Tire sizes are easy to read.

For example , a 12" x 12" x 24" tire is a 12" wide tire....on a 12" diameter wheel (or rim size) and a 24" over all height. Mixing tire sizes and even tread styles can cause uneven cutting and steering problems. Don't forget to check your air pressure when diagnosing uneven cutting.

The term NHS on the side stand for "Non-Highway Service" in other words, a low speed tire not made for the road.

Best to replace in pairs as tire tread wear can have some effect as well.