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Wheel Rate

What is Wheel Rate?

 

Wheel Rate
Wheel Rate
Wheel Rate is basically the Spring Rate but measured at the wheel instead of the where the spring attaches to the linkage. The figure to the right shows how wheel rate is determined.  It is basically the Spring Rate multiplied by the motion ratio squared.  The motion ratio is the ratio between how much the spring is compressed compared to how much the wheel is actually moved.  For example if the spring only compresses 0.6 inches when the wheel is moved 1 inch, that would be a .6 motion ratio.

This motion ration can be estimate by knowing the distance of the wheel to the pivot point of the suspension arm and the distance to the spring from the pivot point.

So the equation for Wheel Rate is the Motion Ratio squared times the Spring Rate.

    Wheel Rate = Spring Rate * (Motion Ratio ^ 2) * Spring Angle Correction

The "Spring Angle Correction" is typically a small correction equal to the cosine of the spring angle from vertical.  With a vertical spring angle, the cosine of 0 degrees is 1, so the correction has no affect.  At 10 deg from vertical, the cosine of 10 degrees is .985, only a 1.5% effect.  So with springs relatively vertical, the Spring Angle Correction can usually be ignored.

The figure shows the equation for calculating wheel rate from spring rate in it's simplest form. The figure shows that the spring may compress a very different amount than what the wheel actually moves. There are additional corrections for spring angle, wheel offset from the ball joint, camber change, etc. to make this equation more accurate but more complex to understand.

In the Suspension Analyzer program, we actually move the wheel a known rate and see what the resulting spring compression is.  This very detailed method takes all the factors above into account and is the most accurate method of doing Motion Ratio and Wheel Rate.

Programs that work with Wheel Rate

We have 5 programs that work with Wheel Rate when conducting Suspension Simulation. Roll Center Calculator v3.6 works with the front Wheel Rate only. Roll Center Calculator Plus v3.6 and Circle Track Analyzer v3.6 work with and can calculate Wheel Rate of the front and REAR of vehicles.  

Our Suspension Analyzer v2.4 program is our top of the line Suspension Program and works with Wheel Rate with more precise 3D (X, Y and Z coordinates) inputs so you can design your suspension to perform the way you want. And our Suspension Analyzer Full Vehicle v2.4. also work with Wheel Rate of the rear suspension.

And Circle Track Log Book v1.1 allows you to document your vehicles setup for a given track or track conditions. You can record the Wheel Rate of both the front and rear suspensions for future analysis.

 

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