I have a road bike with front suspension. In May, I'm doing a charity bike ride through the some mountain terrain and I've heard from others that a front suspension adds significantly to mechanical drag when climbing hills. Unfortunately, I can't lock out my front suspension, nor is it practical for me to find a another road bike to use on this ride.
I've thought about switching out the front fork for times I do rides with these types of climbs, but I'm not sure how much that would cost.