Miata Aerodynamics

Running in 130 at World of Speed at Bonneville in September - 1991 Miata with required safety equip. inc. 4 pt. roll bar... if allowed to run top down would aerodynamics be better top up or top down? Thanks

top up for sure! get a hard top aswell

Top and windows up.

A low-buck top-speed mod is a home depot lip spoiler or a diy front splitter.

That miata gots some mods right? Running on salt is like jogging in sand, you need way more power than you think.

KJ

Running on salt is like driving on icy snow.

The hard top is worth 7mph vs. open cockpit on a Spec Miata. That's with 120hp.

I gained 3-4mph top end on my CRX with a DIY lip spoiler.

The car is also much more stable at high speeds now.

What class are you running? There are whole hosts of things you can do in Modified Sport.

Remove window, add lots of aero devices, etc.

Our Alfa Spider has done 230 on the salt.

(oh, and running on hard dry salt isn't like icy snow- it just looks like it)

Thanks, I'm only running stock 130 mph so only have modifications for that (4 pt roll bar, drive shaft loop, fire extingisher, H or V tires). No hard top - just soft. I am aware of traction issues. I'm only trying to see how fast a stock 91 Miata will go:)

I dont think a stock miata will go 130 MPH with wind resistance. I've run one on my dyno (no wind resistance), and think in 5th gear @ the rev limiter was in the 12X MPH.

KJ

Good point. The class you choose to run will dictate what you can, and cannot do regarding motor and aero. However, if its just for personal satisfaction, do what ever you feel is right and what ever class you're in, so be it.

Top up, and pull the mirrors and antenna off. That's the easy stuff :)

A 1.6 Miata is geared for 135 mph at 7000 rpm in top on the stock tires. They're drag-limited, though. I'd expect to see a top speed around 115. And of course, Bonneville is at altitude so you'll be down on power.

On my old NA around 90mph it would really start to struggle with the soft top on it, if it was down it was struggling to even think about breaking 100mph. With the hard top I saw 110-115 easy. Be warned though, a miata at those speeds is REALLY twitchy.

Around Michigan International Speedway I think I got to about 110.

Joey

My '90 Spec Miata at Daytona runs about 121 by itself, and 130 in a bump draft with a '88 Accord. That's with a cone style air filter, and a race exhaust, which puts 112hp to the ground. 130 from a stock '91 with a soft top is pretty optimistic.

I have heard that because of the shape of the rear of the hard top, aerodynamics are actually worse than with the soft top up or down. I thought it was something like how when Mythbusters proved that pickup trucks are more aerodynamic with the tailgates closed and the beds uncovered.

Hmm. Some magazine I read apparently has lots of Miatae. Perhaps they might want to test this? Here's the Myth: a Miata is actually more aerodynamic, and therefore faster, with the top down than in any other configuration.

Best of luck to you Bradnree. Keep us posted.

It has been tested. At Sebring on the Ulman straight, a hard top is worth 7mph over no top on a Spec Miata.

Data points:

Down the front straight at Lime Rock, with an instructor friend at the wheel of my previous 1.6 Miata, top down, he was drafting a Viper at 112, and GOT A POINT-BY! But as soon as he pulled out of the draft it was like hitting a brick wall. He couldn't maintain even 112, nor make the pass.

Same track, same place, same day, I - a lesser driver, with no one to draft, but with the soft top up - touched 115 before braking for Big Bend.

So leave the top up. :)

Miatas are definitely more aerodynamic with the soft top up, and more aerodynamic yet with the hard top. I used to do a long trip between Ottawa and London, Ontario regularly. That involves about 6 hours of 65 mph+ cruising on a fairly flat highway. Great for measuring changes in fuel economy, which reflect aerodynamic efficiency. The hardtop gave me the best economy by far. So whoever's posting random theories on the internets about the hardtop having more drag than anything else, they're just plain wrong.

At the old C&D Superfour Challenge, cars finished off their run with a blast up to 140 mph then down to a full stop. Other competitors showed up with wings and other aero addenda. We showed up with a hardtop on our Miata and no passenger mirror. By the end of the day, there was a pile of wings and addenda sitting beside the start line...

Keith wrote: By the end of the day, there was a pile of wings and addenda sitting beside the start line...

Less weight always works too

Cut off the windshield. Tonneau the cabin.

mad_machine wrote:

Keith wrote: By the end of the day, there was a pile of wings and addenda sitting beside the start line...

Less weight always works too

Not as much as drag in the 100-140 mph range, though! My Locost accelerates like crazy up to 80 mph, then it just hits a bit wall of air.

DILYSI Dave wrote: Cut off the windshield. Tonneau the cabin.

Oooh ... Brooklands screens ...

Keith wrote:

mad_machine wrote:

Keith wrote: By the end of the day, there was a pile of wings and addenda sitting beside the start line...

Less weight always works too

Not as much as drag in the 100-140 mph range, though! My Locost accelerates like crazy up to 80 mph, then it just hits a bit wall of air.

Yea.. I once coaxed one of my Fiat spiders to almost 105 (indicated) with the top down... it was a white knuckle affair with the beating I got from the wind coming over and around the windsheild.