This formula is only the ratio of the length of the TT to the truck. When people ask how long of a TT can I tow, this is a good starting point. You may find a TT that weight wise, it is in limits. But when you get a longer TT, you can run into the tail wagging the dog so to speak. You still have to use the other measuerments to determine can I tow this. I ran into this on my first TT. I left the dealership and hit the freeway in Atlanta. About the time I hit 50 mph, my truck began to swing from side to side. Trying to drive under 45 in Atl. is scary, but the sway was scarier.