I'm a bit confused. Not the first time though. A tow bar is used to tow something behind. I doubt you're towing something with your bike, but you might be. I think you might be referring to a bike rack for a car. I don't know of any that attach to the seat post and with a dropper post, I'd never do that anyway. Sorry to be of no help, but can you clarify? This is what I think of as a tow bar.