Weight of leather & options

[BMWJ]

Originally Posted by Sedan_Clan

taking a good shit before you drive will net more of a weight savings

[hayasa]

Originally Posted by Brosef

this is no general rule there. that is obviously only true for a car whose weightower ratio is 10:1. maybe that's the case for your Audi.

in the case of the M3/4, the rule would be about 8:1 (~3.5k pounds to 430 hp).

Actually that rule is pretty standard, but was derived from 1/4 mile times. It just happens to work out that all the other factors kind of wash out when you look at a single result (times) derived by graphing data (hp). Just a weird engineering trick for "back of the envelope" calculations for gear-heads. Check out some quick 1/4 mile calculators online and play with the numbers if you don't believe me. And yes, there are a whole bunch of other factors that might sway the ratio a tick either way, but it is just a little easy shortcut.

[Jeff_DML]

if you care about weight then you should use that $8k for the exec package and buy the carbon ceramic brakes instead. Still wondering if the brakes are going to be a nightmare like the porsches are rumored to be.

edit: on the M5

42.7lb weight reduction of rotating wheel masses

[Black Gold]

Originally Posted by Jeff_DML

if you care about weight then you should use that $8k for the exec package and buy the carbon ceramic brakes instead. Still wondering if the brakes are going to be a nightmare like the porsches are rumored to be.

edit: on the M5

iirc its 14 lbs reduction on the m3 per bmw

[JoeFromPA]

$8k for brakes is just silly. A 12-13% increase on the base price of a vehicle for rotors, pads, and calipers? C'mon. And though the rotors are rotating mass, they are nowhere near the impact of lighter wheels and tires.

I admire them, I really do, but the pricing is just goofy.

[JoeFromPA]

Originally Posted by hayasa

Hey folks, just my $0.02 regarding the effect of weight on performance. The general rule is for every 10 pounds you add, you lose the equivalent of 1 horsepower. Unsprung weight, even more so. This means that to maintain the same level of performance, you have a 10:1 ratio. The other rule of thumb is that you can't "feel" anything less than a 5% change in horsepower (although butt-dynos vary in sensitivity.) Since the M3 has a reported 430 hp, you would only be able to begin to feel the difference of ~20 hp, or about 200 lbs. Of course, weight is also the enemy of braking and turning, so any weight savings is good. But for the "I don't want to add weight because it will slow me down" crowd, I'd keep the 200 lb as the sweet-spot of whether or not to "add lightness."

If this were an accurate statement, then the entire weight-savings achieved by M on the F80 over the e9x series would not be noticeable to the driver, because it's solidly under 200 pounds.

Congratulations M, all of your efforts were for naught - the driver can't tell the difference in whether there's another 170 pound passenger in the car or not!

[CanAutM3]

Originally Posted by Jeff_DML

if you care about weight then you should use that $8k for the exec package and buy the carbon ceramic brakes instead. Still wondering if the brakes are going to be a nightmare like the porsches are rumored to be.

edit: on the M5

Only 13-15lbs total weight reduction on the F8X...

The reduction in rotating mass is greater than this though, since the weight saving of the discs is offset by the bigger callipers.

Reference in this thread

[hayasa]

Originally Posted by hayasa

Actually that rule is pretty standard, but was derived from 1/4 mile times. It just happens to work out that all the other factors kind of wash out when you look at a single result (times) derived by graphing data (hp). Just a weird engineering trick for "back of the envelope" calculations for gear-heads. Check out some quick 1/4 mile calculators online and play with the numbers if you don't believe me. And yes, there are a whole bunch of other factors that might sway the ratio a tick either way, but it is just a little easy shortcut.

Great, now you all have me doubting my own track wisdom. And now that I tested it on a calculator, I see that the error rate is pretty wide. I'm thinking this 10:1 lb/hp nugget was passed down as a quick way to calculate ETs after a few Budweisers. That being said, I still think you can calculate the sweet spot of "significant weight" if you know the hp and the car's weight. Based on a rough estimate of the published M3 hp and weight, I'm going to guess about 150 lbs before it is noticeable on the butt-dyno, all things being equal.

[JoeFromPA]

Originally Posted by hayasa

Great, now you all have me doubting my own track wisdom. And now that I tested it on a calculator, I see that the error rate is pretty wide. I'm thinking this 10:1 lb/hp nugget was passed down as a quick way to calculate ETs after a few Budweisers. That being said, I still think you can calculate the sweet spot of "significant weight" if you know the hp and the car's weight. Based on a rough estimate of the published M3 hp and weight, I'm going to guess about 150 lbs before it is noticeable on the butt-dyno, all things being equal.

So I'll posit something here: I can feel weight in braking and handling and I'm very sensitive to it, but lets talk about butt dyno for a second.

In my various 200-250hp cars, they tended to lose about 5-10hp if running on 87 octane vs. 92-93.

It was very unusual I would need to run such, but I did upon occasion, and I could feel it at the upper 1/3rd of the tach.

Now It's probably different in these higher HP applications. I probably can't feel 1000 feet of elevation difference, so most likely 5-10hp isn't going ot be felt either.

I'm just sharing that, to me, even 50-100 pounds of weight difference is important to my joy in daily driving. 200 pounds is 100% important and notable, and 300-400 pounds of vehicle weight makes the difference between an agile, fun-to-drive car and something that no longer feels tossable.