Plug the size you have now into this site on the left & the size you are looking to go with on the right.Tire Size Calculator - Tire & Wheel Plus Sizing
Play with the 15" to get one that is close & you should be okay. Quite a few of us have replaced our 16" with 17.5" with no problems
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Mike
2002 42' Monaco Signature Triple Crown tow 2014 F-150
2014 Voltage V3605 Sold 5/3/17
2012 F-350 6.7l CC 4X4, Sold 10/10/17