What is oil used for in a system? Trivial answer: it is used to brake. The oil is found inside the hydraulic pipes that connect the brake lever (pumping element) to the brake caliper. When we press on the lever, the oil transfers the force exerted to the two pistons, which push the pads against the disc and thus allow braking.
Why does this happen? This is possible thanks to the incompressibility characteristics of the oil. The main characteristic of oil is the boiling temperature and, if the heat inside the system exceeds the boiling point, it passes from the liquid state to the gaseous state, thus filling the system with air bubbles that no longer work. the brake works well (fluid fade). Very dangerous situation but it is a very rare hypothesis in the bike world, unless we squeeze out a system worse than a PRO from the Enduro World Series.
In the bike sector, 2 types of oil are used: DOT and mineral oil. Just to give some statistics, here are the main systems and the oil used:
- SRAM: Dot (new models with Minerale)
- SHIMANO: Mineral
- BCA: Doctor
- Magura: Mineral
- Hope: Dot
- Formula: Dot / Mineral
- Braking: Dot
- Hayes: Doctor
OIL DOT
The abbreviation DOT followed by a number (e.g. DOT 3-4, 5, 5.1 or 6) defines the “dry” boiling point (uncontaminated fluid taken directly from the container) and the “wet” boiling point (fluid after it has absorbed a certain amount of water). This is a synthetic glycol-based oil (except DOT5, which is silicone-based). DOT 6 is extreme fluid, used in the world of motors.
ADVANTAGES OF DOT OIL
- High Boiling Point: DOT brake fluid has a high boiling point;
- Greater availability: being an oil also used in the motorcycle/car sector, it can be found in any workshop. And with lower costs.
- There are no proprietary standards: being a regulated oil, there are no slightly different versions as in mineral oil.
- Low compressibility: DOT fluids have a low coefficient of compressibility improving brake modularity.
DISADVANTAGES OF DOT OIL
- It is corrosive: DOT fluids are acidic, they corrode metals and paints (and it is highly advisable to use gloves and goggles when bleeding);
- It is hygroscopic: unlike mineral, it tends to absorb humidity, lowering its performance if regular maintenance (purging) is not carried out;
- Greater maintenance: plan for more frequent purging. If a bike remains stationary for a long time, it will hardly be able to perform well without completely replacing the oil.
MINERAL OIL
This type of oil is not synthetic (mineral) obtained through particular refining. In this sector there are various branded oils with slightly different characteristics to be fully compatible with the proprietary brake model.
ADVANTAGES OF MINERAL OIL
- It is hydrophobic so it does not absorb moisture;
- The boiling point never changes;
- It is more stable over time and in different atmospheric conditions: a brake system with mineral oil can remain performing for years without the need for bleeding;
- It is not corrosive: mineral oil is not dangerous for skin and does not corrode metals/frames;
- Less polluting than DOT (easier to dispose of).
DISADVANTAGE OF MINERAL OIL
- There is no standardization and therefore many (for example the “Shimano Brake Fluid” or “Magua Royal Blood”);
- Cost: being a type of oil that often uses proprietary standards, it has higher costs.
CAN I USE DOT OIL ON A MINERAL BRAKE SYSTEM OR VICE VERSA?
Let's start by saying that DOT and mineral oil are absolutely not compatible, you cannot switch from one technology to another simply by changing the oil, otherwise you will ruin the system. Never use mineral oil on brakes that use DOT or vice versa. The two oils have different corrosion values, as well as properties, and the systems take this into account.
BCA'S THOUGHT
PROJECTED IMPACT
There is no one oil that is better than the other, as they have different characteristics. DOT certainly gives the systems greater modulability but requires more care and maintenance. Mineral oil allows you to go for years with good performance (characteristics highly appreciated in rentals) and often drier braking. And then, a small detail, it's not just a question of oil when we talk about braking but the construction quality of the brake is also involved.
