When it comes to choosing the right ratio, one more or less gear wheel tooth can really make a difference in terms of performance. From engine performance, to wear of the pinion, as well as the affect of the track’s grip on the choices to prepare a kart, thanks to Andrea Bossaglia, an IAME engineer, we have debunked some "paddock chatter" and deepened our knowledge in a field as articulated and fundamental as that of kart ratios.
THERE IS NO DIFFERENCE IN ENGINE PERFORMANCE USING TWO EQUAL RATIOS BUT WITH DIFFERENT GEAR WHEELS AND SPROCKETS
With the same ratio, it is the mass of the rotating parts (pinion, gear wheel and chain) that is different and affects engine performance. Let's compare, for example, the "pinion 10/gear wheel 89" and "pinion 9/gear wheel 80” pairs (where the numbers represent the number of teeth). With the same substantial ratio, the sprocket/gear wheel composition with fewer teeth causes the engine to behave as if the ratio is a little shorter, that is, the engine will have a minimum extra tendency to reach high revs quickly, thus obtaining more torque on the axle. In this case, acceleration will be preferred over top speed. The opposite is true for the pinion/gear wheel composition with more teeth: the ratio in this case will be slightly longer, bringing the engine to work at slightly lower speeds, preferring the top speed compared to acceleration coming out of a bend.
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