go down, the tail would come up and they would appear to swivel around a point somewhere in the middle of the car. Then came the crack as the power went back on. Same point every time, one after another, like a fusillade. The cars would formation drift in a snake, curving round the line, each of them yawing at an angle of no more than 10 degrees. It was perfect choreography.
The best efforts seemed to have almost no steering lock applied one way or the other, sweeping round the corner as if guided from outside; but every so often one would pitch the car too hard and the driver would need to whizz the wheel to the left and hold a lurid slide against the power. Then you could hear a slight rise in the revs as the extra body roll picked some more weight from the inside wheel which lost a little of its grip. The rising revs were simply because the driver had kept his foot firmly clamped to the bulkhead but inevitably the one behind would gain by half a car and try and stick a nose alongside up into Druids.
Some would fail to use the braking energy sufficiently to pitch the car firmly enough, and you'd see the touch of understeer which washed them wide and over the kerb on the way down the hill. Paddock has been tightened since Senna's time but the gravel trap has recently been moved back close to the tarmac so too wide here once again carries its own stony penalty. A trip over the shallow kerb in between usually loses a touch less speed than the oversteering alternative though and most are able to get back to the track proper and still keep their position.
We are of course talking hundredths here, which is why Formula Ford was such a great category, although the irony of developing the technique essential to success was that victorious exponents who graduated to Formula 3 then had to unlearn it all. Once it was equipped with slicks and wings, the Formula 3 car had most of the point-at-the-front engineered in the workshop and the driver absolutely had to avoid any slip or slide and keep the airflow running as straight as possible under the car and over the wings.
A Formula Ford might be the plan for a great many cars that came before and after but it is deliberately a minimal concept. Light and simple, it leaves as much up to the driver as possible which is one reason it was such a brilliant training category. Wings and aerodynamic devices are the things that have since complicated the issue. Extra weight is pressed on the tyres from the passage of the air and will exert an influence over the car at a different point and in a completely different manner as the speed rises; the centre of pressure and the centre of gravity are usually in different places along the car. Because such downward pressure is effectively free (or at least any performance gain from the extra grip is usually greater than the loss of speed through drag) almost every aspect of chassis performance in modern professional motor sport tends to be sacrificed towards aerodynamics.
The option to load up the tyres under the brakes and to alter the balance of the car with the accelerator, though, are still options that remain open to the driver; but these days they tend to have discussions with the engineers as to where it is likely to work best, when and by how much. The result is harder for the watcher to pick out than it was with our choreographed snake at Paddock Hill too, but if you watch the in-car Formula 1 you can see the little clues which give the lie to what the driver is trying to do. The aerodynamics of these cars confer a level of grip which allows a Raikkonen or Bottas to seek out a completely different piece of road to any which Clark or Fangio might have used but the sudden twitch of reverse lock on the entry to a hairpin is simply because they have got the timing slightly wrong.
The weight transfer from braking makes the fronts stick that little bit more, while the rears are unloaded a little extra but the arrival of the car at the corner and the application of steering lock to guide it towards the apex are all slightly out of sync. The tail skips out of line and the lap is ruined. The car, of course, is travelling that much quicker towards the corner than in days of yore, so deciding when to apply the brakes such that the speed is exactly right when you get to the hairpin is critical to a nanosecond or less. The stuff of a sixth sense. It is what sorts the very best from the merely good - and it always has been - but the difference between these and the older cars is that the grip comes from the science and it has to be exactly right in order to work. If it's not, even the best in the world cannot compensate.
Older cars allowed more improvisation from the driver. A better chance to optimise things like weight transfer from the cockpit. It was what allowed Fangio to take 12 seconds from the Nurburgring lap record on three successive tours to unlap himself and win a race that looked lost, saying afterwards, "I believe that on that day in 1957 I finally managed to master the Nurburgring, making those leaps in the dark on those curves where I had never before had the courage to push things so far." He had simply made the decision to try a different combination of speed, brakes and steering input, and the car responded. Fangio stalked a different planet, but at least I know what he meant. It's why I like racing old motors...
Words: Mark Hales
To read more from Mark, see the 'Archive' section on his website.
Images: LAT Photo
It does make you think how much fun it would be if F1 could go back to a non-downforce formula with grossly over powered cars.......
Duncan
I asked him to teach me to get out of corners faster, and he taught me where to look.
And I came out of the corners faster and on the right line.
Never a murmer of complaint from him, as this inexpert threw the car around at speed while trying to follow his instructions.
Top man, and this is a most interesting read.
It slows the speed of the contact patch of the tyre, so the tyre sidewalls distort by being stretched from their ''normal' profile as the rest of the mass of the car wants to continue at a higher speed. This is what is generally known as weight transfer.
This weight transfer means that when the car is steered the front tyre sidewalls are less stiff and therefore less able to transfer steering input to the contact patch.
This will inevitably result in understeer as the wheels now need to turn through a larger angle to change the direction of the contact patch
However, as the car is now slowed down, the tyres need to generate less cornering force to follow a certain radius corner than they would at the previously higher speed.
The increased cornering force that comes from lower speed exceeds the lowering of cornering force due to tyre distortion, so the car can corner on a tighter radius.
Weight transfer improving turn in is unfortunately a red herring in this article's explanation.
That being said, in the world of driver training, as long as the driver improves, their understanding doesn't have to be pedantically correct.
What separates highly skilled drivers such as Mark from me, and probably most of the rest of us on Pistonheads, is their ability to sense the difference between, and closeness to the limit of, the front and rear slip angles.
The instructor showed me how to trail brake to the apex, to keep the weight forward and my speed around the tight bends improved dramatically. In a car like an Elan, you can see the bonnet rise under acceleration and dive under braking, surely the springs compressing and decompressing is evidence of weight transfer!
My experience in an Elise and 911 is that turning in on the brakes is vital to get front-end bite. I'm not pretending to know the theory in detail however.
In any case, the article is an interested read.
It slows the speed of the contact patch of the tyre, so the tyre sidewalls distort by being stretched from their ''normal' profile as the rest of the mass of the car wants to continue at a higher speed. This is what is generally known as weight transfer.
This weight transfer means that when the car is steered the front tyre sidewalls are less stiff and therefore less able to transfer steering input to the contact patch.
This will inevitably result in understeer as the wheels now need to turn through a larger angle to change the direction of the contact patch
However, as the car is now slowed down, the tyres need to generate less cornering force to follow a certain radius corner than they would at the previously higher speed.
The increased cornering force that comes from lower speed exceeds the lowering of cornering force due to tyre distortion, so the car can corner on a tighter radius.
Weight transfer improving turn in is unfortunately a red herring in this article's explanation.
That being said, in the world of driver training, as long as the driver improves, their understanding doesn't have to be pedantically correct.
What separates highly skilled drivers such as Mark from me, and probably most of the rest of us on Pistonheads, is their ability to sense the difference between, and closeness to the limit of, the front and rear slip angles.
It slows the speed of the contact patch of the tyre, so the tyre sidewalls distort by being stretched from their ''normal' profile as the rest of the mass of the car wants to continue at a higher speed. This is what is generally known as weight transfer.
This weight transfer means that when the car is steered the front tyre sidewalls are less stiff and therefore less able to transfer steering input to the contact patch.
This will inevitably result in understeer as the wheels now need to turn through a larger angle to change the direction of the contact patch
However, as the car is now slowed down, the tyres need to generate less cornering force to follow a certain radius corner than they would at the previously higher speed.
The increased cornering force that comes from lower speed exceeds the lowering of cornering force due to tyre distortion, so the car can corner on a tighter radius.
Weight transfer improving turn in is unfortunately a red herring in this article's explanation.
That being said, in the world of driver training, as long as the driver improves, their understanding doesn't have to be pedantically correct.
What separates highly skilled drivers such as Mark from me, and probably most of the rest of us on Pistonheads, is their ability to sense the difference between, and closeness to the limit of, the front and rear slip angles.
The bit about the brakes slowing the wheels down?
The bit about the slowing wheels slowing the contact patch down?
The bit about the sidewall distorting?
The bit about a greater steering angle being needed if the sidewall is distorted?
The bit about a slower car needing less force to keep it on the same radius as a faster car?
The bit about the effect of slowing being greater than that of sidewall distortion on cornering force?
The bit about weight transfer being a red herring?
Or the bit about Mark being a faster driver than most of the people who subscribe to Pistonheads?
As the philosopher Schopenhauer is attributed to have said:
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
B: The bit about the slowing wheels slowing the contact patch down?
C: The bit about the sidewall distorting?
D: The bit about a greater steering angle being needed if the sidewall is distorted?
E: The bit about a slower car needing less force to keep it on the same radius as a faster car?
F: The bit about the effect of slowing being greater than that of sidewall distortion on cornering force?
G: The bit about weight transfer being a red herring?
H: Or the bit about Mark being a faster driver than most of the people who subscribe to Pistonheads?
Final judgement (Hales lost, had to pay about £50,000 in damages) was posted on page 26 but I can't get the link to work.
It slows the speed of the contact patch of the tyre, so the tyre sidewalls distort by being stretched from their ''normal' profile as the rest of the mass of the car wants to continue at a higher speed. This is what is generally known as weight transfer.
This weight transfer means that when the car is steered the front tyre sidewalls are less stiff and therefore less able to transfer steering input to the contact patch.
This will inevitably result in understeer as the wheels now need to turn through a larger angle to change the direction of the contact patch
However, as the car is now slowed down, the tyres need to generate less cornering force to follow a certain radius corner than they would at the previously higher speed.
The increased cornering force that comes from lower speed exceeds the lowering of cornering force due to tyre distortion, so the car can corner on a tighter radius.
Weight transfer improving turn in is unfortunately a red herring in this article's explanation.
That being said, in the world of driver training, as long as the driver improves, their understanding doesn't have to be pedantically correct.
What separates highly skilled drivers such as Mark from me, and probably most of the rest of us on Pistonheads, is their ability to sense the difference between, and closeness to the limit of, the front and rear slip angles.
The bit about the brakes slowing the wheels down?
The bit about the slowing wheels slowing the contact patch down?
The bit about the sidewall distorting?
The bit about a greater steering angle being needed if the sidewall is distorted?
The bit about a slower car needing less force to keep it on the same radius as a faster car?
The bit about the effect of slowing being greater than that of sidewall distortion on cornering force?
The bit about weight transfer being a red herring?
Or the bit about Mark being a faster driver than most of the people who subscribe to Pistonheads?
As the philosopher Schopenhauer is attributed to have said:
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
In racing, the effect of braking on cars like the Formula Ford referred to in the article has a dramatic effect on how the car changes direction. Even small amounts of braking and or acceleration can change the steering angle of the car. You have probably heard the phrase 'steering on the throttle'? Or perhaps - 'lift off oversteer'. What you're asserting is that both of these are due to tyre wall distortion and not weight transfer.
Braking during turn in, effectively rotating the car as the grip is at the front rather than the back is exactly how Caterham racers and many other cars without slicks and wings attack corners in their cars.
Whilst I'm sure your correct that tyre distortion due to weight transfer has some effect, it's unlikely to have anything like the difference that weight transfer has, especially in very light cars such as the ones mentioned in the article.
The content rather reminds me of some articles I have read about top level motorbike circuit racing, where at the art of flowing smoothly through the bends and keeping a good amount of power on is slower than piling into a corner, loading on the front brake, standing the bike up and turning hard with the front before going hard on the throttle again. Apparently this gutsy approach is the way the fastest riders do it now.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff