I've seen people state that removing unsprung weight is the same as removing 3 times as much sprung weight.Some others say 2 times as much.

Has anyone proven or disproven these staements with actual timeslips?

The wheel/tire combo that I'm considering will save me 44 lbs in unsprung weight.What's that worth at the track?

 

More like two times (probably 1.7). It's easy to think about, remember back in Physics class, take the tires for example. spinning or not they move with the car so they have the same sprung weight effect, however they also spin, creating rotational momentum.

Rotational momentum has it's own inertia or resistance against accelerating. Trust me, I've left out the rotational inertia part of a physics problem once and got it wrong, my resulting acceleration was too high because I assumed to only calculate the linear inertia of the mass of the rotating item.

Here's the side of a tire, take once slice accross the middle
TT = outside part that touches ground (tread)
M = middle
C = center of radial gravity

TT C MMMM C TT

Because the center of gravity is not at the outermost part then the rotational energy of the whole mass is not as great as the linear energy of the tire's mass because the surface of the center of radial gravity does not move as fast as the tread, but close.

3 times is way tooo much. However it is worth more then removing sprung weight. I'd say unsprung weight in the tires is worth about 1.7 times sprung weight

<small>[ April 19, 2002, 05:34 PM: Message edited by: AlienDroid ]</small>

 

WOW ! I can barely remember physics class much less what it was about!! LOL. I agree it should be 1.7 - 2.0 times sprung weight in theory.I'm surprised nobody has put this to the test at the track though.

 

The only problem with testing at the track is that the gains will likely be small enough to be within the limits of other variables...such as weather, track condition, and even driving/shifting.

Physics aside...I lose 50 lbs when I change from my pure street wheels to my street/strip wheels. It's a no-brainer IMHO. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

I agree, this would be hard. To do a proper experiment on this would take a lot of time and a lot of stress on the cars used

You would have to take around 100 cars that trap between 13.6 and 13.2 or as close to each other as possible. Then run them each one the same night at the same track, each should run several times to adjust for changes if a car gets faster or slower after being run over and over again. Do 50 runs normal weight and then do 50 runs with x pounds unsprung weight removed then 50 runs with only x pounds sprung weight removed from the same general area as the unsprung weight. You take the average diff between the sprung weight loss and normal weight and the diff between unsprung and normal weight.

unsprung test time diff/ sprung test time diff = your unsprung effect multiplier

Take that number above for each car and average it. That would be an accurate guess of the difference, however I don't think anyone is going to run their car like that.

We'll just have to assume it's right. It it's any help when my bro put on the 315 rims on the rear (they weight a lot more then the stock ones) it became noticably slower.

<small>[ April 21, 2002, 12:33 AM: Message edited by: AlienDroid ]</small>

 

I don't think you guys mean unsprung weight as much as rotational weight.

Our F1's are heavy, but there is alot of mass at the outside of the tire. That's where switching to a lighter tire/wheel combo helps. It's how much weight is out from the center. Let's say you have a 20 lb weight that's 4" in diameter vs a 20 lb weight that's 12" in diameter. They are both mounted on a shaft. It takes more torque to turn the larger diameter weight. (just like a 30" long sledge hammer vs a 12", same weight)

So a draglite 15x3 1/2 tire/ wheel combo will save 20 lbs each, but the effect is more than 20 lbs of weight savings.

An easy way to test this is to dyno your car w/ a heavy wheel/tire at the rear, then switching to an ET street/ light wheel in the back. Torque/ hp will go up w/ the lighter combo.

I'm sure that a physics expert would be able to pick apart what I just said, but I think it makes some sense. <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />