downforce, just like on any car. lol, the wing isn't supposed to provide downforce from a stop, where traction is needed. there has to be has to be a large amount of air moving past it. unless you have a giant wing like on top fuel dragsters, any wing isn't going to do anything for traction at low speeds, it doesn't matter whether the car is rwd or fwd.

on the srt-4, the rear only weighs a little more than 1000 lbs. the wing provides i think something like 150 lbs of downforce at high speeds. that's almost 15% of the entire weight of the rear, also since it is located behind the rear wheels, i would think that should help exert even more stabilizing force. so that is going to have a big impact on a car like that, where the rear gets light at high speeds.