i've been day dreaming of this wheel/brake combo to reduce un-sprung weight...

[roastbeef]

and i'm wondering if someone has come up with an even better combo for reducing un-sprung weight;

i would like to ditch my bmw zcp 359 wheels and go with a 18x10.5" BBS FI square setup. this would save approximately 36 lbs of unsprung weight (front and rear) in the wheels alone (no tires).

i would also like to supplement form and function by adding the Essex designed AP racing brake kit for the front and rear. this would save approximately 37 more pounds of unsprung and rotating weight.

the total amount of un-sprung weight shed from the car would be 73 pounds total!

granted the price tag of this setup at msrp prices would be around $16-17k, getting the parts used can save significant money.
from what i have gathered, a pound of un-sprung weight "feels like" four pounds of sprung weight when being removed from the car. so this setup could "feel" like losing 292 lbs!
secondary to that, wider tires and better brakes coupled with less weight would likely produce a wonderful feeling car.

anyone running something similar? please share!

[kawasaki00]

Wont let me link for some reason.
I have been in cars that had super light wheels, brakes etc. Although it feels much better and nimble the reality just like it says below is that if the road is flat and the suspension really is not moving much the car will be no faster than taking the same weight out of the interior. The rougher the road or the faster you go, "track usage" it starts to make more difference. I think that is where people get the so called ratio or sprung to unsprung.

Sprung Vs. Unsprung WeightDefinitions
“Unsprung weight” moves when the wheel moves. “Sprung weight” moves when the chassis moves.
Weight controlled by the suspension, and usually below the suspension, which forces it into contact with the road surface or other components, is unsprung weight.
Weight supported by the suspension, and usually above the suspension, which separates and isolates it from the road surface and other components, is sprung weight.
There appears to be some confusion concerning the definition and behavior of rotating weight. Many advantages that apply solely to reduction of rotating weight have been erroneously applied to reduction of unsprung weight. Among these are the concept that there is a ratio or formula that predicts a greater effect on the acceleration of a vehicle if weight is removed than the actual weight change; there is no single accurate formula (although some rough predictions provide useful information through a combination of generalities), and it does not apply to unsprung weight in any case. There are components on all vehicles that are both rotating weight and unsprung weight, but the effects are frequently, and improperly, combined and attributed to unsprung weight.
Effects
Unsprung vs. sprung weight have no difference in their effect on acceleration or top speed. There is no “1-10” rule (or any other ratio) where 1 lb. removed from unsprung weight “has the same same effect as” a higher amount of sprung weight. Any benefit from weight reduction towards increased MPH or reduced ET will be exactly the same as if the weight were removed from the chassis. Weight removed from an unsprung component, such as a rear wheel or axle housing, may affect traction if the wheel is not under control during launch.
Lighter wheels & tires do have a very small additional benefit due to the lower amount of power required to rotate them (true of all rotating components), but this is not due to their classification as unsprung weight.
The unsprung vs. sprung weight percentage greatly affects wheel control, but its importance is almost entirely limited to un-even surfaces, or conditions where the attitude of the vehicle changes (such as through G forces). This is most important in off-road and pavement road racing, somewhat less important in dirt track, and has almost no value in drag racing. As the importance of suspension travel for proper wheel control diminishes, the value of reducing the unsprung proportion of the total car weight is lessened, and becomes zero if the suspension travel is zero.
Cars requiring precise control of wheel movement, where a low percentage of unsprung weight is an advantage, will have faster lap times and higher top speeds, not because unsprung weight reduction improves acceleration or top speed, but because traction is improved.
The unsprung vs. sprung weight percentage also affects ride comfort, since lighter springs are needed to maintain traction and control with lighter unsprung components (alloy wheels, independent rear suspension, alloy calipers, composite springs, in-board brakes, etc.), the chassis is less disturbed by wheel movement and road surface irregularities.
Unsprung Weight
Here are some examples of “pure” unsprung weight on a typical front-engine rear-drive sedan:
» Brake rotors or drums + shoes, wheel cylinders, backing plates, calipers, pads, caliper brackets, flex hoses, return
springs, wheel bearings, etc.
» Wheels, tires, tubes & valves
» Steering knuckles
» Rear axle housing, ring & pinion, differential, axles, etc.
» Pinion snubber
» Sway bar linkage (but not the arms or center beam)
Sprung Weight
Almost all of the remainder of the car is sprung weight, including some components that move, oscillate, reciprocate and/or rotate, including the motor and transmission, since their movement is still supported by the suspension which isolates them from the road surface.
Hybrid Weight
On some of the remaining components the definition is not so straight-forward. Parts that are attached to the chassis and the wheels are “hybrid” (mixed): both sprung and unsprung. It's generally considered that the weight split is 50/50, but the actual separation is based on the centerline from the pivot point (not the location of the center of gravity). For example: the outer (ball joint) end of a control arm is unsprung, but much lighter than the inner (chassis) sprung end.
For a more extreme example, imagine a driveshaft 60” long, with a tiny U-joint on a 30” aluminum tube in front, mated to a ½” wall thickness 30” long steel tube with a huge U-joint in back. If the 50/50 rule applied, ½ of the total weight would be sprung (on the transmission end), and ½ of the total weight would be unsprung (on the axle end), based on a separation point located at the center of gravity.
This is an incorrect and misleading oversimpification, because the first 1” of the weight of the transmission end moves the same amount as the chassis, the next inch moves less, etc. and the final 1” of weight just before the rear axle hardly follows chassis movement at all - it’s tracking the unsprung rear axle movement. The balance of chassis-to-axle (sprung-to-unsprung) movement percentage doesn't have anything to do with the weight - it's based on a separation point located at the geometric center (30” in this case), where a molecule follows 50% of the chassis’s motion and 50% of the axle’s. Clearly, splitting the motion based on weight will predict that this particular driveshaft is almost all unsprung weight (because the heavier components are in the back), even though ½ of it isn't.
Some examples of parts fitting in the “hybrid” category, including some non-Mopar:
» Upper control arm (front or rear)
» Lower control arm (front or rear)
» Shock absorber
» Sway bar arms (but not the linkage or center beam)
» Leaf spring
» Coil spring
» Ladder bar
» Trailing arm
» Panhard bar
» Watts linkage
» Drive-shaft

[Richbot]

It's not just unsprung but also rotating. You don't just have to hurl that extra weight down the road you also have to add energy just to make it spin faster. a spinning wheel/brake combo has both a rotating and straight line vector component to its total stored energy at a given speed. Changing that rotation takes energy which in simple terms either comes from te engine or the brakes. So yes removing that much weight from the car in the wheels and brakes will be very beneficial, and more so than just removing the passenger seat would be for acceleration and braking.

[pbonsalb]

Would Apex arc8 wheels work at a fraction of the price and close to the same weight?

[surlynkid]

weigh a 275/35-18 Hoosier R6 versus most other tires of the same size. ton of weight difference there.

[Richbot]

Amazing what totally ignoring puncture resistance can get you

[LiM3y]

"It's not just unsprung but also rotating. You don't just have to hurl that extra weight down the road you also have to add energy just to make it spin faster. a spinning wheel/brake combo has both a rotating and straight line vector component to its total stored energy at a given speed. Changing that rotation takes energy which in simple terms either comes from te engine or the brakes. So yes removing that much weight from the car in the wheels and brakes will be very beneficial, and more so than just removing the passenger seat would be for acceleration and braking."

Maybe it's the time of year, but when I read this, I thought of the scarecrow's speech in The Wizard of Oz when he first receives his degree from the wizard

[GTB/ZR-1]

Originally Posted by Richbot

Amazing what totally ignoring puncture resistance can get you

LOL

Been there, done that, on a trip around the block to confirm no rubbing... Sucks!

[roastbeef]

there is a lot of talk here from a guy marketing carbon wheels. much of it makes sense, but i'm also inclined to believe a man pushing product is going to embellish a little bit.
he does a demonstration with two gyroscopes that i found interesting. (the vid should start 6 minutes in, if not, please skip to 6 min.)

[Shartibartfast]

Originally Posted by roastbeef

i would like to ditch my bmw zcp 359 wheels and go with a 18x10.5" BBS FI square setup. this would save approximately 36 lbs of unsprung weight (front and rear) in the wheels alone (no tires).

1. You can potentially save a lot of rotating mass while spending a lot less money by simply moving to Michelin Pilot Super Sports (if you don't already have them). They weigh less than any other max performance summer tire, often by several lbs per tire.

2. When you go down to 18" wheels, the new tires are going to add back some weight at the worst possible location in terms of rotational inertia. But don't take my word for it; check tirerack for tire weights for 265/35/19 vs 265/40/18. Looks like 2-5 lbs per corner gained by going to the larger sidewall, so be sure that the tire you choose does not end up ruining your weight reductions (can't go wrong with PSS, but even they weigh more in 265/40/18).

3. Can you share what numbers you used to calculate 73 lbs?

[bigjae1976]

Stoptech ST40 and 17x10 Alex wheels.

About $5k...win/win

[knolow]

Originally Posted by pbonsalb

Would Apex arc8 wheels work at a fraction of the price and close to the same weight?

Yes and yes

Originally Posted by bigjae1976

Stoptech ST40 and 17x10 Alex wheels.

About $5k...win/win

And hell yeah right on brotha

[roastbeef]

Originally Posted by Shartibartfast

1. You can potentially save a lot of rotating mass while spending a lot less money by simply moving to Michelin Pilot Super Sports (if you don't already have them). They weigh less than any other max performance summer tire, often by several lbs per tire.

2. When you go down to 18" wheels, the new tires are going to add back some weight at the worst possible location in terms of rotational inertia. But don't take my word for it; check tirerack for tire weights for 265/35/19 vs 265/40/18. Looks like 2-5 lbs per corner gained by going to the larger sidewall, so be sure that the tire you choose does not end up ruining your weight reductions (can't go wrong with PSS, but even they weigh more in 265/40/18).

3. Can you share what numbers you used to calculate 73 lbs?

i'm running michelin pilot super sports already.

thanks for the tip on 18" vs 19" tire weights, its something to look at when the time comes.

the numbers i got were from this thread;
http://www.m3post.com/forums/showthr...ssex+ap+racing
i couldn't find the pictures, but the numbers were corroborated by showing a e9x m3 brake disk/pad/caliper on a scale and an essex ap racing disk/pad/caliper. the wheel weights were based on published wheel weights for bmw zcp 359 wheels with published bbs Fi wheel weights. i even took into account the differences in weight in the front and rear wheels, so i believe the numbers i spoke of to be pretty accurate.

[radiantm3]

Originally Posted by Shartibartfast

1. You can potentially save a lot of rotating mass while spending a lot less money by simply moving to Michelin Pilot Super Sports (if you don't already have them). They weigh less than any other max performance summer tire, often by several lbs per tire.

Only PSS are pretty crappy on the track. They get greasy pretty fast, lose grip, and can't really take a beating. I'd rather have a slightly heavier tire that can handle track use and provide more grip lap after lap.

[Shartibartfast]

Originally Posted by radiantm3

Only PSS are pretty crappy on the track. They get greasy pretty fast, lose grip, and can't really take a beating. I'd rather have a slightly heavier tire that can handle track use and provide more grip lap after lap.

Well, they had rave reviews on the Cayman. Perhaps the weight of the M3 is a poor match for them?

@roastbeef, thanks for the sources. I'm still surprised it's 73 lbs, but it looks like a legitimate way to shed a massive amount of unsprung weight.

[roastbeef]

Originally Posted by Shartibartfast

@roastbeef, thanks for the sources. I'm still surprised it's 73 lbs, but it looks like a legitimate way to shed a massive amount of unsprung weight.

its a lot of weight to shed, especially unsprung and rotating weight, but this is also using the most expensive and most light weight parts available.
i'm hoping to get set of brakes under warranty, but if i don't i'll most likely be getting this essex kit. then, hopefully, a square set of bbs fi wheels come up for sale on the forums.