Grit dog wrote:
These last 2 posts are false, OP.
It’s not the tires and wheels increasing the capacity unless Ford “chose” to add higher rated tires to the 20s.
Actually in general if the tire OD is the same (unless the 20s are notably taller), the greater the rim diameter, the lesser the sidewall height and the lower the load rating.
....
Sorry, not true for all tires. Look at the specs for the Michelin LTX A/T2 tires in LT275/65R18 and LT275/65R20. The 18" tire has a max load rating of 3,415 lbs at 80 psi. The 20' tire has a max load rating of 3,750 lbs at 80 psi. That is 335 lbs more per tire than the 18".
Similarly, the LT245/75R16 tire has a lower rating than the LT245/75R17.
Similar Continental tires have the same load ratings as above for the same sizes.
Don't know about other brands or styles.
Michelin