This is what I don't quite understand. I always thought the downside of trailers was simply the resistance of the extra wheel. I can see that weight is weight, and is neither heavier nor lighter in either panniers or trailer, but the constant theme seems to be that trailers are fine until you start climbing. Why should that be, especially if resistance is actually marginal. Is it the positioning of the load behind the bike rather than on it, oe leverage, perhaps, from the weight in the trailer?

I'm confused.