As we have discussed, when a motorcycle accelerates, load is transferred to the rear and increases the weight or load on the rear suspension. This acts to compress the rear suspension just as forward weight transfer under braking acts to compress the front suspension, causing the motorcycle to squat under acceleration. By using characteristics of the rear suspension design and the layout of a typical chain drive, however, we can give the motorcycle anti-squat geometry tendencies that offset the compression from load transfer, in turn improving handling performance on corner exits as the motorcycle accelerates.
One very useful technique for suspension setup is to use histograms and suspension velocity analysis to evaluate spring and damping settings. Histograms put values to how much time the suspension is active in each damping range (high-speed and low-speed compression and rebound damping), and by using some basic statistical analysis techniques, that information can be used to make spring and/or damping adjustments to the motorcycle and improve its performance.
Use this spring rate conversion calculator to convert between units of kg/mm, N/mm and lb./in. for motorcycle spring rates. Input a value in the first field, select “from” and “to” units in the second, and the new value will be output.
Factors used for spring rate conversion:
1 kg/mm = 56.0 lb./in. = 9.81 N/mm
One important aspect of motorcycle setup, especially as bikes become more powerful, is how the suspension reacts when the motorcycle accelerates. As we have discussed previously in the section covering front and rear weight, load transfers during acceleration and braking and acts to compress or extend the suspension. This load transfer causes the bike to “squat” to the rear under acceleration, and in an extreme example, all the weight can transfer to the rear wheel in a wheelie.
Now that we have looked at static weight distribution and also found how cornering forces add to the total weight of the motorcycle and rider, in this post we will show how total weight is distributed between the front and rear wheels. As the motorcycle accelerates, weight is transferred from the front wheel to the rear wheel; under braking, weight transfers from the rear wheel to the front wheel. Note that the acceleration and braking forces act on what we have designated the total weight of the bike and rider, which includes cornering forces.