Mountain bike disc brake

Can You Use Car Brake Fluid In A Mountain Bike?

Disc brakes are typically associated with automobiles, but in recent times, more and more companies started producing mountain bikes with disc brake systems. Nowadays, virtually all off-road bicycles come with disc brakes.

Brake discs offer better durability than conventional v-brakes and can work effectively in different terrains and conditions. Although some All-terrain bikes use mechanical disc brakes, most use hydraulic disc brakes that utilize brake fluid. 

If you are a mountain cycling enthusiast, you understand the importance of having adequate and appropriate brake hydraulic fluid in your bicycle’s braking system. However, sometimes you may face a hydraulic fluid scarcity and wonder if you can use car brake liquid in your mountain bicycle.

The answer is Yes and No. Although it sounds confusing, It all boils down to braking fluid types and compatibility.

Modern mountain bikes use either mineral oil or DOT fluid, and it would be best to use the specific hydraulic fluid designed for your cycle. Otherwise, you might experience braking system issues such as a drop-in performance. Incompatibility such problems as braking fluid separation and pooling can occur when using mineral oil instead of DOT fluid and vice versa. 

Most braking system manufacturers tend to only allow for the use of one brake liquid type. For instance, Avid, Bengal, Clarks, Formula, Hope, and Quad only support DOT fluid, whereas Shimano, Tektro, and Magura companies support Mineral oil in their braking systems.

When it comes to DOT fluid, it is available in four different classes that include DOT 3, 4, 5, and 5.1. Depending on your mountain bike’s braking system, you can only use several or one particular DOT fluid type. However, since DOT braking fluids for vehicles and mountain bikes are standard in quality and composition, you can use your Car’s Dot fluid in your All-terrain bike so long as it’s the same variant or compactible. Simply put, it means if your car uses DOT 4 liquid, you can also use it on your bike’s DOT 4 or DOT 3/5.1 braking system.

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On the other hand, You cannot use Car mineral oil fluid and Mountain Bike mineral oil interchangeably. Unlike DOT fluid, mineral oil lacks standardized varieties, and you can’t know whether car mineral oil will have the same properties as the one made for all-terrain bikes. For this reason, it would be best to use brake fluid specifically made for your bike’s braking system. If you have a Shimano Mountain bicycle, kindly use Shimano bike brake liquid. 

What Brake Fluid Do I Need For My Mountain Bike?

The choice of braking fluid to use in your all-terrain bicycle depends on the manufacturer’s recommendations. Most braking systems typically contain instructional labels stating which brake liquid you should use.

However, since Mineral Oil and DOT oil have different properties, here is a comparison of the two braking fluids to help you decide which is better.

The Boiling Points

The most significant difference between these two braking fluid classes is their varying boiling points. Boiling points refer to the temperature levels required to vaporize the braking fluid within the braking system. 

When brake liquid starts to evaporate, it affects the hydraulic system and can lead to complete brake failure due to its conversion from an incompressible liquid to a compressible gas. DOT fluid and Mineral oil have dry and wet boiling points that refer to their boiling points when they lack and have additional moisture content. Brake fluids tend to have lower wet boiling points than dry boiling points. Mineral oils tend to have a higher boiling point than DOT Fluids. Dot 3, 4, 5, and 5.1 have increasing boiling points as the variant number increases, whereas Shimano and Juice Lubes have the highest BPs among the mineral oils.

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Recklessly mixing brake fluids can have detrimental consequences on your mountain bike’s braking system. You can use DOT 3, 4, and 5.1 fluid interchangeably but not with Dot 5 and mineral oils. On the other hand, different mineral oils such as LHM+, Magura, and Shimano offer limited compatibility when you use them interchangeably and may result in damages while also voiding your brakes’ warranty. These mineral oils aren’t compatible with any DOT oils, and it would be best to avoid mixing them entirely. Also, you cannot use Dot 5 liquid interchangeably with any other braking fluid.

Shelf Life

Since DOT braking fluid contains glycol, it tends to have a higher hygroscopic property, meaning it will begin absorbing moisture once you remove the manufacturer’s airtight seal. Since water can adversely affect the DOT liquid’s performance, it has a short shelf life of approximately 6-12 months. Mineral oil doesn’t absorb moisture because it is hydrophobic, and you can open and use it almost indefinitely.

Nonetheless, these two braking liquid options have varying benefits and drawbacks while also offering different performance and characteristics. So which one is best? According to a survey on, 61.54% of the voters stated they think mineral oil is best, whereas 38.46% chose DOT fluid.

Mountain Bike Brake Alternatives

At times, you may lack the mountain bicycle brake liquid recommended by the manufacturer, but you want to ride your bike. In such instances, it would be best you consider the following DOT fluid and Mineral oil alternatives.

Mineral Oil Alternatives 

When choosing mineral oil alternatives for your bike’s braking system, it would help if you considered a mineral oil with high fluidity and boiling point, such as the Total / Castrol LHM Plus Fluid. This oil serves as a hydraulic fluid in hydraulic-powered automobiles. Another excellent alternative is Fork cartridge oil.

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DOT Fluid alternatives

Since most DOT liquids can serve as each other’s substitute, kindly consider this option first before identifying other alternatives. You can use ethylene glycol antifreeze or soapy water as a DOT fluid alternative. However, these braking fluid options should come as an emergency solution and not for day-to-day use.

Depending on the brake fluid’s compatibility, you can comfortably use or entirely abstain from using your car’s braking fluid in your mountain bike. DOT fluids typically offer better interchangeability than mineral oils, but it’s always best to follow your bike manufacturer’s brake fluid recommendations as they help preserve braking components.

If you’re not sure what type of brake fluid is best for your mountain bike, it’s important to know the compatibility and performance of each.

DOT fluids typically offer better interchangeability than mineral oils but also have a shorter shelf life. Make sure that when using these substances as an emergency solution or in day-to-day use, they are compatible with one another.

Also make sure that if you choose to mix them (DOT 3 and 4) that their boiling points match up so there won’t be any corrosion on the braking system components due to different dry and wet boiling points.

And don’t forget! When choosing which brake liquid is best for your needs, consult manufacturer recommendations first before purchasing anything else – because what may work well for someone else, may not work well for you!