Go Back   Keystone RV Forums > Keystone Tech Forums > Tires, Tires, Tires!
Click Here to Login

Thread Tools Display Modes
Old 04-15-2018, 02:39 PM   #71
Senior Member
notanlines's Avatar
Join Date: Oct 2014
Location: Memphis, TN
Posts: 2,324
Originally Posted by Eastham View Post
What ever happened to just throwing some stuff in the camper and taking off and enjoying yourself.if you have to pack that much crap to go camping that you are over loading the truck and the trailer and the tires .it's to much work stay home or load less and enjoy your self. Life is to short to sweat all this small crap .Good night and lighting up.
I gave serious thought to picking up the stick and poking it through the fence, but I didn't think the dog would be sharp enough to even get upset.....

Jim in Memphis
Wife of 46 years is Brenda
2014 F-350 6.7 Powerstroke
2017 Mobile Suites
20K Reese slider
2001 Road king w/matching Harley sidecar
notanlines is offline   Reply With Quote
Old 04-24-2018, 10:02 PM   #72
Senior Member
CWtheMan's Avatar
Join Date: Feb 2010
Location: Taylors, SC
Posts: 1,078
Tire load/Inflation Charts

Tire load and inflation standards are developed by three different organizations. North American, European, and Japanese.

Here Iím just going to be mentioning those from the North American Tire & Rim Association (TRA).

The charts are standardized. All tires of the same size and construction can use a chart from any manufacturer of that tire. For this discussion Iím just mentioning Special Trailer (ST) tires, Light Truck (LT) tires and Passenger (P) tires. All of those are highway tires and approved by the governing body (NHTSA) for trailer axle service, when approved for that fitment by the vehicle manufacturer. An approved tire size is like this; ST225/75R15 or LT235/85R16 or P175/50R15. A load range, load index, or speed letter in a tires suffix are not part of the basic size.

For our vehicles built under the guidance of the Federal Motor Vehicle Safety Standards (FMVSS), the need to use any of the charts is minimal. The FMVSS instructs the vehicle manufacturers to set an appropriate recommended cold inflation pressure for all vehicles they build and certify. Those recommendations are the minimum standard and none in the tire industry will recommend using less than what the vehicle manufacturer has set and certified on the individual vehicleís placards for the Original Equipment (OE) tires.

Tires on our motorized vehicles provide a percentage of load capacity reserves and their recommended cold inflation pressures are almost always less than what is required for the tires maximum load. In those conditions the difference in recommended inflation pressure and tire maximum load pressure is an optional area. Some vehicles, such as pick-up trucks may even have vehicle manufacturer recommendations for the use of higher inflation pressures when the vehicle is being used for towing another vehicle.

We often see forum posters recommending tire inflation for the load being carried. The major fault with that is two fold. Itís a no-no to use less inflation pressure than what has been recommended by the vehicle manufacturer. And, inflation to the load carried may need to be adjusted every time you use the vehicle. One PSI inflation pressure below the load carried is a loss of about 1.6% of its load capacity. Heat generation for being under inflated comes to mind.

In these forums, everyone posting about replacement tires seems to have a different idea of how itís supposed to be done. The tire industry wide rule is to always use replacement tires that are the same size as the tires that came on the vehicle. Itís a very complex explanation as to why itís a misapplication to use tires that do not match the design of the Original Equipment tires and Iím not going to try and explain it here. This is about tire inflation charts.

Plus sizing is a very popular option many seek when replacing their RV trailer tires. Itís where the tire inflation charts are most needed and part of their basic design is to assist the installer of plus sized tires. Here again, is another tire industry standard that applies to plus sizing your tires. They MUST provide a load capacity equal to the load capacity provided by the OE tires at the vehicle manufacturerís recommended cold inflation pressure. What that means, when looking at your tire placard you will find the OE tires size and their recommended cold inflation pressure. Now itís time to find a tire inflation chart for that particular tire. From the chart you can find the load capacity the tire is providing at the trailer manufacturerís recommended PSI. Letís say the tire size is ST205/75R14 and had a load range letter of D with a recommended 65 PSI. So, from the chart we find that itís providing 2040# of load capacity. There is not a LRE in that tire size so youíll have to ask the vehicle manufacturer about a larger tire for replacement. We all know their answer. If the larger tire was never offered as an option for that trailer they are going to tell you to use another tire just like the ones that came on the trailer. They fitted the OE tires and said they were an appropriate fitment for that trailer and are going to stand with that original decision. To do otherwise would put them in a situation of decision reversal, theyíre not going to do that.

So, now youíre going to have to do some decision making. Normally a smallish tire dimensional size change can work on RV trailer axles. Even those closely spaced. A 10% increase in tire load capacity is a ballpark figure to look for. The ST215/75R14 is the best fit. It will fit the OE wheels. Itís just .6Ē taller & .5Ē wider. The owner would have to make sure there is sufficient wheel well clearances. At 65 PSI the 215 will provide 2200# of load capacity. Looking at the tire inflation chart for the 215 tire shows a load capacity of 2120# @ 60 PSI.

A normal step for the installer to perform, is to identify the different sized replacement tire. For that purpose, NHTSA approves the use of an auxiliary tire placard. On it, the installer can put the new tire size and from a tire inflation chart for that tire size, a recommended cold inflation pressure that insures the tire will provide as much load capacity as the OE tire did at the vehicle manufacturerís recommendation. The AUX placard can then be placed adjacent to the original tire placard. Then a notation should be made in the vehicle ownerís manual.

There really is no need to fool around with RV trailer tire inflation pressures. Only a very few owners travel enough to ever see their trailer tires wear out. They are age-out tires.

Our RV trailers have a very different center of gravity than our motorized vehicles. Trailers tend to fish-tail, bob and weave and travel in an unbalance condition most of the time. All tires are designed to safely operate at their maximum load capacity.

What many trailer owners do not consider is the load on their tires. (Probably the most damaging thing a new trailer owner does to their tires is over load them. Fill-up the water tank, get all the stuff in the basement and other storage areas and hit the road. POP - BANG). Trailers are built to minimum standards for their maximum allowed loads. The tires are not required to have any load capacity reserves. Even when you load your automotive vehicle to itís limit it still has tire load capacity reserves. Itís part of the fitment differences between automotive and trailer tires.

You want full life expectancy from your trailer tires? Give them 10% - 15% in load capacity reserves.

An Old Navy Aircraft Mechanic that writes about tires.
The Black one is mine: http://www.irv2.com/photopost/showfull.php?photo=20678
CWtheMan is offline   Reply With Quote
Old 05-16-2018, 06:42 PM   #73
Senior Member
CWtheMan's Avatar
Join Date: Feb 2010
Location: Taylors, SC
Posts: 1,078
ST Tire Inflation

What seems like a long time ago, Probably about 15 years, I started researching ST tires. At that time there were very few tire manufacturers building the ST tires. The largest and most well known was Carlisle. They saturated the industry with information about their ST tires and were probably the most prolific OEM provider for at least 5 years. (There was also a new and upcoming ST tire builder, Goodyear. They, for a time, overtook Carlisle as leading OEM provider. Then, there was/is CHINA).

When large tire retailing chain stores started stocking Carlisle ST tires, Carlisle provided them with oodles of information about their tires and how they differed from other highway tires.

Carlisle said ST tires could degrade by as much as 10% a year. They had and still have one of the shortest warranty periods of all ST tires. Carlisle recommended their tires be used at 60 MPH or less (TRA sets unmarked ST tires at 65 MPH). Carlisle recommended their tires to be operated at the inflation pressure molded into the tireís sidewall (thatís for MAX load capacity). Carlisle was very stern about their ST tires life expectance saying 3-5 years was the maximum regardless of mileage.

In interviews with information outlets line Modern Tire Dealer, Carlisle spokespersons would spout out their recommendations and ST sellers/users took notes. Almost everything you read about ST tires in Discount Tireís on-line publications are excerpts from Carlisle PDFs. So, their recommendations became the norm.

ST tires on todayís market have come a long way from where they started. But, donít get me wrong. Iím not against max pressure for ST tires. Itís almost always recommended by the vehicle manufacturerís and when thatís the case the max is also the min. But, thatís not so for replacement tires with excess load capacity. The canned answer from the replacement tire rep will be to use what is recommended by the vehicle manufacturer. So use as much extra load capacity as you are comfortable with. Most of the time itís not going to be the 110 PSI the tire needs for max load. 90 or 100 PSI may provide the extra load capacity you need for excess load protection and a better ride.

Just about every ST tire now purchased has a speed rating of 75 MPH or higher. Every MPH you travel under the tires speed rating provides a little more protection from overheating a tire when itís close to its maximum load. Before the higher speed ratings all we had was 100% inflation protection at 65 MPH.

Back to the Carlisle thing. If you did not archive any of their old PDF forms youíre out of luck. Their new ST tires are up-to-date and in line with all other ST manufacturerís and with speed letters in the 81 MPH range. At a recent BASS fishing show the only tires close to outnumbering the Carlisleís were Passenger tires. A lot of the large dual axle rigs really liked the low profile passenger tires. (RV trailers and boat trailers are built to the same FMVSS standards, the vehicle manufacturer decides what fitment is appropriate).

An Old Navy Aircraft Mechanic that writes about tires.
The Black one is mine: http://www.irv2.com/photopost/showfull.php?photo=20678
CWtheMan is offline   Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Powered by vBadvanced CMPS v3.2.3

All times are GMT -8. The time now is 07:57 PM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
This forum is owned and operated by Social Knowledge, LLC. It is not authorized or endorsed by the Keystone RV Company and is not affiliated with the Keystone RV Company or its related companies in any way. Keystone RV® is a registered trademark of the Keystone RV Company.