Tire maxload vs trailer weight

Berkshireba · 02-10-2013, 05:51 PM

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?

**ependydad** · 02-10-2013, 06:02 PM

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.

Berkshireba · 02-10-2013, 07:23 PM

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.

**Herk7769** · 02-10-2013, 07:34 PM

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.

jadatis · 02-11-2013, 07:34 AM

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

jadatis · 02-11-2013, 09:43 AM

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

jadatis · 02-12-2013, 03:37 AM

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.

Ditchooker · 02-13-2013, 12:58 AM

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.

Berkshireba · 02-13-2013, 03:23 AM

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

lbrjet · 02-13-2013, 10:49 AM

Do not put more than 50lbs in C rated tires when towing.

Berkshireba · 02-13-2013, 04:46 PM

I getting the impression c rated tires re not very forgiving on weight, pressure, or towing speed

jadatis · 02-14-2013, 04:22 AM

lbrjet Do not put more than 50lbs in C rated tires when towing.

What I was writing is that you may even put 60psi in a C rated tire of psi50.
On a C- rated tire the YYY in "maximum load xxxx lbs AT YYY psi ( cold) " is not the maximum pressure of the tire , as is written on P-tires and XL tires.
Even the American TRA allows 10 psi extra for higher speed and beter driving conditions. Thoug they only support higher maximum load ( xxxx in Example), for verry low speed, unofficially it would keep the tires undamaged when higher load.

@ Ditchhooker
Your tires probably got damaged by overloading , because 3 of 4 damaged , probably the 4th is also damaged but you cant see it yet.
If you now would highen up the pressure on the already damaged tires, they would blow up and you would blame the higher pressure.
For the new tires , if you stay at C-load/6ply , begin with 60 psi, or better weigh and discover that the tires or one side was overloaded for the tires all the time.
This link leads to a pdf of goodyear with at the bottom of page 1 "inflation limitations" , for truck tires even 20 psi above AT yyypsi is allowed.
http://www.goodyear.com/truck/pdf/edb_loads.pdf
also at page 2 the higher maximum load when more yyy at verry low speed.
So even with The original C-load Ditchhooker most likely ( but weigh first) can keep his tires undamaged.

lbrjet · 02-14-2013, 11:00 AM

That's why I said "when towing". When towing the tire pressure will rise after heat is generated and that is where the cushion of "extra 10lbs" is utilized. Putting in 60 is asking for trouble, but please go right ahead if you wish.

Ditchooker · 02-15-2013, 01:38 AM

Quote:

Originally Posted by jadatis

@ Ditchhooker
Your tires probably got damaged by overloading , because 3 of 4 damaged , probably the 4th is also damaged but you cant see it yet.

I doubt I have overloaded them, 3000 front axle, 3100 rear axle when loaded, the 2 on the slide side are the ones that are both damaged which is the heavy side regardless. never been below max pressure (always 50psi). Seldomly go over 65 mph, generally tow @ 62 mph (speed limit is usually 70 mph), however I have not scaled that specific side yet.

unfortunately I currently have a 14" ST tire on the trailer (Greenball Towmasters) and no where close to LT rated like in the article. I suspect just being close to the max load of the tires combined with some hot weather and the steady running at near the max speed for the tires is what has done it. The load range increase (possible size as well) is more for my peace of mind, as the DW on occation will hook up and go without me for a weekend with the girls from time to time.

**Herk7769** · 02-15-2013, 06:43 AM

Quote:

Originally Posted by Ditchooker

The load range increase (possible size as well) is more for my peace of mind, as the DW on occation will hook up and go without me for a weekend with the girls from time to time.

If you are uncomfortable with the load range on your current ST tire, I would definitely recommend going up ONE Load Range. I do not recommend changing tire size due to the issue of impact with the wheel well or other tire if the suspension should be stressed (load or impact from road hazard).

Ditchooker · 02-15-2013, 10:58 PM

Staying with the factory size would be ideal, however, Finding a 14" tire in load range D, is much more difficult, and looks to be non existant in Canada, whereas the 15" tires are much easier to find.

jadatis · 02-21-2013, 05:03 AM

@ Ditchhooker

What I have gotten out of your reactions is next.
GVWR 7700 lbs.
2 axles 4 tires on the road when driving.
Now having ST ( special trailer) tires with C-load ( maxloadpressure 50 psi)
14 inch rimms.
Probably weightdifference R/L because of the slide on one side.

What I am missing are the exact sises of the tire and the loadindex or maximum load. When you give those , I can put it in my chanced calculator that can be found in the map.
https://skydrive.live.com/?id=A526E0...6e0eee092e6dc&
So you can also play with it yourselves.
I included the tow-barr weight in the pressurecalculation now , so if you take another towbarr weight the needed pressure is also chanching now.
But now the beginning Bumping and Damage border are the same .
Can make a picture of it again and place it here as example.

The ST tires are calculated in their maximum load , for a lower speed , so the tire may deflect more before it gets damaged , and that gives a higher maximum load then a normal road tire or LT with the same sises.
This brings them more to the edges of possible Damage.
By putting from the beginning at an still undamaged tire, the 10 psi extra, wich is supported by the TRA for higher speed then 65m/h, the deflection gets less and so tire-damage does not appear that soon.
But I thougt there where enaugh LT tires in 14 inch , example 185R14 with D-load so 65 psi and loadindex 102 so 850kg/1874lbs times 4 makes 7500 lbs.
Must be enaugh if you substract the tongeweight of 10%.
And then even you could add the 10 psi for extra savety .

**Herk7769** · 02-21-2013, 07:56 AM

You will need to find the load information for your model tires.
Here is one from Maxxis that you can use for a "guide" if you can't find the exact one for your model and brand.

jadatis · 02-21-2013, 08:20 AM

Quote:

Originally Posted by herk7769

You will need to find the load information for your model tires.
Here is one from Maxxis that you can use for a "guide" if you can't find the exact one for your model and brand.

Looked at this list, and saw what is done wrong in America also here.
The B-,C-,D-,E-load tires with the same sises are placed in the same list.
A stiffer tire ( E stiffer then C) needs a higher pressure for the same load.
Or the other way around has lower loadcapacity for the same pressure.
So for every load-letter a different list should be made, and this is common use in Europe. I dare to say that the American used way is wrong, and leads to more deflection then the tire can savely stand at lower loads.
havent checked it , but probably calculated with the wrong power in the formula too.

So better yust look at the sidewall of the tires , look for "maximum load xxxx lbs AT yyy psi ( cold) " or the loadindex mostly directly after the sises.
185/80 R14 102/100 Q for instance , then 102 stands for single use 850kg/1865 lbs? and the 100 li stands for 800kg/1760 lbs for dual load.
Q is then the speedcode and stands for up to 160km/99m/h maximum speed.
N is up to 140km/85m?/h.

**Herk7769** · 02-21-2013, 08:38 AM

Peter,

While I don't doubt what you are saying for a minute, I would like to see the source link (preferrably a site in english) that explains why the commonly in use load/pressure charts are not correct.

I totally get that a E series tire with 10 PSI in it won't support much more than its own weight, but I would like to see a source for why you feel that the manufacturer supplied charts for their tire size, load, and required pressure do not accurately reflect reality.

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