Wall of text incoming, you have been warned Don't know. RF2 has chassis flexing but chassis flexing in karts acts both as suspension and as a cornering aid by lifting the inside rear wheel. Also karts have a solid rear axle the diameter of which is critical because it also flexes, you can use a different diameter rear axle but also tighten it down or loosen it up through the chassis mounts. Just to give you an idea I had my seat break once so I took it to a shop where they build and repair light boats because they work with fiberglass. I specifically asked them to apply the fiber glass lightly so the seat doesn't loose it's flexibility. After getting my seat back my performance in the kart was abysmal. I jumped into an exact same kart of a fellow racer and it felt like I got out of a formula and into a Mercedes, it would ride over curbs where mine would crash into them transferring the shock through my spine. All because those guys just threw some fiberglass on the seat without caring how much, tightening up the whole chassis. In the end, after convincing the team it was not in my head, we loosened the seat mounting wheels so the seat would move around with some freedom. Normally you wouldn't do that because this movement will eat into the fiber glass and eventually destroy the seat but there was no choice pre race. I went out like this and took pole. So then we knew for sure what had gone down. As for body weight transfer is used in rainy conditions where killing understeer is critical. In the dry you want to maintain posture. Sure enough at the end of long straights in high performance karts and in high profile championships drivers will lean forward to reduce resistance. Also , if the kart has only rear brakes then pulling the body back on the brakes improves performance because you want as much weight as possible over the rear wheels, the only ones slowing you down. Generally though in the dry you do not use your body weight, you just make sure that the seat is perfectly placed for the center of gravity per the manufacturer's recommendations and track conditions. Fun fact: One can easily understand that the most efficient way to slow down is to have the weight transfer to the braking wheels, so when you only have rear brakes and overall weight shifts forward during braking it's not ideal. But a kart has more than 60% of the weight at the back and those super fat tires at the rear. So imagine what it would be like if you were braking backwards instead. I had the chance to find out once when after spinning I found myself rolling backwards so I rode on the brake. The kart didn't decelerate, it got literally pinned down!