[casualDIYer]

If I lower my car with the M-Sport bumper on my F30 wouldn’t that be the same as adding a front splitter? Lowering would also close the side skirt-pavement gap as well.

Interested in getting some feedback on this topic

[alohasurftoad]

imo, lowering is lowering.

adding a front splitter is just lowering the chin of the bumper and altering/enhancing aero with designed material(pu or cf).

obviously a front splitter will not reduce the wheel gaps but may cause it to appear lowered if viewed from the front.

not sure, if this is answers your question...

[casualDIYer]

Originally Posted by alohasurftoad

imo, lowering is lowering.

adding a front splitter is just lowering the chin of the bumper and altering/enhancing aero with designed material(pu or cf).

obviously a front splitter will not reduce the wheel gaps but may cause it to appear lowered if viewed from the front.

not sure, if this is answers your question...

The job of the splitter is to limit the amount of air getting underneath the car. But wouldn't adding lowering springs do exactly the same thing? Lowering definitely closes the gap between car and road so, it seems, there would be some areo effect similar to a splitter in terms of allowing less airflow underneath the car.

BMW mentions that if one adds a front splitter, one should also add a rear trunk spoiler as well. If lowering car has the same effect as adding a splitter (i.e. limiting air flow getting under the car), would it mean lowering also means one should add rear trunk spoiler?

[alohasurftoad]

ahh, okay. this is beyond my knowledge of car aerodynamics. but my limited speculation is, the splitter increases the cross section and redirects airflow around the car, so it's actually causing a higher pressure area below the vehicle, which would actually cause lift, so maybe the spoiler is to reduces lift created by the splitter?

if you look at a formula1 car it is actually shaped like an upside down wing so the higher pressure air is above it pushing down, as well as the front and rear wings(also upside down)

idk, this is beyond me, so it's prolly best we wait for an SME in vehicle aerodynamics to chime in

i feel the splitter affects the aero more than lowering but i really don't know. whatever the case, you'd have to be driving quite fast to realize it's affect. most of us on the forum are just doing it for appearance

[visionaut]

The M Perf front splitter (like on my 435) is actually a downforce enhancing design. It’s not an air dam. The wide lower ‘edge’ is actually a beefy inverted wing (flat on top, airfoil on the bottom), generating downforce. At speed it lowers the car chassis from this aero design flowing air thru/past the wing above and below. They advise a paired aerodynamically-matched rear spoiler so the rear downforce balances the car from going nose down at speed.

It’s not = statically lowering the car

[Ennoch]

Originally Posted by casualDIYer

The job of the splitter is to limit the amount of air getting underneath the car. But wouldn't adding lowering springs do exactly the same thing? Lowering definitely closes the gap between car and road so, it seems, there would be some areo effect similar to a splitter in terms of allowing less airflow underneath the car.

BMW mentions that if one adds a front splitter, one should also add a rear trunk spoiler as well. If lowering car has the same effect as adding a splitter (i.e. limiting air flow getting under the car), would it mean lowering also means one should add rear trunk spoiler?

Lots of maths could explain it but, if you're lowering the car you're lowering it equally and not changing the aero balance of front to back. Lots of cars used to be, and many still are, designed so that they would get gentle lift at speed which would push drivers to back off. Performance variations thus really needed air dams/splitters on the front to minimise this effect.

With a splitter air still gets underneath but the less airflow getting underneath the car the better as it pushes the displaced air over rather than under, creating high pressure above the car and low pressure beneath, i.e downforce. Big motorsport splitters do this very effectively, road going ones less so as they're too far from the ground because they need to clear obstacles (look at the rally cars and they use flexible grp things to do that purpose). I suspect the aero balance may move slightly forwards with a splitter on the M bumper but I can't imagine it would be by enough to warrant an extra rear wing given the overall amount of downforce we're talking about (most stuff on a road car is minimising lift rather than creating downforce per a race car that's close to the ground). I mean look at the large STI rear wings on the Impreza, they offer zero downforce unless it's one of the adjustable top plane ones, and 99.9% of the ones you see aren't.

[B58-Hustler]

In my opinion a front splitter is pretty much only a cosmetic upgrade for 99% of people, myself included. That isn't to say it's bad of course, make your car look how you like.

If you want to close the wheel gaps and the side skirt to pavement gap, you need to lower the car via suspension. You can add a splitter and it'll look lower in the front, but not at the sides of course. You can add skirts to close the pavement gap, but you'll still have wheel gaps.

So, a front splitter is not the same as lowering, really not even close.

[cfm56d7b]

Originally Posted by casualDIYer

If I lower my car with the M-Sport bumper on my F30 wouldn’t that be the same as adding a front splitter? Lowering would also close the side skirt-pavement gap as well.

Interested in getting some feedback on this topic

Are you looking to enhance the visual appearance or improve aerodynamics?

[casualDIYer]

Originally Posted by cfm56d7b

Are you looking to enhance the visual appearance or improve aerodynamics?

My car is already lowered on ACS springs to help eliminate wheel gap so I've already made a choice in that regard. I had considered a front splitter as well but in looking into this topic in greater detail it seems lowering the car does improve it's aerodynamics by reducing the amount of air able to get underneath it. Is it significant enough to save fuel or increase top speed? I haven't noticed. I'd estimate the windshield is the number culprit in adding drag to the car and there's not much I can do about that.

As much as I like the idea of adding a splitter to further help reduce under-car drag, plus add cosmetic flair, with the car being lowered, a splitter may end up in the sh*tter crashing into curbs or or any moderate incline, including driveways and maintenance ramps.

[thejeremyman9]

Originally Posted by visionaut

The M Perf front splitter (like on my 435) is actually a downforce enhancing design. It’s not an air dam. The wide lower ‘edge’ is actually a beefy inverted wing (flat on top, airfoil on the bottom), generating downforce. At speed it lowers the car chassis from this aero design flowing air thru/past the wing above and below. They advise a paired aerodynamically-matched rear spoiler so the rear downforce balances the car from going nose down at speed.

It’s not = statically lowering the car

This is a correct answer RE aero of a splitter and why BMW recommends pairing with a rear spoiler. The front splitter (in theory) adds front downforce, rear spoiler adds rear downforce. Also note that these are not necessarily going to reduce drag, especially the rear wing, which will actually add drag as it will cause flow separation and increase the size of the wake behind the car.

Originally Posted by casualDIYer

My car is already lowered on ACS springs to help eliminate wheel gap so I've already made a choice in that regard. I had considered a front splitter as well but in looking into this topic in greater detail it seems lowering the car does improve it's aerodynamics by reducing the amount of air able to get underneath it. Is it significant enough to save fuel or increase top speed? I haven't noticed. I'd estimate the windshield is the number culprit in adding drag to the car and there's not much I can do about that.

As much as I like the idea of adding a splitter to further help reduce under-car drag, plus add cosmetic flair, with the car being lowered, a splitter may end up in the sh*tter crashing into curbs or or any moderate incline, including driveways and maintenance ramps.

The drag is reduced by the underbody shielding. You want as smooth of a underbody as possible so that the streamlines under the car are not disturbed - basically the air goes right under the car and out the back. A rear diffuser has a similar purpose, as it "sucks" the air from under the car and pulls it up to reduce the size of the wake (low pressure zone) behind the car. Smaller wake = less drag. A diffuser coupled with a streamlined shape on the top of the car pulls the air from the bottom up and the air from the top down resulting in a very small wake and low coef of drag. Think tesla shape.

Curious why are you saying that the "amount of air" under the car is going to affect drag? The only thing that matters is the air you are disturbing. There can be a whole bunch of air under the car or only a little bit, the only thing that is going to affect drag is how much of that air the car is interacting with. If the majority of the air goes under the car undisturbed (or rather, the car "cuts" through the air without disturbing it since the car is what is moving), then you will have minimal drag.

[Onizukachan]

Originally Posted by casualDIYer

My car is already lowered on ACS springs to help eliminate wheel gap so I've already made a choice in that regard. I had considered a front splitter as well but in looking into this topic in greater detail it seems lowering the car does improve it's aerodynamics by reducing the amount of air able to get underneath it. Is it significant enough to save fuel or increase top speed? I haven't noticed. I'd estimate the windshield is the number culprit in adding drag to the car and there's not much I can do about that.

As much as I like the idea of adding a splitter to further help reduce under-car drag, plus add cosmetic flair, with the car being lowered, a splitter may end up in the sh*tter crashing into curbs or or any moderate incline, including driveways and maintenance ramps.

Increase top speed? No. Top speed is limited.

Save fuel,not likely. Splitters aren’t airdams and airflow is already well controlled.
Hell I LOST fuel economy after lowering from increased drag in the output shafts. But not anymore than I lost from adding performance tires with higher rolling resistance.

Choose the right splitter and don’t drive into parking blocks or like a tool and you won’t have to worry about breaking it. See my car for an example.

Edit. I know where your theory comes from, and it is applicable to prior cars, but these are flat bottomed skirted cars with nothing hanging out in the breeze, so you aren’t reducing drag by sending more air around the car vs under it.

[cfm56d7b]

Originally Posted by casualDIYer

My car is already lowered on ACS springs to help eliminate wheel gap so I've already made a choice in that regard. I had considered a front splitter as well but in looking into this topic in greater detail it seems lowering the car does improve it's aerodynamics by reducing the amount of air able to get underneath it. Is it significant enough to save fuel or increase top speed? I haven't noticed. I'd estimate the windshield is the number culprit in adding drag to the car and there's not much I can do about that.

As much as I like the idea of adding a splitter to further help reduce under-car drag, plus add cosmetic flair, with the car being lowered, a splitter may end up in the sh*tter crashing into curbs or or any moderate incline, including driveways and maintenance ramps.

While stopping short of asking F-35 aerodynamics engineer to weigh in, the benefits of having a splitter are mainly aesthetic in daily driving conditions.

I would add that worrying about navigating on / off parking ramps may not be worth the trouble.

[visionaut]

Originally Posted by cfm56d7b

While stopping short of asking F-35 aerodynamics engineer to weigh in…

Happens to be I’m an aero systems engineer for LM… I won’t speak for other splitters or spoilers designs or functional capabilities, just the M Perf one for the 4 series, which was developed via wind tunnel testing by BMWs aero group, and they’re some of the best. It can add ~150lbs ‘down force’ to the front at 125mph… thus the need to balance out the cars aero with an equally functional rear spoiler, like I mentioned earlier. The aerospace-level strong composite BMW unit is actually a splitter-spoiler hybrid technically - given the differences at the center vs the outer edges, and how it integrates into & enhances the already excellent body aero EfficientDynamics. The BMW aero-enhanced underbody / fenders assist the desired faster underbody flow from the splitter leading edge. So this one’s functional - helping preload and stabilize the chassis at higher speeds (straight line and turning).

Many seem to confuse air dams (think vertical surfaces), spoilers (think slanted) and splitters (think horizontal). And these with ground effects, also different…

[thejeremyman9]

FYI, i have stock ride height on 335i Msport RWD and my Msport front splitter unavoidably drags on any driveway/incline with even a moderate angle. I would consider it a consumable item and plan on replacing about every 5-10k miles. Mine is a ABS replica and it has worn through on the center. And yes, i know how to drive a low car, take driveways at an angle, etc. It's just low and overhangs even at stock height.

[visionaut]

I hear ya - though I’m well into 2 years with mine, with only some minor scrapes in the center-front so far. (knock on cf)

My 435iX THP is also stock ride-height and I’ve measured the low point on the splitter (which is about 5” back and 1.25” lower than the leading edge) to be only 4.5” off the ground (static). That plus the extension in front of the normal bodywork = be careful out there.