To those who say the 125 SPL understeers badly with RS tires:
I don't agree. I've been able to make it handle just as well as the other karts. If you keep it near the limits (like a "momentum car") through the turns, you can make it steer with the throttle pedal, which is what I do in all the karts anyway. I find that keeping the throttle at least cracked when braking before the apex keeps things more stable. (I haven't thought this through. The physics don't jump out at me, because we're working with a solid rear axle, and only brakes on the rear...) Then you can transition off the brakes and onto the gas keeping some overlap just before and right at the apex. Then you can shoot out of the apex on the gas if you get it right. If you hit the apex too shallow or early, you can still save it by just giving it more gas.
TL;DR: Keep your speed up through the turns. Stay near the limits of the traction circle and you can exploit it to steer with the throttle. Use brake/throttle overlap to keep it stable.
