F1 Braking Systems

F1 Braking Systems

Formula 1 cars can come to a stop from 100
km/h in about 15 metres, which is almost a quarter of the braking distance of your average
road car. They can go from 300 km/h to a complete stop in under four seconds, pulling up to
6G of deceleration force. With such high speeds and tough corners, F1
cars need to be able to produce massive braking forces – not just for performance but for
safety as well. A driver needs to know the car will respond when they press the brake
pedal, and not cream into a wall or the back of a competitor.
Let’s look at the braking system of an F1 car as a whole before we dive into the individual
components. When the driver hits the brake pedal, it transmits
a force to two master cylinders. One cylinder controls rear braking and the other front
braking. Let’s focus on the front braking to start with as it’s much simpler.
The master cylinder acts on brake callipers which squeeze brake pads onto the brake discs
– this hard friction between the brake pads and the discs slows the car down.
Let’s take a closer look at those components then.
These master cylinders are filled with brake fluid – just a couple of hundred milliletres
worth. The fluid fills brake lines that run from these cylinders to the brake callipers,
acting as arteries of the braking system. Fluid is incompressible, so when the pedal
is pressed and the plunger is pushed into the cylinder the fluid immediately puts forces
on the other ends of the brake line. This is how hydraulic systems work.
The brake callipers are like clamshells around the brake discs and house brake pads within
each side of the shell. The hydraulics feed into pistons – no more
than six – within the callipers; these pistons push the brake pads into the brake discs.
As the brake discs are attached to and spin with the wheels, when the pads clamp on the
wheels, the frictional force between them will slow the spinning of the wheel and ultimately
the speed of the car. The callipers themselves are often mounted
low on the discs to keep centre of mass low, but tend to be placed closer to the 5 or 7
o’ clock position rather than lowest 6 o’ clock position. This is partly because the
bleed nipple needs to be fairly high. ‘A bleed nipple?’ you asked with horror
in your eyes. Well, remember when I said fluid was incompressible and that was what allowed
pedal force to instantly translate to the brakes? Well sometimes air bubbles can get
into the hydraulics and gas is compressible. So when the brake pedal is pushed, the gas
in the hydraulic system can deform, reducing the braking force at the other end.
To flush this gas out, you can open the nipple and – as it’s placed high up, the gas
will rise more readily to the top and be flushed out when you force fluid into the system.
You’ll often bleed the system between sessions to be on the safe side.
Onto the actual brake pad and discs, then. The brake discs cannot be larger than 278
mm (11 inches) in diameter [USE SCHOOL RULER] or 32 mm thick. A larger diameter means greater
stopping power as its easier to stop a spinning disc by grabbing it further from the pivot
point than closer to the centre. The restriction of the rules in this area is to limit the
braking power of the car so braking zones can remain somewhat competitive.
Unlike the steel-type brakes on modern road cars, F1 brakes are made of a special carbon
composite called, hilariously, carbon-carbon. It’s called this because it’s two types
of carbon composited together – a carbon lattice like graphite reinforced with carbon
fibres. Carbon-carbon is strong, can withstand very
high temperatures and has a very high coefficient of friction. The coefficient of friction of
a material just tells you how well a material grips when rubbing against another material
– ice, being slidey has a low coefficient of friction; rubber, being not slidey as all,has
a high coefficient of friction. Carbon-carbon also has a very low thermal
expansion and low thermal shock – meaning it won’t deform or crack suddenly under
high temperatures. This ability to stay robust under high temperatures is incredibly important.
The way brakes slow tyres down is by converting energy. The kinetic – or moving energy – of
the spinning wheels is converted by the braked into heat energy.
As the brake pads grip the discs, the high frictional forces turns the energy of the
wheel into tremendous amounts of heat. A cold brake can heat up by as much as 100°C
every tenth of a second in the initial phase of braking.
Carbon brakes work optimally between 400°C and 800°C, though heavy braking can often
push brakes to 1000°C or 1200°C. Brakes being overly hot causes two real problems:
One – if the brake is already hot it has less ability to absorb heat and therefore
take energy from the wheels. If, under braking, the brake disc rises from 300 to 1000°C it’s
acting as much more of an energy pump than if it could only move from 800 to 1000°C.
Two – the main driver of brake wear is thermal degradation – wear due to temperature. At
high temperature, the carbon will readily oxidise, which is essentially burning at its
surface layers. In excessive wear or prolonged overheating,
carbon deeper within the brakes can oxidise and weaken the structural integrity of the
brakes which is why worn out brakes start to disintegrate to dust. In worst cases, the
brakes can simply explode. So, the temperatures of brakes need to be
carefully managed if they are going to late a race distance and as fluid cooling is banned,
the engineers use good old air cooling to solve this problem.
The premise of air cooling is simple and exactly the same as using a fan to cool yourself off
on a hot day: By using a stream of fast flowing air – heat will transfer from a hot surface
to the air molecules passing by, which will carry this heat away from the hot body.
As a car moves quickly through the air, brake ducts channel some of the cooler air stream
into the brakes to do this job. To further improve air cooling, the brake
discs themselves are ventilated. Narrow channels run through the brake disc from the centre
to its circumference. As the brake disc spins, cool air is force
from the centre out through the brakes and away from the system, carrying brake heat
away downstream. Over the years these channels have reduced
in size but increased in number, providing greater overall volume for channelling air.
Now larger drake ducts can be more of an aerodynamic drag but the difference in top speeds between
using larger brake ducts and smaller version are only a couple of km/h.
A greater reason from adjusting the size of the ducts is more to do with the braking nature
of the circuit. If you’re having to brake a frequently and/or heavily, the brakes will
need more intensive cooling as you aren’t coming off the brakes as often and giving
them enough time to lose their temperature. You don’t want to keep heading into braking
zones will the brakes at 800°C. So larger brake ducts will more intensively
cool the brakes in the periods between braking zones.
On the other hand, the brakes don’t actually work very well when they are cold. You ideally
want them at at least 400°C when you hit the brakes. If you’re not braking very often
on a circuit, so there are long periods of time between braking zones for the brake temps
to come back down, you’ll probably opt for smaller brake ducts so they don’t lose too
much temperature. When you hit the brakes at cold temperature,
the brakes can take a few hundredths or even tenths of a second to kick in properly, which
isn’t ideal. The other interesting problem to manage is
that of feeding the thermal degradation problem. As I said, at high temperatures, the carbon
oxidises. This means the carbon atoms bond with oxygen atoms in the air, forming carbon
monoxide or carbon dioxide. Now, the brakes take a while to cool down
and all the time they are at a high temperature, they are still ripe of oxidation. And all
this while the brake ducts are feeding the carbon more and more air, including oxygen,
which can accelerate the process. A tricky problem.
You’ll often see engineers blanking off brake ducts with – aptly – duct tape if
the ducts seem to be feeding too much air into the brakes either temperature or degradation-wise.
So that’s the simple end of the braking system – the front brakes are powered by
a straightforward hydraulic system. The rear end – that’s more complicated.
Since the hybrid power unit was introduced, the MGUK is a significant part of the system
that slows down the rear wheels. This duty is now shared between the brakes and the MGUK.
To manage this effectively, the rear brakes are not operated by a simple hydraulic system
but by brake-by-wire. A brake-by-wire system (sometimes obliviously
referred to as BBW) means the physical action of the brake pedal is not directly attached
to the physical action of the brake callipers. Instead, there’s a computer in between telling
the brakes what to do. The MGUK can take up to 2 mega joules of energy
from the rear wheels per lap. How much energy the MGUK harvests under braking at any given
time is decided by things like brake pedal pressure, harvesting settings and battery
level. The rest of the deceleration is performed by the actual brakes.
The Electronic Control Unit (or ECU) is fed live info constantly, calculating and delivering
exactly how much work the physical brakes and MGUK perform in decelerating the car when
the brake pedal is pushed. Any excess hydraulic pressure not used to
brake the car is automatically fed back into the system via a release value.
This all happens on the fly and is incredibly sophisticated and, while all this is going
on, it has to feel like real braking to the driver.
Now, because the rear brakes don’t have to do as much work as they are sharing the
load with the MGUK, the brake discs themselves are a lot smaller than they previously were.
But if there’s a failure of the MGUK and brake by wire system, the rear brakes will
have to do all the work and this is suddenly a massive problem. Larger discs can manage
and dissipate heat much more efficiently than small discs which overheat very quickly.
This happened to Ricciardo in Monaco after his MGUK failure so he had to move the brake
bias forwards to take the load off the rear brakes.
Brake bias (or brake balance) sets how the braking force is shared between the front
and rear of brakes when the pedal is pushed. Ideally you want each brake doing the exact
amount of work necessary for the weight load it’s managing. At rest an F1 car’s weight
is distributed roughly 45:55 – i.e. 55% of the weight is supported by the rear tyres.
But under heavy braking, the weight shifts forward to as much as 55:45, so you’ll tend
to end up setting a brake bias to about 55% frontwards.
Too much front brake bias and the fronts will grip too tightly and lock the wheels, causing
heavy understeer. Too much rear bias and the back wheels can
lock and cause the car to become unstable and spin.
Ideally, you want all of you brakes to each deliver their maximum force and, if you pushed
slightly too hard, all wheels should lock in unison. But erring on the side of front
bias is wise as a lock up of the front at least keeps the car stable, not throwing it
into a spin. Drivers can adjust brake bias between corners
from within their cockpit but this is only allowed while the car is off the brakes.
F1 brakes are a complicated technology with the potential for phenomenal stopping power.
With such state-of-the-art materials and design, half the battle continues to be managing brake
temperature and bias throughout each session to keep degradation at bay and try to ensure
the brakes are in the perfect temperature region into every braking zone.

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    – I say "fluids" are incompressible but what I meant to say was "liquids" are incompressible as "fluids" includes liquids and gases (and some other matter states). Because my brain was saying "brake fluid" I accidentally used the word fluid instead of liquid.

  2. @2.51 In English, the word "strong" is pronounced with an "s" sound, as in the word "simple". It is not pronounced with a "sh" sound as in the word "shoe". Please stop speaking in that stupid "I wanna shound Merican" accent.

  3. The brake disc ventilation hole reduction in size and the subsequent increase in heat transfer, is more a product of increased surface area than is a product of the increased airflow.

  4. "Over the years, these channels have reduced in size but increased in number, providing greater overall volume for channeling air." Ummm… unlikely. You lose a lot of cross section to a round tube with just a fairly small decrease in diameter. What more cooling channels of smaller diameter provide is less volume, but they offer much higher surface area for the air flowing through them for heat exchange.

    Total flow through a heat exhanger is important, but equally important is the total surface area. Pulling 1000 cfm over a single pass of 3" diameter pipe will do work, but it's not going to be anywhere near as effective as breaking it down to a bunch of .100" tubes and flowing even a quarter of the air over them.

    Why not set up a thermostatic flap inside or in front of the brake ducts?

  5. For the 2018 season I think Formula One cars used 13 inch wheels with a very high aspect ratio tires. These F-1 cars could stop from 300k to 0 in two seconds. Thirteen inch wheels weigh much less than 20 or 21 inch wheels using the same material. So why does Ferrari, Lamborghini and Aston Martin street/sports cars manufactures, push outrageous huge wheels on their customers, when everyone knows that extra mass (20 & 21) of wheel is anti performance. Could these Hyper & sports car manufactures use 17 Inch wheels instead of punishing us with these outrageous ones they sell us????

  6. Great info.

    I love that the graphics of the example they chose to use for an "average road car" appears to be a Ford Focus, maybe even a Focus ST.

  7. What an awesome, and concise explanation. Please do some more Stuart. It's so nice to finally understand the 'big secrets' involved with F1 advances. If you can educate us with a similar video for each subsystem, e.e, steering, suspension, transmission, body aerodynamics, materials etc, that would be amazing.

  8. If your car needs almost 60 meters to stop from 100 km/h, you should really consider servicing the brakes!
    Or maybe don't buy an american car. 😉

  9. Such an interesting account of the F1 breaking system. Thanx. I love everything about the technology aspect of F1 – 🚗 – the most sophisticated 🏎 on 🌍

  10. As a motorbike rider (where you can almost get away with not using the rear brake, under good braking conditions), i find it amazing how little weight transfer F1 cars have

  11. Failure of the MGUK causes a massive rear braking problem? Charles Leclerc can tell you all about it!

  12. thanks for this !!! .
    i did not realise that even the brakesystem can be different depending on the track .
    you have impressive knowledge .|
    keep up with these good videos

  13. Another excellent video. You without a shadow of a doubt make theoretically complicated auto technologies realistically simple.

    Not an easy thing to do but you pull it off


  14. Just took a heat transfer class and it would have been cool to see a (rather simplified) problem about the ventilated brake disks, looks like they are a form of tube banks, and it could be an interesting convection type problem

  15. Liquids are compressible; it's a very tiny fraction of what gasses compress, but they do compress (Howard Hughes famously lost this bet one time and had to re-design the control hydraulics for his big flying boat).

  16. Thanks for the correction on fluids vs liquids, but don't worry you are not the first or the last to accidently misuse the terms in this fashion. However I have one more point to debate,

    The reason for more smaller channels in a brake rotor is IMHO not primarily aimed at increasing volume of air…rather the primary factor is the increased surface area exposed to the air, hence the greater transfer of heat to the air passing by despite the decrease in flow due to the greater surface friction the air will encounter.

    The reduction in size can only be taken so far, as at some point the differential between the temperature of the surface of the passage and the temperature of the passing air becomes so small as to defeat the increase in surface area.

  17. A more to the rear brake bias helps with better front grip at the turn so you need to find a sweet spot. When you transfer the weight to the front the front tires get more grip, but it they are used to brake the grip is shared between braking and steering.

  18. not sure the graphics to scale – it took the focus or whatever it is a long time lose its last few mph – I'm having my adenoids out tomorrow folks – gonna 3D print them carbon-nano-fibre five times the size for the re-implant, now what do you think about that, my dear…………

  19. imagine f1 cars on the le mans track
    forever without breaking and then suddenly mean chicanes
    good that it will never happen because the cars would blow up on the bumpy public roads

  20. The brake split front/rear is much more than 55/45. There is a difference between brake bias and how much braking is actually being done front vs. rear. The amount of braking done by the front brakes would be closer to 90% than 50% due to massive amounts of longitudinal weight transfer under huge deceleration. Overall good video though.

  21. Whoopy carbon ceramic brakes, same brakes you find on a z/28 Chevy or Corvette today and Kenny brown performance has liquid cooled hydraulic brakes of the same, again something else invented by the Hoosiers of the racing capital of the world here in Indy by us hillbillies …so the rest of you think you are something special ..bahahaha

  22. this for somereason reminded me how in gran turismo 5 i would purposefully lock my brakes on the first or second corner of a lap to get my tires heated to optimal tempeture in mear seconds, instead of in minutes

  23. Thank you for your videos. For someone who has very limited knowledge about Motorsports, your videos are always insightful about the finer points. My best to you and yours sir.

  24. These videos are extraordinary. The FIA should be paying you. Someone should be paying you anyway.

    I can’t imagine how much time these take; research, scripting, animation… thank you so much Stuart.

  25. Everything is compressible, most liquids and solids just not very much so. Else the elastic modulus would be infinite.

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