I had a small front of 26 and rear of 34 and found I wanted something even lower, so I install a 24. Since you currently have 26-36-48 crank the FD can handle the 22 difference (48-26=22). You can install a 24 and see it if shifts appropriately, and if not, you may need to drop your 48 to 46. My current setting is 24-36-46 with a rear mega cassette with 34 as the largest. Also, you rear derailleur needs to be able to handle the large cassette. If it is a long cage (SGS in Shimano language), then it should be fine.