Quote Originally Posted by 29arod
check out or call one of the brake vendors for verification.

"The smaller the tube, the more pressure it creates and the better the brake system will work. Disc brakes require about 1000 lbs of pressure and drums about 300 lbs pounds. Disc brake cars use 3/16” tubing and drum brake cars use ¼” tubing. If you are building a street rod that has front discs, the entire system is typically plumbed in 3/16” tube."
Not to belabor the point, but the vendor quote above is misleading because of the first sentence. On a higher system pressure a smaller tube is used due to the higher burst strength of the tube - less internal surface area for the pressure to affect leads to the tube being capable of carrying more pressure within its yield strength. That, however, does not mean that the system pressure is higher with the smaller tube. The tube is able to carry more pressure due to its dimension. Jack's explanation is right, IMO.