NOT FADE AWAY Updated 2 December 2001

This paper covers the following subjects, Brakes, Braking and Steering.

One or two things need to be set straight; the first is "how do brakes work"? Brakes are energy converters nothing more, they turn the stored movement (kinetic) energy into heat energy through the medium of friction, this heat builds up and (usually) through convection dissipated into the environment. This is a very efficient way to stop, and it's as old as the hills. Even the first carts had some kind of friction brake acting on at least one wheel of one axle. These first brakes were not very good, so on long hills the Carter /coachman deployed a 'beetle' as well just in case his old leather brake shoe caught fire, if you've ever suffered a rope burn you'll understand.

So braking efficiency is a function of thermal dissipation efficiency. At this point I am tempted to lapse into formulae, I won't, so by way of explanation. When the Brakes are cold the temperature difference between the ambient (air) temperature and the disc is small so most of the energy has to be spent heating the discs themselves, this is slightly less efficient than the convected dissipation. This is why they are less effective and need to be warmed to their task. Modern discs are made of quite a 'mild' steel which absorbs heat very readily and cools equally rapidly some even have a small amount of sodium added during the smelting process, as sodium assists in heat transmission. Vented discs are merely 2 thin discs with an air space (gap) between them, again assisting in the dissipation of heat. The normal operating temperature for 'saloon' type discs is around 250* C and start to fade after 350*C due to the friction properties of low temperature pads, add another 150*C to both and you have 'sports' type brakes, right up to 1400*C for carbon 'F1' type brakes.

Let us talk about pads, their function is quite different from the discs, pads are made of a sort of insulating material, they impart the friction TO the disc and the disc can glow 'red hot'. The pad must not take-up the heat within its structure, it can be very hot at the point of contact but the temperature must drop very rapidly across its thickness, if the heat manages to get right across the pad you are in trouble. The first thing that can happen is that the brake fluid starts to boil. This causes air pockets to form much in the way that a pan of boiling water bubbles; the brake pedal movement becomes 'spongy', as air is more compressible than the oil in the pipes. Brake fluid starts to bubble from about 350*C to 550*C (dependant on type and condition). A word or two about brake fluid, it is a mineral oil and has a particular crystalline structure formed during the 'cracking' of crude oil to petroleum which makes it nearly inert and therefore very suitable for brake fluid. Unfortunately this process leaves it hydroscopic (can absorb moisture directly from the atmosphere) in nature so the system has to be partially 'closed' or sealed. This absorption also lowers the boiling point of the oil and a tiny amount of moisture in the system can halve the critical temperature!

That is why we have special little filters in our brake systems so as to avoid this contamination. Even so, we should replace our brake fluid occasionally, and never let anyone steam clean your engine compartment unless they know to cover and seal the brake system first! In fact don't ever steam clean the engine compartment.

Returning now to the different types of pad. As the design operating temperature increases, i.e. Fast Road type, the co-efficient of friction at the interface is intentionally reduced. Simply put, the higher the design temperature, the less friction there is at the surface and therefore the longer the time taken to warm them up, so, the worse they are for urban use. They just don't 'grab' the disc so firmly. This is an essential function of the pad, if at 700*C an 'abrasive' pad was in use the disc would almost disappear in a hail of red-hot shards! On our forum recently it was mentioned that Camry pads fitted our cars. They may well do, but think of this, they may feel to have more bite at low speed, but they flatter to deceive, at high speed when our discs run very hot these pads would wear away the disc 5 to 10 times more quickly than the Genuine Soarer pad. When buying pads always go for the ones designed for your car and if you change you have to be aware of what may (or may not) happen.

Try to ensure the pads are the 'sacrificial' part of the system, not the discs. Quality pads keep the Grim Reaper at bay.

As the interface temperature seriously increases strange things happen at a molecular level, the disc itself wishes to expand, as the molecular structure becomes more excited, finds itself confined, raising the temperature further and the pad effectively starts to 'float' on a layer of hyper-thermals generated by this 'quasi-luxating' layer. This element of braking function was not even known about 12 months ago and is the subject of some dispute as to whether it is even possible for super-heated materials to do this. My opinion (for what it is worth) is that it does happen. This layer is thought to be only a few microns thick and irregular in formation, the surface friction is modulated by it; effectively it is a layer protecting the disc from being destroyed. The common term for this is a 'Glaze Coat' or 'Proofing'. After the disc has released these photons once, the surface looks slightly glassy and the new 'finish' seems to more readily perform this magic trick and the efficiency of the braking is better achieved. The temperature for this piece of near Quantum magic varies but generally is confined to over 800*C.

The strangest thing is, as it floats the pad/disc combo has a natural constant co-efficient of friction, you can press on the brakes as hard as you like it will not stop any better. I have encountered this form of braking effect only once on the road, I once had to stop from 190MPH in a real hurry, no ABS in this, a Former Le Mans drivers BMW 535 fitted with an after market Turbo. (18lbs over-boost, about 650HP, 6-8 MPG!!!) The brakes were already up to temperature and the 'bite' happened at 'I guess' around 160MPH, the car slowed dramatically to 60 at this point it all became too much for the front tyres, (9" hand grooved Goodyear racing Slicks) and had to resort to cadence braking, only to stop about ten feet from the accident that had happened 'miles' ahead of me! I would think that the 100mph drop was achieved in the same time as the last 60!

I promised Charlie that I would explain what 'Cadence' means, so here goes, first practice on an airstrip or some genuinely deserted area not on the roads, please. Get up to a reasonable speed, say 40MPH, slam the brakes on and skid to a halt, no faster or you will flat spot your tyres. Of course if you have an old set to swap over to, all to the better. Now go back and this time when braking take the "pressure" off and on the pedal SLIGHTLY and as QUICKLY as your foot allows, don't take your foot off the pedal and the movement should be only very small. This is what an ABS system does. After about 20 attempts you'll be pretty good at it, and after about 50 you'll be safe to try it the next time you really brake hard, it has to become a natural response not connivance. Done right it will save your or (more importantly) someone else's life, do it wrong and the reverse applies.

Lets talk ABS, it means A.nti-lock B.raking S.ystem and it does what has just been described above but much more effectively.

In the 1960's as aircraft became larger and landing speeds increased as a consequence (to avoid stalling); the need for really effective brakes became urgent. To this end the developers of the disc brake (Dunlop) had an ingenious answer, mechanical cadence braking. This system was called Maxaret a corruption of Maxima and Arrete =Ultimate Stop As production tolerances became smaller it became possible to fit this system in a Motorcar this was the Jensen Interceptor FF. (F.erguson F.ormula) This car was really quite extraordinary; Four wheel drive, 3 Ferguson viscous couples, ABS, Traction Control, 7 litre V8, and drop-dead gorgeous Vignale coachwork based on the Maserati of a few years earlier. Built in a couple of sheds by a scary mix of eccentrics and petrolheads, and not a computer within 15 years, how in Gods name did it work! Well it did, mostly, and I drove one in 1976 and the lingering impression is of bulk and the strange kickback from the brake pedal, (I performed a needless Emergency stop). Because of the huge additional weight of the secondary hydraulic system the pedal did a 'ghost' form of cadence braking by pushing it up against my foot half a dozen times. I did not like that! A good friend's father (a local Publican) owned it, and said that on many occasions it saved his life when driving home 'half-cut' from the LVA. The system could 'go-off' half-cocked if you took a hump-backed bridge at speed and then the brakes would not work on first application afterwards, I don't fully understand how this could happen, but I think the wheels had to leave the ground. If that is the case, perhaps FF stood for the first 2 letters of a normally 4 now 5 letter word you uttered as you hurtled toward oblivion!

Most modern systems are based on the principle of a series of little bar magnets with gaps between them mounted at each wheel, and as they pass a sensor it switches on and off. When it stops switching and if the car is still moving the brakes are switched off, when the switching returns they are reapplied until the car stops. The system switches out at a factory set speed so that the brakes work when stationary. As you can see if the wheel starts to spin too fast in relation to the others then the same sensor can act in a Traction Control capacity. And that is all there is to it, use the brake circuit to apply the brakes to bring the wheel back in unison with the others, but, remember it only works on the powered wheels, it has no effect in adding traction to the front of our cars!

Let's return to our wonderful Soarers, sweet little detail this, ever noticed how we seem not to attract brake dust onto our front wheels? (Unlike most cars on the road) Ever wondered why? Do you remember that brakes turn movement into heat? And you have to get rid of that heat, don't you? So if you suck that air in under the car, the wheels stay clean, the brakes are cooled more efficiently, disc wear is reduced and all this a by- product of clever aerodynamics generating negative pressure under the car, assisting in high speed handling/ dynamics. Yep, you guessed, we have it all. And a drag co-efficient below 0.30 to boot. You have permission to feel the self-satisfied glow of smugness.

Turn it in
In this part I will deal with driver inputs at the steering wheel and road information output from the steering wheel. I have coached a few people how to drive their cars and the one consistent thing with them all is their failure to notice the more subtle feedback given by the steering wheel.

My overwhelming conclusion is that for the most part this is because they learnt how to drive small Front Wheel Drive cars. Because of the need to overcome the inadequacies of FWD the more subtle feedback is lost, and their encounter with a high performance Rear Wheel Drive car usually results in scary moments for them and sometimes us their fellow road users. I think the most awe inspiring thing to a fwd'er is that you can subtly tighten or open your steering line with the accelerator, with fwd its more of an on/off affair and completely lacking in finesse and beauty.

Using weighted turn-in to enter a bend, placing the car across the apex and then powering out the other side with the arse end dipping down like an Arab mare in transition from a trot to full blooded gallop is a moment of utter joy and satisfaction, so addictive to me that I go out late every night just to do it.

I'm a very sad, sad, sad individual, with a severe and incurable addiction. When I analyse this piece of motoring ecstasy the greater part comes from the accurate positioning the car. This is accomplished by detecting subtle messages at the steering wheel, unfortunately due to our kph to mph conversion our steering is a bit over-assisted for my liking and the feedback is somewhat muffled. It is still many times more 'talkative' than fwd but I am determined to sort this soon. How do you hold the steering wheel? Sound daft? I assure you it's not, a light touch is all you need.

I am going to give you a 'trade' secret and with it you will, with a little practice, steer your car better than you have ever before! Look at your hand, at the 4 creases where the fingers join the hand, above each crease on each finger there is a tiny muscle with a soft tissue 'pad', below is a contiguous 'pad' across and below the four fingers, this part of the hand should have 4 slightly harder nodules and these are points of contact with the wheel that inform you of the state of the road. And this is what you do, when driving in a straight line both hands hold the steering lightly with all points in contact with use your thumbs to regulate the pressure, it will feel slightly awkward at first, but persevere. When you set yourself to turn a corner increase the gripping force between the thumb and the first 2 fingers, (index, and biggest) don't tighten the other 2 fingers, fix both hands like that and shuffle the wheel between the hands without ever having both hands losing contact.

Don't wear driving gloves, modern cars are very mild mannered, gloves may be needed in an old Healey 3000 or Alvis or even some fwd's, but they are counter productive in our Soarers. Above all concentrate; notice the different qualities of road surface and how different the steering 'feels' just after the change point, try to equate coarseness with the inputs and how much deviation different surfaces induce in your course.

Take your time, it is surprisingly tiring. There is a reward for all this effort. This time and not quite so 'techy' and 'only' 2600 words. The next piece is about our Engines and Gearboxes and is looking like 12000+ words so brace yourselves; I am trying to précis where I can. Look after yourselves out there.