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. 

 

 

Stainless air hose extender

 

Received this question:

"What is the easiest way (tools, parts, technique, education, practices) to easily add air to the inside dually of the 1996 Holiday Rambler Navigator 40 pusher and daily work truck 2007 GMC 3500 Sierra. I have large hands and have trouble with this simple task. I have been reading and enjoying technical knowledge for some time now."

The quick answer is just to get a "double foot" Air Hose Extender end as seen here.

However, having used this type of hose end myself, I know that achieving a solid connection to a valve with minimal or no air leakage can be challenging.

Also, what you do if you are using an external TPMS sensor on the end of your valve stem? It can be difficult to get the sensor screwed off and back on again without dropping the sensor down between the inner and outer tire. My solution was to get a set of "Hose Extenders as seen here

This is a Wheel Master hose kit #8001 as seen on my RV.

I DO NOT recommend the similar "airless" hose kits from other manufacturers as your TPMS sensor will not register the tire pressure

I selected and prefer this hose kit because it provides for a SOLID attachment for the hose ends.

I see posts with complaints about TPMS sensors on the end of a hose or even just the hose itself failing and causing a loss of air but I believe it is not the hose itself that fails but the flimsy "spring" clips or rubber donuts that are suppose to support the hose where it goes through the "hand hole" openings in the wheel.

The task to install this extender kit does require some mechanical ability, a few tools and a bit of planning. You will need to do all these things safely.

1. Jack up the rear axle and remove the outer tire. Be sure the jack is on solid ground and using a 6 point socket of the proper size to remove the lug nuts. I keep the inner dual on the hub by placing at least 2 lug nuts back on the studs finger tight, to keep the wheel attached to the axle while working on the hose attachment
2.  Attach the hose with the straight end to the metal valve stem after cleaning the threads and confirming the valve core has no leakage. Now is the time to replace the valve core with new core and I recommend you use the "clicker" valve core tool available at many auto parts stores. The tool is less than $8 and "clicks" at the specified 3 to 5 In-Oz torque.
3. Attach the hose end with the 90° end to the outer wheel (that also has new valve core) and run the hose back through the hand hole.
4. Orient the outer wheel with the hose at 180° from the hose from the inner wheel and re-mount the outer wheel. Be sure neither hose can contact the edge of the outer wheel hand hole. Be sure to apply the lug nuts with the proper torque spec for your RV. I have a low-cost torque wrench from Harbor Freight, as I keep this wrench in the RV so it does not get a lot of usage. The spec for my RV is 140 Ft-Lb so I would select a wrench that is capable of at least 50 Ft-Lb greater than what is required.
5. Now comes the hard part. You need to attach the 90° angle brackets to the center hub after making sure the long threads on the hose are well through the bracket. There are two nuts for each hose end to secure the hose in the bracket. Once the bracket is located with no part of the hose contacting the wheel you can mark and then use the "pop-Rivits" to secure the bracket to the hub. NOTE: If you have stainless "wheel simulators" you will need to be sure the hose does not contact the sharp edge of the simulator as that can "saw" through the hose and cause a loss of air. So you need to pay attention when locating the "L" bracket to the simulator.
6. BIT of ADVISE, when adding air to the hose, I suggest that you support the hose in the bracket with your hand as the force from the air hose could loosen the bracket.
7. You can now attach your TPMS sensor to the end of the hose and you should be good to go.

New Info on Michelin Agilis CrossClimate posted on the Keystone RV Forum

Micheline Agilis CrossClimate versus Bridgestone Dueler Ascent

I know this is "late information for this thread" but might help someone at a later date. The Michelin Agilis Cross Climate is not a "long distance/high mileage" tire. It's more of a "snow tire" with a commercial application. The Michelin Warranty for the tire does not have a "mileage warranty" but rather a "6 year warranty based on the remaining tread depth". That "sounds pretty good" until you start reading the footnotes in the warranty brochure for the Agilis line. Footnote 2 states: "Based on a treadwear test using tires in size LT265/70R17 121/118R on 2018 Ford F250 pickup trucks, loaded to 9800 lbs, versus the following competitors. Actual on-road results may vary. Average projected mileage to wearout: Michelin Agilis CrossClimate : 24,500 miles,"

When you "do the numbers" most people buy truck tires expecting 50-60 thousand miles of tread life. For most people with a 11-15 K annual mileage, that means 5 or 6 years on a set of tires before needing to replace them. The Agilis line "Michelin projected tread life to wearout is 24,500 miles. Somewhere between 1/3 to 1/2 the typical Michelin LTX tire.

There's an old thread from a couple years ago where one member from Florida bought Agilis tires for his truck and only got around 20,000 miles before the tires were "worn out" and needed replacement.

The Agilis is a "good tire" for its intended purpose (winter tire operation in all road conditions) but is not the best choice of Michelin tires for a "true all season tire with a high mileage tread longivity"...

Just something to think about if you're looking for "tires for a truck used as a daily vehicle and to tow a travel trailer (typically summer "hot road conditions" use)...

While I have no personal knowledge on this it is reasonable to pay attention to the use of "Winter"  tires in RV service.