[CanAutM3]

Originally Posted by g21

Cd refers to computer generated number based on 3D shape of the car front to back all the way.

maybe 0.33 without M Performance parts, 0.34 with the front lip and rear spoiler

but then i expect the M4 to have a lower Cd without MPP

Incorrect. Cd are empirical numbers that are calculated off the actual measured aerodynamic drag of the car obtained in either wind tunnel or road testing.

Originally Posted by g21

but it really could be as simple as narrower option tires for 0.33 and wider 275 285 for 0.34

Tire width would definitely affect the Cd value, but all tire options are the same widths.

[CanAutM3]

Originally Posted by Fugly M3

CanAutM3 disagrees, but I'm still inclined to think it's the cruise control blob that's not offered on the base cars. I can't think of another reason (variable) why the M3 would have two numbers I think the base M4 coefficient should probably be lower and is a misprint by BMW. Having said that, the performance difference in the two, particularly the braking from higher speeds where there is more drag, may well come down to the Pirellis vs. the Michelins. But then there is ambient temperature and humidity of testing that comes into play as well.

As I stated previously, the M4competion is quoted with the same Cd numbers as the base M4, which tends to indicate that the cruise control radar is not a factor.

Maybe the fins on the CF roof have a greater impact on the M3 due to its greater height, so a greater difference between CF and sunroof options? Just speculating here, it could be many things.

[G30M]

Originally Posted by CanAutM3

Incorrect. Cd are empirical numbers that are calculated off the actual measured aerodynamic drag of the car obtained in either wind tunnel or road testing.

Tire width would definitely affect the Cd value, but all tire options are the same widths.

did some more reading and it turns out you are right. i had read somewhere it was generated by CFD

but what i don't understand -

M550i Cd is 0.22
M340i Cd is 0.23

Why is the M3 so bad?

[G30M]

Originally Posted by CanAutM3

As I stated previously, the M4competion is quoted with the same Cd numbers as the base M4, which tends to indicate that the cruise control radar is not a factor.

Maybe the fins on the CF roof have a greater impact on the M3 due to its greater height, so a greater difference between CF and sunroof options? Just speculating here, it could be many things.

they do run their MPP in the wind tunnel, my guess is the higher Cd is with MPP

[CanAutM3]

Originally Posted by g21

did some more reading and it turns out you are right. i had read somewhere it was generated by CFD

but what i don't understand -

M550i Cd is 0.22
M340i Cd is 0.23

Why is the M3 so bad?

“Bad” is relative. Often, a “slippery” shape yields a lot of lift. To counter lift, downforce features need to be added and they increase drag. Further, as I posted earlier, radiator air inlets are terrible for drag and the M3/4 have a lot of them for performance reasons.

[PLF69]

Originally Posted by CanAutM3

As I stated previously, the M4competion is quoted with the same Cd numbers as the base M4, which tends to indicate that the cruise control radar is not a factor.

Maybe the fins on the CF roof have a greater impact on the M3 due to its greater height, so a greater difference between CF and sunroof options? Just speculating here, it could be many things.

I would bet on the top shape, when you see both cars one beside the other the roof line is drastically different.

[Kminor2578]

I want to trade my RWD in for an AWD so bad. I wish I would have wait 4 months to order one. Oh well.

[Fugly M3]

Originally Posted by CanAutM3

As I stated previously, the M4competion is quoted with the same Cd numbers as the base M4, which tends to indicate that the cruise control radar is not a factor.

Maybe the fins on the CF roof have a greater impact on the M3 due to its greater height, so a greater difference between CF and sunroof options? Just speculating here, it could be many things.

Originally Posted by PLF69

I would bet on the top shape, when you see both cars one beside the other the roof line is drastically different.

This I can see. There is a bit more long flat roof on the M3 with those two pieces running pretty much the whole span. Additionally, the sharp rake of the M4 roof probably directs more air to the trunk and spoiler I'd think. This is more downforce, but I could see it overall contributing to drag.

[TVonthe80]

My guess is that the transition from roof to trunk on the m3 interacts with the rear MPP spoiler slightly more than the smoother transition M4 which is why the m3 has a range and the M4 does not. Otherwise everything else on the cars are either the same or static and wouldn’t drive a variance.

[FCX5]

Originally Posted by Humdizzle

definitely puts up good numbers. GTR fast in the 1/4 mile and 1g in the skidpad. surprising that car and driver couldn't get a better time out of it at lightning lap as it placed #66 and behind the new RS3.

https://www.caranddriver.com/feature...storical-data/

Impressed to see the last two corvettes among true super cars! Unfortunately many BMW fans tend to look down on them 🤷🏻‍♂️

[CanAutM3]

Originally Posted by Fugly M3

This I can see. There is a bit more long flat roof on the M3 with those two pieces running pretty much the whole span. Additionally, the sharp rake of the M4 roof probably directs more air to the trunk and spoiler I'd think. This is more downforce, but I could see it overall contributing to drag.

It’s actually the opposite regarding the coupe shape, the sloping roofline of the coupe is better for drag. Think of a teardrop: it’s the most aerodynamic shape. The shape of the coupe is why they need the integrated (CSL style) gurney flap on the rear deck-lid to reduce lift, and you'r right about this feature increasing drag by kicking the airflow upwards and increasing the turbulence behind the car.

[jmg]

Originally Posted by g21

did some more reading and it turns out you are right. i had read somewhere it was generated by CFD

but what i don't understand -

M550i Cd is 0.22
M340i Cd is 0.23

Why is the M3 so bad?

Cd is a coefficient. The M3 could still have less drag with a higher Cd due to surface area differences. Note that the M340i and M550i have active grills that open and close. I wonder if this Cd is with them closed?

[amrazM]

Originally Posted by wesleyan92

Cadillac must not have paid their monthly "Blackwing #1" dues to C&D.

Historically people would joke that c&d was on the books for bmw as they could never find something negative to say about a 3 series, which changed with the F30

[zero21]

All the things being equal, longer cars have smaller drag coefficients. The m3 is slightly better due to floor length.

[CanAutM3]

Originally Posted by jmg

Cd is a coefficient. The M3 could still have less drag with a higher Cd due to surface area differences. Note that the M340i and M550i have active grills that open and close. I wonder if this Cd is with them closed?

You probably mean frontal area. "Surface area" is already imbedded in the coeficient.

[Fugly M3]

Originally Posted by zero21

All the things being equal, longer cars have smaller drag coefficients. The m3 is slightly better due to floor length.

Both cars are the same length with the same wheelbase per BMW specs. I’d assume that means the floor length is, near as makes no difference, the same.

[astroricardo]

Originally Posted by 2011ninja

100%!

I have a G80 6MT. It’s an effort to go fast.

I can’t imagine anyone with AWD version automatic not driving fast all the time or launching the car.

It's a challenge, but traffic mostly limits that if you want to keep your car in one piece. I mostly drive in comfort mode and it's still plenty rowdy and hard to resist.

[DO444]

Originally Posted by CanAutM3

“Bad” is relative. Often, a “slippery” shape yields a lot of lift. To counter lift, downforce features need to be added and they increase drag. Further, as I posted earlier, radiator air inlets are terrible for drag and the M3/4 have a lot of them for performance reasons.

Well, there is no doubt at all that this car is a hell of a lot safer at speed than a 340i. Lift is a real issue after ~115mph, but not in this car.

F series I did not feel safe over 105. It was like driving a marshmallow.

[Fugly M3]

Originally Posted by DO444

Well, there is no doubt at all that this car is a hell of a lot safer at speed than a 340i. Lift is a real issue after ~115mph, but not in this car.

F series I did not feel safe over 105. It was like driving a marshmallow.

Interesting...never felt that way in the F series cars I had...and pretty much all my track time (and a good chunk of my Autobahn time) was in them.

[CanAutM3]

Originally Posted by DO444

Well, there is no doubt at all that this car is a hell of a lot safer at speed than a 340i. Lift is a real issue after ~115mph, but not in this car.

F series I did not feel safe over 105. It was like driving a marshmallow.

F3X or F8X ?

Because both my F82 felt very well planted up to their top speeds (over 170mph).

[DO444]

Originally Posted by CanAutM3

F3X or F8X ?

Because both my F82 felt very well planted up to their top speeds (over 170mph).

F3x, specifically talking about vs m-lite cars, 340i etc. conversation turned to lift and designs regarding lift specifically, to which I can confirm regardless of design the m cars are much better at negating the effects of lift vs m-lite cars.

It’s really a night and day difference in my experience. One feels like a strong breeze could flip you traveling @ 120mph (340i) and the other feels rock solid (m3).

[Fugly M3]

Originally Posted by DO444

F3x, specifically talking about vs m-lite cars, 340i etc. conversation turned to lift and designs regarding lift specifically, to which I can confirm regardless of design the m cars are much better at negating the effects of lift vs m-lite cars.

Never had that issue with my 230i THP (the lightest of the bunch). Hummed right along at 120+ for nearly 100km on Autobahn 3 on way down to Frankfurt from Cologne for ED drop-off. GPS unit registered 157 as the top out. The 228/230 with THP were unsung standouts of the non-M F range.