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Old 04-23-2016, 02:52 PM   #1
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Tire pressure

on my 2016 Ford F350 superduty dually with Goodyear LT 245/75R/17E tires.

The Door sticker says 75 front 65 rear cold.

Tires say 80 PSI cold.

Pardon my ignorance, but which one do I go by.

I will be towing a heavy fifth wheel trailer.

I questioned this at the dealer and one of the mechanic's in the shop said the 75/ 65 was just going down the road , no towing PSI. I think that is B/S, but then again I do not know for sure.
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Old 04-23-2016, 03:08 PM   #2
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What does the door sticker say you can haul (axle or tire rates) with those tire pressures?
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Old 04-23-2016, 03:31 PM   #3
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Quote:
Originally Posted by 1bigmess View Post
What does the door sticker say you can haul (axle or tire rates) with those tire pressures?
Front GAWR 5940
Rear GAWR 9650
GVRW 14000
Occupants and cargo 5488.

I understand all the numbers, I just do not know why there is a difference as stated in my original post. Is it because it is a dually?
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Old 04-23-2016, 03:49 PM   #4
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Tires have a max weight carrying capacity at a cold tire pressure.

The axles have a rated carrying capacity despite the tires weight carrying capacity.

Don't exceed the lower number of the two components. Your tires might be able to carry more weight in a dual configuration than the axle can carry. I don't think exceeding the rated capacity of either component is a good thing to do.

You might know all this stuff already. Other maybe not. I would use the door sticker as a minimum inflation pressure, and the sidewall as the max. The difference might have to do with the axle capacity being lower than the tire capacity.

You might find more info on RV Tire Safety
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Old 04-23-2016, 04:07 PM   #5
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Originally Posted by 1bigmess View Post
Tires have a max weight carrying capacity at a cold tire pressure.

The axles have a rated carrying capacity despite the tires weight carrying capacity.

Don't exceed the lower number of the two components. Your tires might be able to carry more weight in a dual configuration than the axle can carry. I don't think exceeding the rated capacity of either component is a good thing to do.

You might know all this stuff already. Other maybe not. I would use the door sticker as a minimum inflation pressure, and the sidewall as the max. The difference might have to do with the axle capacity being lower than the tire capacity.

You might find more info on RV Tire Safety
Thanks ,but that still does not address why the two numbers are different! In my dealings over the many years of towing, this is a first for me. Perhaps i wonder too much, does anyone know?

Yes, I will more than likely use the 80 PSI when towing.
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Old 04-23-2016, 04:15 PM   #6
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If you know the safety side of towing and weight capacities, then you are just curious, and I know what that's like. I'm sorry I couldn't provide the answer you were looking for or explain it so it was understood. I am also very curious about how things work and why there are differences, but I just stick with maximum inflation and drive carefully. I know what my weights are, so I'm looking to tip the scales more towards economy once I know that safety is covered. Max inflation helps reduce rolling resistance, but also makes for a slightly harsher ride, but I can live with that.
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Old 04-23-2016, 04:28 PM   #7
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Originally Posted by 1bigmess View Post
If you know the safety side of towing and weight capacities, then you are just curious, and I know what that's like. I'm sorry I couldn't provide the answer you were looking for or explain it so it was understood. I am also very curious about how things work and why there are differences, but I just stick with maximum inflation and drive carefully. I know what my weights are, so I'm looking to tip the scales more towards economy once I know that safety is covered. Max inflation helps reduce rolling resistance, but also makes for a slightly harsher ride, but I can live with that.
Thats good my friend, and yes i am curious, thanks for your response. Perhaps someone knows the answer.
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Old 04-23-2016, 04:51 PM   #8
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Your truck’s manufacturer builds it to his specifications and in accordance with federal safety regulations. The axle capacities (GAWR) will have a load capacity above the trucks maximum load capacity (GVWR). Tires must meet the requirement of the axles maximum load capacity with a percentage of load capacity reserves. Some trucks will have recommended tire inflation pressures in the truck’s owner’s manual that will be higher when hauling trailers. Most dually trucks will just have tire inflations for all conditions.

The inflation pressure found on the tire sidewall is the minimum pressure needed to carry the maximum load of the tire, also listed on it’s sidewall.

The strength of your tires is provided by the actual cold inflation pressure. Because of the way tires, wheels and axles are fitted to your truck the maximum load capacity is not needed and the manufacturer has set the recommended tire inflation pressures to a value that will carry the truck’s heaviest load with some left over for reserve load capacity protection for the tires.
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Old 04-23-2016, 07:01 PM   #9
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Quote:
Originally Posted by porchdog2 View Post
on my 2016 Ford F350 superduty dually with Goodyear LT 245/75R/17E tires.

The Door sticker says 75 front 65 rear cold.

Tires say 80 PSI cold.

Pardon my ignorance, but which one do I go by.
Neither one. The 80 PSI is the max. The max of 80 PSI is the max, period. But you rearly need anywhere close to 80 PSI on the rear tires.

The door sticker inflation pressures assumes your truck will be loaded, including hitch weight, to the GVWR of the truck. But when not towing or not hauling heavy, you need to reduce the tire pressure to match the closer to the actual weight on the tires.

You go by the tire and rim assn (TRA) load/inflation table for your exact tire size and specs.

Quote:
I will be towing a heavy fifth wheel trailer.
So assuming you have enough brains to not exceed the GVWR of your dually, then when loaded with the hitch weight of a heavy 5er, you'll probably need close to the 75 front 65 rear cold on the door sticker.

Quote:
I questioned this at the dealer and one of the mechanic's in the shop said the 75/ 65 was just going down the road , no towing PSI. I think that is B/S, but then again I do not know for sure.
I know for sure, and with a little bit of knowledge you'll know for sure too.

The TRA engineers determine the specs for all tires sold in the USA. They publish an annual report that includes specs required for all those different sizes and specs of tires. But you must be a member to receive that report, and membership is extremely expensive. So generally only tire companies (rubber manufacturers) and government agencies are members. And because the load/inflation tables are somewhat difficult to interpret properly, most tire companies no longer make the tire/inflation tables available to their customers - because of lawsuits and such.

So you probably won't find a recent load/inflatable for car and light truck tires from Goodyear, BFGoodrich, Firestone/Bridgestone or Michelin, and a few other rubber manufacturers. Yeah, they're available for the "commercial" tires on big trucks, but not for pickups and cars. I guess they think truck drivers are a lot smarter than us RVers.

But if you hurry, you can still get a recent load/inflation table made available by Toyo tires. The name on the tire doesn't matter, so you can use that Toyo table for any brand of tire.

To use the table, you must weigh the rig on a truck scale so you know exactly how much weight the tires have to handle on each axle. Then divide the weight of each axle by the number of tires on that axle, then apply the load/inflation table to that weight.

Weigh the rig at least twice.

Once when loaded for bear with the 5er loaded and everybody and everything in the truck, including a full tank of fuel, all the tools and jacks and junk you haul when towing. Use that scale ticket to determine the load/inflation of the tires on each axle.

Then weigh it again, but this time without the trailer and with only the minimum junk in the truck that is always there when you are driving unloaded.

Determine your correct inflation pressure under both conditions, and maybe write them down so you won't forget them.

Note that your dually rear axle will have a different load/inflation table than the same tire on a single axle.

Okay, here's the link to that load/inflation table:


https://toyotires2-1524598101.netdna...s_20151020.pdf
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Old 04-24-2016, 02:34 PM   #10
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Your tires I googled and found Loadindex 121/118 for Q speedrated .
This is maxload single ( yours front) of '3200 lbs and Dual ( yours rear) of 2900 lbs. This AT 80 psi because of E-load.
If I fill this in my motorhome calculator it gives for the GAWR's with no reserve a pressure of Front 74 psi and Rear 66 psi, but this is calculated with a more pessimistic formula , but is about the advice the carmaker gives.
If I set my calculator to standard then it adds 5% to the GAWR Front and even 13% to the GAWR Rear to cover overloading and unequall loading R/L.
Then it gives Front 79 psi and Rear 75 psi. This is highest advice with still acceptable comfort and gripp.
With this maximum reserve for things like , pressure loss in time, unequall loading R/L , misreadings of pressure and misyudging of loads.

If you ever weigh it might prove your weights to be lower so lower pressure is possible. The Heavyer Motorhomes in America are not that soon overloaded , so lower pressure might be save for the tires too.

Hope my calculations gives you a handle , to yudge these differences.
Often tires can barely carry the GAWR rear together, but in this case the motorhome-maker gave them a comfortable reserve.
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Old 05-10-2016, 10:24 PM   #11
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I strongly believe that the pressures on the door decal represent the required tire inflation to carry the maximum weight your truck is rated for. Your rear tires, if 80 psi, is your max pressure on the tire is a 10pr tire.

That said, being a dually, doesn't require 80 psi to carry your trucks max rated weight. Used to be, the mfg. gave "reduced" pressure for driving empty but am sure that through the years people didn't understand the difference and hauled to max capacity with the empty pressures and had tire failures. Lawsuits i'm sure, especially after the Ford and Firestone fiasco. For the most part, it was Fords fault for not requiring a high enough pressure in the tire to carry the vehicles maximum hauling weight. To sum it up, the pressures called for are for your vehicles "maximum" hauling capability.
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Old 05-10-2016, 10:52 PM   #12
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I agree with the door sticker, but my truck gets noticeably better fuel mileage, and tracks better, when the front tires are at 75-80 PSI instead of the door sticker 65.

This might change after I replace the Les Schwab tires with Michelins.
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Old 05-11-2016, 01:25 PM   #13
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http://octopup.org/img/car/tires/Rub...ruck-Tires.pdf
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Old 05-11-2016, 04:59 PM   #14
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Mostly correct but not 100%

Quote:
Originally Posted by SmokeyWren View Post
Neither one. The 80 PSI is the max. The max of 80 PSI is the max, period. But you rearly need anywhere close to 80 PSI on the rear tires.

The door sticker inflation pressures assumes your truck will be loaded, including hitch weight, to the GVWR of the truck. But when not towing or not hauling heavy, you need to reduce the tire pressure to match the closer to the actual weight on the tires.

You go by the tire and rim assn (TRA) load/inflation table for your exact tire size and specs.

So assuming you have enough brains to not exceed the GVWR of your dually, then when loaded with the hitch weight of a heavy 5er, you'll probably need close to the 75 front 65 rear cold on the door sticker.

I know for sure, and with a little bit of knowledge you'll know for sure too.

The TRA engineers determine the specs for all tires sold in the USA. They publish an annual report that includes specs required for all those different sizes and specs of tires. But you must be a member to receive that report, and membership is extremely expensive. So generally only tire companies (rubber manufacturers) and government agencies are members. And because the load/inflation tables are somewhat difficult to interpret properly, most tire companies no longer make the tire/inflation tables available to their customers - because of lawsuits and such.

So you probably won't find a recent load/inflatable for car and light truck tires from Goodyear, BFGoodrich, Firestone/Bridgestone or Michelin, and a few other rubber manufacturers. Yeah, they're available for the "commercial" tires on big trucks, but not for pickups and cars. I guess they think truck drivers are a lot smarter than us RVers.

But if you hurry, you can still get a recent load/inflation table made available by Toyo tires. The name on the tire doesn't matter, so you can use that Toyo table for any brand of tire.

To use the table, you must weigh the rig on a truck scale so you know exactly how much weight the tires have to handle on each axle. Then divide the weight of each axle by the number of tires on that axle, then apply the load/inflation table to that weight.

Weigh the rig at least twice.

Once when loaded for bear with the 5er loaded and everybody and everything in the truck, including a full tank of fuel, all the tools and jacks and junk you haul when towing. Use that scale ticket to determine the load/inflation of the tires on each axle.

Then weigh it again, but this time without the trailer and with only the minimum junk in the truck that is always there when you are driving unloaded.

Determine your correct inflation pressure under both conditions, and maybe write them down so you won't forget them.

Note that your dually rear axle will have a different load/inflation table than the same tire on a single axle.

Okay, here's the link to that load/inflation table:


https://toyotires2-1524598101.netdna...s_20151020.pdf
Load & Inflation tables are available for the major tire companies. Here is link to Michelin RV applications.
If you have ST type tires MAXXIS has a nice chart.

While it is true that TRA publishes a "Yearbook" about the only difference year to year is the addition of new sizes. Older sizes simply do not change in either dimension or load/inflation capacity. Having said that, and agreeing that you can use just about any company chart, there is an exception and that is Michelin. They do have some tires that are slightly (a few %) different that what appears to be the same size from another company. I suggest that if you run Michelin to be sure to follow Michelin chart. If some other company then jsut about any chart is probably OK.

An important clarification on "Max" inflation. In all cases the inflation pressure that is being covered in when the tires are not warmed up from either running or from sitting in sunlight. The inflation on the tire sidewall is actually the Minimum inflation needed to support the stated Maximum load.
I have a blog post just on the topic of "Minimum & Maximum"

Now to what I think is the original question.
tire placard (sticker on door jam) inflations are the minimum cold inflation needed to support the stated GAWR (max for that axle). This is assigned by the vehicle mfg as they have the legal responsibility to inform the customer (you) and to set the pressure needed to carry the load.

Tire sidewall load is the max the tire can carry. For a given tire size this is a fixed number and there is no way for the tire company to know what vehicle any specific tire is going to go on.

When replacing tires you should ALWAYS select a tire with equal or greater load carry capacity than the capacity of the OE tires.

You should get your RV weighed to ensure you8 are not exceeding the max rating for the tires or the axle. It is a sad but established face that a majority of RVs on the road have one or more tire and/or axle in overload.

RV companies tend to select the MINIMUM size/cost tire that will support the stated load for the RV. There is seldom a margin of reserve (excess capacity) load.

Hope this clears up some of the questions and misunderstandings of various regulations posted in this thread. My blog probably can answer any other questions you have on tires in RV application.
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