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Old 06-09-2016, 10:53 PM   #1
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Tire Pressure (Upgrade from Load Range D to E)

Seasoned experts - once again, an amateur with a tire pressure question.

OE tires were Load Range D and I have swapped them out with Load Range E.

Sticker on the TT states to inflate to 65 psi (cold). My question is does that still apply now that I have the L/R E tires installed? Or do I inflate to the max pressure of 80 psi annotated on the L/R E tire?

Thanks!
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Old 06-10-2016, 07:32 AM   #2
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The first thing to check is your wheels are capable of running the higher pressure.


Also, the tire manufacturer should have a curve of load capacity vs. pressure. You want at least enough pressure to maintain the load capacity of the original tires. If you want higher capacity than the original tires, you can go higher. When I went from C's to D's, I asked Kumho for that curve and never got a response. I believe the GY Marathon curve is available on their website.


Since just changing the tires without changing wheels, axles, springs, etc doesn't change the GVWR of your trailer, you have a couple options of what to do with the pressure and you'll get opinions on both sides.


I wanted a heavier, better quality tire, not a higher load carrying capacity and I liked the smooth ride we got from the torsion axles running at 50 psi with the OEM tires. So after discussing this question with the tire shop that did the switch, we kept the pressure at 50 psi per the manufacturer's sticker rather than go up to the 65 psi max on the tire sidewall. So far, very happy with that strategy.


For OEM ties, you always run max sidewall pressure to get the maximum load capacity of the tires - and that pressure will match the yellow sticker. When you upgrade the tire you can't run the max sidewall pressure and the yellow sticker pressure from the rv manufacturer because they don't match anymore and I don't think there is a clear cut answer as to which one to go with.
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Old 06-10-2016, 07:48 AM   #3
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Rule of thumb is to run Max Cold Pressure molded in tire. Running less will build up heat and possible initiate tread separation. JMO
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Old 06-10-2016, 09:08 AM   #4
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I would run the maximum (cold) pressure on the tire. You are probably ok running a little less, but I would not be concerned about the wheel at all. By buying higher load rated tires, you have bought yourself a little margin of safety. I do not see the point if you reduce load capacity by underinflation of the tires.
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Old 06-10-2016, 11:44 AM   #5
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Quote:
Originally Posted by OldCoot View Post
Rule of thumb is to run Max Cold Pressure molded in tire. Running less will build up heat and possible initiate tread separation. JMO
Not disagreeing with the case to run the max pressure - but my TPMS doesn't bear out the increased heat. With ambient temps in the low 70's, I typically see 8-12 degree rise in tire temp with the LR D's at 50. No difference from the LR C's at 50. Based on the advice of the tire shop, I stayed at 50 to preserve the ride quality. And, with an average (don't have individual wheel weights) wheel weight of 1300 fully loaded on the scale, I didn't see the need for higher pressure. At 65 psi, those LR D's are rated for 2094 lbs each.

In my case, I didn't need more load capacity. If the old LR C's were close to maximum rating, that would have been different. I just wanted that cheap OEM crap off the trailer. Got very lucky when the first one had a 360 degree tread separation with no collateral damage. The LR D tire was a better quality (I hope!!), heavier tire so I went with it.

But as long as the wheels are good to go, no reason the OP can't run the max pressure on the sidewall.
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Old 06-10-2016, 01:27 PM   #6
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My success has been running maximum cold pressure as stated on the tire wall or slightly less. Ours are rated at 80 PSI and that's where I try to keep them cold. They run cooler, keeps the shoulder away from the debris or rocks that might be where you drive. That combined with travelling at or below that maximum seed for the tire (65MPH) I believe has kept me trouble free over the years. Last year we put 14000KM on our Marathons and 1600KM of that was on the gravel Dalton Hwy in Alaska and had no flats or issues.we average about 16000KM (10000Miles) annually and I keep an eye on them and change every four years on the average.
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Old 06-10-2016, 11:10 PM   #7
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All - thanks for the sage advice!
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Old 06-11-2016, 06:29 PM   #8
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Upgraded oem tires from class C to class D. Was concerned about increased tire pressure on sidewall of Duro tires. Emailed Duro and a follow up call. Was told to get best life out of tires, run at 65 pounds on sidewall at cold temp. Only issue was tt seems to bounce a bit more on rough roads.
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Old 06-11-2016, 07:04 PM   #9
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I think that the major purpose of upgrading the tires is to build in some type of safety margin into the tire. ST tires have NO built in safety margin and I feel that is one of the major reasons that we see so many tire failures. I would recommend that you have your unit weighed ready to go camping and see what the exact weight is. Then set the tire air pressure so that you have a safety margin of 10-20% above that number via the tire inflation chart. If you run tire pressures there the tire failures will be drastically less for you.
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Old 06-13-2016, 08:57 AM   #10
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One more thing. When I was at Dunlop, I do not remember a single failure of the load test. I do not know about other tire brands, or trailer tires.

What I am saying is, tire failures are probably due to impact (potholes and sharp objects), low pressure, or excessively high speed. Or combinations of those. That is my opinion. YMMV.

I am seriously considering some kind of TPMS for my camper tires. My concern is, if I have a puncture or some other reason for low pressure, I would just keep driving because I would have no way of knowing.
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