faffi
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Norway
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Not quite sure I followed your intentions/questions, so please excuse me if what I will type here is not the information you wanted.
Final drive gearing is always the ratio for the final reduction. The total drive-train, from crank to wheel, can have multiple reductions, but mostly motorcycles have two or three reductions beside the gearbox. For instance, the the LS650 and 650 Vulcan S have two (crank/clutch and output shaft/rear wheel), my Virago 750 have three (crank/clutch, output/shaft and shaft/final drive), the Shadow two or three, depending on whether it has chain or shaft final drive.
The overall gearing is found by multiplying all the reductions. Note that some reductions can be negative, causing an overdrive condition, but usually this only found in the upper gear(s), not in the primary, secondary (if present) or final reduction.
Overall gearing, together with wheel circumference, determine how fast a bike (or car etc) can theoretically travel at the rev limiter/redline. The overall gearing will differ for each gear, and so will the maximum theoretical speed. The change in rpm will always be the same for any given gearbox when you go up or down a gear, regardless of what you do to the primary, secondary and/or final drive ratios. By that I mean if your engine drop from 8000 to 5500 rpm when upshifting from 1st to 2nd gear, it will always have the same drop, whatever you do to the final drive ratio, which is what we typically alter.
However, the speed you will attain at those revs will alter with the final drive ratio. So let us say you have a stock gearing allowing you to go 40 mph @ 8000 rpm in first, then it will do 58 mph in 2nd gear at 8000 rpm for the example above. Now, if you alter the final drive gearing so that you now hit 8 grand at 30 mph, 2nd gear will only do a bit under 44 mph at 8000 rpm. But just as 2nd would need 5500 rpm to do 40 mph with stock gearing, you will now need 5500 to do just 30 mph. The difference in maximum speed between first and second gear have dropped from 18 to a little under 14 mph with the gearing change.
Any gear reduction will improve torque reaching the rear wheel. Let is say you have a gearbox with a 3:1 ratio, where 1st is 3:1 and top gear is 1:1. This gives you 3 times as much potential torque at the rear wheel in first gear compared to top gear. Engines with wide spread of torque typically have wide ration gearboxes (2.5:1 or greater) while peaky engines tend to have narrow-ratio gearboxes (2:1 or less). This is because the former have power/torque to pull itself back up to higher revs despite big drops in rpm with each gear-change, whereas a peaky engine will "fall on its face" if rpm drop a lot. The irony is that you end up with a bike that will do well over 100 mph in 1st gear, with another 5 to go. This is a liability in town or if you want to tour two-up with luggage, going over steep mountains, but fine for race tracks.
Not sure if I managed to make sense of this at all. But most cars will have a 1:1 ratio between the engine and gearbox, while 1:1 used to be the most common ratio for top gear. Now, most cars - and many bikes - feature one or two overdrive gears. Overdrive only means that speed going out will be greater than the speed coming in. Or put it differently; the engine revs will drop with an overdrive. But the gearbox itself does not matter much - it is the overall gearing that matter. For instance, a vehicle with a 0.8:1 overdrive with an overall ratio of 2.5:1 must rev faster for any given speed than a vehicle with a 1.2:1 top gear with an overall ratio of 2:1. Provided similar wheel diameters.
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