Try it in a Viper moded up all the way. That should be the easiest car to do it in... Umm i cant remember what speed. its different for every car. and some cars are harder to break through than others. But i found using the viper one of the easiest. Just makes sure its supped up all the way.
Keep trying if it dont work. You have to hit the corner just right. It took me about 15-20 times before i got it right.
i did it with a plain o' viper. That was hooked up all the way.
When you get that down then you can try doing it to the escudo or anyother car that can does the weelie trick. And you will be able to hit like a few trillion mph! but dont save the game if you do this cause you will have hella miles put on your car. pluse the ps2 might freez on you when you do this.
awww thats where i went today.
I see someone took a pic of my car . 
:reallyodd
