need tire size help

hey guys need some help here never been a tire guy or really anything until i got my hummer and when i bought it it came with the tire and rims so i have been looking for a upgrade something thats a little tougher and meaner looking and been checking out nitto, well when i put my tire size in it comes back with 2 out of the 4 tires. well i have now a 275/60/20 and i googled that a try to convert it and it comes back at 33x10.8x20 well i cant find a tire that matches that at all i have seen a 33x12.5x20 so theres my problem. if i want the mud grappler they dont show it in 275/60/20 but show it in 33x12.5x20 thought it was the same but i have no idea. if any one can explain better to me. what can i put on a 20 inch rim same tire or can i swap so if any1 can help the confused i would appreciate it


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Your tire sizes are going to be metric, i.e. 285/75-16. If you want to go to a 20" you can easily do a 275/55-20 or 285/55-20. Take a look on websites like tires.com for help. Most tires aren't listed in the older format like 33x12.5x20 any more.

If you are going to go offroading I wouldn't recommend going above an 18" rim.

not gona go off roading just wana keep the 20 inch rim i have now but put on a tire with a little better look.so can i put on any tire as long as its for a 20in rim like i said i have a 275/60/20 now. so can i change to anything ending in 20 ir do i need to keep the middle number the same or what

275/60-20
The first number is the tire width in millimeters.  The second number is the sidewall height expressed as a percentage of the tire width (or aspect ratio).  The last number is the wheel/rim diameter in inches.

The middle number will be smaller for lower profile tires.  Also, you are limited on how wide a tire you can put on a given rim.

 metric to standard 1st#/25.4x2nd#x2+3rd#= highth  1st#/25.4=width

I think the Mud grappler only comes in standard sizes the 33x12.50 should fit fine it will just be a little wider.
305/55/20 would be a good size it the terra grappler I think.