My new to me 08 GL/Motor Trike with 12K miles gets only 30 mpg at 60 mph and in the high 20's at 70 mph. It has a new air filter and seems to run normally, but I expected better mileage. In my Prius, I keep the tires aired up more than the dealer recommends because I get better mileage. On the trike I have been running at 40 in the front and 24 in the rear as recommended. If I increase the rears to the high 20's would I get better mileage or just a harsher ride?
Gerald