Big Wings: Helpful or hurtful? What's your opinion?

[M3SQRD]

Originally Posted by bigjae1976

Something I found is that the material can make a big difference. I went from a plywood to a carbon splitter, both were the exact same size with the same mounting. The carbon splitter changed the balance from understeer to oversteer.

This suggests the increase in aero efficiency of the front CF splitter moved the COP forward of the COG. Does the CF version have a better leading edge radius than the plywood version?

[bigjae1976]

Originally Posted by M3SQRD

This suggests the increase in aero efficiency of the front CF splitter moved the COP forward of the COG. Does the CF version have a better leading edge radius than the plywood version?

Similar. Easier on the plywood with a router vs trying to chamfer foam.

It had to do with the stiffness. The plywood would cause the front of the car to porpoise at 140mph (quite scary) because the plywood would flutter.

I’m sure the front of the plywood splitter would be pushed down at speed instead of the front end.

[M3SQRD]

Originally Posted by bigjae1976

Similar. Easier on the plywood with a router vs trying to chamfer foam.

It had to do with the stiffness. The plywood would cause the front of the car to porpoise at 140mph (quite scary) because the plywood would flutter.

I’m sure the front of the plywood splitter would be pushed down at speed instead of the front end.

WOW! That does sound scary! How did you determine it was the plywood vibrating at 140 mph and causing the porpoising? Could you hear it?

[bigjae1976]

Originally Posted by M3SQRD

WOW! That does sound scary! How did you determine it was the plywood vibrating at 140 mph and causing the porpoising? Could you hear it?

It was insane. The bouncing was so bad that the splitter was really the only plausible thing it could be.

[M3SQRD]

Originally Posted by bigjae1976

It was insane. The bouncing was so bad that the splitter was really the only plausible thing it could be.

That would have resulted in a major shunt if that thing had failed mid-corner!

[nickauger]

Just My 2cent but i ve run an e90 without aero and was getting 220kmh in the stretch, after gt4 lip and apr gt250 61" i'm now getting between 210 and 212 on same stretch but feeling more confident in high speed curve get me better lap time.

[e92BMW///M3]

I recently added a GT4 rear wing to go with my chassis mounted GTS front lip/splitter. No idea if the wing is functional to any great extent, but anyone who is installing this I highly suggest adding reinforcement under the wing (maybe obvious).

I used 1/8" x 2" x 7.875" aluminum purchased from a hardware store and JBWelded it (the trunk and aluminum plate) all together. there was about 3" both front and back of the mounting points. Dramatically increased the stiffness of the wing on the car to the point it barely vibrates when I slam the trunk closed.

[pirategenes]

Originally Posted by e92BMW///M3

I recently added a GT4 rear wing to go with my chassis mounted GTS front lip/splitter. No idea if the wing is functional to any great extent, but anyone who is installing this I highly suggest adding reinforcement under the wing (maybe obvious).

I used 1/8" x 2" x 7.875" aluminum purchased from a hardware store and JBWelded it (the trunk and aluminum plate) all together. there was about 3" both front and back of the mounting points. Dramatically increased the stiffness of the wing on the car to the point it barely vibrates when I slam the trunk closed.

Very cool and thanks for this helpful information. I'd love to see some pictures of your setup if you are willing to share. I should be receiving my Ridgeline Motorsport Ring Spec Wing soon and am planning the mounting strategy. I'm also planning reinforcements - thinking of under the trunk between the exterior and interior skin with JB Weld to bond. Probably some carbon base plate on top of the trunk too. Did you mount your reinforcements under the trunk? If so, I assume you had to cut through some interior skin parts? Would you be willing to share pictures and details? Many thanks, and may the downforce be with you!

[e92BMW///M3]

Yes, you have to cut some skin underneath. I used a dremel with metal cutting attachments. I'm not that skilled so its certainly not going to win any awards but it was pretty straight forward. Couple pics attached, including the measurements I had for the GT4 wing with standard risers, in case its helpful but highly suggest measure 2-3 times before drilling (i.e. don't blindly follow these measurements).

[pirategenes]

Originally Posted by e92BMW///M3

Yes, you have to cut some skin underneath. I used a dremel with metal cutting attachments. I'm not that skilled so its certainly not going to win any awards but it was pretty straight forward. Couple pics attached, including the measurements I had for the GT4 wing with standard risers, in case its helpful but highly suggest measure 2-3 times before drilling (i.e. don't blindly follow these measurements).

This is super helpful to see - thanks so much for sharing! It looks like that project turned out great and I'm sure the wing will be MUCH more stable at speed as a result of the reinforcement. I have a few different cutting tools, so with some luck will be able to hack the inner skin sections away without touching the outer skin, which I'm a little nervous about. Thanks again for sharing, and let us see your final install picture when you're ready. I bet the GT4 wing looks great and will help with rear end stability.

[kolosy]

Originally Posted by pirategenes

This is super helpful to see - thanks so much for sharing! It looks like that project turned out great and I'm sure the wing will be MUCH more stable at speed as a result of the reinforcement. I have a few different cutting tools, so with some luck will be able to hack the inner skin sections away without touching the outer skin, which I'm a little nervous about. Thanks again for sharing, and let us see your final install picture when you're ready. I bet the GT4 wing looks great and will help with rear end stability.

fyi you can get a set made at sendcutsend pretty cheaply. you don't even need to cad things for a simple plate with holes, their online editor lets you specify dimensions and distance. you can even get them threaded or countersunk (depending on mounting specifics). i think i paid like $40 for mine.

[e92BMW///M3]

Originally Posted by kolosy

fyi you can get a set made at sendcutsend pretty cheaply. you don't even need to cad things for a simple plate with holes, their online editor lets you specify dimensions and distance. you can even get them threaded. i think i paid like $40 for mine.

This is great advice... since I spent $18 on the raw aluminum anyway, $40 ready to install would have been the way to go.

[pirategenes]

Originally Posted by kolosy

fyi you can get a set made at sendcutsend pretty cheaply. you don't even need to cad things for a simple plate with holes, their online editor lets you specify dimensions and distance. you can even get them threaded or countersunk (depending on mounting specifics). i think i paid like $40 for mine.

Very cool, thanks for the tip. Though I wouldn't want this new carbon fiber plate and diamond cutting disk sitting and waiting in my garage to go unused. So it will be full send on hacking for trunk reinforcements

[bigjae1976]

Just a tidbit...over the years the front of the bracket shows clear signs of pulling up on my trunk lid. I assumed it would push down. The rear bolt will push down.

If anything, you want more reinforcement on the front bolt to keep it from pulling up.

[kolosy]

Originally Posted by bigjae1976

Just a tidbit...over the years the front of the bracket shows clear signs of pulling up on my trunk lid. I assumed it would push down. The rear bolt will push down.

If anything, you want more reinforcement on the front bolt to keep it from pulling up.

Here’s visual backup for that. Ignore the caliper, was measuring for plugs. Note the stronger imprint on the back side than the front.

[UPSROD]

They are extremly ugley and very hard on the trunk lid!

[e92BMW///M3]

I had the same impressions on the rear as shown above, even after only a short while on the car at highway speeds.

[jmeenach]

Originally Posted by bigjae1976

Something I found is that the material can make a big difference. I went from a plywood to a carbon splitter, both were the exact same size with the same mounting. The carbon splitter changed the balance from understeer to oversteer.

Assuming the weight accounts for some that difference? Do you know what the weight differential was from wood to carbon?

[bigjae1976]

Originally Posted by jmeenach

Assuming the weight accounts for some that difference? Do you know what the weight differential was from wood to carbon?

It is about half the weight.

I can stand and bounce up and down on the carbon splitter which bounces the entire front end. Couldn’t do that with the plywood - the plywood bends too much.

It is all about the stiffness.

[omgzirra_exe]

Originally Posted by jmeenach

Assuming the weight accounts for some that difference? Do you know what the weight differential was from wood to carbon?

Originally Posted by bigjae1976

It is about half the weight.

I can stand and bounce up and down on the carbon splitter which bounces the entire front end. Couldn’t do that with the plywood - the plywood bends too much.

It is all about the stiffness.

I’ve been leaning on my wife for aero work for a while now. She has access to SolidWorks for modeling, FEA for stress and pressure loads, and CFD once we complete a full model. Her professor, a motorsports fan who has known me for more than seven years, sometimes joins our discussions. He usually stays quiet but steps in if we overlook something. At this point my sketches have basically become her unofficial side thesis, which I think is pretty cool. Everything below is pure theory, just numbers on a screen, not track-tested.

Here’s the theoretical data we put together:

Splitter model:
• 67 in wide, 4 in forward of the E92 bumper
• Average speed 97 mph (midpoint of 70–125 mph, speeds seen roughly at BW CW13)
• 80F air temp, aero pressure only

Carbon-foam sandwich, 1/8 in
• Approx. 565 lb downforce
• Approx. 0.03 in flex
• Epoxy good to Approx. 250F
• Lightest, stiffest, biggest safety window
• Downsides: price, harder to DIY (can find CF sheets to ease DIY)

Resin-impregnated birch, 1/2 in (9-ply) with fiberglass skins (something like this here: https://www.penn-elcom.com/us/1-2in-...attern-m847113
• Approx. 475 lb downforce
• Approx. 0.12 in flex, or Approx. 0.06 in with two 3/4 × 3/4 in aluminum ribs
• Resin safe to Approx. 194F
• Cheapest, easy to repair, ribs double stiffness
• Heaviest, needs edge sealing, really wants those ribs for rigidity.

Alumalite, 3/8 in PP core with aluminum skins
• Approx. 377 lb downforce
• Approx. 0.18 in flex
• Core softens around Approx. 176F (hot tracks can see 120F)
• Lighter than birch, cuts easily
• Most flex, narrow heat margin, needs reflective film and regular checks

Why stiffness matters:

A splitter works by staying flat and holding the low-pressure pocket under the nose. Once it bows, pressure rises and downforce drops.

All of this is purely theoretical. My wife ran these sims for me, and while motorsports is not her thing, I back her material-science expertise 100%. Still, the figures are just estimates on a screen, so real-world testing could tell a different story.

[///M Power-Belgium]

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[bigjae1976]

Originally Posted by omgzirra_exe

Carbon-foam sandwich, 1/8 in
• Approx. 565 lb downforce
• Approx. 0.03 in flex
• Epoxy good to Approx. 250F
• Lightest, stiffest, biggest safety window
• Downsides: price, harder to DIY (can find CF sheets to ease DIY)

Interesting! Can you remodel it with a 3/8" thick core? I wonder how much of an improvement that will yield. Increasing core thickness is the best way to improve stiffness to weight.

Actually, making the carbon piece is not hard. You can wet lay the carbon over the foam core against a sheet of melamine, lay peel ply, bleeder and then bag it. Pull vacuum until the initial cure. It won't be beautiful glossy carbon but its a damned splitter...who cares!

THe b!tch is trimming it. That sucks. You at least need a respirator and a diamond cut off wheel but the dust is really fine and it gets everywhere. I'd do it outside. The dust is also electrically conductive so it will destroy power tools if you aren't careful. You could theoretically very carefully and precisely pre-cut the carbon before wetting it out which would eliminate the trimming. You'll need some pricey shears to do the detail work. Easier said then done but might just need some light edge touchup with a flap disc or hand sand.