When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Been a while since being in here. Bought a 2016 ND Miata though so the development begins. Since I am an aerodynamicist, aero work is of course going to be first.
Overall Cp plot on the car. Cp is better metric to look at in my opinion than just pressure. Cp of 0 = freestreem pressure. Cp>1 = high pressure zone. Cp<1 = low pressure zone.
Cp plot on miata with streamlines of the wall shear vectors (aka how the flow regime is acting on the surface)
Underbody shot of diffuser development. Yes this has a simplified underbody as I will be doing a completely flat floor.
Vortex forming at one of the strakes on the diffuser. This helps keep flow attached at higher angles of attack on diffusers
Another vortex on the strake on the diffuser. Notice the low pressure in the core of the vortex.
Yeah I understand that's it's not a nice pretty bubble of pressure inside like having the windows up, it's very turbulent, but the 'parachute' effect is an exaggeration - I don't think the guys who pulled the rear window out were seeing significant MPH changes at the end of straights, from what I have heard it was much more differences in wing performance.
I run a rear lexan window though, so I cannot comment from personal testing. I've considered doing some sort of quick disconnects on it such as Dzus fasteners so that I could do back to back tests.
How high the wing is mounted plays a big role in that too though. The APR GTC-200 for example mounts pretty low, and IIRC even with the 2.5" risers still isn't at the roofline, so the no-rear-window configuration might benefit those wings much more than it would for someone who has gotten their wing up higher..
-Ryan
spec Miata 2007 runoffs, someone with a cracked rear window removed it, picked up a bunch of mph. Instant protests/ban. They don't run wings so yeah, it reduces drag. After that happened, I've even read of enterprising SM racers running "floating hardtops", where side/rear attachment points are raised a bit so cockpit air can escape from underneath rear bottom edge of the top. Also got caught, instant ban. Flyin miata had a track car with a vented rear window, placed on lower lower third of rear plexi. Kept their wing low for lower drag with same downforce (compared to same wing but high mount) . I'm removing rear window to install a vented plexi same as the flyin Miata car. This is all with front windows down. Windows up still best as, pre cage, I gained 4-5 mph on the back straight at mosport. Almost 135 mph. I could probably figure out a way to attach side windows back on for racing but don't think the cockpit temperature issues will be solveable.
Last edited by endura; 12-31-2016 at 12:06 PM.
Reason: sp
Got to be up close to the 2018 VW Pikes Peak Car the day before the Concourse. The aero doesn't look as refined as F1 cars (too many support cables) and I can't figure out why they didn't just widen the rear wing. The front 'canards' are very interesting, never seen anything like them before. 2018 VW Pikes Peak Car 2018 VW Pikes Peak Car - Front Tire 2018 VW Pikes Peak Car Diffuser+dual element wing 2018 VW Pikes Peak Car -side outlets
spec Miata 2007 runoffs, someone with a cracked rear window removed it, picked up a bunch of mph. Instant protests/ban. They don't run wings so yeah, it reduces drag. After that happened, I've even read of enterprising SM racers running "floating hardtops", where side/rear attachment points are raised a bit so cockpit air can escape from underneath rear bottom edge of the top. Also got caught, instant ban. Flyin miata had a track car with a vented rear window, placed on lower lower third of rear plexi. Kept their wing low for lower drag with same downforce (compared to same wing but high mount) . I'm removing rear window to install a vented plexi same as the flyin Miata car. This is all with front windows down. Windows up still best as, pre cage, I gained 4-5 mph on the back straight at mosport. Almost 135 mph. I could probably figure out a way to attach side windows back on for racing but don't think the cockpit temperature issues will be solveable.
I gotta remember to test zipper up vs zipper down on one of the faster tracks at some point... Always forgot about it, would be with side windows opened for sure. And I've got a lexan spoiler. So far always ran zipper down and high speed balance has been fine (150-160kph apex) with the splitter. Curious to see how having the zipper up would change that, but more importantly how it would affect straightline speed, which in my case is crucial lol.
Probably would be next year tho, guessing Calabogie. Going to Tremblant in a week but it's my first time there so would rather not mess about.
EDIT: And now I just realise it's a 2016 post, yay.
Any chance you have a few before shots? Or anyone else?
I'd like to see the rear in varying states of undress (especially for your changes KADET) as I am wondering what i can sacrifice for a DD whilst also having some fun with aero.
Question for you guys. I am trying to figure out what class my car fits into under GTA rules and I dont really understand the splitter rules. It says "Splitters may only extend rearward to the centerline of the front wheel." This is the same for every class up to unlimited rwd. I must be interpreting this wrong but what im getting from this is that you are basically limited to a undertray (there can be no protruding material extending out of the front bumper?)
Question for you guys. I am trying to figure out what class my car fits into under GTA rules and I dont really understand the splitter rules. It says "Splitters may only extend rearward to the centerline of the front wheel." This is the same for every class up to unlimited rwd. I must be interpreting this wrong but what im getting from this is that you are basically limited to a undertray (there can be no protruding material extending out of the front bumper?)
"Rearward to centerline of the front wheel" governs how far BACK it can go (i.e. it cannot form a partial flat bottom). If you splitter ends at the subframe, it will comply. This is entirely independent from how far forward it can protrude.
From the GTA website for Street:
"Front air dams, lips, splitters and diffusers may not extend more than 5-inches beyond any portion of the bodywork. Splitters may only extend rearward to the centerline of the front wheel. Diffusers may only extend forward to the centerline of the rear wheels."
08-15-2016, 10:09 PM
0
