Was going to ride a Century last Saturday, but fortunately a few weeks ago realized my wife would rather me ride with her on the 45 miler. It was her longest ride ever, and first organized one. I find using my small ring and spinning, or changing up and mashing up a hill to burn, are great ways to have us ride together and me get some calories burnt. SHE progresses because I let her ride her pace, and SHE does the pushing at a rate she can stand. Since June, her speed on the flats has gone from barely 12 to over 15, and often can sustain some 17-18 cruising for a bit. We both also ride separately for our training times (and I try to commute regularly), but allowing her to ride at HER pace is the key. She asks to be pushed when its appropriate, which is way more safe than me pushing her.