Reducing tire cirumference, (either by reducing rim size or tire profile), is not "in the same vein" as reducing rear chain wheel size (correct but we are talking reducing rear tire size increases acceleration; no comment about the gearing) .
Reducing the rear chain wheel size reduces acceleration and, (inversely), increases top speed. It has no impact on handling (true, but who said anything about gearing affecting handing; we’re talking lowering the ride height by way of a smaller profile tire slowing the steering, in affect kicking out the front wheel a bit; small change but some may notice a difference).
Reducing rim size a half inch from 17" to 16.5", or reducing tire profile 5mm from 55mm to 50mm affects the handling characteristics of a motorcycle. It does not increase acceleration (smaller circumference will effectively reduce overall gearing) Reducing rim size or tire profile reduces tire circumference. Reducing tire circumference reduces the distance one complete tire rotation moves the bike forward, thereby reducing top speed (true, and at the same time lowering overall gearing, hence the lower speed for a given RPM).
Reducing rim size or tire profile also slightly reduces tire mass. This means that the engine can spin the tire a little faster (yes, called ACCELERATION). But because each spin of the slightly lighter, smaller tire moves the bike forward less distance, any increase in the change of tire rotation speed is offset by a decrease in forward motion. So, while engine rpm will increase slightly quicker due to the reduction in tire mass, the motorcycle won't accelerate quicker. Remember, "acceleration" is a change in velocity, not an increase in engine rpm(if you lower gearing you are raising RPM). With smaller and/or in-line 4 engines that have narrower power bands higher in the rpm range, getting to the power band quicker could inpact acceleration, but this isn't an issue with the 1098 L twin (gearing affect all bikes; the shorter stroke inline fours can rev higher pulling a lower overall gearing to a higher speed)
When measured with a radar gun there will probably be no measurable increase in acceleration with the Corsa III as compared to the Pro. In fact, depending on the amount of reduction in tire mass as compared to the reduction in tire circumference, and factoring in horsepower/torque characterists of the engine, reducing rim size and/or tire profile could reduce acceleration (disagree as already mentioned). If the reduction in tire mass is great when compared to the reduction in wheel circumference, (an unlikely scenario), then there will be an increase in acceleration. If, on the other hand, the decrease in tire mass is small when compared to the decrease in tire circumference, (a more likely scenario, especially when we're talking about a 5mm reduction in tire profile, which will have almost no impact on tire mass), then there will be either no change, or a decrease, in acceleration This is why when some go racing, they are really fast, and others seem to be really slow. You must have a basic understanding of the forces at work and how to make your bike quicker…. and better be able to stop quicker as well, cuz if you are going to go fast you better know how to stop!!!
Elton
