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Discussion Starter · #1 · (Edited)
Hello guys,

I guess it's time now to open an official thread on this upgrade - GMS Carbon rear ducktail hood w/ optional race wing. So what do we have here?

Well, we have lots of carbon fiber put into a good use. Our goal here was to reduce the weight at the back of the car and to provide increased aero downforce on the rear of the car as regardless of the setup always felt the car slightly unstable at high speed corners.

With the GMS carbon rear hood in combination with GMS carbon rear louver, we saved 8600g of weight over OEM parts, increased cooling capabilities (hot air extraction of the engine bay) and gave the car with basic downforce that the integrated ducktail is producing (CFD estimated downforce 20kg - 30kg @ 160 km/h). The hood and the louver are now publicly available.

The additional feature of this unique hood is also ability to install proper GMS race wing on it, which in combination with integrated ducktail significantly increases downforce (CFD estimated downforce over 100kg @ 160 km/h). We are still working on some updates and doing extensively ontrack testing of the GMS race wing, so it will be publicly available in next few months. The optional GMS race wing also has adjustable angle of attack and ranges from 0° - 15° which can be adjusted to your preferences for given track layout. The side brackets connecting GMS rear hood and the wing are T6- 6061 aluminum CNC machined and incognito black anodized, while the brackets connecting GMS race wing and the side brackets are full carbon fiber.

For those running no front aero, we find this GMS kit to work best at about 3° - 5° of rear wing angle on high speed track and up to 9° on medium speed tracks. Anything over than that, results in slight, stable understeer at high speed corners. During winter, we'll also have a look at the front end aero, which will then allow us to run the GMS race rear wing at maximum efficiency at about 7°.

Here are some photos of prototypes in action. I'm aware some of you are against upgrades like this and i completely understand that, but once you get the taste of aero grip and sorted out steering and suspension components, it's hard to go back to stock. Anyway, we are happy with the current CFD results and the handling affect, but what we are the most happy with, is when the idea gets converted to the final product and shows benefits in real life scenario when parts are put into actual use. The rear end grip is just immense. Proof?


Hood Font Bumper Auto part Personal protective equipment Luggage and bags Automotive design Bag Automotive exterior Bumper Car Vehicle Tire Wheel Plant Vehicle Car Hood Automotive lighting Motor vehicle Wheel Tire Cloud Vehicle Car Wheel Vehicle registration plate Tire Vehicle Car Tire Wheel Vehicle Car Automotive tire

P.S.: For this particular and demanding project in terms of effectivity (low drag penalty), we are cooperating with UK based renown wing fabricating company, which also does wings for mainly Lotus cars. All the CFD analyzes were done by them, while we took care of actual on track and on road testing.
 

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Whatever floats your boat, but I'm not a fan of the ironing board on the back for street use.
 

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Discussion Starter · #5 ·
Whatever floats your boat, but I'm not a fan of the ironing board on the back for street use.
I understand your doubts. Personally I can't help myself, I'm an aero addict. When you drive a car with proper aero and experience the 4C finally being planted at 180kmh sweepers you can't go back.

I also got so used to it that I feel like something is missing without a wing.

It's just that there is such a thin line between a useless fake bling bling wing and a proper motorsport effective wing and getting it wrong makes then the entire car look wrong quickly. Trust me that's not the case here.
 

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Whatever floats your boat, but I'm not a fan of the ironing board on the back for street use.
GMS is one of the few vendors out there delivering goods in the aftermarket for the 4C. You are entitled to opine, but it's in slightly bad taste. Sort of like walking into a store that has a new product ad in the window; you don't like the product, so you go in to tell them you wouldn't buy it, then walk past the customers on the way out.

Like... okaaaaaaayyyyyy....
 

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Discussion Starter · #8 ·
@Philster thanks for standing for us. However, no offense was taken. I appreciate every opinion. Positive and negative. I listen to every opinion, but don't bother with it too much if it doesn't help me. I just do what my intuition tells me too, I don't care whether it gets public approval or not.

We are different people, have different tastes and ideas and as long as there is a respect in between, all is good. I used to think I'm always right and my way is the only way. Now with years I used to get better accepting the diversity. There are many things I don't like neither understand. Some are doing air suspension on 4C, other are PPF coating, waxing, polishing cars, keeping them in garages not to put miles on them. Things like this I'd never do, yet I cannot say they are wrong. They are just different. Different thing floats their boat, and that's probably what the @AROC 4C wanted to say. He probably hates our idea, feels bad for our 4C not being pristine, yet it will make me and probably a few other weirdos happy when we'll be setting new PR's on the track with help of this carbon fiber ironing board. For me improving performance is what floats my boat. BTW, some front aero is coming this / next year too.

Just do more of what makes you happy, let it be PFF, more carbon fiber or simply blasting another trackday. Love and peace to everyone. 🥰
 

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Funny how one very clean simple addition, that doesn’t detract, interfere or change a single factory line changes the personality so much.

The big wing turns our cute little rascal into a scary mofo. Unlike eBay tat that’s stuck on a Mazda with tape, this says motorsport prepared carbon asskicker.
 

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Discussion Starter · #11 ·
What's mechanical grip?

It's the amount of grip G-forces, the car can generate through the corners, braking or acceleration. Car's weight and tire grip dictates it. When you are in the corner, the car's tendency is to go straight (centrifugal force), and you prevent doing it so by turning the wheel. The tires friction allows you to maintain the direction unless your speed is too high. After this point the car will either understeer or oversteer out of the corner. Making the car heavier will generate bigger friction between the tires and the surface, but it will at the same time also generate bigger centrifugal force, so we didn't achieve anything. The lighter the car, the faster it will go through the corner, but at some point if the car would be too light the friction between the tires and the surface would be too low to provide any more grip. In very simplified words, a 1000kg car and 2000kg car can eventually achieve same cornering speed but will require different tires to do so, but both will be limited with grip at some point. The heavier the car, the wider the tires are needed.

What tire width is optimal?

Wider tires create more mechanical grip, to a point where they don't anymore. Putting ultra wide tires on lightweight car like 4C would cause the tires not to heat up, reduced friction to the ground and eventually reduced grip. The wider you go, the softer the compound needs to be to make it work. You can try putting square setup on a 4C and have some fun. Soon you'll notice it handles bad. Now take the measurements of the tire temps and you'll notice a significant difference between the fronts and the rears. The reason for that is that the rear tires have to carry about 600kg of weight, while the fronts only 400kg. That means the rears will have 50% more work to do then the fronts. Because of that we have staggered setup right from the beginning. Whatever tire width and compound you run, make sure you get the temps to operating level to perform at it's best. For me 215 / 265 works the best, but this also depends of the spring rates, aero, and actual weight. Definitely, a square setup is not something you would want on your 4C.

How to go faster through the corners then?

We are limited by mechanical grip, but what we can do is increase aero grip. By creating downforce on the car, we increase the downward pushing force on the car, increasing the friction between the tires and the surface, meaning we increase grip of the tires, yet not affecting the centrifugal force in any negative way as we haven't increased the actual car's weight.

So how does aero actually work?

The same principle (Bernoulli) that allows an airplane to rise off the ground by creating lift from its wings is used in reverse to apply force that presses the race car against the surface of the track. On the cars we are using actually a reversed airplane wings design. This creates high pressure area above the wing and low pressure area under the wing. Both forces combined create downforce, a suction effect pulling the car to the ground, increasing aero grip.

How does aero work on 4C particularly?

It works very well because the car is very light so even smallest added aero greatly benefits the performance of the car. Generating 100kg of downforce on a car that weighs 1000kg is 100% more effective than generating 100kg of downforce on 2000kg car. In simple words, the 4C with same amount of aero than a 1000kg heavy car will benefit twice as much from it. If we could increase our cornering speed for 10%, the heavier 2000kg will be able to increase it only for 5%. Once again, lightness is the key and by addign aero we can embrace it so much more.

What about the drag?

This is one and the only negative effect of the aero. At this point, it is very important to work smart and analytic. Having a small wing with aggressive AOT (angle of attack) will cause much more drag then a big wing with low AOT. So the general rule of thumb is, to install as big wing as possible at the least aggressive angle as possible. This will yield the best drag / downforce ratio. With approach like this, the increased grip and speed through the corners and braking will be far more significant then the top speed loss due to the drag. Coming 5km/h faster out of the corner and braking 10m later will make up for the lost power due to the drag. The tighter the track the more obvious this will be.

Did you know?

The higher the speed, the more prone is car to oversteer due to the aerodynamic effects. Doing an instant maneuvering of aggressively turning left at let's say 40 km/h will result in understeer. Doing the same thing at 140 km/h will result in oversteer. Imagine doing this at 200 km/h. Car would easily spin out. First generation of Audi TT, was notorious for being dangerous to drive at high speed due to the amount of lift it was generating. It generated 67kg of lift at 200 km/h which resulted in numerous crashes on highways leading to lawsuits and later recall of all the cars, where all the TT's were fitted with a small rear spoiler. On the other hand too much of rear downforce over the crest could be an issue too.
 
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