Well, theoretically this situation shouldn’t happen. If your car is fairly balanced under acceleration in slow and moderate turns, in fast turns one would expect a bit of oversteer, not understeer.
In slow to moderate turns weight transfers to the rear under acceleration. This adds to rear grip and reduces front grip…classic understeer. Exception: Oversteer can be an issue in very slow turns tho because the high acceleration rate puts high demands on the rear traction budget.
When accelerating in fast turns, however, there’s almost no weight xfer because there’s almost no acceleration. And there’s the additional factor of rear lift because of the low pressure zone over our back deck. The sum of those variables is a light rear end. Therefore a car that is balanced in slow to moderate turns should tend to oversteer in fast turns. The trick, of course, is to create handling that is a good compromise between a bit of understeer in slow to moderate turns and a bit of oversteer in fast turns.
Theoretically, the only time one would want to add front downforce to our cars is it understeers in fast sweepers. But if the car understeers under conditions when the opposite should be true, than something odd is going on.
When I was testing my lip it felt to me that the car was more “planted in fast sweepers”. “Cool”, I thought, “the lip and undertray are working”. Then I start looking at my data and decided that it’s really hard to be objective. The data didn’t show the advantage that I thought I felt.