Chassis Building 101. Ride Height

[bovey]

Last night I was thinking about this some more, and I thought of a more relatable example. On this thread we are all at least interested in trucks, so it's safe to say we've all driven at least one. And, we all know the 'bouncy' feeling from the rear. This is mostly due to two things. 1) Too much spring rate. Trucks are for work, and the have to carry a load, so the springs are set to be 'happy' at appx 60% of total load capacity. At full cap. they are max'ed out, and when the truck is empty, they are 'under-loaded'. (too stiff) and 2). a high % of Un-Sprung weight.

Back to our theoretical C10. rear weight appx 1400 lbs (total weight)
Now for the Un-Sprung weight.
Rear axle, gears, brakes = 265 lbs
Wheels and tires , 2, = 140 lbs
Half of the trailing arms = 35 lbs
Half of the coil springs, shocks = 14 lbs
Half of the driveshaft = 16 lbs
Half of the panhard rod, = 6 lbs
Total unsprung weight = 476 lb

So if the total rear weight is 1400 and the Un-Sprung is 476, that leaves only 924 lbs of Sprung weight. Do a little math and you get an Un-Sprung percentage of 51% !!!!! So think about it, when the trucks back tire hits a bump (one side) and 238 of mass is now moving 'up', it's easier to 'lift' the back of the truck, 462 lbs, than it is to compress the spring.

This is great information. The number times I have people ask me about how to deal with the "light" rear of a truck is amazing. People refuse to believe that the lightness is due to spring rate, not physical weight.



I also want to dig up some info I have in a book at home that I believe would be an interesting add to this thread, it talks about sprung vs unsprung weight vs. rotational weight and how they are not created equal when making a vehicle lighter. Rob, your information about USW being 12% is neat, I did not know that. Thanks for the great intel.