Weight savings cost/benefit benchmarks

[Tom Koh]

Originally Posted by lukester

Great thread. But the issue with removing weight from the M3 is that it changes the car.
If you go through it like I did - basically the stuff which makes sense - only removes weight from the rear of the car which changes the handling.

I did:
Full Akrapovic Exhaust (~23kg/50lbs)
rear seat delete & remove all unnecessary parts and insulation from the trunk (~28kg/61lbs)
55Ah Battery (~11kg/ 24lbs)
Recaro Pole Position seats driver and passenger (~29kg/ 64lbs)
OZ Ultraleggera Wheels with Michelin Pilot Cup tires (~7kg/ 15lbs)

All mods make sense for me as I love track days and would have done it even if it doesn't make the car lighter (e.g. the seats, wheels, tires, ...)

My M3 should be +/- 216 lbs (98kg) lighter than stock at the moment.

But....the car switched from a slightly oversteering M3 to an more understeering M3. There's no power steering available any more as it just
pushes over the front wheels.
(you can still drift it but you have to force it)

It's logical. A lot of the stuff has been removed from the rear or the center of the car.
Nothing from the front or under the hood. So the weight balance moved away from were it should be.

Will weight my car within the next weeks and I'm really interested to see the final results.

What can be done against this new handling?
I'm gonna try some 265/35-19 Michelin Pilot Cup on the front, too. At the moment the setup is 235 and 265 which is not perfect if you like an oversteering M3.

But I'm missing ideas what to do with the front.

A carbon hood will only help with ~4kg/ 8.8lbs. Not really worth it.

What I saw ... but I'm not sure if it's a good idea. Replace the big underfloor plate (it's directly under the engine) with a more lightweight part as this thing is really massive (and we do have good streets in germany so there's no need for such a engine protection).

Luke, I have an E92 M3 and I run 265x35 Dunlop Star Specs all around on 18x9s - it works very well and helps with understeer. You have to be careful what you ask for because when you are at the limit on a track and the rear gives, it will not be as forgiving as a staggered setup. This is fine for me and I like it very much - your throttle control and counter steering just has to be a little bit more quick to respond to what the car is doing. I do much more autorcross than track events so weight loss is big for me, and steering with the throttle is big as well.

One idea that I had which the experts that read this can comment on, is stripping out everything you want and then possibly adding a little weight to the rear to balance the f/r weight distribution. My rough estimates are the same as what has been stated in plenty of times - after I take out the back seat, strip the trunk, and switch out the front seats I would not be suprised if track ready weight of the car (1/2 tank) was right around or even below 3500. I have already thrown the lightest 18x9 rims I could find at a descent price and I run Dunlops which are about the same weight as PS2s. The issue I see is that at that point the f/r distro will be more like 53/47. I had an E82 135i for a couple years before this and as everyone knows, it understeers like crazy. That was mostly due to suspension geometry but the f/r weight distro didnt help, which was also about 53/47.

That brings me to the idea - I heard the 135 has extra weight in the rear to help the f/r distro - I know it will have a marginal effect but I wonder how the M3 would feel if you stripped it down but then added just enough to the very rear of the car to keep about 50.7/49.3 f/r. Experts give us your opinions.
Tom

[lukester]

Hi guys,
has anybody an comparison value for the trunk lid?
Found a replacement made out of carbon/ platic. Reseller says it weights 17.6lbs.
Looks pretty much for me as the stock one is around 23.40 (parts catalog value) and 26lbs (real life)

TRUNK LID
Stock (Steel): 10.625 kg (23.40 lbs) (OC weighed his at 26.0 lbs)
http://bmwfans.info/original/E92/Cou...1/ill-41_1638/
CF Vorsteiner lid: 14.9 lbs (OC Kid weighed it)
Cost: $1362
Weight savings: 11.1 lbs (according to OC's numbers)
cost/benefit: ~$123/lb
http://www.vorsteiner.com/bmw/e92coupe-spoiler.html#
http://www.redline-motorworks.com/product/9306%20BMV

Thx!

[swamp2]

Originally Posted by lukester

Great thread. But the issue with removing weight from the M3 is that it changes the car.
If you go through it like I did - basically the stuff which makes sense - only removes weight from the rear of the car which changes the handling.

I did:
Full Akrapovic Exhaust (~23kg/50lbs)
rear seat delete & remove all unnecessary parts and insulation from the trunk (~28kg/61lbs)
55Ah Battery (~11kg/ 24lbs)
Recaro Pole Position seats driver and passenger (~29kg/ 64lbs)
OZ Ultraleggera Wheels with Michelin Pilot Cup tires (~7kg/ 15lbs)

All mods make sense for me as I love track days and would have done it even if it doesn't make the car lighter (e.g. the seats, wheels, tires, ...)

My M3 should be +/- 216 lbs (98kg) lighter than stock at the moment.

But....the car switched from a slightly oversteering M3 to an more understeering M3. There's no power steering available any more as it just
pushes over the front wheels.
(you can still drift it but you have to force it)

It's logical. A lot of the stuff has been removed from the rear or the center of the car.
Nothing from the front or under the hood. So the weight balance moved away from were it should be.

Will weight my car within the next weeks and I'm really interested to see the final results.

What can be done against this new handling?
I'm gonna try some 265/35-19 Michelin Pilot Cup on the front, too. At the moment the setup is 235 and 265 which is not perfect if you like an oversteering M3.

The seats and tires will shed weight fairly evenly across the wheels. That leaves about 120 lb removed from the cars rear. That is about 3%. I would be quite surprised if that turned a car from over to understeer. As well, from the factory, the car will understeer, not oversteer, that is more or less a legal obligation for safety and to prevent lawsuits. Also the car should not change its basic handling tendencies with out without rear luggage or a passenger whose weight these changes are comparable to

Originally Posted by lukester

But I'm missing ideas what to do with the front.

A carbon hood will only help with ~4kg/ 8.8lbs. Not really worth it.

What I saw ... but I'm not sure if it's a good idea. Replace the big underfloor plate (it's directly under the engine) with a more lightweight part as this thing is really massive (and we do have good streets in germany so there's no need for such a engine protection).

Adjust your tires pressures, despite being very skeptical about the changes you have observed tire pressures can make a decent sized effect. Despite how good your roads are I would NOT remove that plate. Why risk an 18000 euro engine for a few pounds? It isn't a race car...

[gsrbri]

I was at the track for a DE event Sunday and weighed my car on the chassis scale.

3,553 lbs w/no driver and 1/4 tank of fuel

2011 E90, manual trans, no sunroof, manual/cloth seats, no folding rear seats (no ZCW), ZCP. The car does have HK and NAV.

I was pretty happy w/the weight of the car, as the car was optioned to save some weight. I was expecting more in the 3,600 lb range.

-Brian

[lukester]

Just had contact with Seibon Carbon and as it seems it's not really worth the effort to change the stock hood with a Seibon hood.
The trunk lids is ok for the price as the trunk lid is "just" $880 which is cheap compared to others.

TRUNK LID
Stock (Steel): 10.625 kg (23.40 lbs) (OC weighed his at 26.0 lbs)
Seibon trunk lid (part: TL0708BMWE922D-C): 16lbs

HOOD
Stock (Al): 10.20 kg (22.47 lbs)
Seibon hood (part: HD0708BMWE92M3-OE) 22lbs

[klammer]

As mentioned earlier, tire pressures can change things, and this is a street car so it will understeer. That being said have to agree with swamp that the weight you've removed should do little to the bias/handling of the car, but then again, on track at the "limit" it may be more noticeable. I am in pretty much your situation as I've shaved about as much as weight as possible and it's mostly from the rear, think camber plates, tire pressure, or square setup as think these would have a bigger effect on understeer than a few pounds up front, but am still open to suggestions as well:thumbsup

[xchosun1x]

2008 e92 m3
dct, pdc, premium sound, rear sun shade

kw v3
brembo 380/380
akra rear section
gintani catless xpipe
reinforced stock trunk
varis gt wing
luma lip w apr splitter
recaro pole positions x2
autopower roll bar
rear sear delet
full vinyl wrap

3583 lbs full tank of gas topped off, all fluids, no driver
3768 lbs w driver

[armyav8tor]

I stripped out the back to make it easier (more room) for me to remove the glue residue from the last tint job. I'm leaving it stripped out until the guy puts in new tint on the back window on Friday and then everything is going back in. The road noise is much louder than I expected and while there is no doubt that the car weighs less (the rear suspension is actually sitting higher), I can't justify the cost/benefit of leaving it this way. I'm going to get an oem mini 55 amp/hr battery and save 25lbs that way.

[Adriansideways]

Camber plates, front and rear toe, tyre pressures will eliminate understeer but Just remember your driving style can cause it as well

[Dellort_M3]

Anyone know the weight of the speed cloth manual front seats?

[roastbeef]

sorry if i missed it, but what is the weight difference between navigation and non-navigation cars?