Wheel lbs?

I am going to buy new wheels for our trailer, upgrade from 14" to 15". My question is load weight of the wheels.

Trailer lbs #7200 max
Axels lbs #3500 each

Do I need #2150 or #2540 max lbs wheels?

I am assuming that you are talking about a tow behind trailer....it that correct?  If so, you have a GVWR, according to your numbers of 7200 lbs.  A very minimum tongue weight of 720 lbs (10% on the tongue) and a better real world number of 12-13% tongue weight...(864-936 lbs).  Let's round it off to 900 lbs of tongue weight.  So take your 7200 lbs minus the tongue weight (900 lbs) and that leaves 6300 lbs.  Now, divide the 6300 lb of weight that the trailer axles are carrying by four, the number of wheels on the trailer and you get....1575 lbs per wheel/tire.  So clearly, either wheel upgrade would work for you, but the 2540 lb wheels would give you almost a 1000 lbs per wheel of reserve capacity. 

Even if you figure the least amount of tongue weight on the trailer...10% tongue weight, that would leave your trailer weight at  7200 - 720 = 6480 lbs.  Divide that number between the 4 wheels and you come up with  1620 per wheel/tire......which is still clearly in the upgraded wheels rating.  Just make sure that whatever tires that you use for the new wheels also have the appropriate load capacity to carry the weight that they will be carrying.  Hope this helps.

Just curious - I just looked at my cargo trailer and it has 2 - 3500lb axles and shows a GVWR of 7000lbs.

So how does the OP's 2 - 3500lb axles give him 7200lbs ???

There are other factors that are used to determine GVWR besides the axle capacity. Wheels, tires, springs and mounts, frame, etc.

RedandSilver said:

Just curious - I just looked at my cargo trailer and it has 2 - 3500lb axles and shows a GVWR of 7000lbs.

So how does the OP's 2 - 3500lb axles give him 7200lbs ???

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Very easy explanation....if you read my previous post.  The total trailer weight is 7200 lbs.  If 720 lb of that is being carried by the tongue (tongue weight), then the truck or tow vehicle is "carrying" 720 lbs of the total weight of 7200 lbs.  So, deduct the 720 lbs off of the 7200 lbs and you end up with....6480 lbs on the trailer wheels/tires.  Distribute that 6480 lbs between the 4 tires/wheels and that leaves you with 1620 lbs per tire/wheel.  The axle is rated at 3500 lbs and when you add the left and right weights of one of the axles, you get 3240....which is UNDER the 3500 lb axle rating!

kdbgoat said:

There are other factors that are used to determine GVWR besides the axle capacity. Wheels, tires, springs and mounts, frame, etc.

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Yes but wouldn't most (if not all) of those bring down the weight carrying ability? 

If 2 3500lb axles are a max of 7000lbs - using lighter components shouldn't raise the axle ratings - IMO.

xrated said:

Very easy explanation....if you read my previous post.  The total trailer weight is 7200 lbs.  If 720 lb of that is being carried by the tongue (tongue weight), then the truck or tow vehicle is "carrying" 720 lbs of the total weight of 7200 lbs.  So, deduct the 720 lbs off of the 7200 lbs and you end up with....6480 lbs on the trailer wheels/tires.  Distribute that 6480 lbs between the 4 tires/wheels and that leaves you with 1620 lbs per tire/wheel.  The axle is rated at 3500 lbs and when you add the left and right weights of one of the axles, you get 3240....which is UNDER the 3500 lb axle rating!

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That DIDN"T answer how 2 3500's = 7200.

The manufacturers are only required to have the axles/wheels/tires/springs rated to carry the gross weight of the trailer, minus the tongue weight that is carried by the tow vehicle. If the tow vehicle is carrying part of the 7200#, the rolling stock of the trailer is only carrying the rest.

A 3500 lb axle carries 1750 lbs on each wheel IF the load is perfectly balanced. Best to allow for off-center weight distribution, so figure a wheel might have to carry 60% or so of the axle weight. That would be about 2100 lbs in this case.  So, the 2150# wheels are adequate, but the 2540# is better (wider safety margin that allows for a higher load range tire).

That DIDN"T answer how 2 3500's = 7200.

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Per federal highway safety regulation, the minimum trailer axle(s) capacity for a conventional trailer (aka "bumper pull") is 90% of the GVWR.  Nothing says the axle capacity cannot be larger than that, nor that the GVWR must be set at some percentage of axle GAWR. Other factors include brake size, trailer frame strength, the size of the hitch coupler used, and anything else the trailer manufacturer considers relevant to safe operation.

kdbgoat said:

The manufacturers are only required to have the axles/wheels/tires/springs rated to carry the gross weight of the trailer, minus the tongue weight that is carried by the tow vehicle. If the tow vehicle is carrying part of the 7200#, the rolling stock of the trailer is only carrying the rest.

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KDBgoat.....we both pretty much said the same thing, but your explanation was more to the point and hopefully RedandSilver now understands what we were saying!

Thanks for educating me guys.

It's not that I don't believe you - I do.  It makes sense that some weight HAS to be carried by the tow vehicle.

Now the part that doesn't make sense is this:

Per federal highway safety regulation, the minimum trailer axle(s) capacity for a conventional trailer (aka "bumper pull") is 90% of the GVWR.

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But that's our government.  90% of 3500 is 3150.  So you would only need 3150 axles to carry 7000lbs - the way I read it.
What's the point in that?

Now the other thing is, HOW MANY have a tongue scale?  IF you don't and I assume most don't then you are only guessing what the
tongue weight is on the tow vehicle.  So really does 10 -13% tongue weight mean anything if you don't have a scale?  And how many take
their unit to a scale and UNHOOK the trailer and set the jack on a separate pad to get separate weights on the wheels and tongue jack -
which is actually set back some from the actual ball coupler so it not a 100% true weight - unless you have a tongue scale.

And if you don't know the loaded weight (not max) of the trailer then you also wouldn't be able to figure 10-13%

I have a tongue scale and know how moving even a little weight around can make a big difference on the tongue weight.

I doubt the OP thought this would take a side street to his question.

FOR the record I agree with everyone else and unless there is a big cost difference I would go for the higher rated wheels in a heartbeat.

But that's our government.  90% of 3500 is 3150.  So you would only need 3150 axles to carry 7000lbs - the way I read it.
What's the point in that?

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It's 90% of (2 x 3500). That's 6300 lbs.

Clarification: The federal spec is that the combined trailer axle ratings must be a minimum of 90% of the trailer GVWR.  The fact that the axles may be greater than that doesn't alter the GVWR.  See comment by Grashley in a following message.

Thanks folks just wanted to make sure nay thinking was correct.

Looks like I'll be putting new ST tires back on it. Since I can't go to 16" (bolt pattern) I haven't found any LT with the lbs needed.

It's 90% of (2 x 3500). That's 6300 lbs.

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I believe the 90% refers to the portion of the trailer GVWR that the axles/wheels/tires must be rated to carry.

We are all saying the same thing.

GVWR X 0.90 = minimum axle rating.

Tire load rating X 2 (two tires per axle) of the tires MUST equal or exceed axle rating.

You may use a bigger axle, then "derate" it for the tires, i.e. 4000# axle with 2 X 1750 tires derated to 3500# axle max.

The axle rating of MOST trailers is less than the trailer GVWR because at least 10% of GVWR is carried by the tow vehicle, not the axles.

RedandSilver said:

Thanks for educating me guys.

It's not that I don't believe you - I do.  It makes sense that some weight HAS to be carried by the tow vehicle.

Now the part that doesn't make sense is this:
But that's our government.  90% of 3500 is 3150.  So you would only need 3150 axles to carry 7000lbs - the way I read it.
What's the point in that?

Now the other thing is, HOW MANY have a tongue scale?  IF you don't and I assume most don't then you are only guessing what the
tongue weight is on the tow vehicle.  So really does 10 -13% tongue weight mean anything if you don't have a scale?  And how many take
their unit to a scale and UNHOOK the trailer and set the jack on a separate pad to get separate weights on the wheels and tongue jack -
which is actually set back some from the actual ball coupler so it not a 100% true weight - unless you have a tongue scale.

And if you don't know the loaded weight (not max) of the trailer then you also wouldn't be able to figure 10-13%

I have a tongue scale and know how moving even a little weight around can make a big difference on the tongue weight.

I doubt the OP thought this would take a side street to his question.

FOR the record I agree with everyone else and unless there is a big cost difference I would go for the higher rated wheels in a heartbeat.

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You don't need a tongue scale.  Go to a CAT certified scale and do three weights...
1.  Drive onto the scale with your truck and trailer.  You need to have your WDH. hooked up and engaged just like you would when you are towing/travelling.  Front wheels on pad #1, rear wheels on pad#2, and the trailer wheels on pad #3....push the button and tell the operator to take a weight.  When complete, go to #2
2.  Do not move the truck trailer from original position.  Now, completely disengage the WDH spring tension bars.  No need to unhook or take anything off, just release all the spring tension.  Push the button and tell the operator to do weigh #2.  Once complete, you can either hook the WDH back up or you can drive off of the scale.  At this time, you need to disconnect the trailer completely from the truck and get a TRUCK ONLY weight. 
3.  Drive back on the scale and tell the operator that you are ready for weigh #3 (front tires on pad 1, rear tires on pad 2).  Once he or she gets weight number three, drive off and hook your trailer back up, including the WDH and spring tension. 

Go pay for your weights.  Normally the first weight is $11 and each additional weight is $2 each, so you should owe $15.  Collect your three scale tickets and head home and put the numbers to work.

Once you are home and have the scale tickets with you, fire up the computer and go to this web site....
http://fifthwheelst.com/
Once the page loads, at the top of the page you will see a title that says "4 Step Weight Safety Plan"....click on it and follow the instructions completely, including doing the worksheet.  When you are done, you will know everything about your truck and trailer weights that you could possibly know........except the exact weight of the beer in the fridge!

xrated said:

You don't need a tongue scale.  Go to a CAT certified scale and do three weights...
1.  Drive onto the scale with your truck and trailer.  You need to have your WDH. hooked up and engaged just like you would when you are towing/travelling.  Front wheels on pad #1, rear wheels on pad#2, and the trailer wheels on pad #3....push the button and tell the operator to take a weight.  When complete, go to #2
2.  Do not move the truck trailer from original position.  Now, completely disengage the WDH spring tension bars.  No need to unhook or take anything off, just release all the spring tension.  Push the button and tell the operator to do weigh #2.  Once complete, you can either hook the WDH back up or you can drive off of the scale.  At this time, you need to disconnect the trailer completely from the truck and get a TRUCK ONLY weight. 
3.  Drive back on the scale and tell the operator that you are ready for weigh #3 (front tires on pad 1, rear tires on pad 2).  Once he or she gets weight number three, drive off and hook your trailer back up, including the WDH and spring tension. 

Go pay for your weights.  Normally the first weight is $11 and each additional weight is $2 each, so you should owe $15.  Collect your three scale tickets and head home and put the numbers to work.

Once you are home and have the scale tickets with you, fire up the computer and go to this web site....
http://fifthwheelst.com/
Once the page loads, at the top of the page you will see a title that says "4 Step Weight Safety Plan"....click on it and follow the instructions completely, including doing the worksheet.  When you are done, you will know everything about your truck and trailer weights that you could possibly know........except the exact weight of the beer in the fridge!

Click to expand...

Yes you could do that.  But how many others will do that?
And then comes the issue if the weight is high or low - then is the average person going to go back and have 3 more weights done again?
So that they know they are in the 10-13% range of tongue weight on the hitch.

My Cargo trailer doesn't need or can a WDH be installed on it.  So that is one reason why I have a tongue scale.

I guess this boils down to different strokes for different folks.


Oh one more thing is,  they don't have to be CAT certified scales as there are OTHER certified scales around the country too.

In my case, the tongue weight was low.....just barely 10% and I was having trailer swaying issues.  Once the first scale weight is done and you know your tongue weight, it's just a matter of adding more weight in the tongue area and re-doing the calculations again.  I now know, because I added XX amount of weight that I am at approx. 11 1/2% tongue weight and didn't need to rescale for that. 

tcam5 said:

I am going to buy new wheels for our trailer, upgrade from 14" to 15". My question is load weight of the wheels.

Trailer lbs #7200 max
Axels lbs #3500 each

Do I need #2150 or #2540 max lbs wheels?

Click to expand...

The higher rated wheels would be most desired because it would allow for more options with your tire selection.

The following paragraphs are excerpts from FMVSS standards. They are minimum requirements, ALL RV trailer manufacturers MUST comply with them when building your trailers.

This is paragraph  S4.2.2.2, ?The sum of the maximum load ratings of the tires fitted to an axle shall not be less than the GAWR of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle.?


This is paragraph S9.2, ?On RV trailers, the sum of the GAWRs of all axles on the vehicle plus the vehicle manufacturer's recommended tongue weight must not be less than the GVWR. If tongue weight is specified as a range, the minimum value must be used.

One cannot read anything into such standards. They mean what they say and nothing more or less.

Remember, these are written to minimum established standards. The vehicle manufacturer is often recommended to use ?appropriate? fitments. When they do so, those fitments become the minimum standard for that fitment described on the vehicle?s certification label.

Gary RV_Wizard said:

A 3500 lb axle carries 1750 lbs on each wheel IF the load is perfectly balanced. Best to allow for off-center weight distribution, so figure a wheel might have to carry 60% or so of the axle weight. That would be about 2100 lbs in this case.  So, the 2150# wheels are adequate, but the 2540# is better (wider safety margin that allows for a higher load range tire).

Per federal highway safety regulation, the minimum trailer axle(s) capacity for a conventional trailer (aka "bumper pull") is 90% of the GVWR.  Nothing says the axle capacity cannot be larger than that, nor that the GVWR must be set at some percentage of axle GAWR. Other factors include brake size, trailer frame strength, the size of the hitch coupler used, and anything else the trailer manufacturer considers relevant to safe operation.

Click to expand...

FMCSA regulations are not applicable for RV trailers or any other vehicle's using FMVSS standards.

Under FMVSS standards RV trailer manufacturers set the GAWR values to insure the GVWR can be carried by them. The axle manufacturer's certified value is often higher than the vehicle manufacturer's GAWR values shown on the vehicle"s certification label. When that's the case that extra axle load capacity is a reserve load capacity provided by the axle.

An owner cannot gain any GVWR capacity by upgrading axles. They gain reserve load capacity and an axle with better durability.

On any vehicle with a federal certification label showing a GVWR, that GVWR is the ultimate load limiting factor for that vehicle. It can only be changed by the vehicle manufacturer or a certified vehicle modifier.