Z1OwnersClub GB

Ah that same old question! I have rad most of the correspondence on what brake fluid to use on my bike.
The master cylinder cap clearly stated DOT 3.
I have changed all the parts in the callipers and cleaned out the master cylinders with new rubbers where needed. The brake hoses are also new.
So would it not make sense to stick with DOT 3 as specified.
I'm not looking for anything more than how the bike should have performed originally.

Dot 3 and 4 are basically the same but 4 has a higher temp rating.
There won't be any detectable functional difference between the two.
You could use dot 5 if all the brake system is fresh with no trace of old fluid as it is silicone based and cannot be mixed with the others.

DOT 3, 4 or 5.1 will all work perfectly well. The higher the number, the higher the boiling point of the fluid.

Back in the day, you pretty much only had DOT 3 to play with. The warning was to stop mooses using engine oil (seen it done) or similar in the brake systems. I run 5.1 in my Z650 now

As said, stay away from DOT5 though - that is a different animal and does not mix with other brake fluids.