Trying to figure out brake problem with rear disc upgrade

[Apogee]

Originally Posted by PRRC

I would say that 1 problem with this set up your running is the 1/4 line to rear calipers. It's just to large of a diameter for a disc. set up.

Expansion due to pressure within a brake system is referred to as system compliance. All components have some compliance including calipers, hoses, hard lines, master cylinders, etc, however the goal is to typically minimize it as much as possible for the most responsive braking system possible. When comparing various components, rubber brake hoses are by far the largest contributors to system compliance, so if you have rubber brake hoses, it doesn't really matter what the other components are since their contribution is negligible.

If you want to look at the difference between 3/16" and 1/4" brake tubing, it's just a matter of comparing the hoop stresses and associated strain values. Assuming the wall thicknesses are the same (typically .028") and so is the tubing material, the 1/4" tube will expand 45% more than the 3/16" tubing if my math is correct. Considering how little the 3/16" tubing expands under pressure, 45% more than that is still a basically negligible IMHO.

On most street cars, I can't tell the difference at the pedal if a car has 3/16" or 1/4" tubing. If you had a car set up for track use that was right on the edge of locking up the rear tires at threshold braking and you made the swap from 1/4" to 3/16", I would hazard a guess that you might notice the difference, but nothing that a small crank on the ajdustable proporioning valve wouldn't solve. That said, if you were plumbing a car from scratch, I would run all 3/16" since less compliance is ultimately a good thing, even if you are splitting hairs.

Tobin
KORE3