read this.. its from another site:
Posted: Tue Dec 07, 2004 4:36 pm Post subject:
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Ronn, you are correct in that the use of a single rubber line and a splitting the line at the lowest point is primarily a cost concern. Period.
Two separate lines provide a large volume of fluid. This has the advantage of a greater thermal mass to dissipate heat generated by braking.
The effort and lever movement are proportional to the relative volumes of the brake pistons to the master cylinder piston. The meager length of the lines negates any affect the volume has on lever action. Also the slight changes in force due to the bends of a “banjo†bolt versus a straight connection are more than likely minimal.
Brake fluid is essentially an incompressible fluid, (any real fluid can be compressed if you can measure things finely enough, but outside a lab we can assume fresh brake fluid is incompressible.), meaning that what ever you do at one end is transferred to the other end just as if it were a solid connection. There is an opportunity for mechanical/hydraulic advantage since you can vary the sizes of the cylinders and the cam at the lever.
The easiest way to look at this is like you may have in third or forth grade science class when discussing levers. The hard part comes in when we start adding real world affects to the equations. The fluid moves from one end to the other at very low rates, but at pretty high pressure. The reason to use two separate lines is so you can gain greater volume for the heat to work on. The trade off is a little less “feel†to the brake, or spongy feel over a single line to a split line. The best solution is completely straight, solid line with no turns anywhere and constant cross-section. Of course that cannot exist anywhere outside a lab.
Some of the real world affects are primarily as follows:
--Line material, (hard lines are best, over-braided harder plastic lines are better, the over-braid material really doesn’t matter as much as the internal diameter of the fluid line)
--Purity of the fluid, (no air or water)
--Line internal diameter, smaller means less volume per unit length which means the lever will need to move further with a given master cylinder size to caliper piston size ratio, but this offers a finer, or more positive “feel†to the brake over a larger diameter tube. The size of the tube is based on a trade off between friction and pressure front and economy. This is also one of the principle gains you get when changing from rubber to over-braided lines. The small diameter of most over-braided lines, (this is after all only an over-braid protecting the inner plastic tube from abrasion. The only differences between Kevlar over-braid and Stainless steel is really cosmetic and a small amount of weight. The over-braid provides no increased stiffness to the tube it wraps. DOT certified lines have over-braid encased in vinyl as well.) is the primary contributor to harder brake feel as well as a little less flex of the tube depending on the age of the rubber line.
--Next is the rotor material or more probably the stock stainless rotor is not the best material. Thermally it is not that uniformly stable and also holds heat better than cast iron. Mehanite being the best of the irons to use. Sure carbon-carbon brakes are used in racing but they only work once they are warm, hot actually. And they are fragile and expensive.
And at last brake pad material.
The best thing you can do for brakes is change from rubber lines to over-braided lines, then change the rotor material to Mehanite and a good match of brake pad material. And of course keep your fluid clean and fresh.
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Hope this helps
