I have told several people that if they want to only save fuel by riding a motorcycle that they really need a Honda Civic!
The costs of replacing tires compared to a car is where the money loss is. The BMW I have is supposed to have Radial tires. The cost of a motorcycle tire is about the same as a car but less 2 of course. $125 dollars plus mounting the tires. I do all my own to keep the price down.
Radial tires are getting better for motorcycles. When first manufactured the limit was 5000 miles. I have worn out tires in 10,000 miles. Now there is this idea of a dual compound tire which wears longer in the center of the tires.
I have ridden over 139,000 miles on the BMW K 1100 RS that I have had since July of 2007. With a radial tire the mileage is above 50 mpg. However I use bias tires, rear lasts 17000 miles and the front to 20,000 miles.
However I also have tried a Fitch catalyst. Good for 250,000 miles, it is dropped in the gas tank. The previous K bike the mileage jumped from 45 mpg to 55! But then the computer "adjusted" and mileage again was at 45.
The Fitch is claimed to upgrade the fuel in the tank. Putting in regular will raise the octane to the middle grade. I try to use premium fuel with the main gas stations I use is BP. However the fuel changes for winter and of course the mileage drops due to the change as well as the engine doesn't warm up.
Take care! gas is cheap compared to medical or accidents!
Tim Lindstrom
Columbia Heights, MN
1995 BMW K1100RS, 162,300+ miles