I've been noticing that on hard *uphill* sprints out of the saddle the rear wheel is lifting up off the ground quite a bit. It feels like its getting an inch or two of air, and sometimes will jump right an inch or two as well. Anything above 800w at lower cadence (75rpm's) seems to cause it. It isn't an issue on flat sprints where I'm not leaning as far forward.
Am I just not smooth enough? Is it common and nothing to worry about? It doesn't feel dangerous, but it doesn't feel nice either.
It started when I sized down from a 58cm to a 56.5cm bike, however my crank-to-seat angles/distances are the same, but my bars are about 1.5" lower than before. New bike is 2.5lbs lighter, but I can't see that coming too much into play here.