Need some advice on tires/wheels

[Wombii]

I don't know specifics about what would be suitable for 1/12 construction equipment, but page 20 here shows how Tamiya does dual rear wheels.
https://www.tamiya.com/english/rc/rcmanual/56318.pdf
RC wheels are often listed as 1.55, 1.7, 1.9 or 2.2. This is the diameter of the rim in inches. 1.9 is the standard size for 1/10 touring and trail cars. 1.7 is the size used for Tamiya 1/14 trucks. 2.2 is often used for larger or more capable crawlers. The tires are hollow rubber tires. Technically filled with air, but not sealed. They can be used with soft or firm foam inserts, but the tires themselves can also be anywhere on a spectrum from very soft to very firm. The stock Tamiya 1/14 kits have pretty firm rubber and no foam inserts.