Chang_Wufei_05

iTrader: (3)

Trying to get a sense of what a 1 lb reduction in unsprung weight would be equal to in terms of sprung weight. I know there are nuances between rotational and non-rotational unsprung weight, so let's assume at 60 mph for any physics majors out there

Ultimately trying to figure out what is a better deal per $ in weight reduction, lightweight wheels or lighter parts (carbon fiber trunk, maybe wing, etc.).

Thanks!

jackygor

iTrader: (9)

I was under the impression that unsprung weight will ultimately yield better result than sprung weight.

KevinD

iTrader: (56)

you really have 3 different classifications of weight.

sprung weight

unsprung weight

rotational weight

sprung weight is anything that is on the car that is carried by the shocks/springs. so trunk, seats, engine, etc...

unsprung weight is everything that touches the road before the springs. so wheels, brake rotors and calipers, hubs, and half of the shock itself.

rotational weight is the stuff that rotates. here there is a bit of a mix between sprung and unsprung weight. your driveshaft is rotational weight, but it is also sprung. your wheels are rotational and unsprung.

ideally, your suspension will work best with the least amount of unsprung weight (quicker response, less inertia), so better handling. your car will accelerate best with the least amount of rotational weight. so wheels, brake rotors, drive shafts, light weight clutch, etc. reducing sprung weight helps everything, but not quite to the effect that the other two will.

so if you look at it that way, taking rotating, unsprung weight off the car will help the most. wheels, brake rotors, lug nuts, tires. there is no set number like a lot of people pass around like "1lb of rotating mass is like 5lbs of regular mass". thats just not easily quantifiable because if you take a pound out of a tire, its going to have a much bigger effect then taking a pound out of a driveshaft. the reason is the tire has a much higher moment of inertia then the axle does.

supergengo

iTrader: (2)

This is complicated even further when you try to equate the advantages of one type of weight removal versus another. As stated above, reducing unspung weight will generally improve handling more than a similar reduction in sprung weight. But to then turn that into a financial equation, you have to put a dollar value on an incremental improvement in handling, i.e. what is .01g of grip worth to you? While this is a logical approach, I don't believe you will find unbiased evidence (results) that would allow you to validate you made the better investment.

You might think more about what you want the car to do better... hold more grip? accellerate/decelerate more quickly?... go around the mall sounding awesome? etc. If you think in terms of what outcomes/results you really want, experts and tuning shops will be able to help you pick a decent modification path that you can afford.

Chang_Wufei_05

iTrader: (3)

Thanks for the great info guys! Understand the complexities of what I'm asking, that's why I said rough estimate (80/20) haha. For ex, wheelweights.net says
Not trying to distill it to a full equation of $/lbs reduced. Just to get a sense of whether Volk/SSR wheels are worth it, for ex.

Also, because I have an MR Touring, I max out power after intake, exhaust & tune so then gotta goto weight reduction.

PS you forgot partially sprung weight (control arms)