Quote:
Originally Posted by sgtlethargic
I believe I've heard on this forum that aerodynamic cars have stability issues. Is that true? How so? What can be done about it?
Thanks
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Lots can be done about aero instability!
1)
Reduce lift.
Most cars have a lot of aerodynamic lift - in some cases, hundreds of pounds. Furthermore, the latest research shows that aero lift has
a disproportionate impact on vehicle stability. That is, what should theoretically have very little impact (considering the mass of the car and the magnitude of the aero lift force) does in fact cause stability issues. (This may be because the oscillations in lift forces match the resonant frequency of the suspension ie around 1-2Hz - and so the car is more easily unsettled.) It's pretty easy to reduce lift - on any modern car, best achieved by a smooth undertray and rear diffuser.
2)
Move the centre of pressure rearwards.
This is easily achieved by rear fins. I see some other replies have also said this, but what they haven't said is how
dramatic the impact can be of rear fins. If your car
turns away from cross-winds, a rear aero rear fin (or two) will make it far more neutral. (If it turns
towards crosswinds, more side area is needed ahead of the centre of gravity - not common, though.)
My Gen 1 Honda Insight (900kg - 1980lb in the form I drive it) is now amongst the most stable of any cars I have driven. (I used to be a car magazine new car test driver - I've driven lots of cars.) It develops downforce at 100 km/h (~60 mph) via its undertray, and uses two rear fins.
I think 'aerodynamic stability' is an area with so much potential gain in road car aero modification - it truly makes a radical difference, especially if you live in an area that has strong winds. (And even with 100 km/h / 60 mph speed limits.)