turotufas

iTrader: (7)

From 949
Dammit I did that when measuring the ride height!

But I measured around 12.4/12.8. Can't be off too much. Feels good still.

theshdwconspracy

iTrader: (1)

this thread hates me.

Oh yeah the optimal ride height is dumped

18psi

iTrader: (76)

the only time "dumped" is optimal is in the bathroom

hustler

iTrader: (6)

I lol every time someone talks about measurements anywhere but the pinch welds...it's 2011, get with the times.

damir130

You'll have to explain the physics of that one to me.. Splitter+full undertray = less resistance when re-introducing undercar air into ambient air = higher velocity at the choke point. And the choke point is the front of the car at the undertray before the diffuser. But always interested to hear other arguments.

greeenteeee

That's why I measure pinch welds... due to 949!
Not trying to argue, but you said "A diffuser mostly reduces lift at the front" and I typically refer to a diffuser as a piece after the rear subframe to the bumper. That would act on the rear aero, not the front, whether it be drag, lift, dF related.

BTW: I also added some tire blockers, found on many cars from the factory today. Who knows if what I have works, only way to test is to try. Which is why I wanted to try it being the only new addition to the car, rather than adding a wing at the same time. I know the APR wings work, but who knows about the splitter I made?

http://autospeed.com.au/cms/article.html?&A=2456

turotufas

iTrader: (7)

Measured the pinch welds today. Its easier/quicker and whatnot. Learn something new everyday... I'm at 4.5/~4.75.

wannafbody

iTrader: (1)

I measured at the pinch welds today and got 2.5 inches due to snow

damir130

Ah, but thats the surprising thing. Even though a diffuser is mounted out back, it affects mostly the front..aero wise. So adding a diffuser will do very little to balance out a front splitter. It's more likely to do nothing at all or make things worse. Just something to keep in mind.

wannafbody

iTrader: (1)

That's interesting. I thought the purpose was to smooth airflow at the rear.

greeenteeee

I should probably just PM you my reply for the sake of keeping this on-topic, but others might chime in with useful input.

On my old car I used to take to the track, the rear end gets really light at 90mph sweepers unless it was at full throttle. After I added a front undertray and rear semi-diffuser, it helped alleviate these issues.

Here are pictures: It is a FWD...









Here's a pic to show the angle... never measured the degrees though...



I felt more of a difference in rear stability than in the front with these additions...



BTW: I read this today:

http://www.supermiata.com/forum/show...13&postcount=2

owenwilliams

"Ah, but thats the surprising thing. Even though a diffuser is mounted out back, it affects mostly the front..aero wise. So adding a diffuser will do very little to balance out a front splitter. It's more likely to do nothing at all or make things worse. Just something to keep in mind."

I think that can be classed as dangerous misinformation, so I feel a need to put you right on this for the benefit of anyone reading.

I'm not sure where you're getting your information from. I'm getting mine from the newest (very up to date) edition of 'Race Car Aerodynamics - Designing For Speed' by Joseph Katz. In it, it is clearly stated that a rear diffuser effects downforce over the rear axle. Longer, massive tunnels that start somewhere in the middle of the car, such as those featured on Le Mans prototypes, do effect downforce over both axles. Neither type of diffuser effects downforce over the front axle only, or indeed effects even "mostly the front".

Pictures speak a thousand words, so see the two below. Both are taken from the book mentioned above. I don't think you can get a clearer, more simple couple of photos that illustrate how much (dangerous) bullshit you are talking. If you'd like detailed quotes on the matter, I can provide them too.

The first illustration shows whereabouts on the car front wing downforce, rear wing downforce, and Venturi (rear diffuser, like what we can use on Miatas) downforce pushes down on the car. So, the type of rear diffusers we use on our cars, that start in line with the rear axle, effect downforce over the rear axle only.
The second illustration shows whereabouts on the car front wing downforce, rear wing downforce, and 'tunnel' (huge Venturi channels, like what Le Mans prototypes use) downforce pushes down on the car. In other words, huge tunnel Venturis that start roughly in the middle of the car create downforce over both axles.

greeenteeee

Since my last measurements, I moved up to 12/8 spring rates, felt great at the track like this. I went down to 3.5" pinch w/ rake.. tires hit the frame so it's a bit too low, going to either do 3.75F or 4.0F next, but I'm still doing another track day at this height to test consistency in my lap times first.

I also added front and rear aero. Rear diffuser is basic, 24" wide tunnel, tested at 6.5* and 9.8*... With an air dam 65mm from the ground, the 9.8* worked best according to the string taped along the bottom surface. It starts after the eccentric bolts and extends about an inch past the bumper cover.

@owenwilliams: You were right and I was over-generalizing. My front aero is adjustable with splitter height, can move it forward and back, etc. Front only aero made the rear lighter than with only a basic TR style lip... adding the diffuser balanced things out more.

EDIT: Here's a pic at this height:

Got 1:36.5 on 205 ZE912s. (yes, all seasons)
Trying again Dec 10th at this height/alignment before raising it up again lol.

atlnb

i have my height set where the control arms are parallel to the ground, which for me is 12.5F and 12.75R. They're not totally parallel but because I want more suspension movement in the rear and 0.25" rake i have it at that height. I'll probably lower it to 12.25F and 12.5R to make it more parallel but the car has decent balance when cornering. but its oversteery with my spring rates and the condition of my tires

Seefo

iTrader: (5)

^what rates?

greeenteeee

Weird. The NB should have better geometry than the NA.

I measured my NA over the weekend at full droop (12.75" hub to fender) since I can't measure the pick up points when on the ground (equivalent of 4.75" pinch) and at the 12.75" hub to fender, the outer pivot points of the tie rod and the lower ball joint are HIGHER than the inner mounting points. Though, the arm looks parallel, you need to consider the pivot point.. the center of the eccentric bolt and the center of the ball joint.

I'm 100% sure for the FLCA to be 100% parallel, it'd be 13" or higher. I'm not curious enough to find out.

atlnb

7/6 front/rear

atlnb

Yea I didn't consider the pivot point. I only looked at the control arms. From other people I've talked to about that, they have pretty similar heights for NA and NB. Give or take a quarter inch

greeenteeee

Mind giving more insight at your 12.5" height? Have you ridden it any lower?

I was @ 4.75" pinch (about 12.75" hub fender on my car) for a few months after DD/track use at around 4" pinch (3 15/16", 4 1/8", and now at 3.5"). 4.75" felt best only in that it is more numb to bumps (bump steer) and generally more stable. At 3.5" I see bumpsteer at the wheel but I don't necessarily feel it in the car's behavior. 3.5" pinch, slight rake, DIY corner balanced, DIY aero and it is as stable as it's ever been.

I do have a McPherson car lowered too much as well with 255s... the tramlining and bumpsteer on that car make the Miata look so much better in regards to driving feel, even when too low.

atlnb

yea, i went down to 12" in the front and 12.25 in the rear. it certainly turned the best and that was the lowest i took it. i only did it for a month because the lack of shock movement was too much so i raised it to 13" front and 13.25" rear. wasn't happy with that so i lowered to the height i'm at now and seem to get the best results.