12-21-2011, 02:24 PM
I did this for 3 or so years with my 1988 Carrera. Those cars had real rain gutters and regular Thule racks, properly affixed, worked great. I used two horizontal stacks but others used four vertical tires. I always thought my method was more stable and easier to strap down securely. The only real downsides were (1) lots of lifting tires onto and off of your roof, (2) decreased fuel mileage, and (3) increased oil temps because the airflow was affected. Neither (2) nor (3) was a real issue.