Quote:
Originally Posted by mthreat
I'd love to hear from some experts here, but I was under the impression that it wasn't about getting the extra grip for acceleration, but rather for stability. Here's my thinking:
At low speeds, the wind resistance is very low (since it's an n^2 thing, as you mentioned). So the rear tires aren't having to "fight" the wind too much, and traction is fairly even all around. However, at higher speeds, say 100mph, the air resistance is actually a factor, and the rear tires (on a RWD car) are having to "push" harder against the air. Taken to the extreme, it would be like pushing against a brick wall, and the rear tires would just spin, causing loss of traction. The air doesn't exert as much force as a brick wall, but the loss of rear-end stability is still there, so when you go to turn at 100mph, your rear end is less stable than it was at 50mph.
Is my thinking correct? I've never really read an explanation, but that's the only thing I've come up with on my own. Any Formula 1 wing designers in the house?  |
Your thinking is not necessarily incorrect. I'll try to put it in perspective. Using the drag area (drag coefficient times frontal area) of 7 sq ft (which I extrapolated from a sales brochure for the MK2), at 100 mph the car is getting 179 lb of drag force from the air.
Now back to our assumption of the car without a wing, and also assuming the car itself produces no lift either up or down, thus you have 1700 lb of force on the rear tires and similarly 1700 lb of grip, if our tires/road have a friction coefficient of 1.0.
Using the same spreadsheet it's easy to plot the drag force vs. speed, and it turns out that the point at which the drag force equals 1700 lb is about 310 mph. Now, here we have reached your theoretical brick wall, where the tires are exerting maximum grip just to maintain speed against this incoming air. Any more torque will cause the wheels to spin.
Now, thankfully it's also very easy to plot required power on the same spreadsheet (power required being drag force * speed, once you get the units right). At this speed you require about 1430 rwhp
just to overcome wind resistance. This isn't taking into account other resistances, such as rolling resistance from the tire/road interface. So you'd have to be big balling to be making that kinda power.
More realistically, we can look at speeds we might actually encounter. At 140 mph, 132 rwhp is required to overcome the wind resistance. Adding in rolling resistance (which is constant based on the car weight, in this case around 80 pounds for all 4 tires), and you can see that 160-ish rwhp would be required to top out at 140 mph in a MK2. I haven't driven my MK2 to that speed so I can't verify the accuracy of my assumptions.
Back on topic..
I think where the wing might be helpful is in tuning the balance of the car for high speed turns. So you can tweak the under/oversteer with the addition of some downforce in the back, or the front, and it might be just enough to make a difference between under or oversteering. And hey, more grip never hurt anyone.
Edit: when i was talking about "acceleration" that you mentioned above, I didn't necessarily mean speeding up. It would be any kind of acceleration, whether it be speeding up, slowing down, or turning.