Why are Euro gears bad for fuel mileage?

[inanecathode]

Gentalmen,  There has been some discussion here about primary drive gear ratios, and that the Euro 550's have a higher ratio than the US models. Is is fact? Has someone counted teeth on the primary drive gears to see what they are? Also it was said that SR500's have this taller primary ratio. I have a SR500, and a TT500, Both of these machines have a 2.56 gear ratio, that is 30 teeth on the crank gear, 77 teeth on the clutch gear. My Vision, an 83, has 33/73, whitch is 2.21, that gives higher overall gearing than a SR. One of the reasons the singles have a lower primary drive ratio is to spin the gear box faster to take some of load off the gear set, as you can gear them up with a smaller drive sprocket, difficult with a Vision.

  Ken G.

The tt and sr have different final drive ratios. The sprockets are different sizes. The vision has different primary drive ratios but the same final drive ratio. The reason being that for some reason yamaha decided that it was easier to modify the primary drive system than to go back and make different ring and pinion gears for the shaft drive, or different middle drive gears.

[Rick G]

They probably already had the primary gears in the parts bin. All shaft drive Yamahas of that vintage have the same final drive gears. Probably the same for the middle gears.