In a motorsport environment, the car components work much harder than they would on the road, particularly in the case of the braking system. Due to the higher speeds and multiple hard presses of the brake pedal in quick succession, the temperature of all the brake components quickly rises to levels that easily surpass any that you would encounter on your daily commute.
However, it is easy for these temperatures to spiral out of control if you don’t install the kind of brake parts and components that are capable of withstanding these higher temperatures – and this doesn’t just apply to the brake discs, pads, and calipers; but also your brake fluid.
Once the temperatures exceed those acceptable levels, the performance begins to significantly decrease, also known as “fading”. Any deterioration in brake performance is a bad thing, but it is made worse by being multiplied in a motorsport environment.
In terms of the brake fluid, if the temperatures become too high, then the effects will be felt by the driver through the brake pedal. Driving a car where the brake fluid has boiled due to excessive temperature is not a pleasant experience, as you will find yourself approaching a corner expecting to hit the brake pedal in the same manner as you have done previously, only to find out that the pedal has developed a spongy feeling, that the amount of travel has increased and the braking ability has been significantly reduced. You are suddenly faced with the task of stopping the car for the upcoming corner without the full performance of your braking system.
As such, avoiding this situation is of vital importance both for your performance on track, but more importantly, your safety; which is why ensuring that the brake fluid in your car is up to the job is of paramount importance.
Having the correct fluid in your braking system doesn’t just protect you from having a loss of braking performance, it also plays a vital role in providing the driver with a consistent pedal feel which has a profound effect on both confidence and consistency.
Most drivers will develop a degree of muscle memory over time that helps them to apply the same braking pressure to the pedal on a consistent basis, which in turn allows them to maximise the braking performance through threshold braking and reducing the chances of locking a brake. This consistent pedal feel is provided through the compressibility of the brake fluid used in the system.
Before selecting the type of brake fluid that you need to use, there are a couple of things that you need to consider.
What does the DOT rating mean?
As part of the manufacturing process, brake fluids are designed to meet certain standards that are set by relevant industry organisations. One of the most commonly used standards is the DOT rating, which is set by the US Department of Transportation.
Ratings such as DOT 3, DOT 4, DOT 5 and DOT 5.1 are among the most widely used in the automotive industry. As a general rule of thumb the higher the number, the greater the performance the brake fluid is able to provide.
Brake fluids with a rating of DOT 3, 4 and 5.1 are all Glycol based fluids and, as such, can be used in the same braking system. They can also be mixed if necessary, but the boiling point will remain at that of the lowest rated fluid in the system. So, if high brake temperatures require you to use a high boiling point brake fluid, it is best to use a single type of brake fluid.
DOT 5 brake fluid is silicone based and is not compatible with any of the other types of fluid. As such, it is best used when you have had a complete braking system overhaul including new hoses, as any traces of other brake fluids will be detrimental to braking performance.
Understanding boiling points
When looking to select an appropriate brake fluid, you will undoubtedly come across the terms “dry boiling point” and “wet boiling point”. At initial glance, this may appear to be a rather odd specification for a fluid that is always going to be wet, but there is a valid reason behind the name.
As we’ve touched upon already, there are two different types of brake fluid available: Glycol or Silicone based. A brake fluid that is Glycol based is what is known as a hygroscopic fluid, meaning that it will absorb moisture. Even though hydraulic brake systems are sealed with no chance of water getting in, moisture can be absorbed through the air in the reservoir in a phenomenon known as vapour lock.
In contrast, a silicone brake fluid will not absorb any water, resulting in a much more consistent pedal feel and brake system performance. However, it is worth noting that not all braking systems are compatible with a silicone brake fluid. Cars that feature ABS systems are not compatible with Silicone brake fluid as this can lead to aeration of the fluid when the ABS system kicks in, this will have a detrimental effect on the braking performance.
So, with this in mind, the dry boiling point is the temperature at which the brake fluid will reach boiling point when it is first added to the system. This is before the fluid has the chance to absorb water. This means that the wet boiling point is the maximum temperature that the fluid will withstand once water has been absorbed into the fluid.
Each different type of brake fluid will have its own boiling point temperature limitations. If you are not sure about what the operating temperature of your braking system is, there are some useful brake temperature indicator strips available that record the maximum temperature reached during a run. This will help you to select the correct type of fluid for your application.
Our best-selling brake fluids
There are many different types of brake fluid available on our website, each of which has their own individual specifications. We have picked out our five bestselling brake fluids that will ensure that you have a consistent pedal feel and reduce the possibility of losing braking performance throughout the course of a race. So, let’s get into it.
1. Castrol React SRF
One of the most sought-after brake fluids in all of motorsport, Castrol SRF is the choice of many of the leading teams from all forms of top level competition including Formula 1, endurance GT racing and touring cars.
Not only does it have a very high dry boiling point, but it also has an excellent wet boiling point, meaning that it will provide the best performance from the first press of the brake pedal and will not suffer from a large drop in performance over time.
- Dry Boiling Point: 320°C
- Wet Boiling Point: 270°C
- DOT Rating: 3 and 4
2. Motul RBF660
Being a high performance DOT 4 brake fluid, RBF660 from renowned lubricant manufacturer Motul offers the highest dry boiling point of this selection of brake fluids. This makes it superior to many DOT 5 and DOT 5.1 brake fluids that are available and ideally suited to cars with all forms of braking system including those with carbon and ceramic brakes.
- Dry Boiling Point: 325°C
- Wet Boiling Point: 204°C
- DOT Rating: 4
3. AP Racing Radi-Cal R2
One of the major players in motorsport braking systems, AP Racing offer a complete range of brake fluid variants that have been specifically designed for motorsport. With a high dry boiling point that is suitable for everything from standard discs through to carbon or ceramic discs, the Radi-Cal R2 brake fluid is a popular choice for many teams and drivers throughout motorsport.
- Dry Boiling Point: 312°C
- Wet Boiling Point: 204°C
- DOT Rating: 4
4. Millers Oils 300 Plus
As effective on the road as it is on the track, the 300 Plus racing brake fluid from Millers Oils is capable of withstanding the high demands of motorsport. Used in many modern high performance brake and clutch systems, this particular brake fluid has a high level of resistance to vapour locking and offers a nice consistent brake pedal feel.
- Dry Boiling Point: Above 312°C
- Wet Boiling Point: Above 194°C
- DOT Rating: 4
5. Automec Silicone
Being one of the most popular silicone brake fluids, this particular fluid from Automec provides long lasting performance due to not being affected by moisture intake. As a result, you will have a more consistent pedal feel and the boiling point will remain at a similar level throughout the life of the fluid.
Being a silicone fluid also means that it is safer to use as it won’t damage paintwork should it end up being spilled or catch fire. However, it is worth mentioning that it should not be mixed with ordinary Glycol brake fluids, so a complete system flush is recommended.
- Dry Boiling Point: 260°C
- DOT Rating: 5
So, there you have it, our 5 most popular brake fluids. Be sure to check out the complete range of brake fluids that are available on our website for many more options. If you still have questions on which brake fluid is right for you, our helpful sales team are on hand to help point you in the right direction.