How to select gearing for best ¼ mile performance.
Changing the final drive gear ratio is one of the easiest and cheapest modifications you can make to your motorcycle to increase acceleration. By changing this ratio, you essentially change the amount of torque you are putting to the ground. The more torque you have, the harder and faster the motorcycle will accelerate.
Why can’t we just change the gearing to give us the maximum amount of acceleration? Traction and leverage. The rear tire will reach a point where it can no longer hold the amount of torque you are trying to put to it. Soft compound drag tires are able to hold more torque and that is why they are used. Leverage pertains to the wheelbase and center of gravity of the motorcycle. The longer the swingarm and lower the bike, the more leverage the bike has to put more torque to the tire and keep the front wheel grounded. Anyone who has tried to launch hard with a stock height or stock wheelbase bike knows this. You can’t launch hard without the front wheel coming up. You need more leverage.
Let’s say we have a bike lowered and stretched 6” with a good sticky tire and a great track. The leverage is at a constant. Now, how do we choose our best gearing?
First, you must be able to lock the throttle in first gear. If you’re feathering the throttle through first gear or lock the throttle and the bike wheelies, you need to change to a taller ratio. (Smaller rear sprocket). Anytime the front tire is in the air, acceleration is being lost and time wasted.
Second, look at your 330’ ET more and your 60’ ET less. Most of your ET is made up in the first 330’. Your 1-2 and 2-3 shifts are often in this area of the track so you need to spend more time looking at it. Many racers focus on the 60’ ET to determine their gearing or how their launch was. Most haven’t even reached full throttle until after the 60’. Your 330’ time will give you a better indication on how gearing changes are affecting your ET. Play around with different rear sprockets to determine what combination gets you the best and most consistent 330’.
Third, make sure you are not shifting just before the finish line. This doesn’t affect your ET, but will affect your MPH. A slower MPH than normal may cause you to think something is going sour with your engine. ET racing can also become difficult if you are trying to shift gears while trying to determine where the rider in the other lane is.
Follow these simple steps and you can easily determine the best gearing for your ride.