Rick F Guyon - Speed Degredation on Uphill Grades - Richard F Guyon

Rick F Guyon - Most modern passenger cars traveling on highways are capable of negotiation uphill grades of 4 to 5% without speed decreases blow their initial level-highway sppeds. (Older cars with high mass-to-power ratios and some smaller-sized "economy" vehicles may experience speed decreases.)

Heavy trucks experience greater speed degradation than passenger cars. The primary variables affecting actual speed decreases are the grade steepness, the grade length,  and the truck's mass-to-power ration. Mass to power ratios are commonly stated in pounds per horsepower and kilograms per kilowatt.