Any open rear is capable of turning both tires when traction is identical. The short wheel base and and excellent "straight back, both sides equal" weight transfer of the BDR suspension is what's making this "one legger" work so well here. Assuming it IS a "one legger". There is no discernible body roll to one side or the other based on the picture. Well done! I wonder what, if anything, BDR has done to make the suspension work better as far as "weight transfer" goes? Like put the battery on the side of the car that "lifts" under accelleration (as an example). Or different shock valveing, spring rates per side. Perhaps the BMW suspension itself has incorporated desiqn features to compensate for the weight transfer?
Longer wheel base and softer suspension travel (a typical "car")will exagerate the car body lift to one side. Shifting weight to one tire while "unloading" the other. In that case the unloaded tire breaks loose well before the loaded tire does (IF it does).
On a road course in a turn where one tire is under greater load than the other it is much more difficult to get the unloaded tire to hook up (if not impossible). In a low speed sweeper turn the inside tire WILL go up in smoke. This was quite common "back in the day" and was the main reason various forms of "posi traction", "lockers" etc. became popular.
Look at the "body roll" of the old 289 Cobras in a corner on a road course. It was extreme to say the least. One way to overcome the unloaded tire traction problem is to "drift" the car. Throttle over steer just as you enter the corner. That helps keep the car "flatter" through the turn, but VERY tricky and NOT the "fast way" around a corner.
Detroit offered "posi" like units on passenger cars mainly to deal with snow and mud related traction problems. A one legger with a tire in the mud and one on the pavement aint going nowhere!
I understand there were a number of law suits against GM "back in the day" when posi units were first introduced. With both back tires spinning the rear end wants to come around one side or the other. Particularly troublesome in the snow, people would loose control to easily. THAT led to "softer" semi posi units, there are a great variety of them on the market today.
It appears from the picture here the driver (Sid?) is correcting by turning the front wheels slightly to the right to compensate for the rear end trying to come around. THAT to is a sign that indeed BOTH rear tires have equal traction (for some reason)!
