I don't know about Rosedale Chimney, but as you know Hardknott isn't a consistant climb. The first bit is tough and many people stop because they are in the red look up to the top and think "I can't get up this, I'm already blowing a gasket". In fact after the first steep bit it evens a out (well, it's less steep) and even gets a bit 'flatish' at one point before kicking up at a pair of hairpins just before the last gradient.
I might be making it sound easy, it might just be local knowledge, I don't reckon it's as tough as it's made out to be.