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Old 02-10-2013, 05:51 PM   #1
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Tire maxload vs trailer weight

Thanks in advance for all the knowledge being shared about tires here. I decided to go check the tire pressure and look more closely at what I have on my waiting to be used for the first time 2013 surveyor sv291. Here's what I found:

Tires:
maxload 1760 at 50 psi. LR C
1760 x 4 = 7040 pounds.

Trailer yellow sticker:
5519 dry weight
1962 cargo
7481 max weight

Am I missing something or are these tires inadequate for my trailer?
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Old 02-10-2013, 06:02 PM   #2
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Your tires aren't carrying the tongue/pin weight. So, say that's 1,000 pounds- the maximum the tires would carry is 6,400-something.
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Old 02-10-2013, 07:23 PM   #3
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Thanks ependydad I thought I might be missing something. But, using nice round numbers, 7500# trailer max less 1000# tongue = 6500#s on tires rated at 7000#. I don't feel very comfortable with each tire within 125#s of max rating. That's if the load is perfectly balanced.
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Old 02-10-2013, 07:34 PM   #4
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Trailer tongue load must fall between 10% and 15% of total camper weight for safe towing. Optimum handling occurs at approximately 12%.

If loaded to maximum gross weight, The tongue load at the absolute worse case loading would be 10% of 7,481 pounds. or 748 pounds.

7,481 - 748 = 6733 pounds carried by the 4 tires (or 1683 pounds per tire).

At 12% Optimum balanced loading, tongue would be 898 and the tires would carry 1646 pounds each.

At your max PSI of 50 PSI with a C rated tire you are "safe" at all safe load balances.

My camper came with C rated tires and I replaced them with D rated ones when my first tire blew out my second season. I run my D rated tires at 58 PSI which is correct for Load and 10 MPH speed boost (75 MPH) on my camper.
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Old 02-11-2013, 07:34 AM   #5
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I registered to this forum to give , what I think , usefull information about tires.
End of 2007 I got hold of the formula , the European tyre-makers use to determine the advice-pressures for cars, and went running with it.
Learned myself Excell to make spreadsheets for it, and translated a few from Dutch to English to go worldwide with it.
Even last year made new spreadsheets that are multi-lingual, so you can translate from English English to American English if you want.

By reacting on several fora, came to the conclusion that this European formula was adequate for normal and XL tires , but gave to low pressures, or to high load-capacity for C-load/6ply and up . Your tires here C-load with reference-pressure of 50psi wich is not the maximum pressure of the tire, tire-makers allow 10psi higher for better handling and higher speed then given on sidewall. Normal car tires and XL/reinforced/Extraload give only maximum pressure on the sidewall, reference-pressure to calculate with is 35psi and 41 psi ( XL) in America.

To make a long story even longer, look around on my public map of skydrive , that belongs to my hotmail-adress, with the same username as here.
There are a lot of English maps between the Dutch.

One for Caravan/trailers in wich I also give the tonge-weight percentage.
It calculates a pretty high pressure , for reserve for loadshifting, pressure-loss in time, miss-readings of scales, misjudging of weight etc.
I based the reserve of 10% adding to the GVWR, going from the Dutch and probably European situation. Most caravans, as whe call the houses tot tow behind a normal car, have a towbarr weight of 50 to 90 kg/ 110 to200 lbs and so about only 5% tonge-weight. For your 10 to 15% the warnings have to be different I think, but you could fill in the GAWR instead of the GVWR for same reserves. Then the calculation of the tonge-weight goes wrong, so better lower the reserve in the info sheet to say 7% to get better division.
the weightdifferences at wich tire-damage begins or bumping still are what they should be.

But also I am working on a CamperRV calculator, all results placed in that map. Pretty reddy now, only needs a lott of explanation in the info sheet.

So see what you can use for the topic here.
https://skydrive.live.com/?cid=a526e...E092E6DC%21128

Greatings from Holland, and If you cant work it out, give me the details, and I will do it for you as an Example.
Peter
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Old 02-11-2013, 09:43 AM   #6
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Someone got confused by using my skydrive, had to log in with his hotmail adress and password. So I will explain how skydrive works.

Skydrive is a free storing place that every Hotmail adress user can use , and I used the public map of it to store pictures and spreadsheets and other documents I want to share with the world.

If you yust leftclick on a document, first the document is tried to be opened in the browser ( IE explorer, Crome etz) In the cloud it is called, and In that cloud there is a simpler version of word and Excell , but these cant handle some things I used in my spreadsheets. One is Sheet-protection, I use to prevent you overwriting cels with formula's in it. Other is data-validation, wich I need to make droppdown-boxes to select things like loadindex KG/LBS.
so most spreadsheets have to be used on the Excell that is on your computer.
If you dont have Excell you can use the free Open-Office-Calc ( search for Libre Office wich is the open version that is updated still) .
To use the spreadsheets on the computer you have to download it first, and not click "open in Excell". For that last one your Hotmail-adress and password is asked, I think even if you already opened Hotmail .
You have to right-click on the document, then choose "download"and after download and eventuall viruscheck, open in Excell or OO Calc to use it fully.

But try this skydrive out yourselfes, once you know how to use it, it is a handy storing-place for these things.
I also made a speciall hotmail adress for the puppy's of a dog we had, to store and share photo's and video's.
Those open in the browser and wont give the problems here mentioned.

Greatings again from Holland
Peter
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Old 02-12-2013, 03:37 AM   #7
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Made an example with my spreadsheet and made a picture of it .
Had to chanche some things like reserve and calculated for axleweight instead of vehicle-weight and , something to review for me in the spreadsheet.
This because of the somewhat different tongeweight situation then I included
Asumed it to be tandem-axle and not dual-wheel axle ( so 2 axles 4 tires )
Here the picture that can also be found in the caravanmap under examples, togeter with the spreadsheet in wich you can chanche things if you like.


Mind that this is the English English version, so Tyre instead of Tire.
Highened up the reserve to even 11% to get a good balance between bumping and damage border, and used the GVWR-tongeweight.

Also mind the speed limit to 60m/h , that is because the pressure is higher then the referencepressure of 50 psi , there are lists for more maximum load at lower speed and higher pressure. If you dont go over this speed , you can fully benefit the bumping and damage borders.
But mind that the real weight is seldomly what you think it is, mostly more.
Weighing would be the best thing to do.
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Old 02-13-2013, 12:58 AM   #8
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my trailer has a very similar weight, (max 7700 lbs) and currently has the load range "C" tires on them. I had a new set installed in 2011 under warrenty. this new set when I was on my last trip of the season last year, started to show signs of tread seperation on 3 of the 4 tires. Trying to decide if i should go for warrenty again or just replace with load range D tires for the piece of mind and better longevity.
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Old 02-13-2013, 03:23 AM   #9
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It's all coming together for me now the trailers max weight is just a factor of the axle capacity ( 2 x 3500# in my case) and the tire rating is chosen to coincide with the axle capacity. The balance of the trailer weight is the tongue load. A higher tire pressure will help control the tire heat at higher speeds but will not increase weight carrying capacity. Also weigh your set-up and it is never a good idea to push anything but your cooler to max capacity and most of all
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Old 02-13-2013, 10:49 AM   #10
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Do not put more than 50lbs in C rated tires when towing.
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