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Old 05-21-2017, 06:05 PM   #1
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Important ST tire SPEED information

Important ST tire SPEED information

Special Trailer (“ST”) Tires

Trailer tires are widely used in a variety of towable trailer applications and are designed and marked as “ST” (Special Trailer) tires.



• Special Trailer tires, with the “ST” size designation, are speed rated at 65 MPH (105 km/h) under normal inflation and load conditions as shown in TRA table ST-M1. Prior to 2016 almost none of these tires had a Speed Symbol letter.

• This speed rating is based on Tire and Rim Association loads and inflation pressures for ST trailer tires without a Service Description for speeds up through 65 mph.

• If tires, with the ST designation and a Speed Symbol are used at speeds between 66 and 75 mph (106 km/h and 120 km/h), TRA directs the cold inflation pressure be increased by 10 psi (70 kPa) above the recommended pressure based on the trailer placard for normal inflation and load conditions.*


• If tires, with the ST designation, are used at speeds between 76 and 87 mph (122 km/h and 140 km/h), it is recommend the cold inflation pressure be increased by 10 psi (70 kPa) above the recommended pressure based on the trailer placard for normal inflation and load conditions and the load is to be decreased by 10%.*

You should also consult your trailer manufacturer’s Owner’s Manual for maximum operating speed recommendations for the trailer.


• No matter the inflation and load adjustments tires should never be operated at a speed higher than what is indicated by the speed symbol.


o Even if Inflation and Load adjustments have been made to a tire with a Speed Symbol, it is never appropriate to use an ST tire at a speed above 87 mph.


o Increasing the inflation pressure by 10 psi (70 kPa) does not provide any additional load carrying capacity.

o Do not exceed the maximum pressure for the wheel or the valve.

o If the maximum pressure for the wheel or valve prohibits the increase of inflation pressure, then the 65 mph rated speed must observed as the maximum speed.

o It may be necessary to dismount the tire from the wheel to determine the maximum rated inflation for the wheel and valve.*

o All the references to inflation here are about the "cold inflation pressure".

*Details about wheel and valve inspection:

a) If the rated (maximum allowable) inflation pressure is not visible on the wheel, consult the wheel or trailer manufacturer. Lacking documentation for a higher inflation the maximum allowable inflation pressure should be considered to be the maximum inflation on the OE tires.
b) Tubeless snap-in type valves, depending on the type valve, are rated for a maximum inflation pressure of 65 (TR413) or 80 (600HP) psi for nominal 0.453” diameter valve holes. If a higher cold inflation pressure is used, a clamp-in valve such as TR416S valve (200 psi maximum inflation) must be installed.

The above is a summary of my understanding and opinion as a tire engineer of steps that need to be taken for operating ST tires. Some will recognize that much of the above were covered in the Goodyear technical bulletin on ST tires
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Old 05-21-2017, 06:31 PM   #2
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Add 10 psi, ...check.
Keep it under 87mph...check.

Why don't they just write that on the side wall seems pretty simple.
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Old 05-21-2017, 08:37 PM   #3
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Links for above post

Service Description, Speed Symbol, speed rating,

Tire & Rim Association
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Old 05-21-2017, 08:44 PM   #4
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Originally Posted by J-Dog View Post
Add 10 psi, ...check.
Keep it under 87mph...check.

Why don't they just write that on the side wall seems pretty simple.
Because you only need to add 10 psi if you will be traveling at 66 to 75 mph and the increased inflation does not increase load capacity.

Because some would miss, as you might have that if above 75 you ALSO need to decrease load.

Comments about max inflation for valves & wheels are safety related information and must be considered.

Not enough room on the tire sidewall

People can't seem to read and understand the tire "size" so IMO it is unlikely they would understand the above primarily because print size would be too small for some to read.

Also if you don't tow above 65 you do not have to make the above changes.

I have already read where some feel it is OK to run up to whatever speed in on the tire sidewall, even if it is above 87.
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Old 05-22-2017, 12:12 PM   #5
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Question... I have read that GYM was developed years ago when most highway speeds were still posted at 55mph. The time has now come when GY has come to terms with the 21st century, and developed the GY Endurance. Reading the sidewall of these tires the change in information has changed significantly from the GYM. Have you checked these out?
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Old 05-22-2017, 12:14 PM   #6
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Quote:
Originally Posted by Tireman9 View Post
Thanks for this post Tireman9. I hope everyone reads until understanding. With E rated tires and in most cases, D rated tires the majority of our Airstreams can run the hiway at speeds in excess of 65 if trailer weight and tire air pressures follow the above guidelines. It's not that anyone should pump up the pressures and plan on driving 75 or even 85. But, if we use the above numbers as an extra edge for safety, we will be in good shape when and if we find ourselves in that higher speed range going down hills or the occasional passing.
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Old 05-22-2017, 01:28 PM   #7
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The TRA recommendation comes across like consent or approval to exceed the posted speed limit. Nobody with any common sense should be towing their trailer at a steady speed of 65 or above, especially when pulling trailers that outweigh their tow vehicle. They are a danger to themselves and everyone else on the road, IMO. If common sense isn't enough, then perhaps a speeding tic of $100 for every MPH above the posted limit would get their attention.
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Old 05-22-2017, 01:38 PM   #8
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I'm in Montana right now, speed limit 80. My wife is driving 70. I have 16" Sendel wheels and Michelin LT tires. I'm playing on the forum and I'm a happy camper!
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Old 05-22-2017, 01:42 PM   #9
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Quote:
Originally Posted by m rafferty View Post
I'm in Montana right now, speed limit 80. My wife is driving 70. I have 16" Sendel wheels and Michelin LT tires. I'm playing on the forum and I'm a happy camper!
Are there any special speed limits posted for trailers? I see some online sources saying 65 MPH is the Montana speed limit for trailers.

Happy Trails!

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Old 05-22-2017, 02:04 PM   #10
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Quote:
Originally Posted by tireman9 View Post
important st tire speed information

special trailer (“st”) tires

trailer tires are widely used in a variety of towable trailer applications and are designed and marked as “st” (special trailer) tires.



• special trailer tires, with the “st” size designation, are speed rated at 65 mph (105 km/h) under normal inflation and load conditions as shown in tra table st-m1. Prior to 2016 almost none of these tires had a speed symbol letter.

• this speed rating is based on tire and rim association loads and inflation pressures for st trailer tires without a service description for speeds up through 65 mph.

• if tires, with the st designation and a speed symbol are used at speeds between 66 and 75 mph (106 km/h and 120 km/h), tra directs the cold inflation pressure be increased by 10 psi (70 kpa) above the recommended pressure based on the trailer placard for normal inflation and load conditions.*


• if tires, with the st designation, are used at speeds between 76 and 87 mph (122 km/h and 140 km/h), it is recommend the cold inflation pressure be increased by 10 psi (70 kpa) above the recommended pressure based on the trailer placard for normal inflation and load conditions and the load is to be decreased by 10%.*

you should also consult your trailer manufacturer’s owner’s manual for maximum operating speed recommendations for the trailer.


• no matter the inflation and load adjustments tires should never be operated at a speed higher than what is indicated by the speed symbol.


O even if inflation and load adjustments have been made to a tire with a speed symbol, it is never appropriate to use an st tire at a speed above 87 mph.


O increasing the inflation pressure by 10 psi (70 kpa) does not provide any additional load carrying capacity.

O do not exceed the maximum pressure for the wheel or the valve.

O if the maximum pressure for the wheel or valve prohibits the increase of inflation pressure, then the 65 mph rated speed must observed as the maximum speed.

O it may be necessary to dismount the tire from the wheel to determine the maximum rated inflation for the wheel and valve.*

o all the references to inflation here are about the "cold inflation pressure".

*details about wheel and valve inspection:

A) if the rated (maximum allowable) inflation pressure is not visible on the wheel, consult the wheel or trailer manufacturer. Lacking documentation for a higher inflation the maximum allowable inflation pressure should be considered to be the maximum inflation on the oe tires.
B) tubeless snap-in type valves, depending on the type valve, are rated for a maximum inflation pressure of 65 (tr413) or 80 (600hp) psi for nominal 0.453” diameter valve holes. If a higher cold inflation pressure is used, a clamp-in valve such as tr416s valve (200 psi maximum inflation) must be installed.

The above is a summary of my understanding and opinion as a tire engineer of steps that need to be taken for operating st tires. Some will recognize that much of the above were covered in the goodyear technical bulletin on st tires
excellant information: Thank you:d
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Old 05-22-2017, 02:26 PM   #11
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Thanks to all of you, especially Tireman....This is the most sensible thread I have seen on the subject of tires. I've run GYM's now for at least 15 years with no problems. I use the pressure/load chart on the GoodYear web site plus 10% and I never exceed 65mph. My average speed is 55. Like someone else said, there is no point in towing at a higher speed when common sense says a towed rig increases the chance of a mechanical failure and having twice the weight and more than twice the length makes avoidance of an accident more difficult should something go wrong.
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Old 05-22-2017, 02:39 PM   #12
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Thanks for Posting the update. Now if I can just keep from being rear ended doing 65 mph on Nevada 80 mph roads.
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Old 05-22-2017, 02:58 PM   #13
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The new Goodyear Endurance ST tires carry a N speed rating.
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Old 05-22-2017, 03:28 PM   #14
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So far really good for my Goodyear Endurance E rated 235-75x15 st's....2 months and 6500 miles. Try to do 65 or less but slip now and then. I think these will be fine but time will tell the story. These miles included terribly rough stretch of I 40 WB rt lane in Arizona.
Classic 31 and 07 Tundra
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