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Old 10-21-2015, 04:18 PM   #21
cathcartww
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Question here is it OK to put car tires on a trailer? My trips are usually 300 miles and a couple 500 miles thats one way. I usually travel at normal highway speeds 70 to 80 mph. Trailer is not overloaded. 238ml passport.
Generally speaking, no. ST tires are not designed to be towed at high speeds - and in my opinion, depending on your tow vehicle to trailer weight ratio - anything over 70 mph is nuts.

The only non-ST tire I know of is the Kuhmo 857, which is a euro-sized tire rated for trailer use. It also has much higher speed ratings ...
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Old 10-22-2015, 03:26 AM   #22
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Originally Posted by Dodgeman View Post
Question here is it OK to put car tires on a trailer? My trips are usually 300 miles and a couple 500 miles thats one way. I usually travel at normal highway speeds 70 to 80 mph. Trailer is not overloaded. 238ml passport.
Car tires, NO. They re not made to handle the weight. Now if you are thinking LT tires, that's another issue that has been debated many, many times on this forum. You can go to the tires, tires, tires section of the forum or use the search function for more information.
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Old 10-22-2015, 11:23 AM   #23
CWtheMan
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Question here is it OK to put car tires on a trailer? My trips are usually 300 miles and a couple 500 miles thats one way. I usually travel at normal highway speeds 70 to 80 mph. Trailer is not overloaded. 238ml passport.
Passenger tires are more commonly used on large dual axle bass boat trailers. They are not recommended for the taller RV trailers because of the sway forces. However, they do provide a softer ride for the trailer and are often reported as being used by Airstream owners in their forum.

In your case you would have to step up to a 15” tire such as the Michelin Defender P235/75R15 109T XL. For trailer service it would have to be derated to 2064# of load capacity at 50 psi. It’s about 1 & ½” wider and more than 2 & ½” taller then the OE tires. Your wheel wells and axle spacing would have to accommodate those larger dimensions.

IMO the Kumho tires previously mentioned are the best option.
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Old 10-22-2015, 02:53 PM   #24
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Thanks for the info.
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Old 01-14-2016, 12:04 PM   #25
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I was curious about the stock tires on my Passport and looked at the speed rating. I assumed it was 65. On my boat trailer it was 65. What I noticed is that the Trailer King ST Radial speed is L, which is actually 75 MPH. I have been keeping the speed at 65 or below, it's good to know these are rated higher.
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Old 01-14-2016, 12:51 PM   #26
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I was curious about the stock tires on my Passport and looked at the speed rating. I assumed it was 65. On my boat trailer it was 65. What I noticed is that the Trailer King ST Radial speed is L, which is actually 75 MPH. I have been keeping the speed at 65 or below, it's good to know these are rated higher.
We have a "resident expert" on tires that's a member of the forum, I'm sure he will "tune in" before long and give you some information. In the mean time, it's my understanding that the ST tire regulations are undergoing some changes in not only tire specifications but also in how they are regulated. A part of that is upgrading (for lack of a better term) the speed rating on ST tires. You're correct, in the past, the speed rating for most ST tires has been 62 or 65 MPH. In the future, many ST tire manufacturers are listing their tires at a 75 MPH rating, but not all manufacturers are "upping the speed rating", so your tires may or may not be upgraded.

Something that "confuses the current situation" is a comment on many ST tire manufacturer's websites that has "disappeared in the past year". That comment said something to the effect of this: "ST tires may be operated above 65MPH (maximum 75MPH) by increasing the cold inflation pressure by 10PSI." The comment went on to state not to exceed the maximum wheel pressure and the increased pressure did not increase the tire load rating. This, if one tends to "overanalyze" things, can be "twisted" to maybe interpret that "IF" tires back then could be operated at 75MPH with increased pressure, can current tires also be increased? and does that mean that current tires and older tires are actually the same tires with different speed rating or ???

Now, a question I have not seen any answers for is: Does this increased speed rating include any "change in the physical tire" or is this just a change in paperwork???? I can't tell you, but I do feel very confident in saying that the increased speed rating won't affect any tires that have already been produced, so unless you buy new tires that are marked with a speed rating of L or buy new tires that somehow are "designated for 75MPH" during the next few years, I'd be very suspicious of any ST tires that aren't physically marked with a speed rating. My "best guess" would be that they are rated at either 62 or 65 MPH unless specifically stamped with a higher speed rating.

CWtheman, what say you ????
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Old 01-15-2016, 11:36 AM   #27
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I have recently visited a large RV showing here in SC. All of the Keystone RV trailers (large & small) were fitted with new Trailer King tires serviced with 100% nitrogen. All of them were also marked with a speed letter "L" for 75 MPH.

Without an official modification in the ST tires testing I will have to assume the higher speed rated ST tires have been beefed up in some way so their maximum load capacity can be carried at higher speeds. It's very hard to get such information from tire manufacturers if they don't publish it. However, I have read that the TRA now approves ST tire manufacturers to go as high as 81 MPH with their speed ratings. The TRAs previous approval for all ST tires was 65 MPH unless otherwise marked.

I've only seen a single official publication from any ST tire manufacturer that approves their ST tires to be inflated 10 PSI beyond the PSI rating on the tire's sidewall, to increase the speed by 10 MPH. That's Goodyear, for their Marathon brand ST tires. Evidently GY has determined by making the tire stiffer with the additional 10 PSI it allows it to carry its maximum load capacity 10 MPH faster. I would not recommend that procedure to be used with other brands unless approved by their manufacturer.

I don't know where Goodyear stands legally with the TRA and FMVSS on that subject. But, personally, I don't think they would publish such a procedure without their approval.

On the subject of Passenger tires on RV trailers. FMVSS 571.110 clearly gives approval for their use up to 10,000# GVWR. However, they must be degraded by about 10%. It's done by dividing the tires load capacity by 1.1.
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Old 01-15-2016, 11:45 AM   #28
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Do you know why the tires have two load ranges? Are they de-rated at the L speed designation. My tires show 100/96L.
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Old 01-15-2016, 11:25 PM   #29
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Reference Trailer Life, February edition, on page 8 in a discussion of tire failures. Having read and commented on tire problems on this Forum I would like to add one of the people commenting in Trailer Life. "Tires tended to fail when ever he was carrying more then about 70% of the recommended load rating for the trailer." "Since adhering to the 70 percent rule, we have had no more trailer tire incidents" The writer states that they have logged hundreds of thousands of trailer miles for vacation travel and with racecars. Myself I run Tire Minder, 55MPH is my speed limit and at each 1-hour of driving stop and check by feel each tire and axel to see if all match temperatures as well as look over the tire for any damage.
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Old 01-16-2016, 06:21 AM   #30
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Do you know why the tires have two load ranges? Are they de-rated at the L speed designation. My tires show 100/96L.
That is single/dual wheel configuration ratings.
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Old 01-16-2016, 01:01 PM   #31
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Do you know why the tires have two load ranges? Are they de-rated at the L speed designation. My tires show 100/96L.
The 100/96L is what is know as a tire's service description. The 100 is the load index for fitment as a single on the end of an axle. The 96 is the load index when two tires (dual) are on the end of each axle. The letter L is a speed symbol for the tires speed restriction (75 MPH).

Service descriptions are not the official indicator for a tires load capacity on ST or LT tires. For them it's the load range letter. However, tire manufacturers are allowed to put both methods on a tires sidewall. It is becoming more and more common to find service descriptions on ST tires. Especially now when all foreign ST and some LT tires must have a speed restriction on the sidewall to qualify for reduced tariff fees.

Any ST tires not marked with a speed letter are 65 MPH tires. Currently there is no speed letter for 65 MPH.
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Old 01-17-2016, 06:07 AM   #32
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Just my 2 cents. 65mph is fast enough when hauling over 14,000lbs of trailer. I still need to be able to respond in an emergency. I could have 80mph tires and still only drive 65.

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Old 01-17-2016, 11:26 AM   #33
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IMO the most important thing about speed codes for RV trailer tires is weight. On all tires the speed letter is telling us that the tire can travel at that speed and carry its maximum load capacity. Once over the limited speed the tire starts to degrade. As the speed goes above the tires limit it degrades faster. Pretty soon tread separation starts.

Lets say your tires are rated at 65 MPH and you’re in a hilly area. The tendency is to increase speed down hill to build momentum to climb the next one. Every time you exceed 65 MPH going down hill its possible you’re tires are degrading.


NOTE: The polyester cording found in most ST tires starts to melt at about 200 degrees C.
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Old 01-17-2016, 10:42 PM   #34
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IMO the most important thing about speed codes for RV trailer tires is weight. On all tires the speed letter is telling us that the tire can travel at that speed and carry its maximum load capacity. Once over the limited speed the tire starts to degrade. As the speed goes above the tires limit it degrades faster. Pretty soon tread separation starts.

Lets say your tires are rated at 65 MPH and you’re in a hilly area. The tendency is to increase speed down hill to build momentum to climb the next one. Every time you exceed 65 MPH going down hill its possible you’re tires are degrading.


NOTE: The polyester cording found in most ST tires starts to melt at about 200 degrees C.
That's 392F. A pretty good margin, I'd say.
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