Tires

[jj2spirit]

I need to purchase 4 tires for my 21WSK size 205-75 R14. Any suggestions ?
Are LT tires better for it than ST tires on my camper now ?

 

[Travels with Yoly]

ST tires are made specifically for trailers for a reason and are usually recommended. Most 14 inch tires of that size are rated to carry about 1760 lbs at 50 psi max air pressure. If you take your loaded trailer weight and subtract about 10% as tongue weight carried by the tow vehicle, then that's the weight carried by your tires. (subtract about 15% if you have a weight distributing hitch). Multiply the number of tires by their capacity to get the total capacity and see how much larger that number is than the calculated weight of the trailer. I personally like to see about a 20% margin or greater capacity in the tire load rating than the trailer weight.

Our second trailer was a single axle chassis with two of these tires. The loaded weight was less than the tire capacity but not by 20% so we chose to buy a higher rated tire. Khumo makes an LT tire, but exclusively for trailers. It has twice as many plies as the Chinese made tires (99% of all RV tires), and was rated for 2,200 lbs at 65 psi. Off the top of my head I can't remember the specifics but I have posted it somewhere here in a thread about tires. They were awesome tires (since sold the trailer for our Fun Finder). We put over 8,000 miles in the heat of summer through Utah and Nevada and never had a glimpse of an issue. Tires and wheels were barely warm to the touch with no signs of wear what so ever even on 110 degree days.

Your 215WSK is very close to our 214WSD weight wise. If I take a loaded weight of 6,000 lbs and subtract 15% for weight carried by the tow vehicle I see that the 4 tires are carrying about 5,100 lbs. If I add the 20% buffer to that number I get 6,120 lbs. Now if I multiply each tire's capacity of 1,760 lbs (x4) I see a total capacity of 7,040 lbs which is well above the 6,120 lbs I'm looking to support which includes my 20% safety margin.

We just got back from a tow of approximately 1,300 miles and the stock tires ran perfectly, again very cool to the touch with no signs of wear anywhere.

If you already know all of this load dialog and are just wondering about the difference between LT & ST tires, there is tons of dialog here and elsewhere recommending ST tires for trailers exclusively for many, many reasons. Some people choose to install LT tires but usually for convenience (they have a tire issue somewhere while traveling and don't have options) and not because there are any technical advantages.

That's my $0.04 worth

 

[jj2spirit]

Thanks for the info...so if you were buying tires for your FF , you would buy the higher rated Khumo 's if I'm reading you right.

 

[LJAZ]

In addition to what Yoly said, ST tires are built with a stiffer sidewall which helps to minimize flexing. Flexing leads to trailer sway. I would not run LT tires on my trialer.

 

[Travels with Yoly]

Thanks for the info...so if you were buying tires for your FF , you would buy the higher rated Khumo 's if I'm reading you right.

No that's not what I'm saying at all. I said to do the math and see if the stock tires are overloaded or compromised at all. Our Cobblestone (single axle) was compromised so that's why I bought the higher rated Khumos.

Using the formula I stated above, the fully loaded Cobblestone starts out at 3,500 lbs. I subtract the tongue weight with the WD hitch (-15%) = 2,975 + 20% safety margin = 3,570 lbs. The total capacity of the two tires were 3,520 lbs so I wasn't comfortable with the stock tires, that's why I chose the Khumos. Keep in mind, that they are not cheap. It cost $575 to have 3 of them mounted (2 per axle + 1 spare). Now if money was no object I'd gladly buy the Khumos, but then again, if money was no object, I wouldn't have a Fun Finder either

Our new Fun Finder is well below the load ratings on the stock tires so I don't see an issue with them. As I said, they worked very well and had no issues.

The fully loaded FF starts out at 6,000 lbs. I subtract the tongue weight with the WD hitch (-15%) = 5,100 + 20% safety margin = 6,120 lbs. The total capacity of the 4 tires are 7,040 lbs so I'm comfortable with that.

The leading cause of tire failure is heat - usually caused by under-inflation. This allows more flexing in the sidewall which generates more heat. This condition is made worse when traveling at higher speeds or on extremely hot days. Every time we stop I get out and put my hand palm down on the sidewall of each tire. In cold weather, they will be almost cool to the touch. In hot weather, they will be warm but not so hot that you can't keep your hand on them. (I do the same for the wheels separately). As LJAZ stated, the ST tires do have stiffer sidewalls which help minimize sidewall flexing. They also have chemical constituants in the rubber compound to resist UV degradation and cracking due to prolonged storage conditions that LT tires do not.

 

[Dakota 1120]

Yoly ~ thanks for the great information on trailer tires.

I don't need any yet, but great info when that time comes.
8)