Zinn Cycles Standard bicycle fitting This site will help you fit the bike to your body. Seat position and stem length go a long way to ending back pain. I found the right position for me and I use cycling as part of my physical therapy for lower back pain due to muscle imbalance. My current machine is a Roadmaster with a step through frame I bought used for $80. It is much like what you have from what you describe. Upgrade to mountain bike pads and get out the WD-40 and some diet cola to get rid of the rust. Get everything working smoothly and adjusted. Find a seat with coil springs if not already equipped. Plot your gear combinations so you know the best shift sequences. Hill climbing comes hard at first but after ten days you should start getting your wind. Aero mods will help. Disk on the rear wheel only. See the tail cone used on Oscar Egg's Rocket. Check the state laws on motorized bicycles, top speed allowed will be 30 mph or less.