warrenIsAnIdiot said:#1. The rubber on the sole provides a soft cushioning to the veins and cappilaries in the feet not allowing for efficient blood flow. IOW the heart rate will not go up as efficiently as it should.
I have once tried using shoes with rubber soles and my speeds went down there...way down like 5mph on a 1hr ride. :o
😕 Perhaps if you were talking about a shoe with rubber on the inside of the sole, but even then, I do not think the effect on the circulation in the feet could have any difference on heart rate or cardiac output. You must have been using shoes with flexible rubber soles, as opposed to rigid soles with rubber on the outside to have that much effect on your speed.
What the OP asked is why road shoes could not have a surface with more traction on the outside of the sole, and not why the soles do not flex like walking shoes do. The answer is that unlike mountain bikers, most roadies do not get off the bike and walk any distance. Therefore, anything put on the shoe just to improve the ability to walk is unnecessary added weight. I was riding with a fellow last weekend who left his shoes clipped to his pedals when we were at a rest stop. I, on the other hand, like to go for long rides, but do not care about speed. I have mountain bike pedals and shoes on my hybrid, and will use them on my road bike when I get it.