Originally Posted by
Iride01
But DOT 5.1 and DOT 4 are compatible. Who'd have thunk that DOT 5 and DOT 5.1 wouldn't be compatible? But DOT 5 as you say is silicone based and DOT 5.1 is glycol ester based.
I wonder why SRAM went with DOT fluids, given that they can be a skin irritation for some. And I have to wonder why they didn't go with DOT 5 since it is not considered hydrophilic. But I suppose there isn't much fluid in a bikes hydraulic system for water absorption to be an issue. But I've had vehicles with rust inside the steel brake lines that was an issue.
DOT fluid has more resistance to heat than mineral oil. Moreover, when water enters a DOT brake, its dissolved evenly on the fluid, so the chances of it boiling are few.
On a mineral oil system, if water gets on the system it tends to accumulate in the caliper because it's heavier. If it boils, you could suddenly find yourself without brakes.
You should change brake fluid regularly in either system.
I have bikes with SRAM and Shimano brakes and I prefer to wrench with Shimano because they're easier to bleed and I don't have to worry about corrosive fluids.
BTW, in theory DOT 3, 4 and 5.1are interchangeable. DOT 5 is not.
Avid / SRAM recommends DOT 4 or 5.1, so that's what I would use. Personally I always use Motul DOT 5.1 fluid.