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It takes torque to move a vehicle.
This torque fights the weight of the vehicle, the rolling resistance and the drag.
In lower gears, there is a fair multiplicator on the engine torque which is the reduction given by the gearbox.
Usually the reduction of the gearbox is 1 or above in top gear and the bike is geared to be able to hit its rev limiter in top gear or just about.
So basically, the engine is tuned to make full use of those several gears : very low rpm are not taken into account in the flywheel mass, bore to stroke ratio, alternator output, oil pump capacity (we are talking reliability here).
Why ?
Because of the weight !
You could have an engine wich would turn very low rpm hence be super efficient and yet not so useful on a vehicle like a bike.
Truck engine turn low rpm and are quite fuel efficient at the task that is theirs.
But the price they demand in return is weight, they are super heavy.
Their power to weight ratio is lame whereas their capacity to load is excellent (load being what they can carry).
Also, a small rev-range would mean massive gear ratio required (more weight) and stratospherical self braking ability.
My point is why mis-use an engine if you bought to big a one to start with ?
(250 all the way)
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