i have oversized my 1997 hyundai tiburon wheel.before i was using silverstone 215x35x18 for the both rear n front till one of my front tyre lose psi when i cornering (about 60km/h) and cause the tyre burst.that time i use 30psi with nitrogen gas.then i change to nankang 225x45x18 (rear)and 225x40x18 (front) with 30psi of ordinary air.still i face the problem of losing the psi on 1 of front tyre when cornering but luckily i didn't burst the tyre.then i pump my 4-tyre with 35psi and keep check it in a week because if i forgot to add psi within 1-2 week, the tyre will lose all psi when i cornering.i have check my rims, tyres and valves in 3 different tyre shops but they could't fine any mistake or problem since the rim and tyre is still new.for your knowledge i use a brand new rim and tyre.anyone have any idea to help me so that i would't drive my hyundai tiburon home with punctured tyre anymore...

 

Sorry about this old thread:
But, other people have had the same problem, when going to over-sized tires, specially wider tires if they still use the same narrow wheel. People use extra pressure in the tires, thinking that will cause the tire greater adherence to the wheel. However, it only causes the tire to fit tightly at the wheel's very outer edge. While the tire balloons outward above the wheel & beyond the wheel's width, any stiffness in the tire sidewall, levers the tire, at its minimum radius, away from the wheel. The minimum amount of tire/wheel contact, only at the wheel's outer edge, allows air to escape, specially while cornering. When going to wider treads, the wider tires, must be matched with wider wheels. Some websites have pictures, that show how the inner radius of the tire is forced away from the too narrow wheel, leaving only partial tire contact with the wheel.