Top up or down I get 20-21mpg in a JLU. I would think a hard top would be more aerodynamic but considering a Wrangler is a heavy brick on wheels it's going to be negligible. If we were talking about a lightweight Prius with a small engine there would be a noticeable difference. If fuel costs are a concern then I'd be more worried about oil prices reported by OPIS. Fuel prices go through cycles and one day it will cost $100 to fill the tank again during one of those cycles.