The bike material makes almost no difference- even if you had a glass bike, there is still a significant dielectric effect that will cause the the flashover to occur along the interface between the air and the bike. You can't predict it. The best place to be is inside a well-grounded Faraday cage. Failing that, inside a building is better than outside. Inside a car is better than outside. Away from trees and power lines is better than near them.