Unsprung weight (do I understand this correctly)?

[naaman]

So, unsprung weight is the weight of the suspension and other parts directly connected thereof? The less unsprung weight, therefore, the smoother the ride AND more agile the car because the suspension has to do less "work" to redistrubute the existing weight? I.E. it is easier to move 300 lbs of unsprung weight than 400 lbs... right?

I'm raising this question because I was doing some research on magnesium wheels. One thing that always comes up when talking about wheel performance is "unsprung weight." I had always assumed the phrase referred to the weight of moving parts.

A tangeantial question that I have, which originally inspired my curiosity in mag wheels is this: if a car (say, an NSX) has magnesium wheels all around, and those wheels save a total weight of 25 pounds over the aluminum wheels, is that 25 lbs reduction equivilant to the acceleration perfomance of the car as would be 25 lbs of sprung weight? (That is, since the wheels are lighter, less power is required to turn them, so does power at the wheels (or "ground") increase as well?)

 

[Carguy!]

So, unsprung weight is the weight of the suspension and other parts directly connected thereof? The less unsprung weight, therefore, the smoother the ride AND more agile the car because the suspension has to do less "work" to redistrubute the existing weight? I.E. it is easier to move 300 lbs of unsprung weight than 400 lbs... right?

I'm raising this question because I was doing some research on magnesium wheels. One thing that always comes up when talking about wheel performance is "unsprung weight." I had always assumed the phrase referred to the weight of moving parts.

A tangeantial question that I have, which originally inspired my curiosity in mag wheels is this: if a car (say, an NSX) has magnesium wheels all around, and those wheels save a total weight of 25 pounds over the aluminum wheels, is that 25 lbs reduction equivilant to the acceleration perfomance of the car as would be 25 lbs of sprung weight? (That is, since the wheels are lighter, less power is required to turn them, so does power at the wheels (or "ground") increase as well?)

Unsprung weight would be anything that doesn't move directly with your suspension: tires, wheels, brakes, etc... I have heard and read various formulas on how much more important it is to cut down on unsprung weight than other types of weight. I know the auto companies spend a lot of money working on cutting down the unsprung weight on high end sports cars.

 

[W]

A tangeantial question that I have, which originally inspired my curiosity in mag wheels is this: if a car (say, an NSX) has magnesium wheels all around, and those wheels save a total weight of 25 pounds over the aluminum wheels, is that 25 lbs reduction equivilant to the acceleration perfomance of the car as would be 25 lbs of sprung weight? (That is, since the wheels are lighter, less power is required to turn them, so does power at the wheels (or "ground") increase as well?)

Power to the ground is slightly higher. I'm sure someone will post up the formula as I've seen it before. The small benefit of lightweight wheels is also realized during braking. So a 25 lb weight reduction in the wheels has a greater benefit for acceleration and braking than 25 lbs lost in let's say the middle of the car.