DOT 5.1 vs. DOT 4

[MWEISSEN]

What is the difference between DOT 5.1 brake fluid and DOT 4?  KTM recommends DOT 5.1 in their manual, but I can't find ANY of it in stock at local shops (including two KTM shops!). 

 

[Layton]

If I remember right they have different boiling points.

You can mix DOT 5.1 and DOT 4. Just don't mix DOT 5 with anything.

Most of the riders that I know are using DOT 4 in the KTM's.