Brake line size?

[Zachalanche]

I need to be educated on brake line sizing. I am basically building my brake system from scrtach. I'm running dual master cylinders and have 4 piston calipers all the way around. is there reason or benefit to using larger than 3/16 brake line?

[jpgolf14]

I need to be educated on brake line sizing. I am basically building my brake system from scrtach. I'm running dual master cylinders and have 4 piston calipers all the way around. is there reason or benefit to using larger than 3/16 brake line?

3/16" is what all cars use these days. You really want the smallest lines possible that still can move enough fluid. The smaller the line, the less flex for the same wall thickness. Its a balance between line flex and friction in the fluid. I would use 3/16" for everything.

[Zachalanche]

3/16" is what all cars use these days. You really want the smallest lines possible that still can move enough fluid. The smaller the line, the less flex for the same wall thickness. Its a balance between line flex and friction in the fluid. I would use 3/16" for everything.

Thanks.

so to feed my curiosity, whats the tradeoff? I assume larger tubing has less pressure loss and would allow for less pedal force, but with that would come more line flex. is that right? Just curious what applications the larger tubing would be for.

[jpgolf14]

Thanks.

so to feed my curiosity, whats the tradeoff? I assume larger tubing has less pressure loss and would allow for less pedal force, but with that would come more line flex. is that right? Just curious what applications the larger tubing would be for.

In the old days they used 1/4" for rear drums. I drums require more fluid as they don't sit as the shoes don't sit as close to the drum as pads sit to your rotor in a disc brake setup. More fluid means, the fluid moves more in the line. The velocity of the fluid through the line would likely be very high, especially during a panic stop. As fluid moves, there is friction between the fluid and the tube walls. This is a system loss. With the larger 1/4" line, the fluid does not move as far and the ratio of cross-sectional area to circumference is much larger with the larger line. So you get more flow with less friction. However the larger line expands more, due to the nature of pressure. In the old days "nobody" cared about brake feel and nobody other than real racers, were out there beating the crap out of their cars on a road course. It just wasn't as important.

With disc brakes, there is much less fluid movement, so the friction losses are lower and you can get away with a smaller line. The side benefit, or more likely the prime benefit of the smaller line, is less flex in the tube.

Granted, we are way down in the weeds here. Almost every other consideration in a braking system is way more important than 3/16" vs 1/4" brake lines. I am confident of that opinion, even though I have not done any actual back to back testing.

John

[jpgolf14]

It also important to mention:

In general when analyzing hydraulic systems, its common to assume no pressure loss due to friction or line flexing. So in the general sense the size of the line does not matter at all. When I do all my normal brake calculations I assume no friction / no flex in the lines. The pressure at the master equals the pressure at caliper. The hydraulic system is a closed system and is self stabilizing.

The size of the line really doesn't matter if you ignore the factors in my previous post.

[Zachalanche]

ok. makes sense.

what about hydraulic clutches. with the significant increase in travel, and decrease in pressure, I would think a larger line would be required, what size is commonly used?

[jpgolf14]

ok. makes sense.

what about hydraulic clutches. with the significant increase in travel, and decrease in pressure, I would think a larger line would be required, what size is commonly used?

I am not sure about what is "normally" used, but I can tell you that I know the T5 and my T56 both use 1/4".