Most of the time, when guys ask these kinds of questions, it's for one of three reasons:
1) They have some other brand of tire, and they're trying to find a replacement that will 'match' without being lop-sided...
2) They're working with an application that either has, or WILL have other driven axles (i.e. FWD/FWA) and are trying to match driveline proportions.
3) They're concerned about wether it 'looks right' in a fender.
A tire, when mounted on a rim, will assume a shape based on the tire's design profile, but heavily affected by the rim width, and as a result, the standing height of the tire, and it's free circumference, will change slightly.
The tire, when installed, will exhibit a curious flat-spot on the bottom, where it contacts the ground. This flat spot will do several things... first, it affects the distance from the center of the hub, to the ground... i.e. the 'loaded radius'. As a result of that flat spot, the forward travel that the tire makes in one rotation, is not exactly the same as the distance it would travel if it was exactly the same as if it was perfectly round.
This is why, when you do a measurement of an automotive tire, then look up it's design dimensions and rated Revolutions Per Mile, they don't match up- it's because the manufacturer has calculated in the actual running radius when loaded, and at the proper temperature.
One can minimize the variation, aka the 'size of the flat spot', by increasing tire pressure. On a very hard surface, this reduces the surface contact area, but causes the area in contact to be subjected to extreme loading... lots of heat, and accellerated wear.
One of the cool things about tire design, is that when rolling, the actual area in contact with the ground is an entirely DIFFERENT shape, from what that same tire area is when NOT in contact... and it is because of this change-of-shape, that a tread that has become plugged with mud, readily sheds that mud... Escoteric information, but necessary for understanding real life operation.
IF you're asking because of driveline considerations, then the most important point prevails- an all-wheel drive circumstance ALWAYS results in a disparity between wheels... there's a right-to-left disparity due to change in rolling distance in a turn, and there's a front-to-rear disparity as a result of Ackerman Angle (front wheels travelling farther than rear). The exception here, is that MANY articulating tractors have symmetrical front/rear pivot distance geometry, and as a result, the theoretical travel of front and rear axles SHOULD be the same...
But in the end, you have some wheels that need to roll farther than others, and when there's a load on the drawbar, or a hill to climb, the driveline binds up a little bit, and eventually there's enough force against soil that Mother Nature finds some way to resolve the dispute.
If you're worried about how it looks, there isn't enough mud on your tractor yet...
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