Originally Posted by alcjphil

I can offer an anecdote. For what it is worth, a few years ago my friend and I started down a hill. We were both riding similar bikes, and identical wheels. However, I was riding on supple road tubeless tires and he was riding puncture resistant tires. He outweighed me by almost 20 pounds. We started the hill side by side at the same speed both sitting in about the same position on our bikes. One might think that the heavier rider would descend faster but I was about 50 meters ahead of him at the bottom of the 600 meter long hill.
Tires matter