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Old 10-26-2013, 03:10 PM   #1
Bill
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Default Goodyear Marathons - overinflate/overspeed

We have talked a lot about Goodyear's overinflate/overspeed statement in the past, and no one was quite sure how to interpret the rather ambiguous wording on their web site. I spotted the following this morning on RV Tire Safety http://www.rvtiresafety.com/2013/10/...ype-tires.html. "TRA" is the Tire and Rim Association. I have no idea who they are.

I'll be interested in any comment from wmtire.

Bill

Quote:
For Goodyear Marathon tires only:
There is a Goodyear Tech bulletin PSB#2011-13 that uses information from TRA.
The tech bulletin says that the normal max speed for Marathon ST type tires is 65 mph. This speed can be increased up to 75mph only if the inflation pressure is increased by 10 psi. This new inflation can be 10 psi higher than the pressure molded on the sidewall of the tire that is associated with the tire max load.
The load does not increase beyond the load molded on the tire sidewall.
Goodyear does not support or condone operation above 75 at any time.
The trailer owner is responsible to confirm the rim is rated for the new inflation level.
While TRA indicates a further increase in speed might be achieved Goodyear has decided not to adopt this option.

The person I talked with at Tire Rack said they had already changed their web site to indicate this applied to Goodyear tires only and that they were attempting to learn if any other ST tire manufacturers were willing to make a similar change. As of Saturday Oct 19, 2013 they had not identified any other tire manufacturer willing to make an increase in max speed above 65.

++++++++++++++++++++++++++++
Info added 10/26/13 10:51 AM EDT
Example:
If you have a Goodyear Marathon ST225/75R15 LR-D it is rated for 2540# @ 65psi and a max speed of 65 mph. If you increase the cold inflation to 75psi the tire would now be rated for 2540# @ 75psi and a max speed of 75 mph.
The example currently only is OK for Goodyear Marathon ST tires as I have not seen a published document from any other tire manufacturer.


The pressure increase must not exceed the max pressure capability of the wheel. You need to find a max pressure rating stamped on the wheel or get something in writing from the wheel MANUFACTURER.

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Old 10-27-2013, 07:39 AM   #2
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There are a few roads in this country where it's legal to drive 75 MPH towing a trailer. Recently we took a trip that took us thru Nevada, Arizona and Utah. I was taken by surprise when the 18 wheelers were blowing past me doing 70 to 75 MPH. I found myself tempted to try it; however I decided not to, because the outside temperature was in the 90's and a blowout would have spoiled my whole day. California has a 55 MPH max towing speed and we normally put the cruise control on 60, so setting it at 65 in Nevada and Arizona seemed plenty fast enough. The faster your traveling the longer it takes to stop in the event of an emergency.
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Old 12-23-2013, 08:06 AM   #3
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So the practical application I'm getting from Tech bulletin PSB#2011-13 is to increase the pressure of the Goodyear Marathon tires to 60psi yet still drive on the highway at 65mph max. The increased pressure gives an additional +10mph buffer (75mph red line) for things like going downhill; passing traffic; not paying attention to speed; etc.
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Old 12-23-2013, 09:11 AM   #4
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That is how I read it as well. However, there is no hint given as to whether the extra pressure will result in an over-inflation wear pattern, in which the center of the tread wears out rapidly. I suspect that it might, but since I moved to 15-inch tires and run them at 60 psi, I don't have to experiment to find out.

FWIW, if I increase the pressure in the Michelin tires on my Explorer to 40 psi (sidewall max is 44 psi), I definitely experience rather rapid over-inflation wear. This tells me that sidewall pressure on my Explorer tires (and presumably on my TM tires) is related to tire safety, not tread wear.

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Old 12-23-2013, 12:00 PM   #5
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Good point about the safety vs tread wear relation to tire pressure.

Since it is recommended that the Goodyear Marathons ST tires should be changed out every 3-5 years, excessive center tread wear due to over inflation by 10psi should not be a very big issue during that time frame for the average yearly mileage put on TM's. I agree that Goodyear is siding with the safety and not tread wear issue with this bulletin but the big assumption/expectation is that the TM owners are changing out the tires every 3-5 years and not putting extremely high mileage on the TM tires every year.

Each TM owner has to evaluate their own circumstances to see if the 10psi over inflation works for them. It should for most.

Of course having Goodyear redesign this 14" tire to carry a bigger load would be ideal even if it costs consumers a bit more.
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Old 12-23-2013, 01:00 PM   #6
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Vedddy interesting.

Many of us folks who are running Load Range E tires (80 psi) are complaining about the extra "trailer bounce" with tires that hard. The fine china is getting a bit more jumbled. In fact, some are lowering the psi (while staying within the necessary load capacity) to get a bit softer ride.

I expect there may be some of the same experiences if you take the Marathon Load Range D tires up to 70-75 psi.

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Old 12-23-2013, 03:53 PM   #7
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And yet the sticker that TM puts on the camper says inflate to 65 psi for the 15 inch st tire. Or at least that is the label on our 2720SL. Our experience has been to run trailer tires at the side pressure to obtain the load rating on the side wall. In all our years of trailer towing, about 30 plus we have experienced two blow outs. One was a 480-8 on a boat trailer when we hit a pot hole. The second was the Goodyear Marathon. On the Marathon tire pressure was set at 65 psi cold before leaving the CG. 60 miles later we stopped for supplies. 30 miles and 45 minutes later we peeled the tread off the tire. The tires were 4 yrs and 1 week old, looked brand new and had maybe 20k miles on them. They had been sitting in a warehouse for two years. A cat scale check later showed the us to be 40# over on the TM axle.

We are currently running e load range tires at 70 psi. This gives us the desired load range. They are not showing unusual wear and have about 8k miles so far. These are the only ST tires we have not run at the sidewall pressure.

And as REDTAIL said most states have trailer speed limits well below 70 to 75 MPH.
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Old 12-25-2013, 12:20 PM   #8
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Scrubjaysnest,

Ditto on the Load Range E at 70 psi. Just FYI, Texas used to have trailer speed limits in years past, but no longer. Here in the Lonestar State, the speed limit is the same for all vehicles.

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Old 12-26-2013, 05:07 AM   #9
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Quote:
Originally Posted by davlin View Post
Scrubjaysnest,

Ditto on the Load Range E at 70 psi. Just FYI, Texas used to have trailer speed limits in years past, but no longer. Here in the Lonestar State, the speed limit is the same for all vehicles.

Dave
Yes, we noticed; 75mph for the "nest" seems a bit excessive but then We feel Fl's at 70 is also. Of course Ga is on the other end at 55 and doesn't recognize Fl's drivers licensee to tow
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Old 01-12-2014, 04:29 PM   #10
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http://www.boatus.com/trailerclub/trailer_tires.asp

BoatU.S. Trailering spoke with experts at two trailer tire manufacturers: Goodyear (maker of Marathon radials) and Kenda (maker of Karrier ST Radials and Load Star bias ply tires).

How fast?

Industry standards dictate that ST tires are restricted to a speed of 65 mph unless a different speed restriction is indicated on the tire sidewall. If speeds from 66 to 75 mph are used, the tire cold inflation pressure can be increased by 10 psi without any increase in load. -Goodyear Tire Company

Like a passenger car tire, which has a speed rating, trailer tires are also designed with a certain speed rating. However, the trailer tire is used to sustain the higher loading weight and will generate higher heat than the tire going at the same speed on a car. Since heat build up will potentially degrade a tire's structure and cause either a blow out or separation, trailer tires are usually designed at lower speed rating. -Kenda Tire Company

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Since my 14" TM factory rims are rated to 1870lbs max, the assumption is the max pressure is then limited to 50psi. Increasing to 60psi would exceed the max pressure of my rims by 20%. For those using 14" Goodyear Marathon tires - only non-factory rims rated to 65psi will benefit from PSB#2011-13. But that would beg the question: if one has 14" non-factory rims rated to 65psi (load range D), why are you using Goodyear Marathon (load range C) 14" tires? Especially considering their history!
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