Trailer Tire Discussion ..... ST, LT or C-Type ?

[Indy]

I have an 18 foot enclosed trailer and someday I'm going to need a new set of tires and I want to know what I'm going to do before I come to that day. I don't want to rush around and just find something that's round and fits my rims in the next 24 hours before heading out of town.

@inmanlanier you mentioned the C-Type tire and that got me researching trailer tires including your CType tire, also the ST and LT government standards, but I have found very little about the CTire. Have you found anything on the European standard for the C-Type tire that you have mentioned in another thread? I found this very informative thread about the ST and LT standards and the differences between them. This guy "SeniorGNC" does a very nice comparison of the two standards without interjecting his opinion.

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In the link above he references the Federal Motor Carrier Safety Administration (FMCSA), but his post is from September 2009, so if you want to read the actual standard then use my link and click on the table of contents, then click on 571.109.

Federal Register :: Request Access

www.ecfr.gov

From what I have found, going to a 16 inch tire does more for the load carrying capacity of the tire than anything else you can do such as the ST, LT or CType. The Michelin Agilis CrossClimate in a 205/65R15 102T C5 has a load index of 1874 lbs, but if you go up to the 235/65R16 121R C8 the load goes up to 3197 lbs. [I believe this a CType tire???]

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www.discounttire.com

Or the Firestone Transforce CV 205/65R15 102T C5 and the 235/65R16 121R C8 goes from 1874 lbs to 3197 lbs.

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I know it's a ST tire, but just for illustration, the Goodyear Endurance tire in a ST235/80R16 123N E1 has a load rating of 3418 lbs.

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Going to 16" tire will require new rims, but a wider 15" tire will also require new rims. Will still have to make sure that such a combination will fit in the fender well.

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Comments Please !

 

[Action]

You would want to size the tire to the load and then add a margin.
The margin I like to use is 15%

18 foot trailer, single axle or dual? (My assumption would be single.)
Running it across a scale when it is loaded to the max would give you needed data to make tire choice.

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[Indy]

18 foot trailer, single axle or dual? (My assumption would be single.)
Running it across a scale when it is loaded to the max would give you needed data to make tire choice.

I was really wanting to debate the pros and cons of the tires, but the trailer is a dual axle (each axle is 3500 lbs). I did go to the Cat Scales this summer. The first time is $13.50 and and anytime in the next 24 hours is called a re-weigh and cost $3.50. Therefore I crossed the scales 4 times that day in various configurations.

Navigator + Trailer + TBucket
Navigator + Trailer + TBucket (Moved Back in Trailer, to see how it changed the Nav rear axle weight)
Navigator Only
TBucket Only




Dual Axle or 7500 lbs Total

 

[Action]

The title, "ST, LT or C-Type ?" maybe mixing some things.
ST and LT are tire types.
A C tire type is a Commercial tire not to be confused with a C load range. A Euro-metric C tire type is intended to be used on vans or delivery trucks with steering axles and drive axles. Something that trailers do not have.

For your application -
The Gross Vehicle Weight Rating of the trailer is 7000 pounds with the recommended tire of ST205/75 R15 with a load range of C inflated to 50PSI
The trailer axle weight came in over the scale at 5240 pounds

An ST tire in a C load range has a max inflation of 50PSI. (just like the tire placard) for a max load of 1820 pounds
The same ST tire size ST 205/75R15 can be had in a D load rating with a max inflation of 65psi for a max load rating of 2150 pounds

1820 X 4 = 7280 (at max side wall psi)
2150 X 4 = 8600 (at max side wall psi)

If you moved to a tire load capacity of 3000+ pounds with 4 tires the max load of all 4 tires is 12,000 pound range. However, the trailer is only designed for 7000 pounds and in actual use the load is in the 5200 range. You can move to large diameter tires or commercial tires, but why??? You will never be able to utilize the addition load capacity of those tires. The trailer is not designed to handle that! Plus, those tires would cost a lot more than the recommended tires.

Let's just say at some future point, you will max the trailer load to the 7000 pound number.
I believe in a margin. (Unlike it seems most trailer manufactures including this one) So, I would want tires that could handle 7000 pounds x 115% = 8050 pounds
Moving to a ST205/75 R15 D load range will get you that. No added cost for new rims. Or Commercial tires

You can do the same for LT rated tires if you wish. But the load ranges are different and LT tires are designed for steering and driving axles. Neither of which you will need.

BTW Nice bucket! If it were my bucket, I would never move to a commercial tire or a 16inch rim. The higher load capacity tires are stiffer. Which is how they achieve the load rating. That would transmit more road bounce and less cushion. Especially if inflated anywhere near the max sidewall psi. Bigger is not always better.

A postscript on Michelin. They do not make ST tires. In any communication with them they will state they do not recommend any of their tires on a trailer application. Because, well they do not make ST trailer tires. However, it is well documented on a different forum, that any Michelin tire installed on a trailer has the same warranty coverage as any other installation. In fact, I have seen Michelin make adjustments on tires that I would not have made. I like Michelin and have those on my Navigator. My boat trailer has ST tires.

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[Indy]

The title, "ST, LT or C-Type ?" maybe mixing some things.
ST and LT are tire types.
A C tire type is a Commercial tire not to be confused with a C load range. A Euro-metric C tire type is intended to be used on vans or delivery trucks with steering axles and drive axles. Something that trailers do not have.

Yes, that's why I called it a C-Type instead of a "C" load range. I learned about it in the thread below.

2021 Tow Capacity - Is it Safe

As a followup, the dealer is now changing the oil at 8k intervals. I did the 1st one at 4,500 using only full synthetic. I provide full synthetic to the dealer now and they pull a sample for Blackstone. I'm a firm believer in good oil for the inner workings of an engine as we plan on running a...

lincolnforums.com

Let's just say at some future point, you will max the trailer load to the 7000 pound number.
I believe in a margin. (Unlike it seems most trailer manufactures including this one) So, I would want tires that could handle 7000 pounds x 115% = 8050 pounds
Moving to a ST205/75 R15 D load range will get you that. No added cost for new rims. Or Commercial tires

You make a good point! It's that I have not heard good things about ST tires, especially after reading how they are tested in this guys post #1. Nearly all of my miles are highway miles, so my speeds are going to be around 65 mph for hours during the HOT summer months. If I stay with the ST tire, it's most likely going to be the Goodyear Endurance tire.

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You can do the same for LT rated tires if you wish. But the load ranges are different and LT tires are designed for steering and driving axles. Neither of which you will need.

That's next on my list to check into, LT tires. If they can steer and drive, then they can also go straight.

BTW Nice bucket!

Thanks! It's a lot of fun to drive and scary fast!

A postscript on Michelin. They do not make ST tires. In any communication with them they will state they do not recommend any of their tires on a trailer application. Because, well they do not make ST trailer tires. However, it is well documented on a different forum, that any Michelin tire installed on a trailer has the same warranty coverage as any other installation. In fact, I have seen Michelin make adjustments on tires that I would not have made. I like Michelin and have those on my Navigator. My boat trailer has ST tires.

Thanks for the info about Michelin. I also just installed the Michelin Defender LTX on my Navigator also.

 

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Trailer tires in general got a black eye for a couple of reasons.

Trailers are not regulated like passenger vehicles.
It is possible to install a tire that has a max load rating (under max inflation) that matches the max GVWR of the trailer.
No margin.
This was a common practice to lower the cost of the tires for the trailer. And there was no regulation to provide for a margin.

Then trailers, specifically travel trailers got big. Err fat if you will. You see buyers wanted more than a hard sided tent. They want options. Things that weighed a lot. That meant bigger tires but trailer manufacturers did not want more space to go to tires and tire manufacturers (making ST tires) were not exactly making higher capacity tires. Plus they were getting beat up by trailer manufacturers for lower cost.

Goodyear has always had a very significant chunk or the trailer tire market. But the previous tire model (Marathon) was not made in larger sizes nor at higher load ranges for bigger trailers. And were an inferior design to Endurance. Goodyear just did not change with the market. So a tire that was marginal may have been neglected and the tire pressure was too low for the load and it failed.

As far as using an LT tire on a trailer, may not make much difference on a single axle trailer. Multi-axle trailers and the side wall is not the same as ST. Added tire pressure may be needed in an LT tire to get the same stiffness of an ST when turning. Low speed sharp turns puts a lot of added stress on tires that the ST design was made to handle. In addition travel trailers (not yours) frequently are loaded unequally on all four tire positions. Water tanks, appliances and other heavy items cause this condition.

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