I just received my touring bike, an 08 Jamis Aurora, and I know I need to put on a lot of miles before I begin the Transam in July. But I don't want to. The problem is, a month before that I bought a Specialized Tarmac Elite, and I'm having trouble putting it down. My question is, is it bad to switch between bikes when training, given the considerable differences in the geometry between the Aurora and the Tarmac? If I spend the next month and a half on the Tarmac and then jump on the Aurora for three months after only putting a few miles on it (100-200), am I going to wind up with back pain or other discomfort?