1. The problem statement, all variables and given/known data Determine an equation for rolling resistance for a wheeled vehicle @20 mph. 2. Relevant equations (1) Drr = Crr * g * m * V 3. The attempt at a solution (2) Drr = Crr * g * m My real question: is velocity a valid part of the rolling resistance equation where speeds are slow (~20 mph)? I would like to check this with you because an equation I used in the past (1) includes velocity, yet other equations I found neglect it - most seem to neglect it. Are the two equations above over-simplified; do they have practical worth? Thanks.