I am not sure how much this translates into road biking, but it made a massive difference years ago when I raced mountain bikes. I raced in rain and muddy conditions at times. On one particular course there was a section of wet red dirt/clay. It stuck to my tires and didn't let go. Even when I hit dryer firmer ground the weight of my wet shoes and the mud laden tires were a major drag. Can we say that where the weight is carried matters perhaps more than the overall weight?