Aerodynamics discussion

[CSG Mike]

I think we're getting at the same point from different perspectives :p

[Dimman]

Originally Posted by fatoni

the only reason i bothered mentioning the lift/downforce thing is because cars are shaped like aerofoils and have lift inherently. i think its important to talk about them separately because at any net amount of lift (positive or negative) you can have any drag coeffecient. adding downforce and removing things causing lift can be different.

there is some confusion going on here. we arent talking about the same things. i understand the importance of downforce and the grip that is provided. i was addressing the thought that running smaller tires would be a good idea in order to keep the drag coeffecient down. i was just saying that i would rather have mechanical grip over dropping a hundredth or so off the cod.

i also think aero grip is equally wasted if you are going wot. there are many people running around in miatas with 275s and in nearly every situation the miata with 225s is faster than the one with 195s. i do get your point though but wonder if it might be turning into a historical kinda myth. i think newer compounds are making the optimal tire width greater than they used to be but thats just speculation on my part.

No. There is only a single force: lift. If it is positive it pushes up. If it's negative it pushes down. It's that simple.

You can't 'add downforce' with a giant wing if the net lift is still positive. It may seem like semantics but it's important to think of the whole system.

[ayau]

Is it safe to assume that the FRS/BRZ has negative net lift? If there was positive lift, then the tires would lose more traction as speeds increased.

[Dimman]

Originally Posted by ayau

Is it safe to assume that the FRS/BRZ has negative net lift? If there was positive lift, then the tires would lose more traction as speeds increased.

Almost all cars generate positive lift.

[ayau]

Originally Posted by Dimman

Almost all cars generate positive lift.

Those large Voltex wings suddenly don't so bad now.

[ayau]

Originally Posted by Dimman

Almost all cars generate positive lift.

In @CSG Mike's s2000 CR example, he said that the BRZ could take the sweeper faster in the BRZ than in the CR. Keep in mind that the CR has wider tires and front and rear aero.

CR:


Based on this, it appears that the CR could potentially generate more lift than the BRZ even with all the "downforce" parts. I wonder how a base S2000 would handle on the same sweeper.

[CSG Mike]

My unsubstantiated belief based only on anecdotal evidence is that the BRZ generates less rear lift than the my CR.

Honda's own documentation states that the CR wing eliminates 70% of rear lift [with hardtop].

The front of the s2k is proven to make substantial downforce via windtunnel testing.

[Dimman]

Originally Posted by ayau

In @CSG Mike's s2000 CR example, he said that the BRZ could take the sweeper faster in the BRZ than in the CR. Keep in mind that the CR has wider tires and front and rear aero.

CR:


Based on this, it appears that the CR could potentially generate more lift than the BRZ even with all the "downforce" parts. I wonder how a base S2000 would handle on the same sweeper.

The center of pressure can affect that. If that wing is reducing lift at the back, but not the front, the rear will grip better than the front at speed, meaning high speed understeer.

Keep in mind that all aero lift does is change loading on tires at speed. Tires generate grip based on load. So balancing which end of the car sees more or less load from aero affects under/oversteer relative to speed.

[fatoni]

Originally Posted by Dimman

No. There is only a single force: lift. If it is positive it pushes up. If it's negative it pushes down. It's that simple.

You can't 'add downforce' with a giant wing if the net lift is still positive. It may seem like semantics but it's important to think of the whole system.

there is only a single force but there are multiple things that affect that force. i think were talking about the same thing. i just think too many people get fooled into thinking that you can get downforce without consequence if you dont acknowledge that more than one thing may be happening at the same time when you refer solely to the net results.

[ayau]

Thanks for the clarification.

I still wonder if the OEM "diffuser" is actually decreasing lift, or if it's just there for aesthetics. For a sub 30k car, I have a feeling it's the latter.

Even something like the OEM diffuser is probably for aesthetic purposes as well.

[Dimman]

Originally Posted by CSG Mike

My unsubstantiated belief based only on anecdotal evidence is that the BRZ generates less rear lift than the my CR.

Honda's own documentation states that the CR wing eliminates 70% of rear lift [with hardtop].

The front of the s2k is proven to make substantial downforce via windtunnel testing.

This is what I could find for wind tunnel testing on the S2k. It, like most stock cars, generates lift front and rear.

http://www.c-westusa.com/labs/fudo1_s2000spec.asp


But it does show that you can get a lift AND drag reduction with a good package.

[ayau]

This makes sense now when you say that most cars will generate lift. The shape of a car is similar to the shape of an airplane wing. The air above the car has to travel a longer distance than the air below the car. This pressure difference generates lift.

[ame="http://www.youtube.com/watch?v=YQwh2fdfYiM"]Audi: Aerodynamics of planes and cars - YouTube[/ame]

[ayau]

So in theory, if you install panels underneath the vehicle and speed up airflow, then the net result should be an increase in lift. However, if you have a rear diffuser, then that should reduce lift. Is this correct?

[CSG Mike]

Originally Posted by Dimman

This is what I could find for wind tunnel testing on the S2k. It, like most stock cars, generates lift front and rear.

http://www.c-westusa.com/labs/fudo1_s2000spec.asp


But it does show that you can get a lift AND drag reduction with a good package.

from http://www.maxrev.net/site/index.php...blog&Itemid=54