The problem lies in the amount of silicon in the type of tire you are using. Cars act as a big capacitor and absorb an electrical charge as you drive them. Because silicon is a very good electrical insulator, the charge (electrical potential) can’t transfer to ground until is has and unsuspecting victim – you.
I don't know were you can find any info on silicon specs - You might just as a toll booth operator which cars hurt the most.

...Brad