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Friday, September 10, 2021

Are you qualified to drive an RV if you don't know how to check the air in your tires?

 Quick post on the need to know how to properly maintain your tire inflation.  Another personal opinion piece from this Tire Design Engineer.

Read this question on an Facebook page

Where do you take your motor home to get air pressure in tires checked?

There were a number of comments questioning if the person asking the question should even be driving. Some offered that they could get air at a truck stop. Others felt the person asking the question might not be sufficiently trained in the safe operation of a large Motorhome.

I offered the following.

Safe operation of your RV, and car or truck includes having the tires properly inflated ALL THE TIME. A tire failure is just not an expensive inconvenience but your vehicle on the side of the road is a safety hazard for both you and every vehicle that passes your disabled vehicle. More than half of all tire failures can be traced to their operation with insufficient air pressure. 

In my opinion every RV, 45' Motorhome to 8' trailer should have a Tire Pressure Monitor System or TPMS that have been properly programmed and checked for operation at least once a year. Since 2005 almost all cars have been equipped with this critical safety device as mandated by DOT. 

I can only guess why DOT decided to exclude RVs from this safety requirement. Was there push-back from the RV industry and the importers of lower cost ST type tires? As there might have been when improved qualification tests were implemented on Passenger and Light Truck tires in 2002 when ST type tires were excluded from the requirement to pass more demanding testing? IMO there is no excuse for not having a TPMS on your RV.

While it is true that personal injuries due to tire failures in RV application are minuscule compared to the number on cars and trucks, they are not zero. It does appear that reducing personal injuries are the driving force behind DOT safety requirements and with so few injuries occurring that involve tire failures on RVs there is probably little or no pressure on DOT to improve the safety of tires in RV application (ST type).

 If you check the TPMS each morning you should notice any loss of air pressure and can adjust the tire pressure while at the campground where you don't have a car passing 6' away at 70 mph. No tools are required to install a TPMS. No special mechanical knowledge is needed to program the system either other than being able to read the instructions. 

Claiming that you check your air pressure at each rest stop isn't good enough unless you can let us know how you check the pressure while driving 50 mph down the highway, or guarantee with 100% certainty that no valve core will ever leak after a tire had its pressure checked.



Friday, August 27, 2021

Want to hang something off bumper of your trailer? You need to do some math!

Been monitoring a forum thread about a guy who wanted to hang a 250# tool box off a mount from the rear bumper of his trailer. He just didn't understand the implications of changing the hitch load if he made such a change or the shift in tire loads between axles.

THIS video from Facebook shows the potential of not doing the calculations and for ignoring Science.

Distance from axle to tool box could be a serious issue when you consider how levers work.
I have also seen some Class-C Motorhomes with platforms attached to the trailer hitch receiver. Some have mobility scooters on them some tool boxes and some even have motorcycles. These items might be 100# but I am afraid that the total might approach 500# in some applications. While the hitch and platform might be rated for 500# or more the back end of the RV may have lower limits.

Here we see a 5,000# hitch on an RV with only a 250# load limit.

It is important to remember that just as with axles, springs, and tires, the load capacity is limited by the weakest link or component.For axles, the weakest component is many times the tires. You may have an axle rated GAWR of 3,000 and the tires may only be rated for 1,510#  but swapping the axle with a 4,000# unit will not raise the GAWR unless you also change the tires and probably also the springs, brakes and spring mounts too.

This same situation can occur for the hitch. Class-C Motorhomes are many times built on the "Cutaway" frames of standard vans. But the RV company extends the wheelbase by cutting the rear of the frame than welding in a couple pieces of steel to make it longer. This does not result in a longer but equal strength structure. In fact, it may mean the total frame strength is now lower.

Back to the question of what happens even if you don't have load limitations of the frame or receiver? Hanging weight off the rear bumper does TWO things. First, It obviously increases the load on the rear tires. Second it decreases the front tire loads and transfers that load onto the rear axle and tires. You need to be sure that this addition is not overloading any of your tires.