Measuring Unsprung Weight

[MrSuspension]

Hello Everyone,

I am a student at the University of California, Riverside and we are just beginning to bring back the FSAE program. I'm currently involved with suspension and I have just been trying to gain as much knowledge by reading Race-Car Vehicle Dynamics and How to Make Your Car Handle. I understand this question might have already been asked before, but I'm wondering how one can go about measuring the unsprung mass of the car. I read in RCVD that the individual unsprung weights are located at the center of each wheel, but for measuring the unsprung mass, it can't be the same method as for measuring the total vehicle weight correct? So it is not as simple as rolling the car up onto four scales? Any help would be appreciated and I'm sorry if I posted this in the wrong area of the forum. It's my first time posting here. Thank you

[Edward M. Kasprzak]

The easiest way to measure the unsprung mass is to remove it from your vehicle and put it on a scale. Note that the statement "individual unsprung weights are located at the center of each wheel" is only a first guess/approximation. If you want greater accuracy you could find the true center of gravity of each unsprung mass, but it's for you to decide if you think it's important enough to put forth the effort.

Did I understand your question correctly?

[Claude Rouelle]

1. Put your car on the scales and measure each corner weight
2. Jack the car just a bit lets say 50 mm
3. Disconnect the push or pull rod on the rocker. Each non suspended mass is now on its scale. Read the numbers
4 The difference between 1 and 3 is the suspended mass per corner

There are a few traps like the ball joint friction but you won't be too far off. Accurate enough to be useful

[BillCobb]

Claude's method also lends itself to measuring the total un-sprung inertia.

[MrSuspension]

Hi Edward M. Kasprzak, yes you did and thank you for the response. Also, thank you for the additional comment for an even more accurate measure, I'll make sure to take bother methods into consideration.

[MrSuspension]

Hi Claude Rouelle, thank you for the response and the information. I'll make sure to try this out with our 2009 FSAE vehicle.

[MrSuspension]

Hi BillCobb, this will be very helpful for the total load transfer calculation. I really appreciate the help.