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Which fluid should I put in my hydraulic bicycle brakes?

Different hydraulic brake models use different types of hydraulic fluids. Here’s a table guide, followed by a long explanation of what, how and why if you are interested to learn and know more.
I wrote this article “in reverse” – first answering the frequently asked questions, and then providing in-detail explanations.
If you have any comments, questions, or you find any errors, please use this BikeGremlin forum thread.

Table Of Contents (T.O.C.):

  1. Which fluid for which brake model – table
    1.1. Buying recommendations
    . 1.1.1. DOT brake fluid
    . 1.1.2. Mineral hydraulic oil
    . 1.1.3. Red rubber grease
  2. DOT fluid and Mineral hydraulic oil don’t mix!
  3. DOT 3 vs DOT 4 vs DOT 5.1 vs DOT 5
    3.1. Mixing various types of DOT fluids
  4. Brake fluid standards and composition
    4.1. DOT brake fluid standards and composition
    4.2. Mineral hydraulic oil standards
  5. Brake fluid properties
    5.1. Boiling point
  6. Brake fluid compatibility table
  7. Mythbusting
    7.1. Mineral oil doesn’t absorb water so you needn’t change it
    7.2. DOT 5.1 absorbs water faster so it’s race-only
  8. Red rubber grease
  9. Sources and footnotes


1. Which fluid for which brake model – table

For brakes that use DOT fluid, you can use any DOT 4 fluid from automobile parts stores, petrol stations etc. For hydraulic mineral oil, Total LHM Plus (Amazon.de affiliate link) is very good and cheap.
Those are the fluids I’ve been using for years with no problems. For more details, read the following chapters below.

Note:
I do my best to keep the chart below up-to-date, but it’s safest to check the manufacturer’s instructions about the fluid type for your particular brake model.

DOT 4
fluid
Mineral
hydraulic
oil
Avid / SRAM
Bengal
Clarks
Formula
Giant
(depending on the model)
Giant
(depending on the model)
HayesMagura
HopeShimano
QuadTektro
DOT 4
fluid
Mineral
hydraulic
oil
Hydraulic brake fluid type according to brake model
Table 1


Change your brake fluid every 12 months. 24 months if you are feeling lazy and aren’t riding in a lot of rain, mud, freezing temps, or steep downhills.

That’s all you need to know. The rest is for the curious ones, those who want to know more or “have heard that…”

– T.O.C. –


1.1. Buying recommendations

I’ll be using Amazon affiliate links (’cause yachts won’t pay for themselves! 🙂 ), but you can find all this in local automobile lubricants and accessories stores, or even your local petrol stations.


1.1.1. DOT brake fluid – buying recommendation

Liqui Moly DOT 5.1 brake fluid. Liqui Moly DOT 4 has served me well for amateur motorcycle racing. DOT 5.1 is even better. However, know that any decent DOT 4 fluid will work just fine. It’s more important to change your brake fluid regularly, than it is to by some super-expensive fluid.

– T.O.C. –


1.1.2. Mineral hydraulic oil buying recommendation

No need to pay an arm and a leg for “Royal Blood” (that’s how Magura calls their mineral oil) or Shimano mineral oil and other marketing nonsense. What’s worked beautifully for me for years is Total LHM Plus mineral hydraulic oil (Amazon.de affiliate link).

An alternative available on Amazon.com (and, hence, in the US), is MANNOL LHM Plus (Amazon.com affiliate link). Based on its specs, it should work fine, but I haven’t personally used this oil.

In chapter “4.2. Mineral hydraulic oil standards” I’ve explained what LHM+ is (and why it’s good for the bicycle brakes designed to use mineral oil).

Note/disclaimer:
Based on the below-linked feedback (forum comments), LHM+ may not be an ideal choice if you ride at below -10 °C temperatures (it is a bit “thicker” than ideal at those temps and the brakes respond a bit slower than ideal).

Based on the information I have in general, I would say that even the “original” Shimano/Magura/etc. oil may not perform as well as DOT fluids in deep freezing temperatures. This is to a great degree because of how mineral-oil rubber seals behave when very cold, not necessarily because of the oil itself. I would say that mechanical brakes are probably the best option for the deep freezing temperatures.

– T.O.C. –


1.1.3. Red rubber grease buying recommendation

For an explanation about what this is and why you might need it, see chapter “8. Red rubber grease“. Now, if you decide to buy it thanks to that info (or in spite of it 🙂 ): Millers Oils 5196TB Red Rubber Grease (Amazon affiliate link).

– T.O.C. –


2. DOT fluid and Mineral hydraulic oil don’t mix!

Some brakes use a DOT 4-compatible brake fluid (details in chapter 3), while others use mineral hydraulic oil. Those two can’t be mixed!

If you use mineral oil with brakes designed for DOT fluid (or vice versa *1 ), brake rubber seals will swell and the brakes will not work very well (it rhymes! 🙂 ). **2

* Using DOT fluid with mineral oil brakes will cause more rubber seal swelling, because DOT fluid is more aggressive.

** For brakes designed for DOT fluid, if they’ve already worked (so the rubbers are soaked with DOT fluid), if you use mineral oil and realize that mistake right away, you can often save them by cleaning it all and re-lubing (re-soaking) with DOT fluid.

– T.O.C. –


3. DOT 3 vs DOT 4 vs DOT 5.1 vs DOT 5

The order (5.1 before 5) is deliberate.

These different “models” can be confusing. Let’s try to make some sense of it.

Briefly
For bicycles, with brakes designed for DOT brake fluid:
DOT 4 is great, DOT 5.1 is needlesly more expensive but good, while DOT 3 should be avoided (the last resort, to be replaced ASAP if you had to use it), and DOT 5 is not compatible and won’t work well.

DOT 5.1 ESP is a specially designed DOT 5.1 fluid for working with automobile ABS (and ESP).
“DOT 4+”, “DOT 4 Plus” and “Super DOT 4” are marketing terms for a “somewhat better” DOT 4 fluid that still doesn’t satisfy the DOT 5.1 standard.

For the in detail explanation – read on.

– T.O.C. –


3.1. Mixing various types of DOT fluids

In chapter 4 you can learn about the DOT fluid types and standards in more detail, if you wish to understand why I recommend this:

  • Systems designed for DOT 5 fluid (silicone-based) are not compatible with any other DOT fluid (all the others are glycol-based).
  • Systems designed for a given glycol-based DOT fluid can take any “higher” glycol-based DOT fluid. For example: a DOT 3 system (these are no longer made in this century) can take DOT 4, DOT 4+, or DOT 5.1 fluid.
  • If you don’t have an ABS and don’t ride in deep-sub-zero temperatures, you can use DOT 4 or DOT 4+ fluid even in a system designed for DOT 5.1 fluid (in my opinion and experience).

For a table overview, see chapter “6. Brake fluid compatibility table“.

– T.O.C. –


4. Brake fluid standards and composition


4.1. DOT brake fluid standards and composition

Standards

DOT brake fluids have been standardized and used for decades in the automobile industry. Here’s a brief overview of the standards:

  • DOT is the acronym of the US “Department Of Transportation.” DOT mark on a brake fluid designates standardised grades according to the US “Federal Motor Vehicle Safety Standards” (FMVSS).
  • US “Society of Automotive Engineers” (SAE) defines the DOT grades under J1703, J1704, and J1705 standards.
  • The “International Standards Organisation” (ISO) defines DOT classes 3, 4, 5.1, and 5 under the ISO 4925 standard.

Composition

DOT brake fluids consist of:

  • Solvent – from 60% to 90%.
    It is either silicone-based (DOT 5) or glycol-based (DOT 3, DOT 4, and DOT 5.1).
  • Lubricating agents – 5% to 30%.
  • Additives – 2% to 5%.
    Additives are corrosion inhibitors (preventing rust of any metal parts), and antioxidants (preventing solvent breakdown and deposit formation inside the brake system).

Here, we see the main difference between the DOT 5, and all the other DOT brake fluids – the solvent’s base. In chapter 5, you can read how their properties differ.

– T.O.C. –


4.2. Mineral hydraulic oil standards

Unlike DOT brake fluids which are standardised, with mineral oils the situation is a lot more “colourful.” Every bicycle hydraulic brake manufacturer sells “their own” mineral oil (the quotation marks are because I believe those oils are made by third party factories and just branded for the bike brake manufacturer). No specifications or standards are published, but marketing is rocking it – for example, Magura brands their oil as “Royal Blood.” 🙂

Fortunately, there is a somewhat standardised option of mineral hydraulic oils for old (“vintage”) Citroen cars. That works quite well with bicycle hydraulic brakes designed for mineral oil. Let me explain this “standard:”

In the late 60s (of the XX century), the French automobile manufacturer Citroen tried to standardise fluid for their hydraulic suspension automobiles. They required a higher viscosity and better lubrication compared to the existing DOT fluids.

  • The first liquid used for this purpose was LHV (French: Liquide Hydraulique Vegetal).
    Red-coloured. Basically a DOT fluid with a castor oil based thickener. It was hygroscopic and that led to corrosion inside the systems.
  • In 1964, the formula was improved, and we got a synthetic-based fluid, LHS (French: Liquide Hydraulique Synthetique).
    Red-coloured. This liquid too had problems with being hygroscopic (and with lower than ideal viscosity and lubrication).
  • In 1996, LHM (French: Liquide Hydraulique Minerale) came to the scene.
    Green-coloured. LHM is a mineral oil based fluid that has the optimal viscosity, provides enough lubrication, and is hygrophobic (didn’t mix with and repelled water).

The current version is the LHM+ (or “LHM Plus”). It is an improvement over the original LHM, but compatible with all the rubber seals designed for LHM. An example that’s worked very well for me in practice: Total LHM Plus (German Amazon.de affiliate link).

As far as I know, there is no ISO (or DIN) standard defining the LHM+ oil properties. However, I’ve noticed that LHM+ oils satisfy the following standards that are relevant for hydraulic fluids in general:

  • ISO 7308
  • DIN 51524

Some manufacturers today are making synthetic-based LHM+ fluids. They swear it is compatible with the mineral LHM+, only better in deep freezing temperatures (I haven’t yet tested this to confirm). An example: MANNOL LHM+ Fluid 8301 (Amazon.com affiliate link).

– T.O.C. –


5. Brake fluid properties

What are the most important properties and how do they differ?

Ideally, a brake fluid should possess the following properties:

  • Non-compressibility – Because compression means spungy brakes.
  • Low viscosity – it shouldn’t be thick, even at freezing temperatures (this is especially important for compatibility with ABS, but that part is less critical for bicycles).
  • Lubricity – Hydraulic systems are closed, and the brake fluid is the only lubricant present in the system.
  • Corrosion resistance – For protecting braking system components.
  • High boiling point – Once the brake fluid starts to boil and make bubbles, your brake lever becomes just a decorative ornament (you can squeeze it all the way to the bars with no braking power exerted on the caliper end). This is called “vapour locking.”
    This last “item” is further explained in chapter 5.1.

Before I explain the main differences between various brake fluids, I’ll start with the fact that mineral oil is hygrophobic, while most DOT fluids absorb water (i.e. they are hygroscopic).
One exception is the silicone-based DOT 5 (not to be mixed with the glycol-based DOT 5.1). DOT 5 fluid is not a champion when it comes to non-compressing. Basically, its only practical use is for conserving old-timer automobiles. For everything else, one should look at DOT 4 or DOT 5.1 fluids.

Here’s a brief table overview:

PropertyDOT 5DOT 3, 4 and 5.1LHM+
Base
(solvent)
SiliconeDOT 3: Glycol
DOT 4 and 5.1: Glycol ether and borate ester compounds
Mineral oil
Hygroscopic
(absorbs water)
NoYesNo
Damages paint
in contact
NoYesNo
ColourBlueFrom colourless to amberGreen
Various brake fluid properties
Table 2


For those riding in low temperatures, an important info is the viscosity at freezing temperatures (the lower, the better):

Brake fluid typeViscosity at −40 °CViscosity at 100 °C
DOT 3≤ 1500 mm2/s≥ 1.5 mm2/s
DOT 4≤ 1800 mm2/s≥ 1.5 mm2/s
DOT 4+≤ 750 mm2/s≥ 1.5 mm2/s
DOT 5.1
DOT 5.1 ESP ***3
≤ 900 mm2/s
≤ 750 mm2/s
≥ 1.5 mm2/s
≥ 1.5 mm2/s
DOT 5≤ 900 mm2/s≥ 1.5 mm2/s
LHM+≤ 1200 mm2/s≥ 6.5 mm2/s
Various DOT fluid type viscosity
Table 3


– T.O.C. –


5.1. Boiling point

When you brake, brakes transform your kinetic energy into heat (video: “Inertia, kinetic energy, and mass VS weight explained“). That heat eventually goes into the air, but before that happens, brake surfaces, pads, and brake fluid heat up.

When the brake fluid starts boiling, your brakes stop working. Boiling creates vapour bubbles that will compress instead of transferring breaking force when you pull on the brake lever (this is referred to as “vapor locking“). Therefore, it is desirable that the brake fluid has as high a boiling point as possible.

With hygroscopic brake fluids (glycol-based DOT fluids), another important property is the boiling point when the fluid has absorbed a certain percentage of water (which happens over time, since the brake system is not 100% hermetically sealed). We know that water boils at 100 °C (at atmospheric pressure), and therefore it will reduce the boil boint of a hygroscopic brake fluid.

The table below shows the boiling point stats for different brake fluid types:
Wet boiling point is defined as 3.7% volume of water in the brake fluid.

Brake fluid
type
Dry boiling pointWet boiling point
DOT 3205 °C140 °C
DOT 4230 °C155 °C
DOT 4+230 °C155 °C
DOT 5.1260 °C180 °C
DOT 5260 °C180 °C ****4
LHM+249 °C249 °C
Boiling points based on brake fluid type
Table 4


– T.O.C. –


6. Brake fluid compatibility table

If you haven’t figured out already, I really like table overviews. 🙂 They provide a quick and easy to use reference. So, at the cost of regurgitating the already provided info:
I know, this might look awful on a smartphone. 🙂

Compatible fluid:DOT 3DOT 4DOT 5.1DOT 5LHM+
Factory
recommendation
DOT 3XYesYesNoNo
DOT 4NoXYesNoNo
DOT 5.1NoMaybe3.1XNoNo
DOT 5NoNoNoXNo
LHM+NoNoNoNoX
Brake fluid compatibility
Table 5


– T.O.C. –


7. Mythbusting


7.1. Mineral oil doesn’t absorb water so you needn’t change it

An error I often hear is that mineral hydraulic oil needn’t be changed regularly because “it doesn’t absorb water so its boiling point doesn’t drop.” Why is this wrong? Here are some facts:

  • Mineral oil doesn’t absorb water nor does it mix with it.
  • Water gradually seeps into the braking system because it’s not 100% hermetically sealed.
  • Water is heavier than oil, and will end up at the lowest point, near the brake calipers.
  • Brake calipers are the spot where the brake fluid gets heated up mostly.
  • Water’s boiling point is only 100 °C.

Besides, dirt also enters the system (which is obvious when you change the fluid after a few years of not having changed it).

Do you now understand why I recommend regular brake fluid change, even if it is mineral oil?

– T.O.C. –


7.2. DOT 5.1 absorbs water faster so it’s race-only

It is true that DOT 5.1 fluid absorbs water faster than DOT 4 (and DOT 4 absorbs it faster than DOT 3). However, DOT 5.1 has a lot higher wet boiling point than DOT 4 fluid.

In addition to that, DOT 5.1 has lower viscosity at deep-freeze temperatures, which helps if you ride in the winter.

So, even if you wait for two years before replacing it, DOT 5.1 will most probably outperform DOT 4.

Yes, in my opinion (based on my experience), DOT 4 is good enough for bicycles (and motorcycles, for that matter). But DOT 5.1 is a superior product compared to DOT 4, even if you don’t replace your brake fluid “before every race.”

– T.O.C. –


8. Red rubber grease

If you live near the sea, or you ride a lot in the rain, and especially if you ride on “salty” winter roads – this might help you.

The part of the brake pistons that protrudes outside of the callipers is difficult to protect from rusting. If there’s a lot of water, especially salty water, brake fluid doesn’t help much in practice. On the other hand, “ordinary grease” will damage the piston seals if it comes in contact with them (this goes especially for callipers that use DOT fluid).

What is the red rubber grease?

It is a refined vegetable oil based grease, with non-soap bentonite clay thickener, and with added corrosion and oxidation inhibitors. It is made to be neutral in contact with rubber, and to resist being washed out by brake fluid.

Its NLGI hardness is usually between 2 and 3.

As its name says, it is red-coloured.
Note:
Not every red-coloured grease is the “red rubber grease.” For example, Valvoline makes a high-quality lithium-based grease that is red-coloured, but is not completely neutral in contact with brake calliper seals. Pay attention to this when shopping and double-check (most stores in Serbia will look at you as if you are asking for a spaceship part when you ask about the “red rubber grease” and in 99% of the cases they will sell you the first red grease they have in store).

You can smear a thin layer of red rubber grease over the brake piston side walls to allow them to slide freely and be protected from corrosion.

A shopping example (Amazon affiliate link): Millers Oils 5196TB Red Rubber Grease.


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– T.O.C. –


9. Sources and footnotes

Soruces:

Footnotes:

  1. * Using DOT fluid with mineral oil brakes will cause more rubber seal swelling, because DOT fluid is more aggressive. ↩︎
  2. ** For brakes designed for DOT fluid, if they’ve already worked (so the rubbers are soaked with DOT fluid), if you use mineral oil and realize that mistake right away, you can often save them by cleaning it all and re-lubing (re-soaking) with DOT fluid. ↩︎
  3. *** DOT 5.1 ESP is a specially designed DOT 5.1 fluid for working with automobile ABS (and ESP).
    “DOT 4+”, “DOT 4 Plus” and “Super DOT 4” are marketing terms for a “somewhat better” DOT 4 fluid that still doesn’t satisfy the DOT 5.1 standard. ↩︎
  4. **** DOT 5 fluid is hygrophobic, but moisture does enter the system over time and the given boiling point is the official information that I could find. ↩︎

If you have any comments, questions, or you find any errors, please use this BikeGremlin forum thread.

– T.O.C. –




Please use the BikeGremlin.net forum for any comments or questions.

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