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CWtheMan · 02-03-2018, 05:25 PM

RV tires and “R” ratings

The “R” ratings I’m referring to are limiting factors as in GAWR & GVWR. I know, there’s another one, but I’m not going to mention it here.

RV trailer manufacturers, sometimes, just don’t pay attention to what their doing. Probably because the folks that design - set the limits - don’t talk to the administrators about standards and regulations. Keystone - others too - has had it’s shear of recalls for inaccurate vehicle labeling. Most of those recalls have been about weights and tires or both.

The vehicle manufacturer is solely responsible for establishing and setting the “R” factors. Once they decide what their going to build they must set minimum limits mostly based on weakest link factors. The GVWR is the ultimate limiting factor and all other weights and measurements for the trailer must fit into that limited box, so to speak. Once the GVWR has been established and affixed - certification label - to the trailer for delivery to the consumer or dealer it can only be changed or modified by the vehicle manufacturer or a certified vehicle modifier.

Axle manufacturers don’t make and certify their axles in all weight ratings trailer manufacturer’s may require. So then the vehicle manufacturer has the authority to set their GAWR values to suit the trailer’s fitment requirements. I’ve seen keystone set 5200# Dexter axles to a GAWR of 5080# just so they could fit two 2540# max load capacity tires to those axles. Remember, bottom line, tires fitted to RV trailer axles are not required to have any load capacity reserves. RV trailer manufacturer’s have always taken advantage of that fact. It might be a moral violation but it’s not a legal violation. And, don’t rely on the tag on the axle to be a true representation of it’s authorized load capacity.

Information in the above paragraph causes a lot of misconception about trailer tire fitments. Some people take the time to read the fitment standards the trailer manufacturer MUST follow and assume the can do likewise. The standards are just what they say they are, builders standards, not at large standards. When the trailer manufacturer affixes the certification label the trailer they have sworn, so to speak, to the DOT, that the trailer meets all minimal safety standards, meaning that their tire fitments are appropriate. The tire industry will not violate that minimal standard and the Original Equipment tire fitments will always be the benchmark for all subsequent replacements. To deviate from the OE tire fitments requires an agreement between the vehicle owner and the trailer manufacturer for optional fitments. Normally, a load range increase within a tire’s size designation (ST205/75R14) is not considered “plus sizing”. It’s the same tire with increased load capacity - if available.

I’ve probably mentioned this before but it’s worth mentioning again. The fitment for automotive tires, sort of like the ones on your tow vehicle, are governed from the same standard as RV trailer tires but with a twist. They are required to provide load capacity reserves via excess load capacities above the vehicle’s GAWRs and set by the vehicle manufacturer. They will normally be fitted to axles that have load capacity reserves above the vehicle’s GVWR. Also, provisions have been made via collaborations between vehicle & tire manufacturer’s that allow - with adjustments - interchangeability of Passenger and Light Truck tires for many of the vehicles you tow with. There is no such collaborations for any sort of interchangeability between tire designs for RV trailers. That takes us back to vehicle certification and the standards which allow the vehicle manufacturer to fit what they consider appropriate tires, to the vehicle of what ever highway certified tires they see fit to install. Because they did it to model #1 does not allow others to do it to model #2. The benchmark gets in the way.

You will find some statements every now and then about passenger tires not being allowed on RV trailers. That’s not so. The standards outline the procedure to be used for such fitments.

Oh well, I may have rambled too far. If you got this far and have questions just chime in.

02-03-2018, 05:25 PM	#55
CWtheMan Senior Member Join Date: Feb 2010 Location: Taylors, SC Posts: 3,031	RV tires and “R” ratings The “R” ratings I’m referring to are limiting factors as in GAWR & GVWR. I know, there’s another one, but I’m not going to mention it here. RV trailer manufacturers, sometimes, just don’t pay attention to what their doing. Probably because the folks that design - set the limits - don’t talk to the administrators about standards and regulations. Keystone - others too - has had it’s shear of recalls for inaccurate vehicle labeling. Most of those recalls have been about weights and tires or both. The vehicle manufacturer is solely responsible for establishing and setting the “R” factors. Once they decide what their going to build they must set minimum limits mostly based on weakest link factors. The GVWR is the ultimate limiting factor and all other weights and measurements for the trailer must fit into that limited box, so to speak. Once the GVWR has been established and affixed - certification label - to the trailer for delivery to the consumer or dealer it can only be changed or modified by the vehicle manufacturer or a certified vehicle modifier. Axle manufacturers don’t make and certify their axles in all weight ratings trailer manufacturer’s may require. So then the vehicle manufacturer has the authority to set their GAWR values to suit the trailer’s fitment requirements. I’ve seen keystone set 5200# Dexter axles to a GAWR of 5080# just so they could fit two 2540# max load capacity tires to those axles. Remember, bottom line, tires fitted to RV trailer axles are not required to have any load capacity reserves. RV trailer manufacturer’s have always taken advantage of that fact. It might be a moral violation but it’s not a legal violation. And, don’t rely on the tag on the axle to be a true representation of it’s authorized load capacity. Information in the above paragraph causes a lot of misconception about trailer tire fitments. Some people take the time to read the fitment standards the trailer manufacturer MUST follow and assume the can do likewise. The standards are just what they say they are, builders standards, not at large standards. When the trailer manufacturer affixes the certification label the trailer they have sworn, so to speak, to the DOT, that the trailer meets all minimal safety standards, meaning that their tire fitments are appropriate. The tire industry will not violate that minimal standard and the Original Equipment tire fitments will always be the benchmark for all subsequent replacements. To deviate from the OE tire fitments requires an agreement between the vehicle owner and the trailer manufacturer for optional fitments. Normally, a load range increase within a tire’s size designation (ST205/75R14) is not considered “plus sizing”. It’s the same tire with increased load capacity - if available. I’ve probably mentioned this before but it’s worth mentioning again. The fitment for automotive tires, sort of like the ones on your tow vehicle, are governed from the same standard as RV trailer tires but with a twist. They are required to provide load capacity reserves via excess load capacities above the vehicle’s GAWRs and set by the vehicle manufacturer. They will normally be fitted to axles that have load capacity reserves above the vehicle’s GVWR. Also, provisions have been made via collaborations between vehicle & tire manufacturer’s that allow - with adjustments - interchangeability of Passenger and Light Truck tires for many of the vehicles you tow with. There is no such collaborations for any sort of interchangeability between tire designs for RV trailers. That takes us back to vehicle certification and the standards which allow the vehicle manufacturer to fit what they consider appropriate tires, to the vehicle of what ever highway certified tires they see fit to install. Because they did it to model #1 does not allow others to do it to model #2. The benchmark gets in the way. You will find some statements every now and then about passenger tires not being allowed on RV trailers. That’s not so. The standards outline the procedure to be used for such fitments. Oh well, I may have rambled too far. If you got this far and have questions just chime in.