I see three problems with the RAC design:
1) It appears that the tires are the same size on the front and rear. But there is 50% more weight on the back and the rear tires have to handle all that power. Using different air pressures can help but it would be better if the tire size fit the amount of work that the tire had to do.
2) As mentioned in a previous post, no rear ant-roll bar. This limits the ability to independently adjust the vehicles vertical spring rate, roll spring rate, and fore and aft distribution of roll stiffness.
3) The rear suspension design. If you compare the rear upright of the RAC to the other cars in LFS, it is the only one with the upper attach point so far outboard of the lower one. This is probably done to raise the rear roll center. Maybe an effort to increase the rear roll stiffness without increasing the rear spring rates. As a result, the rear wheel cambers change a lot more than they do for the front wheels. Plus, it tends to have the "jacking" effect of a car with swing axles.
Based on these three factors I think the front of the car is much more efficient than the rear. Usually increasing the front roll stiffness will ease the load on the rear tires at the expense of over working the outside front tire. Therefore making the feel more balanced. I haven't been able to do this with the RAC. Either the frame is too flexible to transfer the roll moment to the front, or there just isn't that much weight that can be transferred at the front, or I am doing it all wrong. So I have tried something that they did on the Auto Union GP cars back in the 1930's when they had lots of power and narrow tires. They would put positive camber on the front wheels to make the car lose grip at the front more easily. Thus, when the driver lost the back end of the car it was easier to catch because the front tires were already closer to their limits. What seems best to me is (a) setting the live camber settings at the front to between 0 and -1. (b) Setting the live rear cambers to between -3 and -4. And (c) raising the ride height of the front of the car to make the initial roll centers more equal for the front and rear. The tire temperature profile for the front tires looks terrible with these settings (outside edge about 5C hotter than inside edge) but I find the car to be much more controllable and easier to save when the back end breaks loose. In fact, I am now trying to dial out some of the understeer in slow corners without losing the stability it has. Lap times ( at least for a slow driver like me) don't seem to be that far off what I can do in the LX6. After all, if you can't use all the extra grip at the front, it really isn't going to be of much help.
But everyone has different abilities and preferences on how they want a car to feel. Just something that works for me and might or might not be of help to someone else. By the way, I really like the car.