Hello Argo gurus out there. Im wanting to replace the tires on my 1980s 8x8 Argo but I'm having trouble finding the same size tires. It has the 20-11-8 tires on it now so do I have to stick to that size or could I go up to a 21 or 22" tire??? If so whats the best tire to use for replacement and where have you found the cheapest deals ????? Thanks for any help