A question on Max inflation on the wheel

 Question and post from Doug, a reader of this blog

Roger Marbles' tire dissertation…. one item I constantly see miss is the allowed tire pressure on the steel wheel. Each wheel is stamped with a code from the National Wheel and Rim Assn. I just happen to have acquired one of their spec sheets. The wheels on my Class A are stamped (embossed) “AF” which means the maximum pressure is 95lbs. Is that ambient cold or maximum hot? That I don’t know and it isn’t explained. I presume it is cold or ambient. So, is there a benefit in buying a higher maximum load tire or not?- If the wheel can’t take up to, say 120lbs of pressure! (Load range F tire).

 My reply:  Unless you are fine-tuning a race car handling, the inflation we are talking about is ALWAYS the “Cold” inflation of the tire. RVtravel.com has a section on “Maintenance & Repair Archives.” Just click in the blue header to find any of my tire-related posts. Or you can click on this to get to my posts. You can also do a “word search” if you do not see the topic you are looking for. BUT in this case I previously covered. If you need greater load capacity, just changing the tire does not increase the GAWR spec for your RV, as the GAWR spec covers the tire, wheel, hub brakes, nuts and bolts, and axle and mounting brackets, etc. So just increasing the load capacity of the tire will not result in an increase in the max load capacity of the RV.

Hi  Roger, I am well aware of the tire ambient air psi, which I have read in your posts numerous times. My specific concern is with the steel wheel vs the rising pressure when traveling down the road. If the wheel is allowed to hold 95 psi, is the rising rolling pressure increase above that safe for the steel wheel? With an F load tire, the MINIMUM pressure to support the load is – say 105 lbs cold, and a wheel at only 95 lbs cold – already over the max steel wheel psi – what happens when the pressure increases even higher to 120-130 or more psi from rolling heat buildup? 

Doug, I thought I was clear but the ONLY pressure we are concerned with is the “COLD” pressure. This applies to both the tire and the wheel. In your example, something is wrong. Either the tire or wheel is too small or has too low a load rating or the load being placed on the tire & wheel is to great. If you know the actual load on the tire & wheel and the inflation shown in the tables for that size tire and wheel is greater than that specific tire capacity, then you are overloading the system and need to reduce the load and or increase the size tire or the tire Load Range (Psi). Example below:
Assume we have a 225/75R19.5 LR-E tire. That tire is rated for 3,195 @ 80 PSI cold in a Single application. Also assume the wheel is rated for 80 psi. If you go on a scale and learn the tire load is 3,445# you MUST change something. Either change to a stronger wheel & Tire or lower the load. A LR-F tire could support 3,640# BUT that would require 95 PSI rated wheels. Just changing the tire to LR-F and increasing the inflation DOES NOT increase the load capacity of the wheel, which is limited to 80 PSI cold.