brake hose and brake line size selection

[shanchan]

How can i select/decide which brake hose pipe(diameter etc) to use for my brake system. I need to know if there are any calculations required for this...
i have to use this with obp 0.625 inch dia master cylinder ??

[MCoach]

Select the lightest brake line available, as long as it is steel.

[onemaniac]

There's not much flow in brake lines, just need to hold the pressure.
-3 lines (= 3/16" OD) are probably the most common and easiest to find the fittings for.

[MCoach]

Originally posted by onemaniac:
There's not much flow in brake lines, just need to hold the pressure.
-3 lines (= 3/16" OD) are probably the most common and easiest to find the fittings for.

Bingo.

[shanchan]

is the diameter of the brake hose and brake line same??

[MCoach]

Slow down there.

Your topic post was unnecessary.

-3 refers to the AN size specification of the lines. This will encompass the fittings you need, the brake line and hoses that will match those fittings and accessories.

The diameter of the brake hose/line isn't that critical. -4 is also easily available for when -3 is not.

[Mostafa Moussa]

I want to know if there are companies that offer brake lines more than 40 inch length ? , I was searching for 50 inch and 130 inch brake lines but the maximum that I found was 40 in.

[Zac C]

25+ foot coils of brake line aren't difficult to find. just supply your own fittings and bobs your uncle.

[MOTO909]

It sounds like you are only looking at flexible stainless steel braided lines. What you should look into is using steel hardline between the front and rear of your car.

[DougMilliken]

It sounds like you are only looking at flexible stainless steel braided lines. What you should look into is using steel hardline between the front and rear of your car.
In USA this is cheap and available everywhere, at auto parts stores, along with the flaring tools and fittings. Used to repair rusted/damaged brake lines on street cars.

[Jonny Rochester]

For a race car, and especially for a small formula car, it is far easier to use flexible brake lines for the whole car. We use teflon hose with a steel braid and AN-3 fittings along the whole car. We don't have to design that part, it's just what everyone uses. You can join bits with T pieces or straight connectors. You just cable tie it to your chassis. For repair work, you just snip the cable ties and you can remove the brake system without having to bleed it or drip fluid. Hard steel lines would be a pain on a prototype car.

[Jay Lawrence]

Jonny, there are plenty of teams that use hard lines F/R with flex lines out to the calliper. Soft lines are easier but are also softer (i.e. more expandable). The hard lines can be a pain to route, but they are lighter, cheaper and offer more consistent pedal feel (no, I haven't quantified that last one unfortunately...). It just needs to be a part of the initial design rather than a last minute exercise

[NickFavazzo]

Not even, the hardline can go anywhere the braided line will go, it just cannot deal with relative movements.
Braided line from MC to Caliper is still good and offers ok pedal feel, after going to hardline, you wont go back, the difference is easily noticeable, and there are few downsides to it.

[Jonny Rochester]

But how do we measure this feel? We must be able to give a number to this feel (movement, pressure etc) to be able to teach this way of design.

[Claude Rouelle]

1. Have look at Dash 2 or Dash 3 Brake line specifications. Calculate how much for example 0.01 mm of brake line diameter change will change the rear brake line volume. Divided this volume by the rear brake master cylinder section. Multiply that stroke by the brake pedal ratio.....

2. Car on stands but wheels off. Ask the driver to push the hard (but normal) way on the brake pedal. Using your vernier measure how much the 2 parts of the brake caliper (the open window where you slide the brake pads) moves away from each other. Also measure the movement of the caliper body Vs the upright.

3. Put a micrometer near the master cylinder attachment point on the chassis and ask the driver to push on the brake pedal.

How much is the driver brake pedal force used to slow down the car and how much is used to fight compliance?

And there many other sources of compliance in the brakes....

[Tim.Wright]

An easier way to quanify it would be to attach 1m of brake line to the master cylinder and block the free end. fill the system with fluid and operate the master cylinder by hanging 20kg off a lever. Measure the amount of lever movement and from this you can calculate the volumetric loss per meter of brake line for both the solid line and the flexible lines.

I'm a fan of solid lines. Cheaper, lighter, stiffer. In my opinion you need a damn good reason NOT to use them on non moving parts.

[Claude Rouelle]

If you use Tim (smart) test do not forget to make sure the 1 m brake line has no air in it ....:) .