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Friday, January 15, 2021

Are RV trailer tires exempt of the physical laws of the universe?

In an Internet forum for owners of a well known RV trailer company, there was a discussion on what the correct or proper inflation and load capacity was for tires on the companies trailers. I jumped in with the following observations.

Tires list the Maximum load they are rated to support and tires also list the minimum cold inflation needed to achieve that load capacity. I have covered this "The Maximum is the Minimum" dichotomy in this blog on RV Tire Safety.

I really do not understand why people seem so afraid of running more than the minimum cold inflation needed to support the actual load.

I am in the process of working through the "Rule Making" documents from DOT when they set the minimum margins on inflation for cars, SUVs and trucks equipped with TPMS. I note that RVs were specifically excluded from this rule making. Could that be because the RV companies didn't want to see any increase in costs even if it meant the product would have fewer failures?
No, that couldn't be. No corporation would ever shave costs if the safety of the product might be compromised would they?

The MINIMUM cold inflation a tire should have would be the level needed to support the actual tire load. They also established that the normal cold inflation should be at least 25% higher than the MINIMUM. Their objective was to minimize tire failures that might result in damage or injury. The DOT knows that tire pressure increases with temperature (2% per 10F) and tire engineers know and design and even depend on this physical fact.

For some reason people with RV trailers feel it's ok to have zero margin. It wasn't till 2017 that RVIA started to specify a small 10% margin and some people argue that the RVIA is not a real requirement as it isn't a legal requirement. For RVs built before 2017 many RV trailers have certification stickers that specify ZERO margin or essentially zero margin as the tire capacity that was to be considered acceptable.

With the above as guidelines I have to wonder why people continue to complain about having tire failures. You are making the conscious decision to ignore established engineering recommendations and safety margin guidelines. What is so special about RV trailers that would make you think they are exempt from scientific principles and physical realities?

Friday, January 8, 2021

Have you considered "sealant" or "flat-proof" or other stuff to prevent a flat tire?

 Just read a tale of woe from a motorhome owner that appears to have been sold a tire treatment that caused nothing but problems. Names have been changed to protect the "innocent".

"We purchased "anti-flat" tire sealant for the 6 tires on our motorhome, to provide some protection from tire leaks on trips.  Our RV has had vibrations running at highway speeds, and based on forum feedback, it was recommended we try a "road force balance" on the tires.
We took our RV to "Billy-Bob-Jo's tire Emporium", which has road force balance machines - and they were unable to balance the tires - the machines got a different reading after each spin. They assumed their machines couldn't handle the motorhome rims.

 Then we took the motorhome to the nearby dealer for the company that made the RV chassis (since the front two tires were no longer properly balanced), and they called us about the "goo" they found inside the tires - because they were also unable to balance the tires.
Once they removed the tire sealant (about 45 minutes per tire), they were able to get all 6 tires balanced.  It cost us around $1000 for the "anti-flat" treatment and another $500 to get the treatment removed and the tires balanced.

Then the RV owner asked  "Has anyone encountered balance issues when using tire sealant???"  and then added  "If we don't have any vibrations on the next road trip, we probably won't put any sealant back inside the tires."

  Clearly the material used either was in-appropriate or improperly applied. Also I do not understand why the owner felt it was necessary to even use such a product rather that use a TPMS and sign up for road service and save some money never mind avoid the aggravation of bad ride and lost time.



Friday, January 1, 2021

I need bigger wheels for my trailer.

So I have seen a few posts like the above, but I'm not sure if they are asking the right question.

First I will assume they are really looking for tires with greater load capacity. They might also be looking for tire sizes where there are more choices in brand and Load Range. Too often the person posting the question/statement has not provided the important information on the current tires so I and anyone else trying to help, has to guess at some facts.

Lets look at a likely situation. The older trailer came with 14" wheels and possibly ST215/R7514 LR-C tires that provide 1,870# capacity @ 50 psi. These "14 inch" tires would be about 26.7" OD and 8.5" wide.

 So what are the options?   The easiest thing to do is to shop for Load Range D tires in the ST215/75R14 size. This would give a load capacity of 2,200# at 65 psi but with similar dimensions as the OE tire. 

When making any change, I would change to bolt in metal valve stems so I can run TPMS and not have to worry about the low cost "snap-in" rubber valve stems failing.

Now if there is another reason to look for new wheels and you want to move to 15" or larger because you want a different brand tire, you MUST confirm that the new tire size can provide AT LEAST 1,870# load capacity (preferably more) AND you need to confirm that there is sufficient clearance between the new tire size and the RV frame, springs and fender skirt. Also that there is sufficient clearance between the top of the tire and the wheel well directly above the tire, and if you have tandem (two) axles don't forget the clearance between the two tires.

So one option might be an LT205/70R15 LR-E which gives 2,150# capacity at 80 psi, is 26.4 OD and 8.2" wide. The 80 psi would give a harsher ride so may not be the best choice.

An LT 215/65R16 LR-D at 1,930# and 27.0 OD and 8.7" wide might be an option.

 So there are a number of options but you have to do some investigating to confirm both load capacity and physical dimensions. Some options may be better than others and there will always be some trade offs as not every size is made by every tire company so you may find a size but can't find a dealer that sells that size in your area.

A side note: Whenever replacing tires you should replace the rubber valve stems with new or bolt in metal stems for improved reliability even if you don't run TPMS. Once you make the switch to bolt in metal valves, I doubt if you will need to change the stems for the life of the next two sets of tires.