About this whole... 'Multi' physics thing of GT5. I believe I have covered this before in another thread.
Now, I believe that Gumpert locked the driver's seat of the Apollo in one place, so that no one could spoil the weight distribution of the car by altering the seating position and therefore the longitudinal position of the rather hefty lump of meat piloting it. I like that. It's a like it or lump it situation. I mean sure, you can alter the pedals and steering wheel position... Sort of like turning the aids on or off in Forza. But you can never alter the makeup of the car to change the basic seating position itself. It is the same for everyone, a constant reality. This is Forza. It's physics engine may not be entirely accurate, but it is alive and reactive, you can see a readout of what is going on, see the tires flex, monitor heat and wear... Softer compounds heat up more quickly but are prone to overheating and accelerated wear, you can watch suspension deflection occur and cambers change... You create your own situations on the fly, via action and reaction in the game world. For the most part the engine handles it well, rollovers, collisions, suspension bottoming out, it's all handled properly (whether it's realistic or not is a different matter).
Then take GT5, where you are left to figure it out for yourself, but with everything helpfully labelled. GT5 has no set physics model, nothing works actively beneath the surface. You chose a basic set of parameters that feel right for you, then the game hashes it into a make believe realm, where everything is very odd and statistically explainable. Like every rank of tire incrementally increasing lateral grip by 0.6g, or a Mini Cooper having the same grip rating as a Corvette ZR1 on the same tires. It might 'feel' right, but that is because you have set it yourself. It is an illusion, nothing more, nothing happens to the car in real time. It is stagnant. Nothing is truely monitored or active, no tire wear means no real monitoring of friction on the road and therefore a guesstimate of what should happen at best. When anything happens out of the ordinary we see the pre programmed script no longer fit the action. This is why the cars roll over like they are in treacle, wobble when they spin, like an unbalanced top. It is also why fitting a carbon prop shaft or lighter clutch makes no discernable difference to the overall weight of the car. Because it does not matter to the game.
I guess that this works for some people. The subconscious is easily pleased and comforted by seeing and feeling what it expects, and the conscious is easily fooled by what the subconscious has quietly set up. What I am driving at is I believe that GT5 in physics is a master stroke of mental subversion, an armchair that swallows you whole and fits to your shape. You should never speak of realism regarding any game, however anyone that thinks GT5 is anyway more complicated or realistic than Forza is clearly having a laugh. I own both consoles, have both games, most versions of both actually and I've never gotten on with the driving portion of GT. It feels stone dead to me.