Okay

First read this:

KM2 tire 33X12.5 R15 58 lbs
KM2 tire 33X12.5 R16 59 lbs
KM2 tire 33X12.5 R17 67 lbs

Bigger is the diameter of the rim, heavier is the tire

Why? I don't understand because the R15 tire has more rubber than the R16, and the R16 tire has more rubber than the R17

 

More steel to support the short side wall? Due to the larger diameter, maybe

Hell, those tires are light! Toyo M/T. 35x12.50x17.... Try 80#'s. "NO RIM" just tire

 

I think your missing realizing something if those tires are all the same sidewall size than each tire is larger therefore heavier. Example: it's not the exact same tire with just a different size hole for the rim.

 

I don't understand

These 3 tires have the same width and the same diameter.
The 15" has more sidewall that the 17". Therefore, why the 17" is heavier?

 

Load ranges have a big part to do with it. IE a "c" load tire will be much softer sidewall than an "e", because of the additional support built into the "e" tire for the increase load.

More radial steel, stiffer compound, etc.

 

good point

 

If the 3 tires were say 215/75/15,215/75/16, and a 215/75/17 stood side by side the 17" is a larger, therefore heavier tire than the 15".

 

Right, but a 33" tire is a 33" tire regardless of rim size. I think as mentioned before that it is most likely due to load range.