That is NOT a tire size. -The size is a much longer series of numbers and letters.
30 is the diameter of the tire in inches. 950 is the width of the tire which converts to 9.5 inches. R means it is a radial tire. The 15 is the diameter of the wheel.
Means that the diameter is about 20", and the width of the tire is something similar to 1.75"
the diameter of the tire (all the way across)
The diameter of this size tire is 24.9 inches and the circumference is 78.3 inches.
The tire size was designed to fit rims that are 17 inches in diameter.
Around 22"
The diameter of the wheel base.
More than likely you can as long as you get a tire size that will keep the overall diameter of the tire/wheel close to the OEM diameter.
The 31 is the overall diameter so it will be 31" tall, the 10.50 with the the width 10.5" wide, x15 will be the rim size.
The standard size of a trailer tire depends on the size of the trailer. The standard size for most of the trailers and the main trailers are 28 inches in diameter.
The question is not clear. Do you mean the size that is half way between the largest and smallest made? or the size with the highest production volume? looking to see what the average diameter is
I doubt it as there is 2" difference in diameter.