Brake pedal "feel" or firmness is the result of the compliance , or elasticity, of the brake system. A firm pedal feel is desirable because it transmits the most information about the conditions existing during braking. The bending of the brake pedal, stretching of the rudder cables, compression of the brake pads, flexing of the calipers, expansion of the brake lines and compression of the brake fluid all contribute to the overall "feel" of the system.  Of these factors the last two are the only ones we can reasonably change.

Compression of the brake fluid is primarily a result of tiny air bubbles in the brake fluid. These bubbles are so small they do not float  and remain dissolved in the fluid. The volume of the fluid is also a factor as the larger the compressed volume the lower the spring rate. Prior to replacing the brake fluid on my airplane I vacuum degas it by putting it in a tank and evacuating the air.  It is amazing how much foam evolves from the fluid. I then carefully use this de-aerated fluid in the brake system.

Expansion of the brake lines is the result of strain of the wall of the tube as a result of pressure induced stress. Stress can be calculated by dividing the pressure (~500 PSI) times the bore radius by the wall thickness. The stress divided my the modulus of the material is the strain. Small bore, thick walled and high modulus tubes will result in a stiffer system. Adding Vaigra to the brake fluid will have no effect.

Bottom line (NPI) is that metal is better than reinforced hose which is better than plastic. A well designed system will use 3/16"  stainless in hot and static areas, aluminum in cool static areas, stainless braided or Kevlar reinforced hose in flex areas (insulated in hot flex areas).  Brakes lines transmit pressure with only a very small transient flow so use small diameter tubing and hose to save weight and reduce the fluid volume.

I think it is time to start a new group consisting of people who believe it is OK to trust their safety to a pair of thin walled plastic tubes. These folks can then attend conventions with people with similar beliefs. People who believe that earth is flat, that the Apollo missions never went to the moon, that the earth is 6,000 years old or that Al Gore invented the internet. The common thread is that all these people firmly hold their beliefs in the face of  overwhelming factual, empirical and  analytical evidence.

I have said it before and say it again, " Nylaflow " should not be used as brake hydraulic tubing. It lacks in mechanical strength, thermal performance and chemical resistance. The time spent replacing it with proper hose and hard line will likely be less then the time spent on the repair when it fails.

To all you Nylaflow Flat Earth Hollywood Moon Landing Society members,  repent now or regret later!

Regards
Brent Regan