but most of the time you're not even going fast enough to notice a difference

 

Another important thought to mention: Most rear wings are detrimental to "normal" or "non-racetrack" performance.

Aero drag is an exponential function which would explain why racing teams spend so much money and resources trying to minimise it. I've also seen some wings cause scratch-like marks on the car finish due to long term air redirection.

It's important to note aero drag shouldn't be your sole consideration. I look for every opportunity to drive with my top down. The aerodynamics are significantly improved with the top up. javascript:emoticon('')

 

Depends on the size of the blade....the angle of the blade and the speed your going.

Spoilers work by increasing downforce on the rear of the car using air pressure much like setting a weight in the trunk. The additional air pressure creating downforce will keep your rear wheels on the road just a little longer at the limits.

All that being said.... I prefer the look. The added stability is a bonus. If you look at the size of the blade on the 3D GT spoiler...you can see that it immediately creates downforce and I don't have to go 70 mph to get it.

Tim

 

You're definitely correct about downforce allowing better traction, which extends the car limits, and increases performance. This generally applies to the track only. It's rare in normal street driving that you would have "clean air" and be going at "at-the-limit" speeds where this would make a difference vs. the additional aero drag. That is, unless you're a hardcore street racer. Even the best aftermarket wings would need car based tuning for optimal performance. In other words, you can buy the best S2000 wing made, however it's ability to function would be based on its install to a specific car.

Most people drive the fastest on the interstate. A wing would be a detriment up to the point where speeds would have you sent to jail. A wing would be useful in this "straight line" situation as you would have to counterbalance the aero lift of the rear tyres/traction.

A big controversy in F1 currently is Ferrari and BMW's use of flex wings. These are carbon fiber based wings based on helicopter technology, where they flex at different speeds due to the carbon fibre weave. In corners they are more rigid creating greater downforce. On straight lines they flex to provide less drag. Rival teams engineers new something was up when they noticed the performance of the cars didn't match mathematics. Of course, FIA is making an example of BMW and ignoring Ferrari [who have been running flexible undertrays for years.] I apologise for the editiorial comment.

Bottom line:
Go with the wing if you like the looks of it or race/autocross. Don't purchase one if you think you'll gain a massive performance advantage on the street. You'd be better off investing in wheels/tyres or engine mods.