It depends upon the size of the tires of your off-road vehicle. The tires of a tractor are typically around 20PSI in the front end and 33 PSI in the rear end. So those tires having valves use an air compressor that holds the rating of 4CFM in 90PSI to inflate.
So if you need the compressor to inflate the tires of your tractor, you must make the selection based on the size of the tires. There are many off-road air compressors are available but you should select the most suitable option.
As far as gallon size is concerned, an air compressor with a 2 to 3-gallon tank size is suitable. Large tank-size air compressors will let you inflate the tire without any refill. But for heavy-duty applications like tire inflation, sanding, and others that need continuous power and pressure, it is recommended to go for a 6-gallon tank size.