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CWtheMan · 11-10-2020, 07:48 AM

Okay, I’m going to reiterate a little bit here. RV trailer manufacturers MUST abide and adhere to all standards in FMVSS when building your trailer. NHTSA directs FMVSS to develop standards that support minimum values. No vehicle manufacturer has the authority to lesson those minimums. Therefore, when certified by its vehicle manufacturer, an RV trailer has met all those minimum requirements.

Now, let’s get down to tires. Because of the wording in FMVSS, the designated size of the tires on the vehicle certification label is considered as minimum. Everything in our RV trailer industry revolves around minimums. It’s a safety violation to deliberately use anything less than the minimums.

NHTSA, in SAFECAR says the vehicle manufacturer’s recommended cold inflation pressures for OE tires are the correct inflation value for that vehicle. USTMA tire industry standards say that replacement tires MUST provide a load capacity equal to or greater than what the OE tires provided via recommended cold inflation for them.

To take a step backward I’m going to quote from a FMVSS standard. It’s just in part but it’s enough to get the drift. Actually this is from two standards. One says that OE tires for vehicle certified axles on RV trailers MUST provide a load capacity equal to or greater than the GAWRs. In the final fitment standard the vehicle manufacturer is directed to set a recommended cold inflation pressure that is appropriate for the axles on that vehicle.

Here’s a little raw meat to grind your teeth on. Before the RVIA 10% reserve recommendation a very large percentage of RV trailer tires could barely hold-up to a fully loaded RV trailer. Here’s a hypothetical. A couple of ST205/75R14 LRC tires are OE on 3500# axles. Those tires at their maximum load capacity of 1760# at 50 PSI are in real danger. With a loss of 5 PSI down to 45 the tires are only providing 1640# of load capacity. If this is a single axle trailer, the total load on the axle can be less than maximum - it can also happen on dual axels. However, the danger lies in an unbalanced axle with one tire position 200# above tire load capacity MAX.

Next up, the long winded replacement tire standards.

11-10-2020, 07:48 AM	#31
CWtheMan Senior Member Join Date: Feb 2010 Location: Taylors, SC Posts: 3,031	Part #4 Okay, I’m going to reiterate a little bit here. RV trailer manufacturers MUST abide and adhere to all standards in FMVSS when building your trailer. NHTSA directs FMVSS to develop standards that support minimum values. No vehicle manufacturer has the authority to lesson those minimums. Therefore, when certified by its vehicle manufacturer, an RV trailer has met all those minimum requirements. Now, let’s get down to tires. Because of the wording in FMVSS, the designated size of the tires on the vehicle certification label is considered as minimum. Everything in our RV trailer industry revolves around minimums. It’s a safety violation to deliberately use anything less than the minimums. NHTSA, in SAFECAR says the vehicle manufacturer’s recommended cold inflation pressures for OE tires are the correct inflation value for that vehicle. USTMA tire industry standards say that replacement tires MUST provide a load capacity equal to or greater than what the OE tires provided via recommended cold inflation for them. To take a step backward I’m going to quote from a FMVSS standard. It’s just in part but it’s enough to get the drift. Actually this is from two standards. One says that OE tires for vehicle certified axles on RV trailers MUST provide a load capacity equal to or greater than the GAWRs. In the final fitment standard the vehicle manufacturer is directed to set a recommended cold inflation pressure that is appropriate for the axles on that vehicle. Here’s a little raw meat to grind your teeth on. Before the RVIA 10% reserve recommendation a very large percentage of RV trailer tires could barely hold-up to a fully loaded RV trailer. Here’s a hypothetical. A couple of ST205/75R14 LRC tires are OE on 3500# axles. Those tires at their maximum load capacity of 1760# at 50 PSI are in real danger. With a loss of 5 PSI down to 45 the tires are only providing 1640# of load capacity. If this is a single axle trailer, the total load on the axle can be less than maximum - it can also happen on dual axels. However, the danger lies in an unbalanced axle with one tire position 200# above tire load capacity MAX. Next up, the long winded replacement tire standards.