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05-31-2009, 11:22 AM
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#1
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Montana Fan
Join Date: Nov 2007
Location: SW
Posts: 255
M.O.C. #7895
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ST Tires And Speed Rating
According to the link from Goodyear it seems they think it's normal to run ST tires usually speed restricted to 65, up to 75 if you add up to 10 psi of air.
I have no intention of doing that, but would appreciate comments from the tire gurus on the forum: http://www.goodyear.com/rv/pdf/marat...nfo_032806.pdf
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05-31-2009, 12:03 PM
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#2
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Montana Master
Join Date: Apr 2004
Location: Apple Valley
Posts: 1,574
M.O.C. #1358
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I'm no tire guru, but I've replaced a few sets...isn't that as good as staying at the Holiday Inn?
No way can a tire rated for 65 mph max be ok running faster...they have those speed ratings there for a reason. Inflating to a higher pressure will crown the tire and cause overheating and failure even at lower speeds. I set my cruise for 62 and it stays there...period.
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05-31-2009, 12:04 PM
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#3
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Montana Master
Join Date: Jul 2003
Location: Clearwater
Posts: 10,917
M.O.C. #420
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I am a bit confused with Goodyears recomendation concerning ST tires.
Quote:
quote:This information is designed to help you obtain the best performance from tires with the ST (Special Trailer)
designation. Please review the following important points with your Goodyear Marathon customers
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Keep in mind that Goodyear is speaking for the Goodyear Marathon and not necessarily other brands.
The following is also quoted from the above referenced Goodyear site..
Quote:
quote:
· Industry standards dictate that tires with the ST designation are speed restricted to 65 MPH under normal inflation and load conditions unless a different speed restriction is indicated on the sidewall of the tire.
Seeing as how most all ST tires have a speed restriction of 65MPH indicated on the sidewall takes any question of over inflation out of the question.
To me the following seems to contradict the above...
· Based on industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph, it is necessary to increase the cold inflation pressures by 10 psi above the recommended pressure for the load.
. 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.
. The cold inflation pressure must not exceed 10 psi beyond the inflation specified for the maximum load of the tire.
. Trailers tires should be operated at inflation pressures that are specified by the trailer manufacturer. The trailer
manufacturer’s inflation information can usually be found in the owner’s manual, tire information placard or
vehicle certification label, usually located on the forward left side of the trailer.
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The tag on the side of my Monty says maximum air pressure of 80PSI for all 5 trailer tires. I'll stay at 80PSI
BTW-Maybe Lonnie can clarify just what GY is talking about.
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06-02-2009, 02:46 AM
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#4
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Montana Master
Join Date: Aug 2006
Location: Texico
Posts: 1,917
M.O.C. #6150
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Quote:
quote:BTW-Maybe Lonnie can clarify just what GY is talking about.
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No, I don't think I can.
This is the first time I have seen a tire manufacturer suggest exceeding the maximum speed rating of the tire. Even though Goodyear suggests the speed rating can be exceeded, they also contradict themselves by saying you should not exceed the vehicle manufacturers ratings or the wheel ratings.
I would strongly recommend staying within the speed and pressure rating molded into the sidewall of the tire.
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06-02-2009, 10:43 AM
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#5
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Montana Master
Join Date: Jul 2004
Location: Manhattan
Posts: 1,144
M.O.C. #1846
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I wonder -- and this is JUST an I Wonder -- if they are advising that 10 psi extra if you are running at less than max sidewall psi. I know that on my truck, the door jamb states 65 PSI yet the tires have 80PSI stamped on them. So, given what I'm thinking, if I were to run at high speeds all day, then I could boost the pressure up to 75 PSI, still being below the 80 of the sidewall.
Obviously, this assumes that the user is running a tire at less than max pressure to begin with (also carrying less than max weight on that tire). This last assumption is what kills this for us as trailer owners -- as I've read in many posts, most of our rigs are running close to max weight so the tires have to be at 80 (or 110 for G rated tires) to carry the trailers.
Hope this all made sense.
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06-02-2009, 01:00 PM
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#6
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Montana Master
Join Date: Jul 2003
Location: Clearwater
Posts: 10,917
M.O.C. #420
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Quote:
quote:Originally posted by skypilot
I wonder -- and this is JUST an I Wonder -- if they are advising that 10 psi extra if you are running at less than max sidewall psi. I know that on my truck, the door jamb states 65 PSI yet the tires have 80PSI stamped on them. So, given what I'm thinking, if I were to run at high speeds all day, then I could boost the pressure up to 75 PSI, still being below the 80 of the sidewall.[/i]
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No not really. The 65PSI is the max inflation recommended by the vehicle manufacturer for the weight being carried on that front tire.
Inflating to 75PSI can be dangerous. Believe it or not overinflated tires will run hotter and than adding high speed to the equation only creates more heat. Not a smart move.
Quote:
quote:[i]
Obviously, this assumes that the user is running a tire at less than max pressure to begin with (also carrying less than max weight on that tire). This last assumption is what kills this for us as trailer owners -- as I've read in many posts, most of our rigs are running close to max weight so the tires have to be at 80 (or 110 for G rated tires) to carry the trailers.
Hope this all made sense.
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06-03-2009, 04:23 AM
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#7
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Montana Master
Join Date: Jul 2004
Location: Manhattan
Posts: 1,144
M.O.C. #1846
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Glen: Thanks.
As I posted, it was an 'I wonder'. Sometimes have to wonder if the pressures listed on the doors are more for 'Engineering' reasons (i.e. load carrying capability) or "Marketing" reasons (i.e. ride comfort.) Given the Ford Explorer / Firestone debacle of years ago, I know that marketing did play a roll in the door jamb pressure establishment -- hopefully the automakers learned a lesson and now go by Engineering demands.
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