When SHOULD you shift gears?

Experienced drivers feel it, beginners don’t. If you are beginning shifter kart racing and are wondering what is the best rpm to shift gears, this article is an explanation that may help you.

When you open the throttle to accelerate off a turn, you feel the effect of engine horsepower pushing you forward. The more horsepower the engine produces at a given rpm the more force is created to push the kart forward with you sitting in it. The fastest overall acceleration for a given engine occurs when the rpms are kept in the rpm range where the average engine horsepower is the greatest. The gear box allows the driver to select the range that does this.

The power curve of a typical 2-stroke shifter engine forms an arch when power is plotted against RPM as this chart. When accelerating through a gear, the engine rpm will climb from below the peak horsepower rpm to somewhere above the peak horsepower rpm. The general rule then is to up shift up to the next gear such that power output of the engine is the same before and after the shift. That will apply the most average power to the rear wheels. If the shift is made too early the rpm will drop to a level where the engine has less power available than the power available at the rpm shifted from.

If the shift is made too late the rpm will drop to a level where the engine has more power available than the power at the rpm shifted from. In either case the engine will spend time at rpms that produce less power than is available and that reduces the average power applied to the rear wheels.

Now, how does this feel? A late shift gives the feel of greater acceleration after the shift is made. An early shift gives the feel of a slight hesitation of bog after the shift before the engine pulls hard again. A perfect shift feels like the kart accelerates the same before and after the shift. And that is how experienced drivers feel it.

For more detailed information about SRS Shifter Kart engine recommendations, call us at 903-769-4140.