Miata Time Attack Takeover: Gridlife 2018 edition
 

flier129 and I might try to run a car next year at RA and Mid-Ohio because of this thread. Set exceptions way lower for us then you guys.

Time Attack Miata motivation intensifies!!!!

Road Atlanta = RA btw.

The "Street" record for GTA and Grid.Life for RWD is ~1:34-ish at RA. If we can get the car setup to work well in T1 and T12 with 300+ rwhp, 2300lbs, "S1" aero, on 245 Rival-S(or RS4s maybe?) on 10s then I think it's possible to put the miata up on the record list for Road Atlanta time-attack :party:

I feel like Mid-Ohio will actually be easier to do well at. We'll lean on other sources to get that accomplished :D (Street RWD record is 1:38....)

Why limit yourself to a compromised solution that you are not required to make?
S1 aero works well for S1 SPMs which run spec aero, but it's by no means the best thing you can have on a time attack car. You're allowed more, do more - build to the extent of the rules, it's more than likely that the class winner and record holders will.

Yeah, roughly "S1". I'm actually not sure if splitter+air-dam is allowed with Grid.Life in Street

Attachment 229643

Obviously aero will be a learning curve, lol.

Its an interesting challenge. Start a new thread just for this event prep and link it here. We can dive into the rules and come up with the best aero within your budget and Fabrication resources.

Agreed on the separate thread.
You're allowed to do quite a bit more than S1, this is a good thing.

agreed on new thread link. I'm looking into Gridlife myself

This forum is awesome.

So I'm fairly 'ngant of aero and what components are actually needed on a TA miata. I've watched Kyle.Engineers videos on YouTube and that's about it! :rofl:

I do know RA decently enough, though. T1(0:17 in video) and T12(1:44 in video) are key in regards to aero. Huge elevation changes in both and both are FAST.
https://upload.wikimedia.org/wikiped...ck_map.svg.png

The top-speed on the front straight after going thru T12 isn't that much lower than the top-speed on the back straight. I think pushing the front-bumper out, Bullet style, can be done and should net some on those turns. An air-dam is obviously key to keep the dirtiness off the front-end on the long straights, but unsure on what can be done on the rear wing. Putting power down out of T7(1:01 in video) is also really important.



I hope we can get Lars' car out to a couple of RA events next year before GL. Then, I'll stick an AiM Solo in it to collect some data. Though I believe the initial testing will be on the ACE's lol. So that data might be iffy. I'm not opposed to putting my car on jack-stands and pulling the Xida race off it to run on Lars' turbo car for the actual event, I even have spare 1000# front springs to use. But I don't want to do that all season long, obviously.

I'd characterize RA as an all-rounder track. Aero matters as much as power or mechanical grip. Gearing will be key. Less an issue with a turbo but make sure you don't have any big gearing dips or throttle response issues.

My read is no limits on front aero, just canards. I'd skip the canards, very draggy. Since it's not w2w, you're not worried about someone running over it. That leaves a big ass splitter. Crusher style air dam. Build the dam to completely shroud the front tires even when turning. Tires should be shrouded with steering wheel at 90°. I'd run something smaller than Bullet for RA ,but not much. The end plates on Bullet were Buttonwillow specific. I'd go maybe 30% that size.

Wing is easy, 2D foil like a GT250 or similar, with Gurney. Max width allowed. OEM NB is 64". With flares, wider. No restriction on end plates so make them huge. Plate area should be roughly 20% above foil and 80% below.

Diffuser allowed but with no flat bottom to feed it it's a waste of resources.

Front undertray to axle centerline, a no brainer. Do your best to get it as close to the tire as possible. We cut ours so it just barely cleared the tires at full droop and lock. The rules allow fwings, and front diffusers but they are hard to make effective with good exhaust flow. Meaning big fender vents and such. I'd skip front diffusers. Likely GL will consider and dive plane or 3D shape in the splitter as a canard and impose the 5" rule. So leave those features out. The gaping hole ion the rules is spliitter and end plate dimensions so go big there.

The B pilllar can be shrouded to reduce drag. Build a flap that extends inwards as far as your seat/cage allow. Remove OEM mirrors if you have them. Very draggy. Lift the trailing edge of the hard top 5-10mm off the rear deck. It relieves pressure build up in the cockpit and reduces drag. That mod is not legal in Supermiata so ours was tight. Make sure your body panels fit as tight as possible. If you have big gaps in the front of the car, cover them with clear bra material. We didn't have any so we used Gorilla tape. Hey, it worked..

While the aero setup in Bullet was effective, it was't the only reason the car went fast. We did a 1:44.9 on fresh 245 A7's but also did a 1:47.4 on 205 R7's. The lesson there is mechanical grip and balance. I want the mech grip to be neutral on turn in and mid corner, slightly tight exiting. This allows fine tuning line on the way in and through mid corner but allows early power application once the exit is lined up. As aero loads increase, I want the car to be tighter on entry, through mid corner and exit. Don't be afraid to work the fronts hard, it's not an enduro. This allows higher entry speeds and earlier application of WOT.

You'll need some big springs rates. Our fastest S2's, with virtually no aero, 225/45 RC-1's and 140whp run 900/500# with 1.125 & .562 bars. S1's are running 1100/500 with 1.25 and .562 bars. Bullet ran the same 1100/500 but needed like 1400/600 probably. We ran the same ride height we run everywhere else, 4.5" pinch weld F/R with driver. Only works with ELBJ's. The S1 splitter on Bullet is 3.5" off the deck. The SLB splitter was built at 4" to make sure we didn't tear it off as we didn't have a spare. Lower is better.. provided you don't tear it off.

With a turbo, it's safer to gear a tad too tall than run out of gear. Don't just look at your redline but the actual shape of the powerband. Our redline was 7400 at SLB but it made peak power at 6000. So we short shifted here and there with a 3.9 diff. If running stock redline, maybe a 3.6 for RA.
275's overkill for 300whp I think. 245's just right.

So much thing to try in that post, great info!
Thanks!

good luck at RA btw, Will be following closely!

Ben

Rule 4 reads that the splitter can only be 5" forward and 5" out to each side. That's slightly bigger and much wider than S1, but still not close to Bullet.

A GT250 can easily balance a 5" splitter with a gurney and big endplates.

5" of extra airdam width still covers 245s on 10"s easily.

oh man, this is gonna be good

Current thought on the wang, is a CoT. We have a source for some uprights and the foil seems to be somewhat available online for not too much $$.

Subscribed, maybe we'll make it down south this year for GridLife and come play with you guys too.

I've been to the Gingerman festival since the first year, it was started by friends of mine and they have done a really amazing job growing the event.

Good luck! If I make it back next year I'll be in HDPE. With a NA car it's too annoying trying to turn a good lap time getting parked in the corners by slowly driven muscle cars who motor you on the straights. If I don't drive, I might come down and just lend a hand if you need one. I know a few folks in the area, so I can usually source spares quickly.

CoT foil is a very low drag shape. Something with a few degrees more camber would be better if you can find it.

I currently have the BFW lexan wing and it's not balancing out well with my current splitter that is extended ~4" from the replica GV lip. GTC250 seems to be the ticket

I have a COT wing on my car with a 4" splitter. Wing is mounted on FM stands and custom endplates. https://cimg3.ibsrv.net/gimg/www.mia...01e9c73207.jpg

Right now the wing isnt as effective as it should/can be. As I havent had a hardtop till recently. I also have an air dam in the works. The wing is very good for the price. I run almost no AOA and even without a hardtop, its very effective.

4" stick out is a fairly sizable splitter already, you're asking too much of the spoiler, S1 balances a 4" splitter with a GT-250.

I'd definitely do a GT-250 over COT wing, as wide as you're allowed to.

Missed the splitter length restrictions. That simply means you max it out. 5" wider than nose and 5" forward. Wrap it around as far back as you can and still stay within the 5" rule. What you want is surface area. Build either a modular end plate for the splitter or something that is quick release. That's how you fine tune a splitter. The bigger the end plate, the more downforce and drag. No end plates gives you a very good downforce to drag ratio. With the power you have, no plates would not be enough. Don't be afraid to build some cartoon oversize end plates. What you don't want to do is discover the car keeps getting faster as you add end plate area and then you run out of area to bolt on.

The air mas hitting the nose stalls and builds pressure. Pushes in all direections, including down against the splitter. That's where your downforce comes from. Some goes over the nose, some goes to the side. As that air moves laterally across the nose, it speeds up. Pressure drops as air speeds up. The end plates serve to slow down the air from escaping around the sides, less pressure loss. If you terminate the end plate against the fender creating a dead end for the air, drag is very high. Better to leave a gap there so air can leave the splitter between the rear of the end plate and bumper. How big a gap is where you experiment. We took a WAG on ours and it turned out to be pretty close. That's why you want a modular end plate setups with a few iterations to try.

If you add cables, try to keep them in the areas where the air mass is moving slowest, like near the centerline of the car. If you need to put them on the corners, make them as short as possible. Cables are shockingly high drag.

I can't seem to wrap my head around this. How does a 3mm cable produce drag? Does it just disturb the airflow and create "dirty" air making the splitter less effective?

I want to try to make it out to RA eventually but it would be with Global Time Attack/Formula Drift and not Gridlife.

Would converting the car into a fast back count as a rear aero device?

I see. But the wire diameter is only 3mm. So wouldn't the turbulence coming off it be negligible? From what im seeing, that low pressure wake would be less than 3mm. What am I missing here?

Just because I feel like being a nerd tonight. Lets assume your 3mm (.003m) cables are each 3ft long (.914m). Frontal area from cables is (2 x .003 x .914) = 0.005484 m^2

Drag is noted by the following formula:
F_d = ½C_dAρV^2

Assuming 60 mph:
= (0.5)(0.47)(0.005484 m^2)(1.2 kg / m^3)(26.8 m/s)^2
= 1.11 N
= 0.25 lbf

Assuming your doing 100mph
= 3.1 N
= 0.70 lbf

So in a nutshell, your tiny little cables could be creating more drag than they actually weigh, which is pretty awful. This is why, as Emillio suggested, that you want to keep cables in low velocity regions as much as possible if they are required.

I understand that they create drag, but .7lbf still doesn't seem like a whole lot if the splitter is generating 80-150lbs of downforce right? The alternative is to solid mount the splitter to the frame. But in that case, it requires a much more involved install/removal than a "quick release" cable splitter. So I guess the tradeoff is ease of install for drag.

Just jumping in here for the aero talk and to say I'll be doing Gridlife Midwest and Mid-Ohio. Street mod RWD. 91 Chassis, VVT Swap, Rotrex C30-84, 15x9 w/ 225's, Xidas, GTC250 w/ 2.5 risers and Singular endplates, air dam + Splitter, and a slow driver that doesn't know what he's doing. I've been there before, just never racing. (Usually gets booked up pretty quick).

Drag and Downforce are forces in 2 different directions. Ideally you want as little drag with as much downforce as possible. Minimizing drag is a lot like weight reduction IMO. Individual components may or may not have a large / noticeable effect, but any little bit helps when you start looking at the big picture and doing multiple items at once. If you are really shooting for lap times, it matters.

If I did this right, I think 1 lb. of drag at 100MPH requires approximately 0.25 HP to overcome it and maintain speed. It starts adding up fast. My calculation could be wrong though if someone else wants to confirm.

That's exactly right.

force * speed = power, so 1lbf * 100mph = .267hp

Depending on when GTA does RA, Lars and I will hopefully be out there. GTA usually does RA beginning of May, which is much cooler than August!

On the whole cable / rod / bracing issue, remember that there are way to build things that require none of them to stick outside the bumper skin, and nothing definitely creates less drag than something.

EDIT to add - for the 5" stickout discussed here in context of Gridlife rules, you should be able to brace the splitter entirely behind the bumper and need nothing in front of it.
If you need cables / rods / anything in front of the bumper skin to support a 5" stickout, you're doing something wrong.

Exactly. Looking at the Formula D 2018 schedule it'll be May 11/12.

Agreed, Alumalite is strong enough when cantilevered 5" for the forces that a 5" surface will generate.

Good to know. I definitely thought we would be doing stanchions,cables, etc. in front of the bumper.

Not Alumalite, but you should be able to do the same, this is a 5.5" stickout on center, ~8.5" at the corners, no external bracing -

https://cimg3.ibsrv.net/gimg/www.mia...5d1552ce68.jpg

Interested in joining this discussion as I too plan on joining the fray in 2018 with GridLife.
Street Mod RWD at all 5 events (hopefully)
In speaking with the director of GridLife he recently informed me that there would be some rule changes for 2018 so keep that in mind as we continue...

Shrouding the front tires means extending the air dam out like this I assume:
https://cimg4.ibsrv.net/gimg/www.mia...10839f17b8.jpg

As I read the rules, the maximum width allowed is only to the OEM body line as viewed from above so adding flares does not increase allowed wing width. Google search says NA miata is 66". Is the NB really more narrow?
Additionally the wing(including endplates) may not be higher than the highest point on the OEM roofline. So something else to consider when designing end plates.

I've done quite a bit of reading on this and if it's allowed, why not do it? Planning a diffuser in a traditional uphill orientation and then cutting the bumper much higher in the rear to allow the air above the diffuser to escape as well. Would this not be beneficial? Or would having high pressure on top of the diffuser because of the lack of a sealed throat create too much drag to be worth it?

End plates, how big is too big?

Interesting thought. I'm having difficulty finding picture examples of this. Do you know where I can find some? I will search harder if not.

Obviously replace with a good quality rear view that allows you a much wider angle view of things though eh?

I think I have settled on using a Treasure Coast/CCP hardtop and was contemplating leaving the rear window out altogether in an effort to reduce drag.
I had thought about maybe adding small lexan panels on the side of the rear window hole to allow the flow coming off the sides of the car to separate cleanly but otherwise leaving a big rectangle hole in the center.
Also considering a hardtop spoiler with small vortex generators to feed the wing since it is limited to OEM roof height and a 2d airfoil like the GT250 would barely be in clean air at that height.

Don't hit me too hard if the hardtop window idea sounds foolish. I'm new to aero and willing to learn.

*EDIT* I just noticed that replacing OEM glass with lexan was prohibited. I wonder if this applies to an aftermarket top that originally comes with a lexan window on a Miata?
*DOUBLE EDIT* Next year's ruleset will clear this up. Aftermarket hardtops will be allowed lexan windows according to Adam Jabaay.

NA and NB are 64". We just measured the cars rather than googling it, go figure ;)

Because improperly functioning aero is, at best, just ballast. The diffuser throat is everything. Without a flat bottom to feed it, there is no throat.

Will take some testing to find the right balance. It's not too big unless you can't make enough rear downforce to balance it. Make up several sizes of endplates and take them to the track. Crank in a bunch of rear wing angle for maximum downforce on that end and find the front endplate size that gets you balanced.

Yes, see Supermiata setups for best no-drag mirror config that has no blind spots.

Vortex generators on top of the rear edge of the hardtop may help with flow to the rear wing. However, a hardtop spoiler only worsens the flow separation over the rear window area, so that's a bad idea.
This subject of leaving the rear window out of the hardtop emerged years ago when guys were running small GTC-200's fairly low on the deck behind the hardtop. They found flow to the wing was actually slightly improved with the rear window out. A larger wing higher up in cleaner airflow is not in the same situation. Venting pressure in the cabin is mostly an attempt to reduce drag these days.

We were just discussing this with Austin who is one of the event organizers at Gridlife. Yes this applies to aftermarket hardtops as well. There was an S2000 with aftermarket hardtop that faced this problem recently. Yes, this is bad news for a street class Miata.

^ What he said

Unless a factory shaped HT must be used, a fastback setup using glass (not Lexan) is the way to go.

Care to elaborate? Just curious is all. I'm using a Treasure Coast fiberglass top with lexan.

For Gridlife street class you're required to run glass, so that's in order to comply with the rules.
The OEM HT doesn't have all that great of a shape, fastback is better.

Oh I thought there was pretty good parity between GTA and Gridlife, guess that is not the case. At GTA lexan is allowed for aftermarket hard tops since glass for them can be either expensive or non-existent in some cases.

Go figure.

Interesting... Because I spoke with Adam Jabaay (GridLife Co-founder and on-track authority) shortly after typing that post (See *DOUBLE EDIT*) and according to him the wording of the 2018 ruleset will state specifically that lexan is prohibited except in the case of an aftermarket hardtop on which it is allowed and will be permitted.
​​​​So... Good news for a Street class miata! ;)

The rules are meant to be an exact copy in order to attract GTA cars to participate in GL. Per Adam this was simply an oversight in an attempt to simplify the rules and should have been more in line with GTA in this regard.

That's great news.

Nevermind

2018 Ruleset released:

Streetmod:
TIME ATTACK RULES ? #GRIDLIFE

I wonder how should this be interpreted? The wing may be as wide as the OEM body lines and the mirrors are included in this width measurement, or the wing may only be as wide as the OEM body lines, OEM body lines is a measurement taken from one OEM mirror mounting location to the other.

I know how I want it to be interpreted...

Seems a little off to use two difference references for wing with.

My guess is that it's like that to prevent someone from putting on aftermarket mirrors that are 2 feet wider than stock.

OEM body lines will likely be interpreted as OEM mirror width.

OEM body lines is also used in reference to other aero, and in that context it sure sounds like it would not include the mirrors in the width.

I read the same seeming contradiction... sounds like a quick email to Adam might be in order.

Clarification:

Maximum wing width for StreetMod is the same as the measurement from the tip of one mirror to the tip of the other OR 5" wider than OEM body lines (Not including mirrors) whichever is greater.

All other Aero is 5" from OEM body lines.

This means that a Miata without side mirrors that measures 64" at it's widest point may have a wing that measures 74"

This means that a Miata with side mirrors that measures 76" from one mirror tip to the other may have a wing that measures 76"

This rule was introduced to accommodate commonly available off-the-shelf wings for BMWs that exceeded the 5" rule but did not exceed the side mirror width.

thanks for the clarification... that would be significantly more wing for us too.

Wing has been acquired. GTC-250. I will need to get some bigger end plates.

Attachment 229648
Attachment 229649

That's a GTC-300. 3D wing
The GT-250 is the 2D wing but yeah, moar end plate.

Isn't the 2D GT250 going to be the more preferred wing here due to less drag? Or are we just throwing MOAR POWER at this equation?

L/D ratio of the GT-250 is better than any of the APR 3D wings. The strength of a 3D wing is when you have to mount it low to the deck. In such a case, the air stream hitting the foil is moving up at the edges of the car and moving downward in the center. The mistake we see so often is taking a nice 3D wing and mounting it so high that only one section of the foil is at the correct angle with the other angled section completely stalled. If the entire air stream is hitting the foil at the same angle a 3D foil is awful.

You'll notice most OEM 3D shaped foils have a long gradual transition to AOA that is usually determined with CFD and tunnel time. Most aftermarket 3D foils have a very abrupt transition from the two angles. Problem here is that you have a small chance of having that twist transition coincide perfectly with the air stream direction change that is actually happening on your car. In practice, and aftermarket 3D foil will almost always have some portion of the foil that is contributing nothing but drag. What's worse is this stalled section messes with the flow next to it that is technically at the correct AOA for the air stream flow direction

If you are getting the idea that I think an aftermarket 3D wing is to be avoided if you are allowed to/can afford a 2D, you be right.

Ryan@Singular thinks its a GTC-200. I'm going to have to try to find a part number tomorrow to figure out exactly which wing it is. Bigger end plates are on the to buy list. The wing was $400 and at that price I couldn't pass it up. It might be slightly less then optimal, but the $1200 saved oher the singular setup will go nicely to some 15x10 6uls.