My wife has a seven speed Townie and has been riding up to 20 miles. Her choice in buying the Townie was being able to get both feet on the ground when stopped. Her problem is that about three quarters of the way through the ride her back starts hurting. I think, based upon watching her, is that she is spending too much time in the high gears and she is not spinning in the 80 - 90 rpm range. The bike has a huge low gear and with it being a seven speed there just isn't a good range of gears for her. My LBS said they could install a different 3 free wheel that give her a better low end range. I was also thinking about adding a double chainring on the front but, I am not sure if it is doable or even practical. So, I am looking for some suggestions up to and including a different bike.
FYI - I am going to put a cadence computer on the bike to help her know what rpm she is at.
Edit: Her back starts hurting