Use rigid hydraulic brake tubing as much as possible and flexible hose only where necessary (to allow for suspension and caliper movement). Even the best flexible hose expands more under pressure than steel hydraulic tubing. Hose expansion gobbles up that limited and valuable pedal stroke.
Stock-type rubber flex hoses are OK to use, but Teflon-lined, stainless-steel braided hoses are best. They swell and expand less, giving a firmer pedal.
For tubing, use only steel hydraulic brake tubing conforming to SAE J524 specs. Use of anything else invites failure.
Inadequate tubing, especially plastic tubing, is subject to work-hardening, fatigue-cracking, heat damage, excessive corrosion (especially internally, where you can’t see it) and mechanical damage.
DO NOT ever use compression fittings or single flares in rigid brake tubing – use only proper fittings and double-flares (be they SAE or ISO – matched to your fittings, of course). AN or JIC fittings of appropriate quality and rating and from a reputable source are suitable for flex hoses and flex hose to rigid tube connections.
Most tube today is 3/16” or ¼”. 3/16” is stiffer, lighter, and easier to bend. It and its associated fittings are also the most common. ¼” has less internal friction (less resistant to fluid flow) and is easier to handle without damaging. Note that ¼” DOES NOT “provide more volume” to actuate the calipers more quickly. The MC piston’s bore and stroke determines the fluid volume displaced and therefore the stroke required applying the brakes. The tubing is sealed and full – its diameter has nothing to do with it (within reason) and you certainly won’t notice the difference between ¼” and 3/16”
Secure tubing to frame with proper size tube clamps to avoid possible fractures and to prevent fittings from loosening and leaking.
Use grommets or some other means to protect brake lines that pass through the frame.
Make sure fittings and connections are in good condition and are properly tightened. Check regularly
3/16” hard-line fittings are 3/8-24 thread, ¼” hard-line fittings are 7/16-24 thread.