Vehicle Setup Calculators
Installation
Motion Ratio
Purpose:
Most of us will know what spring rate we have on each corner of the car, however what we really want to know if the wheel rate. That is effectively the spring rate at the wheel where the tyre contacts the ground. This will also be what the driver feels.
A motion/installation ratio takes into account any suspension geometry to work out how far the spring compresses compared to the distance the wheel moves upwards. This number is useful when comparing vehicles with different suspension geometries.
Going forward we will use installation and motion ratios interchangeably.
Using the Calculator: Not currently available on our mobile site.
The installation ratio can be calculated either by jacking up the wheel a known distance and measure how much the spring has compressed. Another way is we can calculate the ratio using a couple of measurements of the suspension system.
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Enter the dimensions A and B from the diagrams below that best match your own suspension system.
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Enter the angle that the spring is installed at from the vertical.
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The calculate button will give you both the installation and motion ratio.
Goal:
When we have our installation/motion ratio, we are able to determine the wheel rates of the vehicle. Allowing us to understand how stiff each corner of the car is for the purpose of improving handling and grip.
A motion ratio greater than 1 means the wheel travels a greater distance than the spring. So as the number increases, greater the movement of the wheel compared to the spring.
The installation ratio is just the inverse of the motion ratio. So an installation ratio less than 1, means the wheel travels a greater distance than the spring. As the number decreases, the greater the movement of the wheel compared to the spring.
Please use the calculator to work our the installation ratio of your suspension system, this number can then be used on our wheel rate calculator.
suspension Geometry Types
Use the suspension geometry diagrams below to help you calculate your suspension installation ratio.
A-arm suspension
Macpherson Strut suspension
Beam Axle suspension
