# I weighed my 330 sport wheels (M68's) and my Hamann HM2 wheels



## The HACK (Dec 19, 2001)

Galun said:


> *I remember reading about this on a previous thread, but I cannot seem to find it using the search function.
> 
> Can someone please explain how lighter wheels would translate to performance, and maybe qualify it? Let's say I want to switch from the 46lb M68 wheels to the BBS RK wheels which weight 17lbs. How will the car "see" this weight decrease in wheels weight?
> 
> Thanks! *


This is all voodoo science, mind you...And the gains are all relative.

For each lbs of UNSPRUNG weight you loose, it's like 4 lbs you lose in SPRUNG weight. So take that into acount if your M68's weight 24lbs and the BBS RKs weight 17lbs, you're saving 8 lbs a wheel, times 4 corners = 32 lbs of unsprung weight you saved, which translate to losing about 128lbs.

There's another loosely defined formula that for each 10 lbs you shed, it's equivalent to the same car weight with 1 more hp. So losing all that weight would make your car perform like it's ~128 lbs lighter, or like it's got ~12-13 more HP underneath the hood. In real life, the formula isn't going to be as direct as what is stated here, and where you lose that weigh and how you lose that weight will make a lot more difference...Like losing weight up top will improve handling since it lowers center of gravity.

Now, with a 12-13 hp "gain" you're probably looking at dropping 0-60 time by about .1 second on the 330 and about .2 seconds on a 325i/ci (remember, the faster your car is stock, the harder it is to make it go faster in 0-60 time). Is it significant? By all means NO. However, you will notice a lot of the benefits when it comes to cornering, since that will be the biggest impact weight saving will give you. In terms of times around the track, you WILL see significant improvement by dropping significant weight off the wheel.


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## Galun (Aug 14, 2002)

How about effects on acceleration? I don't know if the formulas apply here, but if F = MA, then A = F/M, and if I reduce the mass, it will improve acceleration?


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## Mystikal (Dec 20, 2001)

Galun said:


> *if I reduce the mass, it will improve acceleration? *


Um, well, _yeah_. Do you run faster with a 100lb sack of bricks on your back?


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## Galun (Aug 14, 2002)

Mystikal said:


> *Um, well, yeah. Do you run faster with a 100lb sack of bricks on your back?  *


Haha, well I was looking for a qualtified answer, sorta like the general rules of thumb that Hack posted above. :thumbup:


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## Mystikal (Dec 20, 2001)

Galun said:


> *Haha, well I was looking for a qualtified answer, sorta like the general rules of thumb that Hack posted above. :thumbup: *


LOL, I figured. Just the way you worded the ending was too easy to pass up.


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## pdz (Nov 17, 2002)

Galun said:


> *How about effects on acceleration? I don't know if the formulas apply here, but if F = MA, then A = F/M, and if I reduce the mass, it will improve acceleration? *


ugh.

no, you have to compute rotational inertia, not must the simple force equation.


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## brave1heart (Jan 7, 2002)

pdz said:


> *nate:
> 
> i have no idea what you look like, but somehow, i picture you as the bmw version of "stephen" the dell kid.
> 
> ...


:rofl: :rofl: :rofl: :rofl: That was good... I think Nate lost interest in the thread after your comment, though...


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