I was really hoping that this was true about being able to make tires wider as I am really missing the days of earlier GT hybrid building when you could put the 335's from the Viper on anything including my ole' favorite I created back in the day by taking a Daihatsu Midget and adding the 5.7 LS1 engine from the 2000 SS Camaro, and then puting a set of the 335 Viper rear tires on it. Actually looked decent with the standard golf cart tires on the front and those massive 335's on the rear and it was very drivable.
In GT5 you can add HP and torque to it but we are not able to add the rubber to hook it up, except for the traction adding code but that seems to really mess up the vehicle on the curvy circuits.