Information About Gear Ratios

If you are viewing this page it is possible that you do not fully understand the science of gear ratios and what a change in gear ratios can bring to your bikes performance.  

 

1. Road vs Race Ratios

2. Nova Race Ratios

3. Adding An Extra Gear

4. Ratios For Road Racing MX Engines

 

1. Road vs Race Ratios

The ratio’s used in standard road bike engines do not all lend themselves for use in competition.  This is because the ratios have been optimized for a more relaxed style of riding, whereby the ratios are selected to compliment the torque output of the engine in the mid range, to achieve flexibility when riding on the road.  An engine tuned to ride on the track will produce peak power within a narrower band, higher up the rev range.  If the gear ratios are not adjusted, the engine revs will drop below the power band at each gear change, and therefore the motorcycle will not accelerate as fast as it could. 

 

2. Nova Race Ratios

All the Nova gearsets designed to replace the standard gears in modern sports bikes feature decreasing percentage drops between gears to fully utilize the torque and power characteristics of the engines when used on the track.  The gap between each gear gets progressively narrower and in many cases the percentage drop between bottom and top gear is less than that of the standard gear ratios.  For the same reasons listed above this helps to keep the engine working higher up the power band and allows the motorcycle to accelerate faster in every gear.  It must be noted however that a different final drive pairing may be required to achieve the same top speed.  A lower overall gap between first and top will increase acceleration but slightly higher final drive gearing may be required to optimise overall performance.  Basically don't necessarily use the same sprockets as everyone else on the grid is using!!

 

3. Adding An Extra Gear

Adding an extra gear onto the standard gearset improves the rideability of the engine by offering more choices of gears, especially in the middle gears of the box.  By adding an extra gear and decreasing the percentage drops between gears even more, a gear can be selected which keeps the engine working in the optimum range at all times.  This is especially noticeable on the exit of corners, where in some cases one gear may be too low and the next up may be too high, the addition of the extra gear with narrower gaps helps to optimize drive. 

 

4. Ratios For Road Racing MX Engines

A similar situation occurs when fitting a motocross engine into a road racing motorcycle, as the equally spaced ratios of a MX engine result in slower acceleration in the higher gears.  Our close ratio gearsets designed for road-racing motocross engines including the Honda CRF250 & 450, the Suzuki DR800 and the Yamaha WR450 utilize optimized ratios to take into account the changes brought about by racing on tarmac.  The standard MX gear ratios have nominally the same percentage drop between each gear, this effectively means with each gear change the engine revs drop to the same level.  As the velocity of the motorcycle increases aerodynamic drag increases, this requires more torque from the engine to accelerate at the same rate.  Therefore with each gear change, the drop in engine RPM needs to decrease to keep the engine running closer to the peak torque of the engine.  The Nova road racing gear sets for MX engines effectively give a performance increase as the engine is operating closer to its maximum power for much of its time.  Calculations show that this is equivalent to a horsepower increase of around 8%.  Extensive testing of the Nova CRF450 5 Speed road race kit has shown a lap time decrease of 1.5 seconds around a 2.44 miles circuit.

 

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