On my road bike i have 50/40 crank and 8 speeds cassette 12-30. I want try in that bike 9 speeds cassette 12-30 0r 13-30. And i want try with that cassette different chainrings. 50/34 52/36 52/42 and 53/39. Or maybe i try 52/38. I want use the 12-30 cassette.i found one interesting. I go online in chain length carculator. I put 50/30 tell me i need 56 links chain. In 52/30 and 53/30 say need 57 links chain. But i put cassette 12-32 in 50/32 52/32 53/32 is show me i need 57 links chain for all this 3 combinations, How that is happens so much difference in chain length.