When rubber lines expand, they cause an increase in the brake lever travel because more fluid occupies the lines. However, they do not cause any increase in lever pressure needed. The force required to balloon the lines is exactly the same as the force the expanded lines exert on the fluid. Those two forces cancel each other out.
I am trying to travel back in time to when I was sitting in physics class and this was all a lot fresher in my mind :mrgreen:
When I installed SS lines on my sport bike a lot changed, so some of the results I noticed may have been attributable to other parts of the system rather than just expansion. For instance 2 lines directly from the master cylinder to each caliper instead of a splitter, brand new brake fluid and of course the system was freshly bled.
All of that said, I went from all the braking you could ask for with 2 fingers to only needing 1 finger.
Doing some reading brought me to Poiseuille's law (
Hagen). Which essentially discusses friction within fluid traveling in a tube or pipe. This always exists, but my assertion would be that with the tube expanding and allowing the fluid to move in multiple directions you would have an increase in turbulence in the fluid and more friction causing a lose of force at the caliper.
Now, would that friction cause a perceptible loss? I'm not sure...but I'm still a big fan of SS lines.
What do you think Greywolf? Am I stretching? Attributing my improved braking to the wrong area? I do understand what you're saying about the forces cancelling out.