Hi. Lots of opinions on this topic. Me, I would go to a deserted stretch of road, go about 30 mph, slam on the brakes and see if I could lock up all 4 tires. If all 4 tires don't lockup you don't have enough brakes. IMHO brakes and tires go hand in hand. Put some skinny bias plys on and see how easy the brakes lockup compared to a set of 60 series radials. It's my understanding that you get the shortest stopping distance by keeping the tires on the verge of lockup. Sooo if you can't lockup the tires then you don't know what the tires are capable of in terms of stopping power. If you can lockup all 4 tires then ( in my mind anyway) you've got enough brakes unless you upgrade the tires to the point where they overcome the brakes.
I've been trying to get the rear drum brakes ( 85 Monte Carlo rearend ) to lockup on my 38 Ford PU. The truck stops pretty good but I know it can be made better so that's something to work on this winter.
I have 255/15 70r tires on the back of the truck. My question is, does the large size make it harder to lockup the rear tire? It would seem like it would because of the slower drum rpm ( large dia tire ) which exposes less drum/shoe contact surface per road foot than a smaller dia tire. The tire also has more rotating mass. Also the contact patch of the bigger tire is naturally greater which makes it harder for the brakes to overcome the tire.
Well that's enough rambling for now.