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Discussion Starter #1
For some reason I thought running without a top didn't have any negative effect on acceleration. Yes, it's a counterintuitive belief, but I thought I read this somewhere. Anyhow, on March 21, for the first time in a long time, I ran Thunderhill with the soft-top on. I was hitting the rev-limiter in 4th some place around start/finish. Fast forward to March 26: With the top off, and with even better exit speeds out of the preceding corner, I wasn't seeing the rev limiter until much later.

Thoughts? Is this drag-related? Maybe wind-related (as in I had a tailwind on the 21st and a headwind on the 26th)? Anyone have specifics on how drag changes with the top off?

I tried searching, but my keywords didn't yield any helpful postings.
 

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Imagine running the bottom of an ice cream scoop across ice cream. Now imagine running that same scoop upside down.(the way you would scoop ice cream). Just thought of that. It makes sense to me. :shrug:. It adds another edge that digs into the air instead of slipping through it.


At low speeds like 0-60 I doubt it has any noticeable effect, but at ~110mph the car is already nearing its last legs. With even more drag from topless, its not far fetched at all to see slower speeds.
 

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two words:

air brake
 

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Discussion Starter #4
Imagine running the bottom of an ice cream scoop across ice cream. Now imagine running that same scoop upside down.(the way you would scoop ice cream). Just thought of that. It makes sense to me. :shrug:. It adds another edge that digs into the air instead of slipping through it. At low speeds like 0-60 I doubt it has any noticeable effect, but at ~110mph the car is already nearing its last legs. With even more drag from topless, its not far fetched at all to see slower speeds.
Everything you say mirrors the logic I apply to the situation. But I could have sworn I read somewhere that drag (and therefore speed?) doesn't change when running with the top off. This is all counterintuitive, but what do I know? I certainly don't know much about physics!

I really just want to know if anyone can point me to the "official" word on how speeds, acceleration, top speeds, whatever, are affected by top-off driving in the Elise.
 

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With the top off, I definitely noticed (above 110) a buffeting that pushed my head forward. The air was diving over the windshield and curling back into the cabin when it hit the back window. Lots of turbulence=drag.

Tom
 

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There was an episode of Mythbusters that addressed a similar question with pickup truck beds. Tailgate down, up, or with a tonneau cover. Tailgate up was better than down, because an aerodynamic 'bubble' forms in the bed -- allowing the airstream to slip right over it. I wonder if the Elise makes a bubble? :shift:
 

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^it doesn't make a bubble. The bubble in trucks is caused by the cab being higher than the tailgate and bed, creating a big low pressure bubble in the bed.

If the windshield of the elise were a few feet higher, maybe, but not in this world.
 

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I think these work basically on the same principles:

hpm_0000_0005_0_img0132.jpg

:cool:
 

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Does it matter?

If you are trying for the absolute best time - or in any competitive situation then it's a given that "top on" will be quicker.
In the Dark Ages I raced a Production Sports (spec?) MGB. We always ran with the hood up - or a lightweight hardtop - no question.
When we went modified and could use an aero screen - then the roof disappeared and a tonneau cover would be used.

But - track days are supposed to be for fun (aren't they?). I always run with no top because it's a more enjoyable experience - and I'm (mainly) competing with myself.
I've been playing around with various comparisons and sometime this season I'll do some back to back runs - but running with the top on will be for interest - not enjoyment.
 

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DL1 data confirms that top on gets you a higher top speed.
 

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Discussion Starter #12
Does it matter?

If you are trying for the absolute best time - or in any competitive situation then it's a given that "top on" will be quicker.
In the Dark Ages I raced a Production Sports (spec?) MGB. We always ran with the hood up - or a lightweight hardtop - no question.
When we went modified and could use an aero screen - then the roof disappeared and a tonneau cover would be used.

But - track days are supposed to be for fun (aren't they). I always run with no top because it's a more enjoyable experience - and I'm (mainly) competing with myself.
I've been playing around with various comparisons and sometime this season I'll do some back to back runs - but running with the top on will be for interest - not enjoyment.
Various "fun factors" motivate me to track my car: The sheer pleasure of driving fast; the satisfaction of working on my skills and seeing how they empirically improve; catching up to and passing other cars; and seeing what my car is capable of doing. I guess you could say the last two factors compel me to suss out where more speed is hiding. So that's one side of the coin. The other side of the coin is that from a sheer "what's more enjoyable" standpoint, driving with the top off has lost some allure. The extra noise and wind buffeting, along with significant sun saturation can take its toll (especially on 90+ degree days). I'm weighing the pluses and minuses of putting my hard top on, and its effect on lap times is definitely a factor. (And once the hard top is on it usually stays on because I'm too lazy to constantly put it on and off.)

At any rate, I don't think "simply having fun" and "trying to extract the very most from the car" are mutually exclusive. ;-)

But I do get your point.

Circling back to the main point of this thread, I was just wondering if Lotus ever published anything about the relative speed/drag/whatever merits of top on versus top off. That's all.
 

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Various "fun factors" motivate me to track my car: The sheer pleasure of driving fast; the satisfaction of working on my skills and seeing how they empirically improve; catching up to and passing other cars; and seeing what my car is capable of doing. I guess you could say the last two factors compel me to suss out where more speed is hiding. So that's one side of the coin. The other side of the coin is that from a sheer "what's more enjoyable" standpoint, driving with the top off has lost some allure. The extra noise and wind buffeting, along with significant sun saturation can take its toll (especially on 90+ degree days). I'm weighing the pluses and minuses of putting my hard top on, and its effect on lap times is definitely a factor. (And once the hard top is on it usually stays on because I'm too lazy to constantly put it on and off.)

At any rate, I don't think "simply having fun" and "trying to extract the very most from the car" are mutually exclusive. ;-)

But I do get your point.

Circling back to the main point of this thread, I was just wondering if Lotus ever published anything about the relative speed/drag/whatever merits of top on versus top off. That's all.
All fair points - although I don't think you'll find it much "quieter" with the top on - and you may also find that heat buildup in the cabin is an issue - compared to driving with constant airflow.

Still - whatever floats your boat.

I think I may have been prejudiced by a few years of racing in closed cockpits with the attending discomfort (especially wrapped in FR clothing).
After the removal of sound padding it was much noisier in a closed car than with an aero screen.
If I ever get back into racing I'll endure any discomfort for that elusive tenth - but for now I'll enjoy the breeze.
 

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At the end of the straight at Summit Point, approximately 3/4 of a mile, there was a five MPH difference. Low 120s w/o top, 125-128 with the top in a totally stock 2005 Elise.
 

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For some reason I thought running without a top didn't have any negative effect on acceleration. Yes, it's a counterintuitive belief, but I thought I read this somewhere. Anyhow, on March 21, for the first time in a long time, I ran Thunderhill with the soft-top on. I was hitting the rev-limiter in 4th some place around start/finish. Fast forward to March 26: With the top off, and with even better exit speeds out of the preceding corner, I wasn't seeing the rev limiter until much later.

Thoughts? Is this drag-related? Maybe wind-related (as in I had a tailwind on the 21st and a headwind on the 26th)? Anyone have specifics on how drag changes with the top off?

I tried searching, but my keywords didn't yield any helpful postings.
Were your windows up or down in each case? Windows down adds much more drag than top off.
 

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Discussion Starter #16
Were your windows up or down in each case? Windows down adds much more drag than top off.
Windows down. Always. As per the rules of the track.
 

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Imagine running the bottom of an ice cream scoop across ice cream. Now imagine running that same scoop upside down.(the way you would scoop ice cream). Just thought of that. It makes sense to me. :shrug:. It adds another edge that digs into the air instead of slipping through it.


At low speeds like 0-60 I doubt it has any noticeable effect, but at ~110mph the car is already nearing its last legs. With even more drag from topless, its not far fetched at all to see slower speeds.
One flaw with your analogy... it would make a difference if the scoop was empty or already filled with ice cream.
 

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An way way to determine the drag is to chuck it into neutral at say 120, and see how long it takes to decellerate (to say 80). Then do it with the top on.

Some claims can also be counter intuitive to the math...
 

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An way way to determine the drag is to chuck it into neutral at say 120, and see how long it takes to decellerate (to say 80). Then do it with the top on.

Some claims can also be counter intuitive to the math...
From the mouths of newbies.... good point, holmz. :up:
 

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I also noticed that you can't drive an Elise in a light rain without getting wet (at freeway speeds) as you can do in other targa top cars. That B pillar acts as a wall to air and apparently water too.


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