[Closed] dot oils....

yes to do with technical stuff you need not concern yourself with [ I have forgotten boiling point and water absorption rate iirc]

I thought Dot 3 & 4 = 5.1

and you should never mix those three with Dot 5??

NEVER use dot 5, dot 5 will KILL your brakes. Dot 5.1 and Dot 4 are safe to run (in Hopes at least) but they are not the same, you should try to avoid running brake lines with mixed fluids. Generally the cheaper Dot 5.1 has a higher dry/wet boiling temp than cheaper dot 4. However the really good stuff (Motul 600, Castrol SRF, ATE Super Blue) is Dot 4.

If this was a question about a car with ABS then you would need Dot5.1.
But its not, and Dot 4 will be fine.
Although you could use Dot 5 silicone; its a funny purple colour, is OK for Harley Davidsons and does not strip paint (like Dot 3, 4 & 5.1 do).

Although you could use Dot 5 silicone; its a funny purple colour, is OK for Harley Davidsons and does not strip paint

Noooooooooooooo DO NOT PUT DOT 5 in your brakes!

I use DOT 4 as its more plentyful to swipe some fresh stuff from work (lots of hill climb cars get built up there, so its pretty good stuff).

Although I wish all bike brakes were mineral, as had (with other peoples bikes) literally dozens of spills and leaks to deal with bare hands and nowhere to clean them = buggered skin (or worse) in remote places. VS. mineral which you could practically bath in and survive.