TowMax STR II Tire Pressure above maximum sidewall

[BriaBeck]

Has anyone read this before, or done it? Results?



From TireRack.com:

Special Trailer (ST) Tire Speed Ratings

Unless assigned a specific Speed Rating, industry standards dictate tires with the ST designation are speed rated to 65 mph (104 km/h) under normal inflation and load conditions.
However, Goodyear Marathon and Power King Towmax STR tires featuring the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.
Do not exceed the wheel's maximum rated pressure. If the maximum pressure for the wheel prohibits the increase of air pressure, then maximum speed must be restricted to 65 mph (104 km/h).
The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.
Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.




Link to the TireRack Page




.

[Herk7769]

Yes

Note that it is 10 psi above the psi called out in the tires chart for the actual weight on the tire NOT TO EXCEED the pressure printed on the side wall.

[BriaBeck]

Yep, saw that. No increase in weight rating, only speed. "L" speed rating, up to 75mph.

[Airdale]

I think you'll find a statement in just about all RV trailer owner manuals will prohibit that action without express approval from the vehicle manufacturer.

This is how it's written in the 2019 generic Keystone trailer manual.

"Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the “maximum permissible inflation pressure” on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions."

[Lee Pedrick]

Originally Posted by BriaBeck

Has anyone read this before, or done it? Results?



From TireRack.com:

Special Trailer (ST) Tire Speed Ratings

Unless assigned a specific Speed Rating, industry standards dictate tires with the ST designation are speed rated to 65 mph (104 km/h) under normal inflation and load conditions.
However, Goodyear Marathon and Power King Towmax STR tires featuring the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.
Do not exceed the wheel's maximum rated pressure. If the maximum pressure for the wheel prohibits the increase of air pressure, then maximum speed must be restricted to 65 mph (104 km/h).
The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.
Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.




Link to the TireRack Page




.

I would NEVER go over the max pressure posted on the TIRE itself. I think (my opinion only) that would be disasterous. Do the speed its rated for.

[MR.M]

there are st tires rated to 80+ i believe the new goodyear endurance . also the Carilse are rated to 81 . i always run max cold psi .

[Herk7769]

I think there has been a misunderstanding about the 10PSI business.

In no case can you inflate above the sidewall pressure.

If you need the sidewall pressure to support the loaded weight, you may NOT add the 10PSI and you are limited to the 65 MPH rating of a standard ST tire.

[Herk7769]

Originally Posted by MR.M

there are st tires rated to 80+ i believe the new goodyear endurance . also the Carilse are rated to 81 . i always run max cold psi .

Only load range E tires are rated to 80 PSI
Load range D tires are rated to 65 PSI
Load Range C tires are rated to 50 PSI

You are conflating the manufacturer with the load range.

[BriaBeck]

Originally Posted by Herk7769

Yes

Note that it is 10 psi above the psi called out in the tires chart for the actual weight on the tire NOT TO EXCEED the pressure printed on the side wall.

Herk,


I just re-read your post... and that is NOT what the TireRack.com page says.


It says you may not exceed the wheel's maximum pressure rating... not the tire.

[mwdilday]

If your RV placard inflation is already equal to the maximum tire pressure stamped on the tire you will not have that option. Otherwise I would follow the tire manufacture recommendation. In my case my RV placard is 123 PSI and my sidewall maximum tire pressure is 123 PSI so I cannot increase pressure at all. 62 mph is my max speed. I have learned how to slow down and enjoy the ride.

[Airdale]

Originally Posted by mwdilday

If your RV placard inflation is already equal to the maximum tire pressure stamped on the tire you will not have that option. Otherwise I would follow the tire manufacture recommendation. In my case my RV placard is 123 PSI and my sidewall maximum tire pressure is 123 PSI so I cannot increase pressure at all. 62 mph is my max speed. I have learned how to slow down and enjoy the ride.

Well you got me with that one. I didn't know Forest River ever used European designed tires. That accounts for the 62 MPH. That 123 PSI inflation has me. Is it also a European brand name tire? Michelin LRJ European designed low platform trailer tires have a 120 PSI max permissible inflation pressure. Just got it from their truck tire data book.

Tire manufacturer's don't recommend or set Original Equipment tire inflation pressures. They just provide the charts the vehicle manufacturer uses to set them.

[mwdilday]

Originally Posted by Airdale

Well you got me with that one. I didn't know Forest River ever used European designed tires. That accounts for the 62 MPH. That 123 PSI inflation has me. Is it also a European brand name tire? Michelin LRJ European designed low platform trailer tires have a 120 PSI max permissible inflation pressure. Just got it from their truck tire data book.

Tire manufacturer's don't recommend or set Original Equipment tire inflation pressures. They just provide the charts the vehicle manufacturer uses to set them.

I have Westlake 215/75R17.5 Radial Trailer Tire - Load Range H
Item # LHWL097 onetrailer.com

[BriaBeck]

Hey guys... I think the discussion is maybe getting a bit off track here... the TireRack page specifically said
Goodyear Marathon and Power King Towmax STR tires

I'm going to call TireRack tomorrow and see what they say specifically about this, and where they got this information. I didn't see anything on the PowerKing TowMax website about this. However, the website does show that these tires are already "L" speed rated (75mph) at 65psi...


So, what I'm curious about is not about being able to drive them faster, rather, if it is safe to run them at 75psi, if doing so may help with the rather poor performance record of blowouts. If running them 10 psi higher than the sidewall pressure is really acceptable and if it gives the tire more reliability, then I'm all about doing it.

[Airdale]

Originally Posted by mwdilday

I have Westlake 215/75R17.5 Radial Trailer Tire - Load Range H
Item # LHWL097 onetrailer.com

Thanks, that answers the 123 PSI question. That Westlake tire is a European design. It's manufactured for three applications. Those earmarked for the USA market will have speed letters "L" 75 MPH or "M" 81 MPH. Those earmarked for the European marker will have a speed letter "J"= 62 MPH. That's the speed limit for the European trucking industry.

[Herk7769]

Here is the Goodyear Marathon instruction and it clearly states the maximum tire pressure IS the maximum you should put in it cold. You MUST reduce load below the maximum for the tire in order to use the increased tire pressure. The Tire and Rim Association uses "Rim" when they talk about the metal center and "Wheel" when they talk about the rubber tire. That might be your confusion.


"The Tire and Rim Association permits tire load increases, often with increased inflation pressure, for both Truck-Bus tires and Light Truck tires used on improved surfaces at reduced operating speeds.

In addition, the Tire and Rim Association also permits operating a 65 mph rated tire at higher speeds with a reduced load and increased inflation. (The Goodyear Tire & Rubber Company does not condone or recommend operating speeds above posted limits.)

Goodyear accepts these increases, and they are published in our truck tire engineering data book. Rim and wheel manufacturers mark their products with a maximum load and inflation. This applies regardless of operating speed.

The rim/wheel manufacturer must be contacted to determine if any deviation is permitted in the marked maximum load and inflation capacity of the rim or wheel at the operating condition in question."

[Airdale]

Originally Posted by BriaBeck

Has anyone read this before, or done it? Results?



From TireRack.com:

Special Trailer (ST) Tire Speed Ratings

Unless assigned a specific Speed Rating, industry standards dictate tires with the ST designation are speed rated to 65 mph (104 km/h) under normal inflation and load conditions.
However, Goodyear Marathon and Power King Towmax STR tires featuring the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.
Do not exceed the wheel's maximum rated pressure. If the maximum pressure for the wheel prohibits the increase of air pressure, then maximum speed must be restricted to 65 mph (104 km/h).
The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.
Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.




Link to the TireRack Page




.

In todays ST tire market this procedure is antiquated and kind of moot. Almost all ST tires now have a speed letter on their sidewalls for 75 MPH or above.

Three ST tire manufacturers/brand named - Maxxis, Goodyear & TowMax - touted this extraction from the TRA rule book to appease disgruntled ST tire users.

Now days it only applies to Maxxis as they have not yet put speed letters on their ST tires. TRA clearly says an unlettered ST tire is a 65 MPH tire. Here is what Maxxis offers; "According to the Tire and Rim Association, the U.S. tire industry specification authority, inflation pressures and load specifications in general for any ST Radial trailer tires without a service description, regardless of the manufacturer, are designed and rated at 65 MPH. However, if the speed is higher than 65 MPH, the pressure and load need to be adjusted according to the following guidelines: From 66 to 75 MPH – the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) but requires no load adjustment. From 76 to 85 MPH – the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) and load should be reduced by 10%."

There are obstacles in the procedure.

The USTMA clearly says; "Do not exceed the maximum inflation pressure shown on tire sidewall."

Most RV trailer owner manuals are going to say it something like this; "Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the “maximum permissible inflation pressure” on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire."

[Herk7769]

I agree with Airdale.

My new ST tires have a speed rating of 75MPH. I have no desire to go faster as I can't see a need to pass anyone faster than that.

My previous camper was nearly always at max GVWR so upgrading a load range worked far better in my case. I nearly always cruise at 65 regardless of posted speed.

[BriaBeck]

OK, I doubt that I am confused.



For the majority of my 49 years on the planet, I've been operating with the understanding that the objects 1 and 3 are RIMS, Object 2 is a WHEEL, and Object 4 is a TIRE I'm not using the street terms where wheel and rim are the same thing or could be the same thing. And a tire is always a tire. Just for clarification, so that we know what we are talking about without confusion. I suppose that the complete rim/wheel/tire assembly could be referenced as a wheel as well... one of the benefits of the English language But for the purposes of this discussion, we are talking about the specific parts -- rim (probably not applicable to anyone on this forum), wheel, and tire.


Since we kinda have to pick nits here, I'm looking at my tires on my camper, which are TowMax STR II ST225/75/R15 Load Range "D" tires, on steel wheels. All of my discussion is in reference to this wheel/tire combination.


Looking at the PDF's that Herk uploaded, which are all from Goodyear, using them for my tires, which are from a different manufacturer, would make any application of said documents' procedures toward my tires an assumption at best. We all know what happens when you assume.


The "Has Data" file does not mention any load reduction requirement, only that

• Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.

• Do not exceed the maximum pressure for the wheel.

• If the maximum pressure for the wheel prohibits the increase of air pressure, then the maximum speed must be restricted to 65 mph (104 km/h).
• The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.

And...

• Many trailer manufactures establish the recommended tire inflation pressure based on the 65 mph (104 km/h) rated speed for ST tires. In these cases, the ST tires should be inflated 10 psi (69 kPa) higher than the trailer placard for speeds up to 75 mph (121 km/h) (wheel must be rated for this higher inflation pressure). If the trailer manufacturer’s placard specifically states that the cold inflation pressure is suitable for speeds above 65 mph (104 km/h), no additional inflation pressure adjustment is required.

The "Goodyear Tire Speed ratings" pdf says "trailers" in the title page one, but only specifically discusses Light Truck "LT" tires and "Truck and Bus" tires... ST tires are not mentioned, which is the focus of the TireRack page, specifically, the Goodyear Endurance and TowMax ST tires.

The "Goodyear Tire Inflation Load Charts" pdf only has 1 chart specific to ST tires, and says that the "Letters in parenthesis denote Load Range for which BOLD FACE Loads and Inflations are Maximum." Makes no mention of increasing pressure to increase speed rating. This is the ONLY thing I have seen where it states that 65psi is the MAXIMUM for a load range D tire. Table 1 on page L2 is for LT tire sizes only, which would make that chart inapplicable to ST tires.


I went outside and looked at my tires... the sidewall information gives a maximum LOAD at 65psi... but nowhere does it say that the maximum pressure is 65psi. I have seen some tires that list a maximum pressure for seating beads, but right off hand I don't remember any tires that list a maximum operating pressure... only a maximum LOAD AT some pressure. I am not saying that there are not tires out there that do not list maximum pressures... only that I don't remember seeing any right off hand. My wheels do not list or indicate any maximum pressure, only a maximum load of 2600lbs. The placard on my camper does not reference any speed rating at all, only a tire size with a load (2540lbs) at a pressure (65psi).

Words mean things, the absence of words means things as well... I learned long ago to never read more into something than what it says. Again, if you assume, you make an ass of u & me.

I'm not arguing one way or the other... just trying to get this straight so everyone can get the maximum performance from their equipment while doing it safely... without assumptions... so don't take this as a hostile post... it is merely discussion!! Gotta run, time to go fly.

[NMWildcat]

I've never understood the debate over such a simple thing as tire pressure. If it's a towable, use max cold psi on tire. If it is a TV or MH, use pressure adjusted for load. Easy.

[MR.M]

Originally Posted by Herk7769

Only load range E tires are rated to 80 PSI
Load range D tires are rated to 65 PSI
Load Range C tires are rated to 50 PSI

You are conflating the manufacturer with the load range.

Really wow ! i was referring to MPH not PSI . i know the psi rating of the load ranges of tires thanks