Two primary factors explain why a road tire performs better than a gravel tire on the road. Firstly gravel tires have a rougher surface which results in larger rolling resistance. Secondly a road tire is more streamlined and narrower, so it is easier to cover distances that are the same as the wheel. All of this applies for a gravel tire because it has a wider profile and knobs which offer more drag to the wheel if one wants to maintain the same speed.