Design for over or under steer?

[speedsense]

I would argue that it's just a preference for failure mode. Obviously you want balance, but some drivers have a preference for which end goes first when you exceed the tire's limit, as you will inevitably do at times when pushing for the limit. Some prefer the front to wash out first, others the rear. You set the car as close as you can to a "balanced" setting (there's no such thing really as it can change corner to corner, lap to lap) and then you adjust it so that it's just slightly towards one end, just enough that it's consistent in it's behavior. That is to say, just enough that there is always a small oversteer or understeer moment at the limit, depending on which you desire. A "perfectly balanced" setup may very well vary between these two modes corner to corner; as you can imagine, though on paper it maximize performance, will not make for a happy driver, unless he's driving so slowly he can't feel the limit, in which case, you have other problems to address first.

I would also agree that if you design for one or the other, you're doing something wrong, because it should be adjustable, not something that is set in stone from day 1.

@speedsense; on paper in many ways, understeer is preferable, but i would argue that it is more down to driver preference; some settings/features which cause oversteer at the limit also give you very good turn-in, which some drivers prefer.

The driver who has good rotation skills, and slight understeer, can also achieve a good turn in even with the U/S present, as he puts the car to neutral right at turn in and I might add with confidence to push the entry even harder the next time, pushing into oversteer even, with the same resulting turn capability as the driver with O/S
In my 23 years of racing and working with close to 100 different drivers, I can safely put driver's into two catagories, those who can rotate a car and make it do what they want and those who need the car to rotate for them. The latter is the one who will tend to have setups with O/S tendencies (need for the car to rotate). Doesn't make one or the other faster, but it does change the setup route can end up in opposing directions! IMHO

[Jersey Tom]

Circling back on this now that the thread has been split off... I am a pretty firm believer that for high horsepower RWD cars, there is lap time in setting the car up for various amounts of steady-state understeer. The more engine power, less downforce or less tire you have, the more understeer you need. Gotta be able to put power down early and get off the corner. If your steady-state trim is pretty neutral (or God forbid, free) then there's no way you're going to be able to put the throttle down until very late.

Depending on what the series allows, there's a lot of differential tuning that can be done to add on-throttle locking (e.g. Salisbury diff or e-diff) to handle it a bit more elegantly.

[Paul]

We have also seen that tire wear plays a role, when rear tires go off quicker than fronts a car with slight initial understeer would evolve to being to neutral to slight oversteer, while initially neutral car would develop significant oversteer and a slightly oversteery car would develop huge oversteer (all things being equal.) First scenario would seem best for most drivers, unless they are really good at catching the rear.

[Nando]

You can play around quite a lot with the diff, entry-mid-exit as well to manage the problem on the fly.
Not cure perhaps but manage.