There are many variables:
speed, traffic, flat land or mountains, weight, length of C, engine size, wind, direction of wind, rain (headwind, tail wind, cross wind), towing or not, style of "C", tires, driver, gasoline or diesel, condition of engine, tire pressure, just a few variables.
MSG MADHATTER (Life Member Good Sam)
1500 HD Silverado, 6L
Jayco Eagle Super Light 298RLDS (Hers)
Jayco Greyhawk 24SS Class C (His)