Question: how fast can you drive with a surfboard on the roof?
Answer: w/ proper racks, & the boards strapped down properly (fins up & forward, don't be a kook) you can go as fast as you want. i've done 85 w/ a longboard on the roof in the past. IMO however, going faster than 80 is stupid unless conditions are perfect & you're a good driver. you become a danger to yourself & others.