Tire series size questions...

What are the advantages, and dis-advantages from changing the series tire sizes on a 79 kz1000? Will my top speed decrease? Will my gas mileage decrease? Are there any advantages except looks?

current size: (front) 110/90/19, (rear) 130/90/17

new tire size: (front) 110/80/19, (rear) 130/80/17

80 series tires of the same width are smaller in diameter than 90 series tires. Your fuel economy will decrease because the smaller diameter tires will need to turn faster for the bike to run a given speed which will increase the engine rpm for that speed. Also, your top speed will decrease. Your speedometer error will increase as it will show you traveling faster than you really are. This problem already exists with most KZ speedos, but the smaller diameter tires will make it worse. Ed

650ed wrote: 80 series tires of the same width are smaller in diameter than 90 series tires. Your fuel economy will decrease because the smaller diameter tires will need to turn faster for the bike to run a given speed which will increase the engine rpm for that speed. Also, your top speed will decrease. Your speedometer error will increase as it will show you traveling faster than you really are. This problem already exists with most KZ speedos, but the smaller diameter tires will make it worse. Ed

Very good info… Any advantages?