Excellent "link". Unsprung weight (aka unsprung mass) has nothing to do with tire diameter, only pure mass of weight that is "suspended" in rotating motion.
For example-- take two identical size/brand tires like the Grabber AT2, but which have different individual weight.
TIRE A: Grabber AT2 in P275/65R18, C-Load Range (6-Ply) (32" O.D./44 lbs).
TIRE B: Grabber AT2 in LT275/65R18, E-Load Range (10-Ply) (32" O.D./54 lbs).
Now, using equal pushing force-- shove each tire down the street and let it freely roll on its own merit until it finally peter's-out, wobbles, and falls over. Measure the distance traveled by each tire. You will discover, the heavier TIRE B rolled further due to its combined "suspended" (unsprung) momentum, centrifical force and perpetual motion that kept the tire rolling further. Simply put, it takes more braking effort to stop a heavier tire than a lightweight tire.
When auto manufacturer's design and engineer their vehicles, the OEM brakes are perfectly adequate to stop the OEM tires (and vehicle) within a recommended safe stopping distance set by the automotive industry. There is a window of allowable variance that aftermarket tires may be heavier than the OEM tires and still allow braking distance to be within safe margins.
The tire industry and US-DOT has determined this safe allowable variance of additional aftermarket tire weight to be 10 lbs over OEM tire weight on any given vehicle. This will still allow the vehicle to safely stop within the prescribed stopping distance for that type of vehicle.
Thus; for us VX'ers, since our OEM tires weighed only 34 lbs each, the maximum allowable variance for a heavier aftermarket tire is 44 lbs (10 lbs over OEM). I like to think of excess tire weight as "tire fat", in which case the tire industry & US-DOT allows us to have 40 lbs (10 lbs x 4 tires) of extra "tire fat" per vehicle and still be able to safely stop within a prescribed safe stopping distance.
Of note, most VX's are wrecked/totaled because they rear-ended the car in front of them because they simply couldn't stop in time using the unmodified OEM factory brakes in a safe distance due to very excessive "tire fat" (extremely heavy tires). During an emergency panic stop in conjested traffic, the small OEM factory VX brakes will say (if they could talk)-- "You want me to stop these big humungous meats??? Sorry; not today, ain't happening!!!" That's why I always harp on people to please, please, please allow an extra cushion of space between the car in front of you when running extremely heavy tires greater than the recommended 44 lbs maximum per tire weight on the VX!!! That's why I like
www.TireRack.com as they list individual tire weight on their "spec" chart and is the very first place I check when people ask me about various tires. Riff