Weight savings cost/benefit benchmarks

[ersin]

Originally Posted by lucid

I am just curious, not serious!

No way am I going to replace the driveshaft of a car that is under warranty.

I thought there were some CF options available for the E46 M3 though?

Did some googling and this is the first thing that came up.

[e36jakeo]

For a racing wheel you can't beat the SSR Competition (C-RS). They are light and strong (semi-solid forged). The 18" x 9.5"s weigh just 19.6 lbs according to tire rack:

http://www.tirerack.com/wheels/Wheel...All&sort=Brand

I have had these for my E36 M3 track car for 4 years and they've been great. I think on the E90/92 M3 you can run 9.5" all around (35 mm offset). What do you think Enigma?

[ersin]

I always liked the SSRs and the Comps are the best. But I have heard that they are not that strong, that you wouldn't want them if you drive where the roads are bad. I almost bought a set for the Miata until I read all of this talk. Comments?

[lucid]

Originally Posted by e36jakeo

For a racing wheel you can't beat the SSR Competition (C-RS). They are light and strong (semi-solid forged).

I've been keeping an eye on these on tirerack. What tires would you suggest putting on them for track use?

[e36jakeo]

Originally Posted by lucid

I've been keeping an eye on these on tirerack. What tires would you suggest putting on them for track use?

I ran Toyo RA1s for a long time, which you can drive on the street and track. If driving during the non-rainy season you can have them shaved to 6/32" or less to lessen "tread squirm." If you are switching rims at the track there are lots of Race compound choices (Hankooks, Hoosiers, etc.). Toyos are better to learn on.

In terms of the strength of the rims, I have driven the SSRs to and from the track for 4 years and they have held up even with race suspension. They probably are not quite as strong as the stock rims since they are so light, but I have not had a problem.

[lucid]

Originally Posted by e36jakeo

I ran Toyo RA1s for a long time, which you can drive on the street and track. If driving during the non-rainy season you can have them shaved to 6/32" or less to lessen "tread squirm." If you are switching rims at the track there are lots of Race compound choices (Hankooks, Hoosiers, etc.). Toyos are better to learn on.

In terms of the strength of the rims, I have driven the SSRs to and from the track for 4 years and they have held up even with race suspension. They probably are not quite as strong as the stock rims since they are so light, but I have not had a problem.

Thanks for the suggestions. Good to hear the wheels held up on the streets.

[ersin]

e36jakeo,

Thanks for the input about the SSRs. I've read that they aren't strong but then no real episodes of them breaking so I'll place this idea in the category or urban myth. Now, if I can remember how to work Photoshop maybe I can come up with a picture of them on the M3. Oh wait, tirerack already does this. I'll be back.

Edit: I'm back. They look good on dark colored cars. Only available in 18" and fairly cheap. Unfortunately, tirerack only has a picture of the 335 sedan, not the M3. And they don't have the Jerez Black color for it either. But it does give you an idea how it looks.

[OC ///M]

I think the consensus is that there is not much to be gained over the stock forged. For an OEM wheel, the 19's are aesthetically pleasing and fairly lightweight.

...Although, consideration of a wheel swap may take center stage (becoming necessary for clearance) pending the final fitment test of the Brembo BBK on the car next week-ish.

[ersin]

OC kid,

I'm thinking people will replace wheels purely on aesthetics. When you get the BBK let us know how they are wrt the original brakes. Thanks. And don't forget the pics.

[lucid]

Originally Posted by ersin

OC kid,

I'm thinking people will replace wheels purely on aesthetics. When you get the BBK let us know how they are wrt the original brakes. Thanks. And don't forget the pics.

I am yet to see a set of aftermarket wheels that look better on the car than the stock 19" wheels. They really look great in person. If you haven't seen one up close, they're worth checking out.

[lucid]

Originally Posted by OC kid

I think the consensus is that there is not much to be gained over the stock forged. For an OEM wheel, the 19's are aesthetically pleasing and fairly lightweight.

The 18" SSRs would save about 25lbs over the stock 19" wheels (taking the 18" vs. 19" tire weights into account). That's considerable, provided one can live with the fact that they would be more likely to be damaged than stock...

[ersin]

Originally Posted by lucid

The SSRs would save about 22lbs. That's considerable, provided one can live with the fact that they would be more likely to be damaged than stock...

And I'll remind everyone that it's 22lbs of unsprung and rotational mass too. Somewhere it said that one pound of unsprung weight is worth six pounds of sprung weight, or something like that.

Some of the Z4 M owners have replaced the stock wheels with CSL wheels (and also the Continentals with PS2s). It is reported to have made a world of difference in response and drivability. It's worth it.

[lucid]

Originally Posted by ersin

And I'll remind everyone that it's 22lbs of unsprung and rotational mass too. Somewhere it said that one pound of unsprung weight is worth six pounds of sprung weight, or something like that.

Yes, I am not getting into moment of inertia issue on this thread, but generally speaking for a thin-walled cylinder like mass distribution, I increases with the square of the distance between the wall and the rotation axis. Clearly, unsprung weight would be reduced as well, but I don't know that the effects can be simplied to a linear relationship as that would be a function of the inputs.

[ersin]

I'm sure the relationship was just a rule of thumb. The idea is that decreasing rotational and unsprung mass is worth more than decreasing weight elsewhere. With the possible exception of driver's weight.

[lucid]

I updated the original post of the thread with a bunch of info on Ericsson CF parts. They are way to expensive, so I wouldn't really consider them, but their advertisements were helpful in that they state weights of stock parts for things like the trunk lid and the external door panels. 33.6 lbs to be saved with CF exterior door panels for $10k (stock ones are steel)! If someone crashes into you, you are hosed though as insurance won't pay for CF door panels. Check it out.

http://www.m3post.com/forums/showthread.php?t=135122

[sayemthree]

I think I recall seeing 1# rotational is worth 4# of unsprung. but if its both rotational and unsprung as a wheel is its worth 10# of static wieght.

also for handling its best to remove weight from the top of the car ( 11# CF probably equal to 46# savings in an exhaust) and its worth more in handling to remove it from the ends of the car than the middle (moment of inertia of the car ie turn in).

[lucid]

Originally Posted by ersin

Did some googling and this is the first thing that came up.

Stock 6MT driveshaft weighs 11.469 kg appearently:

http://bmwfans.info/original/E92/Cou...6/ill-26_0239/

[lucid]

Originally Posted by OC kid

swamp:

I am just commenting from my experience when I removed the suspension, the brake assembly felt much heavier than any I have handled before. (I had to double-up on it to keep it from falling to the floor.) I will have more info later because I will be weighing each component (stock and Brembo BBK) to compare the real numbers.

Here are some numbers from a catolog:

Front Disc assembly: 18.784 kg
Front Caliper assembly: 13.193 kg

(That's 70 lbs per wheel for the fronts!)

Rear Disc assembly: 19.102 kg (this is clearly a mistake as they used the same weight for the rear discs as the front discs. I suspect the correct number would be more like ~14lbs)
Rear Caliper assembly: 9.963 kg

http://bmwfans.info/original/E92/Cou...2007/06/mg-34/

As Swamp was saying you need more thermal mass to balance the lack of massive air flow, but the caliper assembly is probably fair game. It will be costly though. Let's see what Brembo comes up with.

[enigma]

Originally Posted by e36jakeo

For a racing wheel you can't beat the SSR Competition (C-RS). They are light and strong (semi-solid forged). The 18" x 9.5"s weigh just 19.6 lbs according to tire rack:

http://www.tirerack.com/wheels/Wheel...All&sort=Brand

I have had these for my E36 M3 track car for 4 years and they've been great. I think on the E90/92 M3 you can run 9.5" all around (35 mm offset). What do you think Enigma?

I have my 9.5x18s all around sitting at home right now waiting for the car. I used to run the SSRs 18x9.5 on the E46 M3, also on all four corners. I had bad enough luck with the SSRs bending that I would never buy them again for a heavy car. I guess I could have given up curb hopping at the track instead...

My new wheels are a 32mm offset.

[OC ///M]

lucid:

I'll have the weights for you on the trunk and BBK this week. I'm picking up my OEM brake assembly from Brembo probably Thursday, schedule permitting, and will update you to keep this informative thread going...

[lucid]

Originally Posted by OC kid

lucid:

I'll have the weights for you on the trunk and BBK this week. I'm picking up my OEM brake assembly from Brembo probably Thursday, schedule permitting, and will update you to keep this informative thread going...

Thanks OC! The catalog says the front OEM brake assembly weighs about 42 lbs per front wheel!? Is it really that heavy? Looking forward to your numbers.

I just removed and weighed the trunk floor cover. It looks like it is secured, but it actually comes off when you pick it up. I bet BMW wanted to give the option of removing it easily. The thing weighs 3.75 kg (8.26 lbs)! Original post updated.

I also removed the lining from the trunk lid. Took me 3 minutes to get the plastic rivets out. That weighs about 2lbs, but I don't have a precise measurement yet.

[icemang17]

A street M3 isn't that light...... I nice target for weight loss is the ALMS race M3 at 2530lbs.... There has to be quite a bit of CF in that machine!!