I'm number challenged! What do they mean? I have a 12-25 (cassette?) on the back and 39-53 (gear?) on the front. Do these numbers refer to the teeth? As an example: The back cassette(?) has a small ring with 12 teeth and the largest has 25 teeth? The front gear/chainring(?) has 39 teeth for the smaller ring and 53 teeth for the larger?
Help me Mr. Wizzzzzzaaarrrrd!