About how much of a gap should i leave between the tire and the box when measuring for a new axle? My other trailer has about a 2 1/2" gap and I'm hoping 1 1/2" is acceptable on the trailer i"m redoing. Tires are 295/75/16 and i dont think i will be airing them down at all. Trailer will be mostly used on dirt roads and logging trails for now. thanks!