Replacement Tire Question

[stevedeiwert]

I have a 1994 25’ Classic Excella, GVW 6500#, tongue weight 750#, on which I am replacing the tires. ST225/75-R15. I have always used Goodyear Marathon, load range D, 2150# and speed range 75mph and have never had any problems. I live in California and respect the 55mph speed limit and always drive below 60 mph and keep the tire properly inflated at 50psi. Am considering Goodyear Endurance trailer tires as replacements. Load range E, 2833# at 80psi and speed range 87mph. Obviously overkill for my trailer and driving conditions. I’m not interested in changing to 16” wheels or to truck tires.
My questions are this: Will I experience a substantially harsher ride with the 80psi tires? Do I need to run them at 80 psi or would something like 60psi be OK? And are my existing aluminum original equipment rims adequate for an 80 psi tire?” Would I be OK staying with the Marathons?

[Bill M.]

You cannot get Marathons any more.

You can get a load range D Goodyear Endurance in 205 x 15 size and it has enough weight capacity for your trailer and a max sidewall pressure of 65 psi like your old Marathons. Other than being just a slight bit narrower it should be a close replacement and they have as much capacity as your old Marathons.

You can get the 225 x 15 Endurance in load range E that you are looking at with the 80 psi maximum.

I would not want to run 80 psi in my older trailer that came from the factory with a loading tag that says 45psi inflation on the trailer. I do not see how bias ply tires could have been that much "better" at handling load and shear.

[BlackAces]

Older trailers were often equipped with tires very low on load capacity reserves. Recently the Recreational Vehicle Industry Association (RVIA) imposed a 10% tire load capacity reserve requirement. That means the tires inflation pressure should be set at a PSI level that will insure the tires are inflated to a load capacity 10% above the trailer's, vehicle certified GAWR (s).

They also no longer recommend the use of bias ply tires on wheels 14" or larger.

Most owners like those recommendations and you should consider them in your tire search.

[crispyboy]

As stated the Marathon tire was replaced by the improved Endurance tire.
Buy the same size as you had before, don't go with the smaller 205 size as this will put your trailer closer to the ground (smaller diameter). While the 225 size is an E rated tire you can run the tire pressure at an amount that will support the load. I use 60 psi cold and my trailer is much heavier than yours.
To answer your question get the axle weight of your trailer at a truck scale and refer to the tire pressure chart below.

[stevedeiwert]

Thanks Crispyboy. That was just exactly the information I was looking for. I was going to buy the 205 size until I saw your alert about the diameter difference. The pressure chart is just what I need.

By the way, to Bill M., Goodyear Marathons are still available at Walmart according to their website information

[Caffeinated]

I replaced my Marathons with Endurance, run them at 75psi, and they seem to ride smoother than the Marathons did.

Mike

[BlackAces]

Inflating tires on your trailer to the load carried is not the way it’s supposed to be done. That method comes from the commercial carrier industry and is really not applicable for vehicles, such as yours, built under the guidance of FMVSS.

Here is an excerpt from the RV section of the USTMA.

“Inflation pressure recommendations may also be determined based on the tire manufacturer’s specifications, which define the amount of inflation pressure necessary to carry a given load. These inflation pressures may differ from those found on the vehicle tire placard or certification label.”

“However, never use inflation pressures lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.”

In accordance with tire industry standards, inflation pressures for replacement tires must first be set to an inflation pressure that will ensure they provide a load capacity equal to or greater than what the Original Equipment tires provided.

(When going to higher inflation pressures, check and make sure the valve stems can withstand the increases. Like tires, they are designed to withstand the effects of thermal dynamic expansions).

[Bill M.]

If it works for the commercial carrier industry why will it not work on a RV?

[ROBERT CROSS]

YEP...GYM's to GYE's, well pleased.
POI...in 13yrs of GYM'S, one curb rash failure,(my bad) and a nail. 😂👍

Bob
🇺🇸

[kpm]

The placard for the GY Endurance ST225/75R15 tires on my 2018 25FB specifies 80 psi and that is what I run. I haven't noticed any harshness.

[CapriRacer]

Originally Posted by Bill M.

If it works for the commercial carrier industry why will it not work on a RV?

Because tires built for commercial carriers are designed and built to withstand that type of abuse. Passenger car and light truck tires aren't - and up until recently, ST tires weren't even up to normal PC and LT levels.

And don't forget, commercial carriers spend a lot of time maintaining and monitoring tires - their income depends on it. This is not the case with the average car. pickup truck, and RV owner.

[BlackAces]

Originally Posted by Bill M.

If it works for the commercial carrier industry why will it not work on a RV?

I'm really not saying it won't work. I'm saying the industry sees it as a misapplication. Just about any tire manufacturer that posts their replacement tire standards on the WWW will have a statement very similar to this one from the USTMA WWW PDF.


"Replacement tires should be the same as the OE size designation, or approved options, as recommended by the vehicle or tire manufacturer. Never choose a replacement tire of a smaller size or with less load-carrying capacity than the OE tire size at the specified vehicle tire placard pressure."


This is a tire size designation, ST235/85R16. This is a similar size designation LT235/85R16. The ST & LT prefixes are part of the size description. They are from completely different designs. Their primary usage is defined in their prefix. NHTSA has a definitions listing. Basically it says the LT is designed for service on light trucks. The ST is a special design to be used only on trailer axles. Both have the DOT logo for highway service.

[CruizinDux]

Originally Posted by Caffeinated

I replaced my Marathons with Endurance, run them at 75psi, and they seem to ride smoother than the Marathons did.

Mike

2X here...and i was all set to go with the Nokians lt235/75 15 E, another fine tire option. I see them a lot around here on trucks and horse/otherwise trailers.

Here is a great gye thread with lots of posts and pro advice... tireman, capriracr etc.

http://www.airforums.com/forums/f438...ml#post2162707

Plus http://www.airforums.com/forums/f438...-167187-3.html

A great discussion re speed/weigh re a ST tire. This took me a couple of reads before the load per tire finally engaged in this senior brain.

[Caffeinated]

Originally Posted by CapriRacer

And don't forget, commercial carriers spend a lot of time maintaining and monitoring tires - their income depends on it. This is not the case with the average car. pickup truck, and RV owner.

We are Airstream owners. We are not average.

Mike

[BlackAces]

Originally Posted by Caffeinated

We are Airstream owners. We are not average.

Mike

"Inflation pressure recommendations may also be determined based on the tire manufacturer’s specifications, which define the amount of inflation pressure necessary to carry a given load. These inflation pressures may differ from those found on the vehicle tire placard or certification label."

"However, never use inflation pressure lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall."


From page #43 in this reference.

https://www.ustires.org/sites/defaul...TruckTires.pdf

[perryg114]

Yes 80psi will ride harsh. The 225/75-XL15 car tires are great tires man rated and speed rated. ST tires are rated for hay wagons that have no value. You don't have to run 80psi unless you are near max load. The proper way to measure tire pressure is your run them and measure temperatures at the middle and the edges. If the tire pressure is too high the center will be hotter than the sides. If too low the edges will be hotter. Another way is to put a chalk line on the tire and roll it a few times. Lighter on the edges means under inflated and in the center means overinflated.



Perry

[CapriRacer]

Originally Posted by perryg114

Yes 80psi will ride harsh. The 225/75-XL15 car tires are great tires man rated and speed rated. ST tires are rated for hay wagons that have no value. You don't have to run 80psi unless you are near max load. The proper way to measure tire pressure is your run them and measure temperatures at the middle and the edges. If the tire pressure is too high the center will be hotter than the sides. If too low the edges will be hotter. Another way is to put a chalk line on the tire and roll it a few times. Lighter on the edges means under inflated and in the center means overinflated.

Perry

I'm going to disagree with this post for a number of reasons.

But primarily about the "chalk" method to determine inflation pressure. It assumes that the tire manufacturer did a good job of getting the footprint right - and especially in the case of ST tires, that assumption is not warranted.

A better way would be to measure the pressure build up. After an hour of high speed operation (say on the freeway), the pressure buildup should be no more than 10%. If it is higher, then the pressure needs to be increased.