We get a lot of questions regarding which oil type to use, so let me explain the differences between the two to help you decide.
Both DOT (this stands for Department of Transport, who set the standards) 4 and 5.1 are glycol-based fluids, meaning that are compatible with one another.
Somer brakes will come with DOT 4 as standard, and often the brakes and manual will usually recommend to only use DOT 4 (mainly on slightly older model brakes). However, DOT 5.1 is fully compatible with brakes that use DOT 4 oil and is included as standard by some manufacturers (especially more recently). Other manufacturers choose to use mineral oils in their brakes, but I will talk about this another time.
So what’s the difference?
The main difference between the two is that DOT 5.1 is a higher performing oil with a higher boiling point and improved heat resistance, meaning that it will perform better under heavy and/or prolonged braking.
Which type do I need?
Most people choose to use DOT 5.1, even if their brakes came with DOT 4 as standard. This is to take advantage of the improved performance due to better heat handling, however under normal riding conditions, both types will work just fine, so it’s a matter of preference.
Make sure you do not ever use DOT 5 (not 5.1) fluid in your brakes unless specifically instructed to do so by the manufacturer. Under no circumstances mix DOT 5 with any other DOT fluid (5.1 is fine). This is due to a completely different make up and is not compatible with other DOT based fluids such as DOT 4 or DOT 5.1.
Need more help?
If you have any questions about which fluid to pick, please don’t hesitate to let us know.