I just got finished ordering some more brake fluid for our race team. They are really sold on this one brand and now refuse to use any other. Its kinda pricey when compared to my old favorite Motul RBF600, but after doing a little research, I think I figured out why. Below is a chart comparing Dry vs. Wet Boiling Points.
DOT 3 Standards - 401F / 284F
DOT 4 Standards - 446F / 311F
DOT 5 Standards - 500F / 356F
When it comes to the highest boiling points, Wildwood seems to be one of the leaders.
Wildwood EXP 600 - 626F / 417F
GS 610 - 610F / 421F
Brembo LCF600 - 601F / 399F
Motul RBF600 - 593F / 420F
Castrol SRF - 590F / 518F
AP Super 600 - 590F / 410F
Ferodo Racing (DOT 4) - 572F / NA (couldnt find data)
When looking at bang for the buck it seems that my favorite, Motul RBF600 is the clear winner (your price may vary).
Motul RBF600 - $12.95 / 500cc - $0.0259 per cc
AP Super 600 - $16.95 / 500cc - $0.0339
Ferodo Racing (DOT 4) - $22.95 / 500cc - $0.0459
Wildwood EXP 600 - $18.75 / 355cc - $0.0528
Castrol SRF - $64.50 / 1000cc - $0.0645
Brembo LCF600 - $64.50 / 1000cc - $0.0645
GS 610 - $39.95 / 473cc - $0.0845
So, whats the big deal? All of them have to have a similar boiling point, right? Sure, when your talking about the Dry boiling point. For the most part, all of them are even pretty close in their Wet boiling points as well. All except one, that is. There is where the difference is not only obvious, but why the team demands one brand over all others. Castrol SRF. Still, is SRF really worth TWO and a HALF TIMES the cost of Motul? As far as the riders on the team are concerned, yes. It is understandable that brake fluid would be an issue for a eight hour endurance race where one would be repeatedly slowing down from 150+ MPH speeds, lap after lap, but is it worth getting for normal street use? After all, there is no way one would even come close to heating up the brake fluid like an endurance racer. IMHO... yes.
The aspect of a race bike heating up the fluid might be true, but it boils down (pun intended) to the absorbing of moisture. Though a race bike will have to deal with moisture by the heating up of the brake fluid, is not because the fluid is breaking down and releasing moisture. Remember, brake systems absorb moisture. They dont create it. From what I have read, moisture can get into the brake system by numerous methods. Even through the rubber of your brake lines. You might have stainless steel braided lines, but what are these little braided lines wrapped around? All braided lines do is all but eliminate the expansion of the brake line itself. Hardly a barrier from moisture. Not to mention those rubber seals in the calipers, master cylinder and even the reservoir cap itself.
So, for the average street rider, heating up the fluid is not really as much of an issue as it is for a racer and moisture isnt that big of a deal, right? That is to a degree (another pun). Time is the enemy of the street rider. We will change out the brake fluid on the race bikes many times over the course of one season, but how often does the average street rider change his brake fluid? Once a year? Only when they buy new lines? Just adding some fluid while bleeding the lines does not count. Im talking about completely flushing out the lines then adding new fluid.
It only takes a couple of months before the boiling point of your fluid is a lot closer to the Wet than it is to the Dry. The fluid will be constantly getting moisture in it from the time you pour it in. How much may vary, but the end results are the same. If the brake fluid has a lower wet boiling point, the absorbed moisture will become an issue a lot faster then with a fluid that has a higher wet boiling point. This might not become apparent when cruising to the local Sonic, but it would be something you would not want to become aware of during a spirited ride on some back highway or in the shut down area of your local dragstrip.
If your brake fluid is been in your system for a while, then it is a given that it will have moisture in it. If you had the choice, which would you feel more comfortable with in your reservoir? Some DOT 4 fluid you bought at Wal-Mart that starts overheating at around 300F or would you prefer the extra buffer that an additional 200+F gives you as you are approaching that apex thats posted at 20 MPH (and your definitely over cooking it)? Ah, but there is a couple of downsides. Castrol SRF only comes in one liter cans and at over $60 a can. The other is that they HIGHLY RECOMMEND that you completely drain the system before putting in the SRF. Im guessing its mostly due to any of the remaining old fluid reducing the performance and of course, so youll use more SRF. Still, its always best to flush than it is to simply refill. Doesnt matter if your changing brands or not.
The upside is that because of its packaging. SRF comes in a metal can with two tops vs. a plastic bottle (which is actually absorbing moisture while sitting on the store shelf). The metal can will absorb far less moisture while sitting on your garage shelf. Even better yet, after you talk about the difference (and you will, I promise), all your riding buddies will be wanting some (of yours, of course). So wether you sell it or give it away, odds are that it wont be sitting on your shelf for the next two years. Our first can lasted about five months.
I now run SRF in my 10R and for those that have ridden with me, they can tell you that Im not hard on brakes. Mostly due to the fact that I ride like a wuss. On the other hand, they will also tell you that I do the distance. If I aint gonna be doing 250+ miles during the day's ride, I wont bother hitting the starter button. Even being a wuss, 250 miles of back highways does not only give my shift foot exercise, it also works out my right hand as well. Because ever time I roll it on, eventually Im gonna be grabbing a handful of lever. The 10Rs brakes are great to start with (especially after removing those damn metal plates behind the pads and putting braided lines on) , but knowing that every time (and I do mean EVERY TIME!) I grab that lever and I am almost startled over its grip... well, its just the way I like it. Reliable and constant. From the first time I pull on that lever to the last time when I pull back into my garage.
I will have to admit, on VERY RARE occasions, there were times I thought my pads were going out or at least getting glazed. Scuffing my pads and wiping the rotors became a ritual in my garage and only with little success. So did getting out the MightVac and bleeding the lines. After switching to SRF, it seems like those rituals are all but forgotten. Sure, Ill do em every once and a while, but that's only because I am bored and at that time I couldnt afford any of those high dollar aftermarket goodies that I could be putting on instead.
Now if I could just get Castrol to send me a free case for this shameless plug, Id be happy. Yeah, I know... wishful thinking. Still, after reading how so many folks have spent big bucks to make sure they have the very best of pads, lines and even rotors, it amazes me that when it comes to the most important part of the system, the part that makes all those high dollar components work... they settle for something that is just good. When a complete set of Perfomance Friction (or like brand)front pads for my 10R cost more than a liter of SRF, it just really doesn't make sense to skimp out on the fluid. If a wuss rider like me can REALLY tell the difference, imaging what you serious riders will be able to tell. Youll be surprised. No matter which category you might fall into.
One last note... DOT 5 fluid is basically worthless. The silicone in DOT 5 is slightly more compressible than glycol fluid. It has a higher wet boiling point because it DOES NOT absorb moisture. Silicone fluids are NOT hydroscopic, meaning that they will not absorb moisture. This is DOT 5s downfall. As the brake system produces moisture, a conventional brake fluid will absorb it but a silicone fluid WILL NOT. The moisture is still in the system but instead of absorbing (mixing) into the brake fluid (admittedly reducing its boiling point), it just sits there in little water pockets waiting for the brake system to get hot so that it can vaporize. Even a well soaked brake fluid will have a higher boiling point than water and even water has a higher viscosity that AIR! Of course, its also not recommended for use in most bikes anyway.
Naturally, this is just my opinion and of course, I could care less what you think.