The difference between 18 & 20 can be a lot of little optimizations. High quality, low rolling resistance tires *could* be a big piece of that equation. But, I don't think your issue is as much equipment, or prevailing winds, or luck.

The tell is the 10 minute run pace. At a 10 min/mile pace, I don't feel I'm running. Only jogging, & jogging poorly at that.

Poor form is what causes injury. The human body is designed to either run or to walk. The sort of half-between, neither that is jogging is begging for aspirations of long durations, long distance with poor form resulting in poor adaption, unnecessary muscle-skeletal stress & eventually injury. Un-coached people when new to running will often trade speed & proper form for distance & time engaged. It's only natural & it is because nobody has told them better. Running takes years to develop. It's hard. Any yahoo can step out their door & jog their way to injury in the hopes of attending an event.

In my mind, this is what you have done here. You have not developed the capacity to sustain the minimum energy expenditure necessary for a 7-7:30 or better pace that would be actual running. This "overhead" in your cardiovascular fitness & mitochondrial adaption would go a long way to feeding your cycling ability.

base2
former runner