Sadly there has been no shortage of brake failure occurring with the new Tesla Model S Plaid. It’s unfortunate and scary – both for those who can potentially get themselves into trouble, and because if this continues, some kind of legislation could come into place restricting the performance level of new cars.
Tesla has developed a unique method of warning drivers of potential braking degradation by modeling the brake temperature and displaying a warning on the dash that brake temperatures are dangerously hot, and braking distance/stopping power may be reduced. So, rather than equipping every car with brakes that can handle track duty, Tesla has taken the less expensive route of offering brakes that are for road use only, and put the onus on the end-users to upgrade their brakes if they are putting them through racetrack level abuse.
The fact that no major lawsuits have occurred yet is amazing, and likely only possible due to the massive fan following that Tesla has! I can’t say I disagree with the model Tesla is using – in a world where there are warnings and safeties that restrict people from all kinds of activities, it’s nice to see that Tesla doesn’t, for example, restrict the power output after a certain amount of time to let the car’s brakes cool down. That would be disastrous for the aftermarket!
Almost all of the brake failures that have occurred have been the result of poor driver education. There are a few different ways brakes can fail, and I want to discuss what those failure modes are, how to detect them as they are occurring, and of course, how to prevent them from ever happening in the first place.
Brake failure typically occurs in one of three ways – a loss of the hydraulic system due to boiling fluid or a leak, loss of friction due to overheating pads/rotors, and finally, an electronic fault causing a loss of control of the ABS system. In most cases there are warning signs and ways to avoid disaster. Let’s try to get you guys up to speed on that!
Loss Of Hydraulics – Boiling Brake Fluid:
In a track day environment, the main reason a loss of hydraulics occurs is because brake fluid overheats and starts boiling, turning from a liquid into a gas. When this occurs, the brake pedal starts to become extremely long, and multiple presses can be required to get any sort of meaningful braking pressure.
Boiling Brake Fluid – What To Do If It Happens To You:
The good news is that when brake fluid starts to boil, there is a way to save yourself. If you feel your pedal going to the floor, the most important thing is to quickly release the pedal and press it again. This will fill the system with more brake fluid, and build up more hydraulic pressure on the brake pads. Pump the pedal multiple times if required. This is something that should be ingrained in your mind as a reflex if loss of hydraulic brake failure occurs.
I once had a brake line fail on a pickup truck coming up to a red light a few years ago. I was able to avoid rear-ending the car ahead by pumping the pedal repeatedly, which produced enough brake pressure to slow the truck down. Without pumping, the brake pressure would have been zero!
The same advice applies if you have a loose bleeder screw or a leaking brake line. Without pumping the pedal to introduce more fluid, the pressure will keep dropping in the system and the braking force of the car will fade away. While it is counterintuitive to take your foot off the brakes when you so urgently need to stop – it is actually the only thing that will give you more braking!
Boiling Brake Fluid – How To Avoid It In The First Place:
Boiling brake fluid is best avoided by using the proper brake fluid to begin with. Tesla cars are shipped with brake fluid that boils below 160 degrees C. When using a Plaid on the track, the rotors and pads can easily get up to and over 800 degrees C! It doesn’t take long before that heat transfers into the brake fluid. The scary thing is that this heat transfer occurs even during the straightaway – while the rotors and pads are cooling down, a lot of that heat is conducting into the brake fluid. So the next time you go for the brakes you may find you have a long pedal – or even no pedal! This is why doing brake checks are so critical – more on that below.
Racing brake fluid has a boiling point of in excess of 300 degrees C when new. HOWEVER, most racing brake fluids have a much lower wet boiling point, which is the temperature at which they will boil when they have been in service for approximately 1 year (when they have absorbed 3% water).
So while racing brake fluid is great, if you’re not flushing it every season at a minimum, it is not all that much better than typical DOT 3!
So it’s important to understand that different types of brake systems will be more or less sensitive to brake fluid boiling. A brake system with racing pads and OEM rotors is one of the worst situations – as the rotors shed the least amount of heat into the air, and the very high fade point of the pads means that the caliper can operate at a very high temperature. Carbon Ceramic brakes might be the only situation harder on brake fluid – as this type of brake system runs at very high temperatures as the rotor dissipates the least amount of heat (both to the air, and through radiation). With the same energy going in and significantly less ability to get it out, the system simply runs hotter. This means a hotter caliper and hotter brake fluid.
Loss Of Hydraulics – Pad Knockback:
There is another way you can experience what feels like a loss of hydraulics. Pad Knockback occurs when the rotor pushes the pads back, usually because the wheel bearing flexes under large vertical loads (such as running over curbs), pushing the rotor against the pad. When the vertical load goes away, the rotor returns to its normal position, and a gap forms between the pad and the rotor. The next time the brakes are applied, it feels like a loss of hydraulics has occurred.
The feeling is no different than when you put in a new set of pads and have to press the pedal a few times to get the pads to seat against the rotor. This isn’t so much a problem on the Model 3/Model S, but it is something to be aware of and another reason that brake checks are so important (see more about that below).
Loss Of Friction – Overheating Pads:
Brake pad fade is a little bit less scary than a total loss of hydraulics – but unlike a loss of hydraulics, there isn’t much you can do about it. When the brake pads fade in the middle of a braking zone all you can really do is press the pedal harder and hope that there is enough friction to slow you down.
The good news is that brake pad fade develops slowly, and there are always warning signs.
Brake Pad Fade – How To Detect It:
Brake pad fade is often accompanied by a smell when using street or sport/trackday pads. That is the first sign that the brake pads are starting to exceed the temperature they were designed to operate in. Race pads won’t have the smell – but there is another warning sign. When brake pads start to fade, the friction starts to drop off. This can be noticed by the brake balance acting strange – usually feeling like there is too much rear brake bias.
Beyond that point, brake fade will typically develop slowly on one or two braking zones, and only later in the braking phase. When this happens – NOTICE IT. It’s easy to ignore when you’re excited on track, but this is your warning sign. It’s your car telling you: take it easy in the next braking zone. Especially if there is no runoff!
Most of us take our cars around the track for fun, it’s not an endurance race with a big prize at the end. So if you experience pad fade, do a few cool down laps and take a mental note of the limits of your braking system. See “Know your car’s endurance” below.
ABS System Failure:
The last failure mode of modern braking systems relates to the ABS system. Modern ABS systems have integrated brake balance adjustments, and when the system reacts erroneously, a very strange braking failure can occur. In our early experience with the plaid, we had a brake failure that caused excessive rear brake bias and locking of the rear wheels – as the system was in a fault state that wasn’t properly programmed by the ABS supplier!
Another way you can get the ABS system to respond in a non-desirable way – is if a wheel speed sensor is damaged. This can occur on the Model 3/Y if the wheel speed sensor wires are not routed correctly and allowed to rub on wide tires. When this happens, the brake balance can also be affected – so not only is the ABS no longer functional, but the brake balance of the car is so bad that the deceleration ability of the car is significantly reduced.
If you have an ABS alert on the dash, always assume that the brakes will NOT work as intended and do not rely on them for more than gentle, street-like braking. Do NOT continue to push on the track!
Always inspect your wheel speed sensors carefully when using large wheels and tires, and check the clearance at full lock left/right – ideally at full droop and at ride height!
Generic Tips To Avoid Braking Failures:
There are also some generic tips that we want to provide from our years racing – to hopefully share some experience to help those of you who haven’t learned how to react to these types of brake failures before. Learn these techniques, practice them, and be disciplined about them. Brake failures very rarely occur, but especially in the case of 1000+hp cars, you need to be aware and educated to avoid issues, and know how to deal with them.
Brake Checks On The Straights:
About halfway down a straightaway, use your left foot to gently tap the brake pedal to seat the pads, and ensure you have a solid brake pedal. This is something that many professional racecar drivers do by habit. In the case of a Tesla, it will momentarily cut power, but if you have a new brake setup or you’re just developing confidence in your car’s capabilities – this is something you should be in the habit of doing.
Bring A New Build Up To Speed Slowly:
What a car “should” be able to do is sometimes different from what it “actually” is able to do. With a new build, always test the limits slowly, and in an area with ample runoff. One technique for brake-related upgrades – involves just braking as hard as possible but significantly early in each braking zone. This way, if something goes wrong you have space to deal with the problem. This is what saved us from car damage when we had the ABS incident with the Plaid early in our testing. In reality – I should have been braking even earlier!!
Know Your Car’s Endurance:
Expanding on the point above – until you know with total confidence how long your car can go (on a variety of different tracks), without any kind of brake degradation, you should be taking it easy and leaving a margin. Brake-related degradation can cause a significant extension of your braking distances, so take it easy until you have confidence in your car’s abilities.
This article isn’t meant to scare anyone. Brake failures occur extremely infrequently, but the sheer power of the Plaid (along with the standard equipment) has resulted in a lot of people getting a wake up call. In the case of the Model 3, I don’t think we’ve ever seen a major brake failure resulting in significant damage, and our different brake kits can go all day long without issue when used with the correct pads and fluid.
Even our Plaid rotors with the right pads are able to outlast the battery with ease, and show almost no degradation in terms of braking performance. So this post isn’t meant to scare any of you from going to the track and enjoying your car. Rather, it’s just to say that 1000hp is different than the ~400 average horsepower a Model 3 has on track, and that this requires even more attention. Things happen much faster – both the speeds approaching the corner, and the speed at which a breakdown in the brakes can occur if they are not properly prepared.
Hopefully this article can be shared with those who are a little cavalier with their cars and some education can be gained. Most of you that read this article will already know all of this stuff, but it’s those that don’t know that we need to share it with and educate. It is critically important to prevent brake failures from causing some kind of regulation being enacted that restricts the power output or fun that we can have with our cars.