I was just wondering what kind of brake fluid for racing was being used on peoples bikes. Thanks, Henry
I use a can of dot4 I bought from NAPA 4-5 years ago. (hate to waste it) I am wondering what the late braking guys use also. I have seen some high $ stuff they use in cars with a higher boiling point, but boiling fluid doesnt seem to be a problem on bikes... Anyone use dot5? I know you're not "supposed" to use it in a system made for dot 3 or 4 but...
Brake fluid is hydrophillic (it absorbs water) when it gets hot it absorbs even more water. Generally the higher the boiling point the more hydrophilic it is and the lower the wet boiling point. Had some REAL high temp brake fluid that was only good for about 24 hours after opening bottle. DOT5 is silicone based(so as not to absorb water) and will destroy seals in system designed for Dot3/4 DOT 5.1 is also silicone based I beleive (has similar properties to DOT5)can be used in DOT3/4 systems but the stuff I have seen does not have as high of boiling point and that is what is needed for racing.
FYI the correct term is "hygroscopic." Hygroscopic means that it absorbs water from the atmosphere. Hydrophilic means it dissolves IN water. No. DOT 5.1 is a glycol-based fluid like DOT 4. It is not silicone-based. DOT 5.1 was developed specifically for ABS braking systems. It is substantially lighter viscosity than DOT 4. It can be used in DOT 4 systems, but it's probably not a good idea. Having said that, some Ducatis specify it for their brake systems; however: It gets very confusing because in Europe DOT 5.1 is just called DOT 5. There have been a few too many people who have dumped US silicone-based DOT 5 into their DOT 5.1 systems because of this labelling inconsistency. FWIW I have found the Motul RBF600 fluid to have the best balance between high boiling point and moisture avidity.
S&S thanks I couldn't remember the term then my Latin not Greek kicked in and I went with what popped in my head thanks for the correct term hygroscopic. Just out of curiosity do you know how good the boiling points are for the 5.1 better worse than DOT4 and does it absorb water?
I agree that Castrol SRF is the best brake fluid out there. I used to use it when I raced cars. I am switching to Castrol SRF from Motul RBF600 because the RBF600 is extremely hygroscopic. Much more so than Castrol SRF or ATE Super Blue. The concern I have is that the smallest container you can buy Castrol SRF in is a liter can. The can will last the whole season. Are there any issues with the can cap letting mositure into the can? Scott
DOT 5.1 is a standard glycol/alcohol brake fluid, so it absorbs water just as well as a DOT 4. Dry boiling points for standard DOT 4 and DOT 5.1 are about the same. Wet boiling points for DOT 5.1 are generally slightly higher than for standard DOT 4. DOT 4 "racing" fluid like Motul RBF600 have substantially higher boiling points, both wet and dry, than DOT 5.1.
