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Old 03-16-2016, 08:29 PM   #11
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I see what your saying, but not a camper out there comes with tires rated more than the axles. As long as both meet or exceed the GVWR, and the tires are of decent quality, all should be fine.

I actually thought that they were federally mandated to.
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Old 03-16-2016, 08:48 PM   #12
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Yikes!

I often post this information but itís so different from what most people believe about their trailer tires, it irks them.

For RV trailers 10000# GVWR or less there are normally three basic tire designs for the vehicle manufacturer to select from, Passenger (P) Light Truck (LT) and Special Trailer (ST).

For RV trailers above 10000# GVWR there are LT tires (Suitable for RV trailer axle service) , ST tires and light to heavy duty truck tires normally used on low platform trailers with a trailer or all position rating.

Vehicle manufacturers have the sole responsibility for selecting the tires for your trailer and setting the recommended inflation pressuresÖ..says so right in the instructions.

Vehicle manufacturers also have the authority to set the GAWRs for your trailer. So, look at the GAWRs listed on the trailerís federal certification label and in itís ownerís manual. Axles with load capacities above the listed GAWR are providing reserve load capacity above the minimum requirement.

In the specifications for your trailer the builder set a target GVWR. All of the strength built into that trailer was aimed at that GVWR. When all is said and done the builder will have set aside a weight value for cargo. A figure for an acceptable hitch weight by itself or in a range. The lowest value will be added to the total GAWR, the sum must equal or exceed the GVWR.

Yep, Iím getting to the tires. The safety standards the trailer manufacturer must meet are presented to them in minimums. Those minimum standards MUST be met by the trailer builder. Because? On the Federal certification label the manufacturer MUST say: ďThis vehicle conforms to all applicable US Federal Motor Vehicle Safety Standards in effect on the day of manufacturer above.Ē NHTSA takes that statement very seriously because they wrote the safety standards.

So, bottom line, the minimum tire fitments for Original Equipment tires is established as tires that will provide via inflation pressure a load capacity equal to or greater than the established GAWR (s). The new wording expands on that to say the tires are appropriate for the fitting.

Once a consumer takes possession of the trailer itís their responsibility to preserve the minimum safety envelop for their trailer.

When the vehicle manufacturer selected the OE tires they set the minimum standard for tires for that trailer. Along with the minimum tire size came the minimum tire inflation pressure.

Tire industry standards - after first sale - are written to support the vehicle manufacturerís minimum standards. So, replacement tires will have to meet those standards. Basically the tire industry standards say replacement tires must be the same size tire or larger and provide the same or greater load capacity as the OE tires provide by inflation. Sometimes very difficult to do if you want to use a tire design not completely compatible with the OE tires.

Donít get duped into the trap that many ďtire peopleĒ will lead you into by saying you only need to have tires to carry the load on them or that as long as your tires provide the load capacity of the GAWR itís OK. The regulations that say things like that were not written for the consumer to apply, they were written for the vehicle manufacturer to Apply. Besides that, airing a tire to the load carried is not a FMVSS regulation. It comes from trucker tire rules where there is no recommended inflation pressures. IMO there is but one way to be safe with your tires, follow the recommendations of the tire industry. When purchasing replacement tires for your RV trailer go up a load range and use the tires maximum allowed inflation pressure for that load range. Or, Get replacements that provide a minimum of 12% of load capacity above total GAWR.

If you think all of this is another line of BS, send me a PM. Iíll provide a reference to the regulation or industry standard that will answer your questions.
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Old 03-16-2016, 09:06 PM   #13
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......................

IMO there is but one way to be safe with your tires, follow the recommendations of the tire industry. When purchasing replacement tires for your RV trailer go up a load range and use the tires maximum allowed inflation pressure for that load range. Or, Get replacements that provide a minimum of 12% of load capacity above total GAWR.
For all of y'all that don't read the fine print, the above quote is everything you ever need to know about tires.
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Old 03-16-2016, 10:05 PM   #14
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IMO there is but one way to be safe with your tires, follow the recommendations of the tire industry. When purchasing replacement tires for your RV trailer go up a load range and use the tires maximum allowed inflation pressure for that load range. Or, Get replacements that provide a minimum of 12% of load capacity above total GAWR.
I just mentioned in another thread- be cautious about going up a load range as that can have implications on the outer diameter of the tire. In my case, I couldn't easily increase my load range as my tires had less than 2" between them. Most tires that I found that had higher load carrying capabilities also had a larger outer diameter and would have further decreased the space between the tires.

Airdale, when did it become a regulation (ballpark year) that the tires had to cover the axle specs?
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Old 03-16-2016, 10:33 PM   #15
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Originally Posted by ependydad View Post
I just mentioned in another thread- be cautious about going up a load range as that can have implications on the outer diameter of the tire. In my case, I couldn't easily increase my load range as my tires had less than 2" between them. Most tires that I found that had higher load carrying capabilities also had a larger outer diameter and would have further decreased the space between the tires.

Airdale, when did it become a regulation (ballpark year) that the tires had to cover the axle specs?
Are you talking about increasing tire size to get a higher load rating, or increasing the "ply rating" in the same size to get the higher load. I checked the Maxxis site and the tire diameter doesn't change at all between tires with the same size but higher load rating (i.e., 8 ply vs 10 ply).
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Old 03-16-2016, 10:36 PM   #16
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Are you talking about increasing tire size to get a higher load rating, or increasing the "ply rating" in the same size to get the higher load. I checked the Maxxis site and the tire diameter doesn't change at all between tires with the same size but higher load rating (i.e., 8 ply vs 10 ply).
Basically any of the above- just that folks should be aware that outer diameter can be important.
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Old 03-16-2016, 11:33 PM   #17
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Basically any of the above- just that folks should be aware that outer diameter can be important.
Yes, outer diameter is important, but looking a various tire specs showing diameter I cannot find any change in the final number based on ply rating. Seems like a, i.e., 225/75R/15 has a 28.1 inch diameter with either six or eight ply rating. I think if adding plys did increase the diameter it probably wouldn't be more than .1 or .2 inch...hardly noticeable.

The Goodyear 245/70R19.5 has a 33 inch diameter for both F and G load ratings. The G load has an additional 500 pound load capacity.
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Old 03-17-2016, 10:01 AM   #18
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For all of y'all that don't read the fine print, the above quote is everything you ever need to know about tires.
2x
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Old 03-17-2016, 11:21 AM   #19
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Originally Posted by ependydad View Post
I just mentioned in another thread- be cautious about going up a load range as that can have implications on the outer diameter of the tire. In my case, I couldn't easily increase my load range as my tires had less than 2" between them. Most tires that I found that had higher load carrying capabilities also had a larger outer diameter and would have further decreased the space between the tires.

Airdale, when did it become a regulation (ballpark year) that the tires had to cover the axle specs?
Going up a load range on the OE tire size will not include a physical size difference, ie; a ST225/75R15D is physically the same size as the ST22575R15E. Changing tire designs or sometimes brand names may cause a tire OD to change. that would be caused by tire tread depth.

Modern tire regulations for trailer tires have always been determined by the GAWR values.

The same regulation is used for both Motor Home and RV trailer tire fitments. However, each fitment is addressed separately within the regulation and MR tires are fitted to the MH GVWR. It sometimes causes confusion, especially when the regulation is not read in its entirety.
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Old 03-17-2016, 11:35 AM   #20
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Yes, outer diameter is important, but looking a various tire specs showing diameter I cannot find any change in the final number based on ply rating. Seems like a, i.e., 225/75R/15 has a 28.1 inch diameter with either six or eight ply rating. I think if adding plys did increase the diameter it probably wouldn't be more than .1 or .2 inch...hardly noticeable.

The Goodyear 245/70R19.5 has a 33 inch diameter for both F and G load ratings. The G load has an additional 500 pound load capacity.
Ply rating increases with Load Range, ie...... PR6 = LRC - PR8 = LRD - PR10 = LRE - PR12 = LRF - PR14 = LRG.

Edit notes; Long ago all tires had cotton plies and their strength was determined by the ply count. When new fibers such as polyesters and nylons were developed, ply ratings became the norm. For ST and LT tires the load range is descriptive of what a particular ply (rated) tire will support at a given inflation value. The load range is the only system recognized by the DOT for the load inflation of ST and LT tires.
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