What makes you say that?  Wheel diameter has nothing to do with tire diameter. 

What are you currently running?  37s & 4.88 or 37s & 5.29?

Because I've tried both. I tried on my buddies 37x12.5x17 before getting my 37x12.5x15 purely to check for clearance in my fenders. His setup was a perfect match for my 5.29s. My 15s have been dogs with a 37" tire. However I get a lot more sidewall wrapping around rocks so it is a give and take.