Just a tick over 35 mph trying to catch onto the draft of a tractor trailer.....I could've gone slightly (not much) faster, but I still had 10 miles left in my ride and didn't want to blow myself up completely. As it was, it took a few minutes to recover from that effort.....mainly since I was going around 23-25 mph behind him (we were all stopped for an accident, and I was behind the truck when we started going again), and then he started accelerating hard when he probably figured out what I was trying to do. It was a truck hauling cars, so he could see me pretty clearly. I started closing in at around 30 mph, then he shifted to another gear and accelerated more, and once I got up to around 35 mph, I threw in the towel and he kept going. I was a good 15 or so feet out of the draft, and I figured I wasn't going to catch it. Would've been fun to do so, though, and would've been cruising along at 40+ mph fairly comfortably if i was able to get in. Ah well.