At 66, one of my knees began giving me problems while riding my road and mountain bikes through hilly terrain (my knee could no longer deal comfortably with the torque from climbing steep hills). My solution was to, at 68 buy a Felt Sport e-bike 95 (400wh battery), which I've much appreciated. I’m now 72 and just formally retired (informally not so much). The Felt solved the road bike knee problem, at least for commuting to/from home to office over hilly terrain (as well as some 20-30 mile RT road adventures). But the Felt didn’t serve as a mountain bike substitute and the range was limited. When I tried rutted fire roads on felt, the lack of front suspension, the narrow tires, etc. were a real problem. Several weeks ago, I tried a Riese & Muller Superdelite GX option and Vario shifting — hard to depart with the $$ but I figure that I can count the years that I have left for mountain biking on one and hopefully two hands. The Superdelite (with the double battery totaling 1125 watt hours) is due to arrive early/mid August. Eager to climb some remote fire roads and take some longer adventures in the SF Bay Area, perhaps even find an overnight camp to do some astro photography.