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grcor asked: Can you please tell us why you are not molding the fenders to eliminate the need for spats, protective film, and splash guards?
Tadge answered: All Corvette exterior features and surface shapes are designed for maximum performance and great aesthetics. Around the front wheel openings, both the C6 (Z06, GS and ZR1) and C7 (GS and Z06) feature what you are calling spats arcing down the forward edge. These features create high pressure on the front/top and low pressure on the back/underside resulting in down force and evacuation of hot air from the wheel opening. The aerodynamic studies for both C6 and C7 independently proved their value. To work, they need to be a very specific shape - specifically a sharp break in the surface where the spat meets the fender. I have been asked many times why we couldn't just form that shape from the front fender so it would be all one painted piece instead of looking "tacked on". We looked at that and decided it looked pretty bad when painted bright colors. Your eye is immediately drawn to that feature and it does not look integrated or graceful. Naturally the question is, "If it is so important, why don't we see it on the C7.R race car?" The reason is that the race car sits so low to the ground it can take advantage of even more efficient aerodynamic features such as an "underwing" that sits beneath the front splitter. "Ok, then why don't we see it on other street cars?". Well, actually you do. There are several, typically very serious performance cars that have similar features such as the Porsche GT3RS.
On the question of why we don't pull the fender behind the tire outboard to completely cover the front tire, there are several reasons for that. The main reason is aerodynamic drag. The air flowing by the side of the car wants to re-attach to the smooth part of the body rearward of the wheel opening. The lowest drag cars in the world actually have a very large radius on the body surface making up the transition from the wheel opening to the body side. Bringing the corner of the bottom of the fender out flush with the outside of the tire creates a stagnation point for the air which generates high pressure on a forward facing surface - drag. That same forward facing surface also makes a perfect target for stones coming off the tire... It gets hammered. So most companies choose to bring that fender corner inward a bit and put some radius on it. Others add what looks like a small mud flap.
Stone throw mitigation is actually an interesting science. With slow motion video we know that many stones don't take the obvious path straight off the tire and into the body side. Some bounce between the underside of the car and the roadway more than once before contacting a part of the car where you might notice the damage. I mention this because the premise of this question is that we can solve the stone throw problem with fender shape. It is true we can help it at the cost of drag, but can't solve it completely.
The last point I would make is that the Corvette is a relatively compact car with massively over-sized tires. Like many sports cars around the world, the architecture and aesthetic choices give the car a very aggressive look. For decades the "coke bottle" shape has been a Corvette hallmark. We could help stone throw by making a slab-sided car with the body skin pushed out to the outside face of the tires, but it would look like a refrigerator on wheels. Instead we typically pull the body skin in as tautly as we can over the mechanicals giving it the lean, muscular shape most people really like.
Interesting! So the aftermarket front stone guards I use to save the rear fenders is probably keeping me from going over 150 at WG'S back stretch, wow! Never would of guessed that.
I love it when Tadge gives us a lot of details in his response like he did here. I almost didn't click on the response because I figured "who cares about the spats?". I learned a lot about the aero design of the car from his response and am really glad he took the time to share with the community.
I love it when Tadge gives us a lot of details in his response like he did here. I almost didn't click on the response because I figured "who cares about the spats?". I learned a lot about the aero design of the car from his response and am really glad he took the time to share with the community.
as a former jet mech an loooooooong time racer thanks for the write up will sick a lot of those that don't understand air flow to this site.THANK YOU. JD
I was of the opinion, as many, that I did not like what appeared like afterthought "spats" used on the GS (Z06.) Since I believe in "form follows function" I now think they look fine!
Also explains why they spent the extra cost for the elaborate plastic covers for the inner fender wells so it was easy to add their splash guards. They could have just used two extra screws to attach the existing plastic inner fender well! Knew it wasn't for the small extra margin they could make on those of us who bought the GM splash guards. With the 50+% dealer discount, inventory, part procurement and other management costs etc, it would not be cost justified! What is delivered with the car cost them essentially what the splash guards cost.
I found the front splash guards did little to protect the side rocker panels so I added side skirts. They have prevented any rocker panel damage for 3 years. Since my planned GS comes with side skirts, will just get rear splash guards.
11-10-2016, 04:44 PM
[ANSWERED] Spats, Protective Film, and Splash Guards
