10 pages of Bimmer madness

8/17/2006 9:02:54 PM

page 10 deserves a pic

8/17/2006 9:13:21 PM

i like bmw's

but

most bmw owners are idiot uppity and lost








that is all

8/17/2006 9:17:15 PM

it looks like subie robbed the fenders of the e30 for the wrx (bugeye to present)

8/17/2006 9:25:31 PM

mwhoric

8/17/2006 9:39:30 PM

Yawn.

You seen one, you seen em all

8/17/2006 9:57:48 PM

somewhat true, but most of the time what makes a good picture is the surroundings, not the car..

8/17/2006 10:04:01 PM

wow that pic w/ the e30 m3 and the storm clouds in incredible. feels like theyre moving!

8/17/2006 10:08:49 PM

1in10^9 sidescrolls another one...

8/17/2006 10:13:35 PM

^^thats an old school pic

8/17/2006 10:36:36 PM

Just picked her up about a month ago.

http://www4.ncsu.edu/~degivens/m3/IMG_0319.jpg

8/18/2006 1:31:21 AM

I have to say, this all makes me want an e30...
Ahmet

8/18/2006 1:55:51 AM

I heard in Russia everyone gets their own e36 M3.

8/18/2006 8:49:44 AM

apparantly in wake county every high schooler gets an e36

8/18/2006 7:11:37 PM

there for a while i thought every guy in a fraternity got a e36 m3 or lifted suv

8/18/2006 9:21:37 PM

they're all into landrovers now.

look mah leather and 4wd

8/18/2006 10:50:54 PM

Quote :

"1in10^9 sidescrolls another one..."

& you act like a douchebag. why bother mention either?

8/19/2006 1:59:41 AM

Quote :

"you act like a douchebag"

oh hi pot, i'm kettle. go farfigwhack on a vw.

[Edited on August 19, 2006 at 2:14 AM. Reason : .]

8/19/2006 2:13:55 AM

why don't you go fall off a bike again

8/19/2006 9:42:17 AM

^ahaha, i have to give you a gg for that one.

8/20/2006 6:43:48 PM

I'm going to go roll around in some dookey now.

8/20/2006 6:56:25 PM

Just how important is unsprung weight? And once we go unsprung, how much more important is rotational weight?

I'm looking at some track wheels, and my choices boil down to the SSR (14.x lbs for a 17 by 8.5 wheel), and Kosei (16.x lbs for the same). The weighs are approx., stock wheel is around 22lbs, and I can only find 4 wheels out of around 70 that are actually lighter than stock.
Ahmet <-- Who realizes that this is oh so not the place to ask this question.

8/25/2006 1:34:00 AM

Here's a picture of the SSR's in question:

and Kosei:


I like how the SSR's look a bit better, and they're forged, but cost just over twice as much...
Ahmet

8/25/2006 1:53:13 AM

i think bimmerforums has a track forum full of club and semi pro racers who might be a better target audience

you know you won't know the diff between 2 lbs. but being forged, maybe theres a durability argument to the SSRs. but i havent heard of many bending issues w/ the Koseis. *shrug*

8/25/2006 8:30:19 AM

well 16 vs 22lb. thats 6lb difference per wheel, 24lb difference on the car. multiply by 8 to get the weight reduction on curb weight. so you are looking at ~ 200lb off.

8/25/2006 8:55:52 AM

ok you lost me w/ your psuedo math...

(i'll give you a chance before i call what you said completely retarded)

[Edited on August 25, 2006 at 9:06 AM. Reason : fdf]

8/25/2006 9:03:26 AM

As a cheapish option, bimmerworld has team dynamics 17x8 wheels @ 17 lbs for $190/piece

8/25/2006 11:32:32 AM

17lbs eh, not bad, not bad... They do look rice-ish though, not that the rest don't, but... Any pics of them mounted on an e36?
Ahmet

8/25/2006 12:03:25 PM

no sir, maybe bf has some

8/25/2006 12:33:56 PM

^^^^

Aftermarket light weight=16 lb
Stock=22lb
Difference=6 lb/per wheel
6lb difference per wheel is 24lb/on car

that’s 24lb of unsprung weight you are reducing. To get an estimate what weight savings would that be on sprung weight you multiply by factor of 8.

24*8=192lb or roughly 200lb of weight reduction.

8/25/2006 1:04:17 PM

So thats why my car feels/handles a lot better with my wheels that are 4lbs each lighter than stock! I knew unsprung weight had some multiplication factor, but I didn't realize it was 8.

8/25/2006 1:31:37 PM

i know what youre trying to say, but thats simplified to the point or being completely meaningless.

24lbs of unsprung weight. yes, i agree.

However there is no meaningful translation to sprung weight. its silly to even try and relate it. just because weight is on the wheels doesnt add 200lbs to the curb weight.

in the context of braking or accelerating where the WHEEL and ROTOR's inertia (there are other unsprung weights that do not contribute to this, ie spindles, suspension bits, calipsers, etc) will resist change. The degree of this resistance to change in movement is proportional to the weight integrated over the radius of the wheel. so yeh big heavy wheels create a more sluggish response just like adding a ton of bricks in teh trunk would, but in very different ways. to try and create an arbitrary conversion factor (x8) between the two is silly.

total unsprung weight including wheels, rotors, calipers, suspension bits, etc also has a big effect on the wheel rate and the wheels sensitivity to vertical movement along the road.

8/25/2006 1:32:47 PM

ahhhh

8/25/2006 1:43:56 PM

^^it's not a fucking opinion, but physics. i didnt just pull factor of 8 out of my ass. what you said is known to everyone in this thread. we do know what is unsprung mass.

start here if you have motivation to do the math:

http://racingteam.manchester.ac.uk/racecar/ClaudeRoulleRacecarDynamicsSeminar.pdf#search=%22static%20vs%20unsprung%20weight%20ratio%22

[Edited on August 25, 2006 at 2:12 PM. Reason : .]

8/25/2006 2:11:51 PM

As much as I hate to agree with him, ^, the multipling factor for unsprung and its equivilant in sprung mass is both well know and accepted.

Now 8 as the factor isn't. Depending on where you look and who's math you follow I have seen it range from 5 to 10.

8/25/2006 2:32:09 PM

what do you have against me now?

8/25/2006 2:35:57 PM

m5?

8/25/2006 2:47:02 PM

sorry, but you said 24lbs of wheels adds 200lbs to the curb weight. thats just silly.

adding wheel weight can have some similar effect to adding chassis weight, but you can't simply throw "x8" at it and have it mean anything at all.

x8 might be true given a certain chassis weight, a certain wheel w/ a certain weight laid out in a certain distribution, at a certain speed, under a certain accell/decelleration. but thats such a narrow set of circumstances its a meaningless metric

8/25/2006 2:54:56 PM

Oh you fellers...
Ahmet

8/25/2006 3:04:59 PM

Im not throwing anything out there. I’m just telling you what is a common factor used to describe the effect of added weight on parts not supported by suspension. Of course everything will effect on it, your spring rates, toe, tire pressures etc. I sure as hell won’t waste my time at work in an attempt to do all the dynamics/physics to show you that effect is on average of 8 or commonly accepted to be 8 for a passenger vehicles

8/25/2006 3:21:48 PM

i don't understand what difference sprung vs. unsprung weight has on the acceleration/braking characteristics of a car. i mean, you aren't getting around F=ma no matter where you put the m.

now i could see sprung vs. unsprung affecting handling. and i could see rotational weight having a higher effective weight when it comes to your drivetrain.

but i don't get this x8 business.

8/25/2006 3:44:51 PM

sprung weight on the car has certain frequency at which it moves. so does unsprung weight.

sprung weight or the weight of the car supported by suspension moves at much slower rate than unsprung weight.

if you think mass will not matter take the dead simplest equation for frequency i.e. nu=square root of k/m, where k is the spring constant of any spring and take any mass you want. now calculate the frequency with approximate weight of your unsprung mass, say m1=200lb (wheels, tires, sway bars what not) and calculate the same equation with approximation for sprung weight, say m2=2800lb. see how much difference you will get in frequency. it will vary tremendously just with slight differences in mass.

8/25/2006 4:01:44 PM

F=ma applies to everything on the car of course including all mass, sprung, unsprung, rotating or not.

but in addition to that, the inertia, (I=mr^2 ) of all the rotating parts takes a hit on the car's ability to get the rotating parts moving which in turn effects the rate of accel/deccel

8/25/2006 4:11:38 PM

F=m*a is not the end of all physics. If you got engineering degree you should know this better than anyone. This is not about mass per se, but deals more with weight transfer. I’m not talking about rotational inertia of the heavier or lighter wheel and how it will affect braking, acceleration and power put down through the wheels. In fact screw wheels, put rotors made out of lead and you will experience same effects.

8/25/2006 4:38:40 PM

Quote :

"F=ma applies to everything on the car of course including all mass, sprung, unsprung, rotating or not. but in addition to that, the inertia, (I=mr^2 ) of all the rotating parts takes a hit on the car's ability to get the rotating parts moving which in turn effects the rate of accel/deccel "

this is i completely understand and agree with.

Quote :

"sprung weight on the car has certain frequency at which it moves. so does unsprung weight. sprung weight or the weight of the car supported by suspension moves at much slower rate than unsprung weight."

i think you lost me here. are you talking about the rate of how the weight will be transferred? like i said before, i can see the arguement about it affecting handling.


here is my question:
if i buy lead sway bars and control arms (non-rotational unsprung weight) and add 25lbs to my car, will it have the same effect on acceleration as putting a 200lb dumbbell in my passenger seat?

i just don't see how it could. and assume that there are no traction issues, etc.

Quote :

"Why is it important to have a low unsprung mass? Road irregularities send a force: F = ma where m = the unsprung mass into the chassis through the shock. Therefore, a lower mass will result in a lower disruption to the chassis, causing less chassis roll. A lower inertia also means that the wheel and tyre will return to its original position quicker so helping to maintain grip after a disturbance."

that's from the link listed above. that makes sense in regard to handling. but i don't see how or what the point of relating that to sprung weight is. maybe you'd have to take off 200lb of sprung weight to equal the chassis responsiveness of 25lbs. unsprung?


[Edited on August 25, 2006 at 5:09 PM. Reason : ]

8/25/2006 4:55:39 PM

^i dont know the exact answer to that question. i realize you are trying to paint the picture, but it is not black and white. possibly it could be true as wheels first have to turn the axle and leaded sway bars before the car will start to roll.

you can google this topic and read about relationships between suspension frequency, weight transfer and effect on static weight.

[Edited on August 25, 2006 at 5:11 PM. Reason : f]

8/25/2006 5:11:16 PM

most of a sway bar is sprung weight.. maybe 15% maybe would be considered unsprung?

for control arms, people commonly say 2/3rd of its weight is unsprung, and 1/3rd is.

8/25/2006 5:30:53 PM

^depends on a sway bar. some are on or drilled onto the axle.

8/25/2006 7:22:27 PM

Quote :

"Just how important is unsprung weight? And once we go unsprung, how much more important is rotational weight?"

it completely depends on your planned use and intended results from reducing unsprung weight and/or rotational mass (disclaimer of sorts: it is possible to reduce unsprung weight without reducing rotational mass, or vice versa, which introduces a whole other sub issue/debate)

basically, it appears to me this discussion/argument is WAY too hung up on one variable. while basic laws of physics, etc. to apply in a literal sense and are true, this isn't a subject that you can solely focus on while keeping real world results/performance in perspective. there is no "rule of thumb" for this conversation or numerous others unless you're speaking strictly in terms of a very controlled environment.

8/25/2006 9:27:26 PM

Any of you bitches want to trade your stock exhaust and $50 for my aftermarket? Its an Ireland Engineering all stainless 60mm piped catback. Looks like a superspring, maybe its a clone or something. It sounds pretty mean, but is a little deep down low and i'm getting old and pussing out. Overall its a hair louder than stock through the rpm range plus some punch down low.

8/27/2006 10:27:38 PM