Explaining the magic of F1 brakes

Even a spirited driver rarely considers their brakes when driving on the road.

An emergency stop usually prompts little more than a fleeting thankfulness for the efficiency of modern braking systems, and in reality what you might consider hard braking for a roundabout uses only a small part of the potential braking performance available to you.

And while that determined late braking might have seemed daring, braking in an F1 car is something else. Not only is the deceleration phenomenal, it's done time and time again during the course of a lap.

At street circuits like Monaco and Singapore the driver spends 23% of the lap mashing the brake pedal rather than the throttle. What this means, and what's often not appreciated, is that huge benefits to lap time can be found by paying as much attention to the brakes as you do to the engine and the chassis.

Consider one of the hardest stops on the F1 calendar - Turn 13 in Canada. Ten years ago the braking distance for this corner was around 117 meters but last year it was just 97 meters.

Some of this is explained away by the faster apex speed of the corner, yet conversely the top speed leading up to the corner is also now also higher. What it does mean is the energy dissipated by the brakes is immense, in this case over 2100kW.

With full electrical energy deployment the power unit can produce a bit over 740kW, you can see that the brakes have over 280% of the power of the engine.

All of this immense power has to be dissipated as heat. The brake disc will have started that particular braking event at somewhere around 500 degrees centigrade, and by the time the driver releases his near 300lb force on the brake pedal the temperature will have risen to around 1200 degrees, the same temperature as molten lava.

The ability of the disc to cool properly is important not because of performance but because of the life of the disc.

The discs and pads are made of a material called Carbon Carbon. This apparent repetition is because the brakes start life with a carbon fibre preform that's purified over a period of about two weeks at high temperature through a process known as pyrolysis. This burns off any organic binder material in the carbon fibre layup, leaving a very pure carbon but with voids in the material.

The material then undergoes densification by exposing it to a carbon rich atmosphere again at very high temperature over a period of several weeks to form a solid and homogeneous carbon material which can be machined into the required form for the disc or pad.

This finished material has a desire to revert to its previous form at high temperatures and so the main mechanism for loss of mass in a brake disc isn't mechanical wear (although this does occur at low temperatures) but oxidisation, which happens with increasing ferocity above 650 degrees centigrade.

It's this unwanted oxidisation that drives the need to dispel the ferocious heat, and which has driven the ever-increasing complexity in brake disc design. That disc of ten years ago probably had around 200 relatively large cooling holes. Today it would have over 1400 holes of 2.5mm diameter.

Anyone who has tried to drill a deep hole with a thin bit will know how difficult it is, and even on sophisticated machines it's not uncommon for a bit to break, thereby rendering the whole disc scrap.

Machining the disc must be done carefully; it takes around 14 hours to complete a single disc. The reason for the small-diameter holes, which are around 130mm deep, is that they increase the surface area over which the cooling air flows and it's this which determines how well a disc dissipates heat.

A nice side effect is that the holes also make the disc extremely light at just 1.2 kg. A similar-sized steel disc on a road car would weigh around 7kg.

But it's not just the carbon friction material that slows the car down. Bearing in mind that a road car in an emergency braking situation may decelerate at around 0.8G, it may surprise you to know that when the driver of an F1 car lifts off at 200mph, the aerodynamic drag of the car will decelerate it at over 0.9G.

Add to this the engine braking that occurs when the throttles are closed and the engine turns into a huge air pump and the 120kW of braking power absorbed by the MGU-K as it harvests charge for the battery, and you can understand how an F1 car can decelerate at around 5G.

But what do we mean by 'G'? Strictly we should express deceleration in 'meters per second squared' - in other words the change of speed over a given time.

But on our planet the force of gravity will accelerate anything you drop, be it a feather or a heavy weight, at an acceleration of 9.81 meters per second squared towards the ground. This then becomes a handy unit to express acceleration.

At 1'G' your body weighs just what the bathroom scales tell you. At 5g your average 75kg person would appear to weigh 375kg, and this is the sort of force that a driver experiences pushing against his seat belts in an F1 car many times a lap as he brakes.

To put that in context, a fighter pilot ejecting from a stricken aircraft is subjected to between 9 and 12G in a once-in-a-lifetime experience.

The performance of F1 brakes is phenomenal and, like every engineered part of an F1 car, it's continuously developing to find the smallest incremental performance gain that makes the difference between winning and losing.