Originally Posted by
Jaeger99
A "bad back" can encompass many different evils. The only way to know which road bike will be most comfortable for you would be to take a number of them out for as extended a road test as the vendor will permit. I do somehow very much doubt that you will find comfort in the ass-in-the-air, teeth-on-the-bars position of an aggressive race bike. A great many people with perfectly healthy backs find those less than tolerable over a long haul. Conversely, you hear few cruiser riders complaining that their back is killing them after riding. I expect that the (only comparatively) more upright riding position of an endurance-oriented road bike will suit you, and they are many to choose from. But ride them and decide for yourself. Who knows. An aero TT bike may be the answer. Probably not, though.
He doesn't have to be in a super aggressive position, but a more upright position will put more weight and pressure on the lower spine and sit bone, which is not something ideal for his situation.
On a side note, I have a perfectly healthy back. Prior to my fit, my lower back always felt tire after 60-70 miles on my rides. After my fit, which the fitter dropped 2CM of handlebar height from my already some what aggressive positioning, I was much more comfortable and never had that nagging feeling on my lower back. Of course there was other things done, but the handlebar height was the most drastic change.