I was following a semi last Summer at about a 3-second interval, hoping he would increase the interval without having to decrease my own speed. (I like a minimum 4 second following distance.) He dropped a "road gator" right in the middle of the lane. Those things stop incredibly quickly! Fortunately, I was able to avoid it. From my point of view, drafting is unacceptably risky.
Another reason not to draft large Semi's is the damage that occurs to your bumper hood and windshield from the debris that is picked up and thrown back by the rear tires on the trailer. So unless you enjoy spending money repainting your bumper and hood every few years and occasionally replacing the windshield don't draft. If you want to see how a vehicle was driven on the highway just take a look at the front clip for paint chips and the windshield. If the vehicle was driven at 55-60 mostly, there will be minimal paint damage. On the other hand if it looks like someone took at sand blaster to the bumpers, leading edge of the hood and windshield you can be sure you're looking at a vehicle that was driven in excess of 70-75 mph. A body guy pointed this out to me using a 308 Ferrari. He asked me how many miles do you think is on this car. I said 75-80K based on it's appearance. He said look at the odometer, it had around 40K miles on it. The owner like to take it out on the weekends and blast up and down the interstate in-excess of 75-80 mph he informed me. Shortly after that I dropped my highway speeds to a maximum of 65 mpg to limit paint damage and better fuel mileage. A small stone may not penetrate the clear coat at 55 mph but at 70 mph it will go all the way through to the bare metal.
Yeah, the coefficient of friction of a tire is the same, whether the tire is on the vehicle or not. Off the vehicle, the tire doesn't have any vehicle momentum to get rid, that would reduce its braking ability. Hey, keep on tailgating. It'll keep your reflexes & body tuned up.... unless you rear-end the semi or the road gator.
