Had a question asked on an RV Forum
The way I found this out is I was calculating PSI # for our MH's weights in two ways. One was to find the corresponding PSI for my actual scale weight, and then add 10% to the PSI, or the second way was to increase my scale weights by 10% and then find the corresponding PSI for that weight. When I compared the resulting PSI's between the two methods, they were different in many instances, but not consistently so.
So the question is why do the single tire increments vary from 140lbs to 230lbs, and the duals vary from 230 lbs. to 410 lbs. Can you explain? Does setting tire pressures really have to be this exact? And which way is correct? You would think that both would have the same results, but nah-Baby-nah.
Simple answer is, The Load formula is not linear as you can see here.
there are values that are exponents
As to adjusting for Dual position there are more instructions we tire design engineers have to follow.
1. Learn actual tire loading on a truck scale when the RV is loaded to your expected heaviest.
2. Assume one end of an axle is supporting 51% to 52% of the total axle load (this estimate is not exact. This is why "4 corner weights" are preferred if you are near the load limit
3. Consult Load & inflation tables to learn the MINIMUM cold inflation
4. Add at least 10% to the inflation in #3 and use this new number for your "Cold Inflation goal"
5. Set your TPMS Low Pressure Warning level to the inflation in #3 above.