Like the title says: "Will an open sunroof provide any usable downforce?"

With the rear part of the FD sunroof lifted, there is a large wedge on the top of the car with a 3" lift on the back. It appears that this could act as a wing to provide extra downforce at higher speeds. Of course, there would be some extra noise, and it isn't as rigid in that position. Any thoughts?

Thanks, Adam

 

heres what i think... you should make an experiment out of it. first take a measuring tape out to measure deflection and press down on it to see how flimsy it actually is. then fasion a device to measure the deflection while driving it. ie: make a rig to hold a ruller strait up that sticks to the top of the car and have someone drive beside of you and take pictures of it at like 90-100 (dont speed~). then when you have pictures that show the deflection of the sunroof you can measure the amount of weight it takes to replicate that deflections. hence giving you a very vauge value for the down force provided... yes i know this is probably about as accurate as trying to **** in a teacup from atop a skyscraper but whatever..

another thing tho.. do you really think that this is worth it? are you really going to benifit from the small amount of down force you might aquire especially when you open a huge hole in the car and increase drag? i really dont see you gaining anything performance except maybe in the cabin cooling system..

 

I would suspect that if there were actually any usable downforce on the sunroof, it would damage the sunroof. I don't really think you would want much weight on your open sunroof would you?

It might act as a spoiler however and break up low pressure areas behind the car.

 

I don't think it would be so good, probably the vacuum created with it open would increase wide resistance as it trys to rush into the top of the car. I hope i explained this correct and maybe it could be right?

 

It probably increases the front surface area of the car (resistance), but I don't think the hole in the top of the car increases that much drag.

For instance, pickup trucks get better areo with the rear door up since the bed creates a soft pocket of air which acts as if it was covered with a friction-less material. If the door is down, the air flows through the bed "rubbing" against most of the surface in it, creating friction.

 

No tracks will let you race with the sunroof open so what good would it do?

 

I've gone 152mph with my moonroof open, nothing negative came from it.

 

If it provides any, and I don't think it would, it would only likely do so with great drag penalty.

 

I was at a corvette club autox last weekend and the car with the fastest time of the day was running a large spoiler mounted to the roof! It looked absolutely ridiculous, but he must've been doing something right...

 

if he was that much faster than everyone else that day, trust me, it wasn't the wing.

 

Its more of a curiosity for me than anything else. I don't really plan on any 100+ mph high speed cornering.

 

This was going to be my comment too. Every club i've run with mandates that sunroofs must be fully closed.

 

The mods that grab FTD at most big autocrosses have wings so large it sounds like ripping silk when they go by. Autocrosses are at the low end of the speed range for competitive events so big wings that provide usable downforce are worthwhile even if they provide significant drag. There are a whole bunch of other factors that apply, but it is much too large and technical a subject to start in on for no reason.

As for the sunroof question, lip spoilers aren't so much about creating downforce as about reducing drag and spoiling lift. An open and angled external sunroof most resembles a spoiler and might actually help reduce drag by separating vortices and creating some turbulent flow that would help minimize lift, but it wouldn't create downforce, per se.

 

m

I agree. The thing to realize is that the roof of the car is like the top of a wing. When you're moving, the roof is a low pressure zone, which is trying to suck the car upward. If you open the sunroof it will do what is mentioned above. If your windows are open and the roof is open far enough, it might provide enough air through the sunroof to counteract some of that vacuum, too.

As for running without a roof -- I have a glass moonroof on my FB, and I can usually successfully argue that it's safer to run without it.

 

as a pilots standpoint, you are disturbing the smooth airflow that would be more efficiently used from a spoiler. i would think it would produce more drag then downforce because of the hole before the sunroof. just a thought...

 

As another Pilot I second that. The interior cabin of the car is a low pressure area, so some air is going to go in. However, I don't see it going out so smoothly.

 

The first time I drove over 100mph with my sunroof open in my TII was the first time I had to "help" it close with my hand. Last time I will ever do that...