Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB - View Single Post - Just a thought... What could the factory have done to lighten then car?

babydriver · 03-31-2015, 03:03 PM

Sometimes it's helpful to me to simplify the problem somewhat.

Imagine that we have a coil spring connecting two weights, one small one on the bottom (the unsprung weight) and one very large one above the coil spring (the sprung weight). Any change in the sprung weight will either compress the coil spring more (if heavier) or less (if lighter). For the purpose of this thought experiment, we will ignore any side to side motion that may be possible; only up and down motion is "allowed".

What complicates matters further is that the lower "unsprung" weight also moves. As force is applied to it in an upward direction, the spring compresses and rebounds. A downward direction will cause stretching and then rebounding. At some critical combination of rate and weight, the unsprung weight will come into resonance with the spring's rate, allowing the greatest motion with the least effort. However, this is also the point at which the entire assembly wants to continue to oscillate at the same speed as long as there is additional energy put into the system. The shock absorber (on the car) is there to reduce this resonance (i.e. bouncing).

The question is: If the damped resonance is something that is desirable or undesirable?

03-31-2015, 03:03 PM	#70
babydriver Hit the road and I'm gone Join Date: Oct 2014 Drives: 2015 FR-S Burnt Orange (Hot Lava) Location: Austin, TX Posts: 1,844 Thanks: 733 Thanked 1,786 Times in 973 Posts Mentioned: 10 Post(s) Tagged: 2 Thread(s)	Sometimes it's helpful to me to simplify the problem somewhat. Imagine that we have a coil spring connecting two weights, one small one on the bottom (the unsprung weight) and one very large one above the coil spring (the sprung weight). Any change in the sprung weight will either compress the coil spring more (if heavier) or less (if lighter). For the purpose of this thought experiment, we will ignore any side to side motion that may be possible; only up and down motion is "allowed". What complicates matters further is that the lower "unsprung" weight also moves. As force is applied to it in an upward direction, the spring compresses and rebounds. A downward direction will cause stretching and then rebounding. At some critical combination of rate and weight, the unsprung weight will come into resonance with the spring's rate, allowing the greatest motion with the least effort. However, this is also the point at which the entire assembly wants to continue to oscillate at the same speed as long as there is additional energy put into the system. The shock absorber (on the car) is there to reduce this resonance (i.e. bouncing). The question is: If the damped resonance is something that is desirable or undesirable? __________________ Slip, slidin' away.