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Old 10-23-2013, 03:29 PM   #1
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Braking News- Max Speed on ST type tires

Finally chased down the answer. Getting to the bottom was a challenge because I ran into "customer service" people who could read from a script but had no idea why they were giving me the answer they were.

Even got to the engineers at Tire & Rim Association and based on their answers it was obvious they had not thought about ST type tires or the unique nature of RV application so acted a little surprised when I identified the engineering analysis that indicated that the current loads too high for many trailers and that the load capacity should be decreased by 15% or more.

Anyway here is the bottom line.

For Goodyear Marathon tires only:
There is a Tech bulletin PSB#2011-13 that uses information from TRA (blind leading the unknowing in my opinion but they are the ones that have to stand behind their warranty).
The tech bulletin says that the normal max speed for Marathon ST type tires is 65 mph. This speed can be increased up to 75 only if the inflation pressure is increased by 10 psi.
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 they had not identified any other tire manufacturer willing to make such a change.
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Old 10-23-2013, 03:37 PM   #2
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Thanks for the info and taking the time to track it down.
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Old 10-23-2013, 03:45 PM   #3
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Any chance you can track down/confirm this response from Maxxis?

http://www.forestriverforums.com/for...tml#post419781
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Old 10-23-2013, 03:57 PM   #4
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Any chance you can track down/confirm this response from Maxxis?

http://www.forestriverforums.com/for...tml#post419781
Check this

http://www.maxxis.com/Repository/Files/m8008load.pdf
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Old 10-23-2013, 04:03 PM   #5
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Yeah, I've seen that. But wmtire somehow emailed them directly and got the more lengthy response indicating similar to good year- with a air pressure increase, you can increase the speed. I wasn't sure if Tireman could confirm that same response.

Not that I have a pressing need to go over 65mph. I'm almost exclusively a 62mph cruise control kind of guy. Just curious.
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Old 10-24-2013, 05:19 AM   #6
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The max is "up to" 10 PSI over the "pressure required for the actual tire load" taken from the charts.

If the tire is already at its max load at its max sidewall pressure, no further increase in pressure is allowed and speed rating is then 65 MPH.
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Old 10-24-2013, 06:29 AM   #7
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If you want too really get (Confused) set your (Cold Max Air Pressure) early in the AM. Now travel with the SUN on one side for a period of time.Now look at your (TPMS)! Should we stop and release some PSI on the Sunny side? or turn around and drive the otherway until the PSI is the same in all Tires? Stop and park in the shade? Now OnStar gives a alert that the Truck tires are (Low PSI) on one side also! There is (Air) in the truck tires,and (Nitrogen) in the trailer tires? What a Dilemma! Youroo!!
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Old 10-24-2013, 07:15 AM   #8
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If you want too really get (Confused) set your (Cold Max Air Pressure) early in the AM. Now travel with the SUN on one side for a period of time.Now look at your (TPMS)! Should we stop and release some PSI on the Sunny side? or turn around and drive the otherway until the PSI is the same in all Tires? Stop and park in the shade? Now OnStar gives a alert that the Truck tires are (Low PSI) on one side also! There is (Air) in the truck tires,and (Nitrogen) in the trailer tires? What a Dilemma! Youroo!!
The first time our "over pressure" alarm went off on our way from Daytona to Orlando in Jul 12, it scared the cra- out of us. Couldn't read the little icon on the monitor, so luckily we were at the entrance to a rest area and pulled in. Did the normal, walk the dog, rest room visits, etc and in the 15 minutes or so time, the tires cooled off and the alarm went off. Finally found the manual and verified it was a high pressure alarm. Sat for another 15 -20 minutes and then took off. Pressure had gone down about 2# and stayed there. The outside temp increased, but the tire pressure stayed constant. 2nd time was coming home from FL in Mar and we just pulled into the first rest area and took a break. Now, when the pressure gets close, we just take a break and let the tires cool. What's funny is once they cool, they seem to stabilize on pressure. Always start off with 65# cold.
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Old 10-24-2013, 07:42 AM   #9
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...
If the tire is already at its max load at its max sidewall pressure, no further increase in pressure is allowed and speed rating is then 65 MPH.
I don't think we know that for sure based on earlier posts. That is the big question.
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Old 10-24-2013, 08:03 AM   #10
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I don't think we know that for sure based on earlier posts. That is the big question.
I think what Herk posted is pretty clear. If at max load, max cold pressure, max speed is 65, no ifs, buts or ?
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Old 10-24-2013, 08:07 AM   #11
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Originally Posted by herk7769 View Post
The max is "up to" 10 PSI over the "pressure required for the actual tire load" taken from the charts.

If the tire is already at its max load at its max sidewall pressure, no further increase in pressure is allowed and speed rating is then 65 MPH.
Herk by what you just said. If my load inflation by the GYC is 55 Lbs. act/tire load and I run them at 65 max PSI which my rims are rated for, I can run up to the speed of 75mph if I wanted to. Did I understand you correctly? I'm quite sure how that is breaking news from the tirerman, that has been published for over a year in there specks. They have said that before and it was discussed somewhere on this forum.
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Old 10-24-2013, 08:10 AM   #12
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Herk by what you just said. If my load inflation by the GYC is 55 Lbs. and I run them at 65 max PSI I can run up to the speed of 75mph if I wanted to. Did I understand you correctly?
Yes according to the bulletin from Goodyear/Tire Rack- so long as the maximum cold pressure of the tire and wheel are capable of 65 psi.
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Old 10-24-2013, 08:13 AM   #13
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Herk by what you just said. If my load inflation by the GYC is 55 Lbs. act/tire load and I run them at 65 max PSI which my rims are rated for, I can run up to the speed of 75mph if I wanted to. Did I understand you correctly?
You're safe Glenn, that old FoMoCo won't run 75mph!
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Old 10-24-2013, 08:24 AM   #14
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Is there an easy way of finding what your rims are rated for, I can't imagine that say 14 inch tires that run at a recommended 50psi would not have a safety margin less than 50%.
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Old 10-24-2013, 08:24 AM   #15
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I think what Herk posted is pretty clear. If at max load, max cold pressure, max speed is 65, no ifs, buts or ?
I agree that what Herk posted is "clear". That doesn't mean that it's in agreement with the facts.

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Originally Posted by ependydad View Post
Yes according to the bulletin from Goodyear/Tire Rack- so long as the maximum cold pressure of the tire and wheel are capable of 65 psi.
No actually, that is NOT what the bulletin says. It says:
"Do not exceed the maximum pressure for the wheel."

No where in there does it say anything about Max cold pressure for the tire.
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Old 10-24-2013, 08:31 AM   #16
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I agree that what Herk posted is "clear". That doesn't mean that it's in agreement with the facts.



No actually, that is NOT what the bulletin says. It says:
"Do not exceed the maximum pressure for the wheel."

No where in there does it say anything about Max cold pressure for the tire.
Max pressure stamped on the sidewall is Max Cold Pressure.
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Old 10-24-2013, 08:31 AM   #17
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You're safe Glenn, that old FoMoCo won't run 75mph!
Thanks your right my Fix Or Repair Daily will not hit that speed. My point is that why wouldn't I keep and run at the rated CPR instead of the inflaton charts. That is why I do not. Also that is why it is better to move up to D rated instead of them boarder rated C that came with the trailer. As long as your rim can hold them and rated for that pressure. They had that out like I said over a year ago when I bought my tires. That is also listed on GY inflation chart. I guess this debate kept me busy for awhile atleast.
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Old 10-24-2013, 08:48 AM   #18
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Is there an easy way of finding what your rims are rated for, I can't imagine that say 14 inch tires that run at a recommended 50psi would not have a safety margin less than 50%.
Yes there is, It is by the spokes in your rim, I think that e trailer has a chart it shows. I know that 5 spoke is rated at 65 psi and I thought that 6 spoke is 80 do not quote me on that but it will show you different style rims compared to the psi of each. I think it was posted last week. Might have been Ependydad that posted that. I think I also found it at the rim manufacturer site on google.
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Old 10-24-2013, 08:59 AM   #19
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Max pressure stamped on the sidewall is Max Cold Pressure.
In this post: http://www.forestriverforums.com/for...tml#post482582
Tireman9 himself says that while he thinks that's the case, he was going to setup a meeting with some industry folks to get a definitive answer.

I had thought that this "Breaking News" thread was to give the results of that meeting, but from what I see, all he's done is to reference the original bulletin which is still unclear on this point.

Note that in the post immediately preceding the one I referenced above, jadatis reports confirmation that it is ok to exceed "max cold" by 10psi (although I read what he referenced and don't see it myself).
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Old 10-25-2013, 10:11 AM   #20
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Any chance you can track down/confirm this response from Maxxis?

http://www.forestriverforums.com/for...tml#post419781

I am not real comfortable with replies from customer support people. Usually they are not engineers and have standard answers for standard questions.

In my communication with Tire Rack I find it interesting that so far they (TireRack) have not been able to get an official company reply to this +10psi = 75 mph question.
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