I ride in San Antonio, TX which is a mixture of flat roads and rolling hills. What would be the best gearing for a 7 Speed. I've got a 52/39 up front The back has 7 speeds but I'm not sure of the teeth count or how to recognize the gearing. I want to be able to use my older bike on fast group rides without having to give away too much. I do have a 20 speed "modern" bike I could use but it has been collecting dust ever since I got into steel.