Top Speed of Yamaha XJ We can do a few simple calculations to calculate what the top speed of the bike should be in various gears and see if the claim is reasonable. The final drive is 5.67 to one overall in 5th gear, so the rear wheel is spinning 5.67 times slower than the motor. Thus if an engine speed of 10,500RPM is observed, the rear wheel is spinning at 10,500/5.67 = 1851.85RPM. But we want revs per hour, so multiply by 60, giving 111,111.11RPH. The wheel is 130/90 factory, and accounting for 5% squish height (pretty common for higher profile tires with the weight of bike and rider) the overall height of the wheel tire combo is the wheel diameter plus the twice the profile of the tire: 19" + 2*130mm*.90/(25.4mm/") = 28.21" tall Minus 5% is 26.80 inches. Circumference is then 26.80*3.14 = 84.20". In feet this is: 7.0167'. In miles this is: .0013289 miles. Thus for every revolution the bike travels roughly .001328 miles. So multiply the wheel revolutions per hour by the revolutions per mile and you get: 111,111*.001328 = 147.5MPH. If he were observing the redline top speed would correspond to period tests at about 141MPH. John Vitamvas 85 Maxim X - Haven't yet determined if it will pull redline in top gear; don't want to. ==== also ==== Actually I have much more than John does, but only have to check a chart I did up. This came about last July when Peter asked about the gearing for the various models. It did make me conclude the gearing is designed for around town use. In 2nd through 5th gear you can go from 20.4 mph to 50.3 mph and keep the revs between 3000 and 4000. Only in first would you shift at 4500 in order be at around 3000 in second. The main reason for my chart to figure out the gear set needed to decrease the final drive ratio while in 5th gear and reduce the revs from 5566 @70 to 4502 or roughly a 20% reduction. Overdrive anyone? An interesting point is the top speed at redline goes up to 160 mph. And at 11,500, the most I've pushed it, that would be 184 mph. Not likely it could pull that, but am sure 160 mph is obtainable. Now were there a reasonably priced method to modify the gear, I'd go for a 25% reduction in 5th and a 15% or so reduction to 4th gear. Or just shoehorn in a 6 spd gear set. Oh yeah, a more simple and accurate method to translate would be: RPM / final ratio * radius of tire (ft)* 2 * pi / 5280 *60 = mph You measure the radius from the center of the axle to the ground while sitting on the bike. This does not factor in this measurement increases as the angular momentum of the tire increases, but found the result multiplied by 1.03 does work. With what I plugged in redline in 5th is 129.49 mph and my stint at 11,500 would 148.91 and puts Travis at 135.96 mph. Might conclude that Travis's speedo reads high and mine low. Still, he did come close to burying it. Mine was at least another 5 mph tick's width past. Best be a real quick glance when doing around 150 mph or how does 220 feet per second sound. Can have some fun with that figure. With 20/20 vision what is the closest you can be and make out the plate, then figure how long it takes to read the plate, then realize why worry about someone making the plate out. Which brings us to Kenny's question... Why stay around to find out. Oh, and the top speed of the '88 FJ1200 was found to be 152 mph. Jeff "The Mountin Man" - '86 MaximX ==== also === gear ratios for XJ650 Primary drive: 1.62 1st gear: 2.187 2nd 1.500 3rd 1.152 4th .933 5th .812 output gear 1.361 middle gear 1.055 final gear 2.909 OR 1st = 15.291 2nd = 10.485 3rd = 8.065 4th = 6.524 5th = 5.679