I'll just assume you're using 700x23 tires, which have a [nominal] diameter of 668mm (622+2*23). You're allowed 26 feet per crank revolution. 26ft = 7,925mm. Calculation: (7925mm)/(668mm/rev)/pi = 3.78 to 1. So your maximum front to rear ratio is 3.78. A 53 front with a 14 rear = 3.79, so you'd probably fail. A 52/14 = 3.71, so you should be good. If I were you, I'd change the front to something like a compact 34/45 and run a 12/~23 rear. 45/12=3.75. You'll not get any closer w/o the chance of failing with any other gearing. You'll have use of all your gears (none blocked out), and you won't have to worry about not being able to find Shimano's special junior cassette.