Roof spoilers: Eye sore and they suck

[Mike RT4]

As a bit of fun, they were so proud of reducing the lift that the did this advert back in the day LOL:

https://youtu.be/Gnp3NMAkbRY?si=l4B7I9ik172ArHRz

[Mike RT4]

CSL bootlid does not have the button/handle to open it nor the tool kit, so that is probably worth two or three pounds.

Agreed, so possibly a fraction lighter when that is taken into account. However, bare weight of each there is a negligable difference. Would be interesting to see how the actual fully fitted weights compare.

[Mike RT4]

I feel foolish for copy+pasting the 200-160 conversion without bothering to check the math, but I'll own that. Very interesting story about the engineering behind the project, especially the note about the weight. A standard CSL trunk is actually no weight difference vs. the standard bootlid?

Also dug a little further and finding that the swing isn't +18 to -10kg, but rather +18 to +10 (std --> CSL). This tracks with the engineers saying the goal was to reduce lift. So now the point is less than 20lbs difference at 120mph.

I did some follow-up research as well, and you are correct, I always thought that the negative figures quoted were in relation to negative lift (i.e. down force), but they relate to downforce, so negative figures are lift. Learned something new myselft today. Thanks for making me question this and what I "thought" I knew.

These are the Sport Auto figures referred to:

[Slideways]

CSL bootlid does not have the button/handle to open it nor the tool kit, so that is probably worth two or three pounds.

[Albino09]

I can give you some insight into how the ducktail actually came about. When we had the 20th anniversary meet-up for the CSL in May last year, we were fortunate to have many of the engineers on hand responsible for all aspects of the CSL. One of those was the aerodynamicist Jörg Ellers.

Gerhard Richter who was in charge of M division at the time the CSL was being developed would do a walkaround of the shop floor every evening to inspect how the work on the project was progressing. Originally the CSL was actually supposed to get a bolt-on wing on the standard boot but Jörg who was responsible for the car’s aerodynamics had calculated that a ducktail would provide the required negative lift and look much better than a bolt-on wing. So having produced a clay model as proof of concept, he decided that on the next evening he would leave the model of the car with the ducktail (complete with a lacquered foil covering to further highlight the design) in plain sight for Mr Richter to see when he was making his rounds, and wait to see what his reaction was. Upon spotting the model, Mr Richter stopped immediately and started to study the rear. Waiting for his moment Jörg then took the opportunity to join him and explain that the ducktail provided the same required aero balance as the much less aesthetically pleasing bolt-on wing. Fortunately Gerhard Richter agreed and responded that he loved it and the rest as they say, is history!

Obviously due to the shape, BMW used their newly developed fibre reinforced plastic material to show case what shapes they could produce and it is actually practically the same weight as a standard boot (so wasn't done for weight-saving reasons).

I would also point out that the speeds quoted for the downforce at 124mph (which is the 200km/h quoted - which is the norm for most downforce figures). I have no idea how someone calculated that to be 160mph......

It is pretty easy to calculate the correct speed, as the 0-100kmh time is equivalent to 0-62mph, so 2 x 62 = 124mph LOL.

I feel foolish for copy+pasting the 200-160 conversion without bothering to check the math, but I'll own that. Very interesting story about the engineering behind the project, especially the note about the weight. A standard CSL trunk is actually no weight difference vs. the standard bootlid?

Also dug a little further and finding that the swing isn't +18 to -10kg, but rather +18 to +10 (std --> CSL). This tracks with the engineers saying the goal was to reduce lift. So now the point is less than 20lbs difference at 120mph.

[old///MFanatic]

M3 E46
Lift Force at 200 Km/h (160mph) : 18kg (39.6lb) at rear
M3 CSL
Lift Force at 200Km/h (160mph) : -10kg (-22lb) at rear

60lbs of downforce vs. the standard M3 at 160mph is hardly what I would a real performance advantage. The true value of the trunk is that it is made of carbon and the rest is a bonus.

200 Km/h is 124mph.

I stand corrected on the material used, but not the rest.

As brought up by another member, apparently you stand corrected on more.

[heinzboehmer]

I can give you some insight into how the ducktail actually came about. When we had the 20th anniversary meet-up for the CSL in May last year, we were fortunate to have many of the engineers on hand responsible for all aspects of the CSL. One of those was the aerodynamicist Jörg Ellers.

Damn, didn't realize the engineers were at that meet too! Would have loved to have the chance to pick their brains.

[Mike RT4]

I can give you some insight into how the ducktail actually came about. When we had the 20th anniversary meet-up for the CSL in May last year, we were fortunate to have many of the engineers on hand responsible for all aspects of the CSL. One of those was the aerodynamicist Jörg Ellers.

Gerhard Richter who was in charge of M division at the time the CSL was being developed would do a walkaround of the shop floor every evening to inspect how the work on the project was progressing. Originally the CSL was actually supposed to get a bolt-on wing on the standard boot but Jörg who was responsible for the car’s aerodynamics had calculated that a ducktail would provide the required negative lift and look much better than a bolt-on wing. So having produced a clay model as proof of concept, he decided that on the next evening he would leave the model of the car with the ducktail (complete with a lacquered foil covering to further highlight the design) in plain sight for Mr Richter to see when he was making his rounds, and wait to see what his reaction was. Upon spotting the model, Mr Richter stopped immediately and started to study the rear. Waiting for his moment Jörg then took the opportunity to join him and explain that the ducktail provided the same required aero balance as the much less aesthetically pleasing bolt-on wing. Fortunately Gerhard Richter agreed and responded that he loved it and the rest as they say, is history!

Obviously due to the shape, BMW used their newly developed fibre reinforced plastic material to show case what shapes they could produce and it is actually practically the same weight as a standard boot (so wasn't done for weight-saving reasons).

I would also point out that the speeds quoted for the downforce at 124mph (which is the 200km/h quoted - which is the norm for most downforce figures). I have no idea how someone calculated that to be 160mph......

It is pretty easy to calculate the correct speed, as the 0-100kmh time is equivalent to 0-62mph, so 2 x 62 = 124mph LOL.

[///Mangler]

Look at the OG E30 M3. The roof bump, at the back of the roof, specifically makes the air hit the OE rear wing with optimum flow. The added 'adjustable flap' was further evolution of this 'system'. This is why the E30 M3 didn't go to the higher wing for more downforce, the roof bump would have put the airflow under it, and not over the top of it.

T

[Arith2]

I'm doing this from memory - but the 60 lbs of downforce is at 160 MPH IIRC. Citing downforce without the associated speed it tied to has no context in reality. How many of these cars are really (lets not kid ourselves) are driven at 160 mph?

Less than that, its about aero drag as much as anything else.

My car saw 140+ often and the extra downforce is very welcome. A full body underbody panel would massively help the downforce and probably reduce drag at the same time. That's a later project when I have more time and the kids get older.

[Albino09]

The point is it’s not purely aesthetics.
Yes the weight savings is another added bonus along with looks. Just to clarify it’s not made of carbon.

I stand corrected on the material used, but not the rest.

[old///MFanatic]

I'm doing this from memory - but the 60 lbs of downforce is at 160 MPH IIRC. Citing downforce without the associated speed it tied to has no context in reality. How many of these cars are really (lets not kid ourselves) are driven at 160 mph?

Less than that, its about aero drag as much as anything else.

Good point and true.
On that point, two earlier BMW articles stated it cut rear lift by 50% @120mph.

[Estoril]

Roof spoilers create separation at the base of the window on our cars making them stupid to use. If it doesn't on whatever car, then it's fine. This is the E46 M3 section though and it sucks. And it's ugly. The CSL trunk adds 60 pounds of downforce without creating a bunch of drag and it's functional on corners without sacrificing the everyday drivability that a giant wing would bring.

I'm doing this from memory - but the 60 lbs of downforce is at 160 MPH IIRC. Citing downforce without the associated speed it tied to has no context in reality. How many of these cars are really (lets not kid ourselves) are driven at 160 mph?

Less than that, its about aero drag as much as anything else.

[Arith2]

Roof spoilers create separation at the base of the window on our cars making them stupid to use. If it doesn't on whatever car, then it's fine. This is the E46 M3 section though and it sucks. And it's ugly. The CSL trunk adds 60 pounds of downforce without creating a bunch of drag and it's functional on corners without sacrificing the everyday drivability that a giant wing would bring.

[Slideways]

The OE CSL trunk material is a composite, IIRC

BMW probably went with Sheet Moulding Compound over carbon fiber for these reasons: "very high productivity, excellent part reproducibility, cost efficiency and the possibility to realize parts with complex geometries and integrated functions."