[CWtheMan]

OKAY, here we go; RV trailer replacement tires. To the RV trailer owner, this is probably the most confusing topic. The factors leading into the replacement action are basically the same as automotive tires. However, RV trailer tire replacements are commonly done by trailer owners. They seek help from unprofessional sources that often provide inaccurate, unsafe recommendations. In this post I’m not going to delve into automotive tire replacements. They differ, and besides that, they are supported by vehicle manufacturers with lists of approved options the tire dealer can use to help them choose the right tires, even plus sized and “P” to “LT”.

First and foremost is the fact that all designated sizes are standardized to provide identical load capacity within that designated size. Speed letters and load capacity letters for load ranges are not part of a tire’s designated size. If present at the end of a tire designated size it’s for informational purposes only.

My definition of tire strength for this post is a tire’s ability to carry a maximum load. A tire’s durability factors have nothing to do with a tire’s strength.

Some brands provide more durability than others. ST tires now have at least two brand names building 15” & 16” rugged off road tires with more durable treads and sidewalls. Those features do not add strength. Some brands now have scuff guard inserts built into the tire’s sidewalls, they do not add strength. Nylon belt overlays are not required for ST tires. Almost all of the major brands now have nylon overlays on 15” & 16” ST tires to help prevent tread separations. Again, that addition does not add tire strength. I mention those few items to encourage the consumer to look for them when considering replacements for the OE tires. All steel constructed tires may be more durable than the standard polyester tires. Currently they are only provided in LRG for 16” tires and LRF &LRG for 15” tires. Their load capacities are identical to polyester tires of the same size designation and load range.

So, now I’m going to get to replacement tire standards for RV trailer tires. The following information is supported by excerpt information found in the FMVSS, 49 CFR part 567 - vehicle certification, USTMA manual for RV tires and a little help from some of the automotive SOP manuals.

First I’m going to establish that when I write a tire size for the first time I’ll refer to it by its official designator, – designated size- after that I may just say tire size.

NHTSA says a tire’s official size is defined as designated size or size designation. It’s important to recognize that when selecting your replacement tires. A designated size for special trailer tires is ST235/85R16. If you see them advertised as 235/85R16 someone didn’t know the proper nomenclature. Vehicle certification labels can be recalled for providing incorrect tire size designations.


The only official deviations from those OE tires will have to be approved by the vehicle manufacturer via an options list, if there is one for that particular trailer. I’m going to do this from a consumer/installer point of view. When the search begins, go and take a look at your vehicle certification label (On RV trailers the certification label is on the left external section of the frailer forward of the axles). The size designation of the official OE tires is displayed on that label. All replacement tires must have the ability to carry the load capacity those certified tires can carry at their recommended cold inflation pressures. Upgrades within a designated size may be available with a higher load range for that size (OE LRC to replacement LRD). Size changes such as OE ST205/75R14 to ST215/75R 14 is known as “Plus Sizing” and would have to be the trailer manufacturer’s option.

When replacing an OE tire with one of the same size having a higher load range, say LRC to LRD, there is nothing special to do. Both tires conform to the same load inflation chart for that size. What has happened is the owner now has the option to increase inflation pressures from LRC 50 PSI to LRD max 65 PSI giving the trailer owner much more load capacity reserves for his axles. I’m just going to mention this here, always change valve stems and use metal caps. Always insure the OE wheels can support the maximum PSI – they can already support the axle loads or they wouldn’t’ be official OE wheels - for the replacement tires. If/when plus sizing always insure the new tire/wheel assemblies have sufficient wheelwell clearances. (Remember, Wheel manufacturers MUST provide specifications on request).

When replacing OE tires with others in the Plus Size category there are some rules that must be followed. First and most important is the industry wide standard that replacement tires MUST have a load capacity that will be equal to OE tires load capacity at the vehicle manufacturer’s recommended cold inflation pressures. With the exception of vehicle manufacturer options, the designated size must be the same design as the OE tires. The most common option with a different designation is the LT235/85R16 LRG. It was offered quite often as a replacement for ST235/85R16 LRE because it has more load capacity and was desirable on vehicle certified GAWR 7000# axles. However, you won’t see that anymore because the RVIA minimum recommendation for 7000# axles is 3850#. GY and Sailun both built that LT tire as a regional service (RST) trailer tire for RV axles only. Sailun quit building it when they introduced the ST235/80R16 all steel LRG tires. Because the GY G614 was also used as OEM they still build it but I suspect that will quit when those OEM tires age out. Anyhow, it’s a misapplication to use a tire size designation other than the one on the certification label without recommendations from the vehicle manufacturer. There are 3 regulations plus the industry standards that support that statement.

Once the plus sized tires have been selected and all other fitment standards have been met, it’s important to register the new tires. There are a couple of technical actions that should be followed to protect all other owners of the vehicle. First is load capacity. A new recommended cold inflation pressure is needed for the replacements. Individual load inflation charts for the old and new tires will be needed. Look at vehicle certification label and determine what the load capacity of the OE tires is at the recommended cold inflation pressures. Use the load inflation chart for the new tires to set a new recommended cold inflation that will equal or exceed what the OE tires provided. Most will go up at least 5 – 10 PSI above minimum. Write that new number down and find the vehicle owner’s manual and pencil it in near the old number. Find some all weather material and build a supplemental tire load and inflation label and place it adjacent to the vehicle certification label. I’m going to insert a picture of an auxiliary label. It’s for automotive tires and you can just modify it to display your new tire size and inflation pressures.