Why are Drum Brakes Making an EV Comeback?
This is a brake drum, and it’s a component the motor industry had thought was starting to be left behind. But with the advent of electric vehicles, drum brakes present a unique set of advantages that have already led to something of a comeback, so today on Twin-Cam, we’re going to explore how
These work, why they died out, and why nowadays, they’re starting to look like a good idea again. Now before we get into things, I just want to make a little video-based caveat, because my channel’s not big enough to have an autocue, and I can’t be bothered learning this
Script. So if my eyes are looking down, that’s why. Don’t comment about it, just live with it. Anyway, I can never claim to know the ins and outs of my audience, but I’d wager that, considering the kinds of cars I tend to cover, a fair proportion of you didn’t know this was
Happening, and see drum brakes as a relic, held onto only by the rear axles of smaller, cheaper cars, and that would be fair to say. After all, the vast majority of mainstream cars had adopted disc brakes by the end of the 1960s, and a pattern of discs front/drums rear
Is what’s found on this little Rover Metro beside me, and it’s from here that I’ve nabbed this drum, so before going any further, let’s figure out how they work. This little mess may look rather complex, but the principle is incredibly simple. When you press the brake pedal,
Hydraulic fluid is forced from the reservoir through the brake lines to a wheel cylinder, mounted here at the bottom. The wheel cylinder then pushes its two pistons outwards, engaging with the brake shoes. The shoes are lined in a friction material, which then contacts the inside
Edge of the brake drum, slowing you down. The springs are here merely to keep everything aligned and to ensure the shoes return once you release the pressure, and there’s an adjuster mounted at the top, tuned by a spanner on the back. Drum brakes have been around since the year dot,
And they do have their advantages, naturally, but even by the 1940s, their weaknesses on even the most mundane of passenger cars were showing through. The biggest enemy of drum brakes is heat, because being an enclosed system, the heat generated by the friction has nowhere to escape.
That means that even if you’re doing something as innocuous as controlling your speed down a hill, the shoes and fluid can overheat, causing brake fade or even total brake failure. But to make matters worse, drums are inherently inconsistent. While small braking forces may be fine,
When you start pushing them, they start to act weirdly, the shoes grabbing at the drums and the braking force rising exponentially despite your pressure on the pedal remaining the same. This means they’re difficult to modulate, and the initial pedal feel isn’t very good as the shoes
Have to overcome the force of the springs before moving to contact the drum. For this reason, drum brakes were a waste of time in racing, so by the 1960s, they were being quickly replaced by disc brakes. While a number of road cars were already using discs, the influence of racing saw
The technology slowly trickle down to the point where they became the standard. Just for the sake of an example, when the Mini was launched in 1959, it featured drum brakes on all four corners. But two years later, we met the high-performance Mini Cooper, a car designed for racing,
And it was gifted discs for its front wheels. As cars generally became faster and more capable, we got to the point where every car had disc brakes on the front, but many, like my Metro, continued to use drums at the rear. Before we get into a comparison though, this is a brake
Calliper, the bit of a disc brake system that actually applies the force, so let’s figure out why these are so much better than these. We won’t get lost in the advantages and disadvantages yet, so let’s see how they work. Just like a drum brake system, you press the pedal, which forces
Hydraulic fluid from the reservoir and through the brake lines, but rather than a wheel cylinder, it ends up in the brake calliper. The calliper sits around a brake disc, and in between, pistons push a set of friction material-lined brake pads into the disc, slowing you down.
On paper, therefore, there are fewer component parts to a disc brake system than a drum brake system, but that brings up issues of its own that we’ll explore later. For now, the advantages – and the main one is that the disk, calliper, and pads are open to the elements,
Meaning heat can be dissipated much easier, and if it’s required, extra cooling can be gained with vented discs, which add a cavity of air between the two faces, or drilling and slotting the discs, which while decreasing surface area for braking, increases surface area for heat dissipation.
Additionally, the pedal feel and ability to modulate you get with discs is far more positive and consistent than you get with drums, so taken from a pure performance or competitive perspective, it’s a no brainer to go for discs. However, while heat and grabbing are major issues,
There is still a lot to be said for a good old-fashioned set of drums, and with the rear brakes only providing around 30% of your total braking force, smaller and cheaper cars have tended to retain them on their rear axles. While there are more parts to a drum brake system
Than a disc brake system, they’re actually cheaper to produce and assemble. Regardless of the individual parts prices, one very basic component makes this argument for rear axles: the handbrake. We’re keeping things simple, so I’m ignoring the exceptions, but in a brake calliper,
The braking force is applied through the pistons by hydraulics. Therefore, it’s difficult to actuate the brake mechanically, making a traditional handbrake unfeasible. In a drum, however, the shoes are actuated by the pistons on each side of the wheel cylinder, and with the
Springs helping return, there’s space down here for an additional lever, actuated mechanically, so when you pull up the handbrake, this lever applies the shoes. The result is that when a car has disc brakes on the rear, manufacturers tend to fit a very small drum brake in the centre of the disc
Purely for the sake of the handbrake, and that is where the expense comes from. But drum brakes also turn out to be more economical in service as they tend to last longer. This is because the shoes
Have a much larger contact patch than the pads on an equally sized disc, so they require less maintenance. Additionally, when something does go wrong, the chances are that it’ll be cheaper to buy a new wheel cylinder than it would to buy a new calliper, so it’s a no brainer why little 800
Kg boxes like my Metro continued to use them. All this is a long-winded way of saying that neither system is perfect, and while discs are undoubtedly better for most applications, there’s a reason that drums have stuck around. But as we move towards electric vehicles, the
Way we perceive braking as a whole is changing. It all comes down to some really basic physics, because an internal combustion engine takes the potential energy of the fuel and burns it to produce kinetic energy. Once that’s been done, it’s tremendously difficult for us to get that
Genie back into its bottle, so we compromise by wasting that kinetic energy, and turning it into heat by braking. EVs, on the other hand, do things a bit differently. They take electrical energy from a battery and convert it into kinetic energy with an electric motor. The clever bit is
That an electric motor can do that conversion both ways. That’s how an alternator works, so EVs can do this on a much larger scale by harvesting the energy back into the battery when you lift your foot from the accelerator pedal. In our world, we call this regenerative braking,
And it’s so powerful that many cars, if configured correctly, can be driven with just one pedal. You modulate your right foot in order to keep the car moving, and if you remove it completely, the car will quite quickly come to a stop. In fact, there’s a serious argument at the moment
About manufacturers whose regen systems do not activate the brake lights, because that could easily cause a crash. But back to the science, and as a result, the brake pedal is scarcely used, and while that massively cuts down on maintenance, it exposes a flaw in the design of disc brakes.
You may remember that back in the 1960s, the disc’s biggest advantage was its open design, being able to dissipate heat much better than their enclosed counterparts. In 2023, however, the advantage is reduced by simple virtue of the fact that the brakes aren’t being used as much,
And the fact that they’re open is now a disadvantage. Brakes work by friction, so the brake discs are bare metal, which means that if you don’t use them, they start rusting. You might have noticed that if you wash your car then don’t use it for even a few hours, the discs
Will flash corrode, so imagine pootling around in the winter, not using the brakes, then suddenly needing them in an emergency, only to find they no longer work as the surface of the disc looks as
Though it lives at the bottom of the sea. Now this isn’t to say that drum brakes are totally immune, but by their very nature, the inside edge of the drum is shielded from the water and salt you might find on the roads. Therefore, when you suddenly need them, they’ll still work as designed.
When we take this into account, while drums are technically worse, they start to make more sense when fitted to an EV. However, we still have the fundamental fault of grabbing to deal with, but as time has passed, this has become less of an issue. While many modern cars do not have the fine
Control of an older car’s brakes, the systems have become much more complex as electronics have started infiltrating them. Anti-lock brakes have been around for decades, but the distribution of the braking force has been electronically controlled on many cars for over a quarter of a
Century now, and that means that the inherent inconsistency of a drum brake can be ironed out somewhat. To take things a step further, Continental, who we will come to in a moment, are working on a totally electronically controlled braking system. Now I don’t like the sound of that
For a couple of reasons, but theoretically, that could grow to eliminate all but the heat element of the drum brake’s disadvantages. Before leaving that point, however, I want to ameliorate the memory of drums, because while the grabbing means they’d traditionally start locking up earlier than
Discs, their ultimate braking force is in fact higher. This sounds weird to say, but remember back to the point I made earlier about surface area. If a drum and a disc are the same size, then the surface area of the shoes is larger than the surface area of the pads. If modern electronics
Can control that greater force alongside the regen, then there’s more of a case to be made. So let’s leave the theoretical world and enter real life, because this comeback for drums isn’t something that might happen in the future. We’re seeing drum brakes coming back into mainstream
Use on cars that had abandoned them years ago. Volkswagen launched the Golf 8 in 2019, and as you’d expect, it has disc brakes on all four corners. However, Volkswagen also launched the similarly sized and electric ID.3 in the same year, but this car has drum brakes on the rear
Axle. If you search around, you’ll be inundated by people complaining that Volkswagen have fitted what’s perceived to be an inferior system to a relatively expensive and very heavy car, but the fact is that, being electric, the ID.3 just doesn’t need discs.
Indeed, all the electronic systems, the regen, and newer, more efficient design means that the ID.3 can cope with drums where a Golf might not, plus you have the added advantage of smaller maintenance bills with the EV, not just because of the general lack of use the brakes get,
But as I mentioned earlier, drums last longer. In fact, Continental, who designed the ID.3’s drums, have come out and said that, theoretically, the shoes should never have to be changed. Now, that’s a complicated statement to work with as it is the rear brakes we’re talking about, which do a
Minority of the work anyway, but the point stands. What’s a clearer point, however, is the environment. After all, that’s the prevailing argument in favour of EVs, and because of their closed nature, drum brakes release much less brake dust into the atmosphere. Now of course,
It goes everywhere when you open the drum, but in a workshop that can be easily dealt with. Back out in the wild, however, brake dust and tyre particulates are the next enemies once exhaust emissions are gone, and drum brakes may just be able to work towards eliminating them.
The environmental issue is an interesting one, however, because for many years now, manufacturers have neglected their braking systems. The electronic elements are a separate issue, but in terms of the physical components, manufacturers have been oversizing their brakes relative to the
Car, then relying on ABS to keep them in check. While huge brakes might look great, they aren’t exactly necessary, and while they’re violently effective, they cost more to produce, take more raw materials, and produce more brake dust than their smaller counterparts. This isn’t to say
That any performance cars are about to reintroduce drums, but it’s a part of a much wider point about efficiency, and to make things even better, disc brakes, by virtue of their simplicity, always drag slightly, the pads sitting right up against the disc, requiring more power to move the car. Drums,
On the other hand, have those springs that pull the shoes away from the drum, only adding to their case when range is such a selling point for EVs. The Euro 7 legislation is still up in the air,
But that’s the one that really starts homing in on these issues, so it’s something all manufacturers are going to have to start caring about. However, four-wheel drum brakes are not about to appear on the upcoming ID.2, the EV that Volkswagen is hoping to sell for
Around £17,000. After all, discs do still retain many of their benefits, and even if better drums are to be developed for the future, the higher-ups at Continental have openly admitted that public perception wouldn’t be kind. But from a theoretical perspective,
Drum brakes do make a lot of sense. They’re lower maintenance, more affordable, and last longer, plus as the tables have turned in favour of EVs, we can add dependability, efficiency, and their environmental impact to that list, so with that, thank you very much for watching. If
You enjoyed the video, then please do click like and subscribe to Twin-Cam as well. I’m forever indebted to my wonderful Patreon supporters, so if you’d like to support me that way, then please do follow the link in the description, and I’ll have more videos coming along soon.
In the past few years, manufacturers like Volkswagen have started fitting drum brakes to their EVs. It seems curious, but in the chase for dependability, economy, and efficiency, drums are making a renewed case for themselves.
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