My son's 24" Giant mtb has a 7 speed 12-26T cassette. The front rings are 24-42T. To make it easier for hills I was thinking of swapping the 12-26T to a 12-32T cassette. Would the Shimano 7 sis rear derailleur has enough capacity for the new 32T (also 7 speed) cassette or I would have to buy a new rear derailleur with a longer cage? I am trying to keep the bike weight down and so not considering a 8 speed upgrade. Thanks for helping. Steve