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Old 04-14-2016, 04:03 PM   #31
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Originally Posted by hbillsmith View Post
Nice thread. Here's where I'm thinking. My Maxxis 8008 call for 80psi cold pressure on their chart that indicates an 'E' rating (65mph) requires 80psi cold. Lower psi, reduces the ratings down to D or C and the resulting load carry ability.

Maxxis Load Inflation Chart

If I'm to accept that the maximum PSI should not exceed 25% of 80psi, then my maximum should not go over 100psi. So if I'm in Texas and the RV is parked outside on hot pavement, the cold-pressure is going to be at a good start point and I'm probably OK getting out on the 100+ interstate.

But if the 5er is parked in a shaded storage bin or maybe for a couple of weeks camping on grass or gravel, the starting 80psi cold will be unusually cold for the hot Interstate I'm about to get out on. In these cases, I will drop the starting cold temp to 70psi and watch it grow as I continue out on the Interstates. This works for me and when the ambient temp outside is 99deg to 103deg, I'll see my TST tire temps go up to about 98deg to 100deg.

Haven't hauled across the Mojave desert yet but if I ever see those towing temps go over 100, I think I'll let some air out.
Again here the link to Maxis ST tires, wich to my conclusions is dangerous.
Goodyear also has such a list for ST tires.
I base this conclusion on the fact that ST tires are calculated in their maximum load for max speed of 65 m/h so more deflection and heatproduction a cycle allowed.
This brings it to the edges of damage , and no reserve.

Second is that they calculate these Radial tires in ST , with a formula that was introduced in 1928 for diagonal tires ( to get sciencetific using 0,585 power in the universal formula instead of 0.8 power in Europe used for all kind of tires). This leads in the lower pressures to higher loadcapacity's , then you would calculate with saver 0.8 power. so more deflection then the deflection for maximum load AT maxloadpressure.
This deflection is for ST tires already on the edges , so more deflection will give damage to tires.

This together with misyudging of weight and Unbalance R/L kills the tires in short time.
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Old 04-14-2016, 05:20 PM   #32
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DavidG, I think what's most important is using the TPMS regularly and recognizing patterns in changes. I knew I had tire issues before major symptoms showed up because I could see that one tire had a higher pressure than the others (not sure why- but it was an anomaly vs. the other 9).

Overtime, I also know to expect a certain PSI increase or temperature increase. If something doesn't follow the pre-established patterns, I'm going to pull over and investigate (as well as I can).

Personally, I wouldn't adjust my cold pressure in the morning based on geographic area and/or weather. Make sure they're topped up and roll. I then watch for anomalies in individual tires and/or extreme changes overall.

Good for you for being aware.
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Old 04-14-2016, 05:21 PM   #33
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I knew I had tire issues before major symptoms showed up because I could see that one tire had a higher pressure than the others (not sure why- but it was an anomaly vs. the other 9).
But, for the love of God- don't ignore it and think you'll limp to 2 different campgrounds... ( )
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Old 04-14-2016, 05:57 PM   #34
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Yep Ependy, your post is the conclusion I have come to. The process has been interesting to say the least, and I've learned a few things along the way, and I hope others reading the thread may have picked up a nugget or two as well.

But keeping an eye out for that one tire that changes in relation to the others seems to be the key. I read one of your other posts on the TST system. I didn't realize that the internal battery would last that long. That's also good to know.

Thanks
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Old 04-14-2016, 07:40 PM   #35
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Looks like the Maxxis 8008's are now stamped according to the new rules and their current trailer tire is "Q" rated (confirmed with Maxxis). Load Index is 119 to 123 or 3,000# to 3420#. Speed Q is 100mph maximum. PSI is 80#. Of course non of this matters if the Tire is sold as an ST (Special Tire). The rules for ST still cap the mph at 65mph.

Here's a dealer web page that so indicates:

235/80-16 MAXXIS M8008 RADIAL TRAILER 123/119Q BSW

Wikipedia Tire Code Explanations
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Old 04-14-2016, 08:25 PM   #36
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Interesting thread. All of the tire failures I have ever had were due to overloading and under inflation. Since paying close attention to proper tire specs, inflation and maintenance, I haven't had any issues. I have always understood that cold inflation referred to ambient temp. I don't run tire monitors (except those included with the TV) and inspect the tires when we stop for uneven wear or blisters. I also don't run faster than 65 and when we stop, I touch each tire. Normally, they are slightly warm to the touch. It is perfectly normal to see pressures increase while towing for reasons already stated. Just make sure they are properly inflated each and every morning and you will head off potential issues along the way.
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Old 04-14-2016, 09:42 PM   #37
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Tireman, based on a lot of information gleaned from this thread and others, I will just run the tires at max cold inf pressure. I plan to stop at a cat scale one day soon and at least get axle weight data. Would love to get individual tire weights, but that type of scale doesn't exist anywhere close.

For worksheet on how to calculate tire loads and some suggestions on how to locate scales check Fifthwheel site
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Old 04-20-2016, 10:16 PM   #38
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Originally Posted by hbillsmith View Post
Looks like the Maxxis 8008's are now stamped according to the new rules and their current trailer tire is "Q" rated (confirmed with Maxxis). Load Index is 119 to 123 or 3,000# to 3420#. Speed Q is 100mph maximum. PSI is 80#. Of course non of this matters if the Tire is sold as an ST (Special Tire). The rules for ST still cap the mph at 65mph.

Bill, I don't think that's exactly right. I copied and pasted an email I received from Maxxis about that exact question for the 8008 tires that I purchased. They allow for higher speed rating as long as the tire load is appropriate to that higher speed. So for example; if the Maxxis load inflation chart says that for a given load, the tires should be at 60 psi, then I can inflate them to 70 psi and run 75 mph. They even allow for 85 mph if the load inflation chart number is reduced another 10%. Now, in no way do i suggest that anyone run 75 mph or 85 mph with these tires, but that's how I read their email.

If I'm missing something, someone explain it to me in a way that agrees with the email I received from them.

Here it is;
David,
The Maxxis M8008 ST Radial is "Q" speed rated. However, 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. 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%.
We hope this information is helpful. Thanks for your inquiry and interest in Maxxis Tires.
Best Regards,
Your Maxxis Support Team
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Old 04-21-2016, 10:29 AM   #39
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Originally Posted by Davidg View Post
Here it is;
David,
The Maxxis M8008 ST Radial is "Q" speed rated. However, 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. 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%.
We hope this information is helpful. Thanks for your inquiry and interest in Maxxis Tires.
Best Regards,
Your Maxxis Support Team
Its the 75mph adj that is confusing. The 8008 (16" with Hispec wheels) have a max of 80psi and provide load of 3420. Since you cannot exceed 80psi, I was told a decrease of load by 10% was the acceptable safe alternate. So the 3420 max is reduced to 3078. Thus 4 tires with trailer weight evenly distributed would allow 13,680 trailer weight. A CAT weighing is required since some of the trailer GVW lies in the tongue carried by the truck payload.

I would never run the 8008 at cold 90psi. I do however run an ultralight 5er whose max loaded CAT weight is typically around 10000. On a straight, smooth surface, 4 lane, low traffic, in good weather, in daylight highway (think many portions of I-10 far west) while my tires are new in age and mileage, I do run at 75mph.

EDIT: Escapees does individual weighings at each wheel for those of us that cant seem to figure out a load balance.
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Old 04-21-2016, 10:58 AM   #40
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all good info . i set my tires at max 80 psi and expect psi to rise as temp rises . this is built into the tire specs . which is why they want you to cold inflate tires .
one thing missed is elevation change . from MO to the middle of Kansas psi rise of about 2 psi cold . from the middle of Kansas to Denver you can experience another 2 to 4 psi increase cold . From denver on up another couple or more psi increase . this is on top of temp caused psi increase .
I will set my psi at 78 cold in denver and when up to 8000 ++ it will be at 80++ so very important to check the psi when traveling at altitude Daily
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