mk e wrote:
no doubt tread pattern came into the game too with the GT tires a sportier design vs standard and DEEPER all season tread on the base model and running the GT tires under inflated in the rain did help quite a bit but best dry handling was like 45/25 f/r psi at the autocross, which to your original point would match up the contact patch sizes pretty well.
The Swift is a tiny vehicle with low contact pressure to begin with. The fact that underinflating the tires (further reducing contact pressure) made it better in the rain says that was a problem with the specific make/model of tire you were using rather than a problem with the tire sizing. Of course you *should* have seen the opposite effect: increasing the tire pressure made it more resistant to hydroplaning. Tire carcass construction can have some really weird effects on handling. GM engineers went wider in front on the Grand Prix GXP with LS4 V8 engine. They were able to dramatically reduce torque steer by playing with the belting angles in the tires they specified for it. They had whichever tire company produce those tires specifically for the car. I'm not sure if the industry as a whole learned that lesson or not.
Rear heavy cars have very benign hydroplaning behavior, especially if they're running square or close to square tire fitment, due to having greater contact pressure over the rear tires. The front tires hydroplane and you feel this in the steering wheel. The rears stay on the pavement. Lift off the gas to slow down a smidge and the fronts touch back down. Easy peasy.
A front heavy car hydroplanes on the rear first, so when the driver tries to slow down, the dynamic instability of braking only with the front tires causes the car to try to swap ends.