Which wheel loses traction first?

[aortucre]

When you drive a real wheel drive too fast around a corner, the two inner wheels lose some down-force due to mass transfer. If you oversteer, does the rear inner wheel lose traction first? And then trigger the oversteer?

If so, are there any equations to determine how the weight is distributed knowing the total mass of the car, the distance between wheels, the height of the CG, etc...?

What we are trying to do is a "split 2 wing dynaimc spoiler" that will raise its left or right half to provide the needed downforce to the rear inner wheel so that it won't slip. What we are trying to figure out is how much of the total weight is being put on that wheel, and how much does it need so that it doesn't slip. The difference will be provided by the spoiler.

Thank you in advance for any help!

[Lycoming]

if by "downforce" you mean "normal load" and "mass transfer" you mean "weight transfer", then:

the weight transfer equations you seek can be formulated from a free body diagram. They can also be found in "Tune to Win" and RCVD, among other sources.

What does it mean to "lose traction"? certainly the inside wheel will be less loaded and will have less "capacity" to generate force as a result, but does that mean it has lost traction? Would you consider it to have lost traction if the wheel was lifted off the ground? Because a car can be in steady state cornering (ie. no oversteer or understeer) with the inside rear wheel off the ground, but both front wheels on the ground.

One method of thinking about oversteer/understeer is to think about moments on the car, as opposed to treating "traction" as a simple on/off thing. A more detailed explanation of this can be found in chapter 8/9 of RCVD.

what do you plan to use to control and actuate this spoiler? What kind of car is this going to be used for?

[autogyro]

IMO it would be better to use a torque vectoring diff.
Mainly because the movable rear wing idea will not work well enough at low speed and at high speed the corners will be long sweepers where the movable rear wing would create more drag than usable vectored DF.

[machin]

The first point is that there is no "mass" transfer... its weight transfer as a result of the difference in height between the wheel contact patches and the CG height... to work out how much force transfers you simply need to work out moments about the inner wheels. For the whole car the total load transfer is determined by the fundamentals:

load transfer = cornering G x Mass x CGheight / Track width.

how much of that force transfers at the rear compared to the front is determined by a load other factors; roll stiffness, suspension geometry, etc, but suffice to say its between 0 and a 100%!

[autogyro]

A better idea would be to design a suspension that would lean the body of the car into a corner, creating a wedge shaped tunnel under the inside floor of the car and transfering underbody DF to the inside of the corner.