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Old 05-09-2015, 06:05 AM   #1
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E Rated LT Tire Pressure ?

Just installed LT E rated tires on the rear of my truck, Ram 1500 5.7, i was told to run them at 45# in normal street driving, and the 80# max while towing, 7,000 max loaded TT.
Opinions Please Jim

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Old 05-09-2015, 08:10 AM   #2
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The way I would do it is to weigh the truck empty and loaded. Calculate the percentage of load versus the max weight rating on the tires. Then use that percentage for calculating the tire pressure. Here is an example (simplified): Tire has a max rating of 3000 pounds weight at 80 psi. Actual weight on tire 1500 pounds. Since the tire is at 50% of weight then 50% X 80 psi = 40 psi. Use your weights for the calculation.

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Old 05-09-2015, 08:28 AM   #3
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When I swapped mine, Michelin said to run them at the pressure giving them the same weight rating as the Factory equipped tires. That turned out to be 48psi. And I shouldn't really load them any more than that weight as I would exceed the GAWR and GVWR of the truck.

But as I like a stiffer ride when towing I do add more air, up to 60-65psi, for the stability, not the weight carrying ability.
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Old 05-09-2015, 10:19 AM   #4
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You probably first had even P-tires , so then if you use original advice its to low for the full GAWR for E-loadrated tires.
A stiffer tire ( E-load ) needs more pressure for the same load then a less stif tire ( P-tire=B-load) thoug in American lists they are all placed in one Pressure/loadcapacity list for one sise.

I am able to calculate it but also need weight on the seperate wheels best, second best Axles , but in lack of that we will have to do with the GAWR's and GVWR ( Gross axle/vehicle weight rating) and empty weight and the way you load it.
The TT of 7000 lbs total weight ( GVWR ? ) gives to law minimum 10% and maximum 15% on towbar.
Unless you use a Weight distribution Hich ( WDH) then more weight is put on front wheels of Truck and TT wheels.

So this all I need to know but also maximum load and speedcode of tires, or sises so I can google for it.
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Old 05-09-2015, 10:49 AM   #5
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Wow !!!! Going to have to go back to math class on this one ????
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Old 05-09-2015, 08:41 PM   #6
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Originally Posted by rideandslide View Post
Wow !!!! Going to have to go back to math class on this one ????
Nah, the math is not that difficult. But ignore the shade-tree mechanics and use the industry standard method to determine the proper PSI for your tires.

In the USA, we have the Tire and Rim Assn (TRA). The TRA is a bunch of engineers that determine the specs for tires and wheels sold in the USA and Canada). The TRA publishes the load/inflation tables for all sizes of tires sold in the USA. They have done most of the math for you, so you just have to do enough math to apply the load/inflation table to your tires.

But the tire companies don't like to publish the TRA load/inflation tables for the sizes they sell because they don't want the liability when someone misapplies the info. So instead of telling you to apply the load/inflation table for your size tire, they beg off by telling you to follow the vehicle manufacturer's instructions. So the TRA load/inflation tables are usually available only from TRA, and you have to be a TRA member to get them. And being a TRA member is expensive.

Toyo tires to the rescue. They publish the TRA load/inflation tables, and make them available to their customers. So click on the following link and you can see them.

Tires 101: Tire Load & Inflation Tables | Toyo Tires

So here's the drill. First you must know the load (weight) on the tire. Weigh the rig on a CAT scale to get the weight on each axle. Divide that weight by the number of tires on that axle to get the weight on each tire. Then apply the load/inflation table.

Example: Load range E tires that might be mounted on a half-ton pickup could be size LT245/75R17E. Here is the load/inflation table (from the link above) for that size tire when mounted on single wheels (not duals).

PSI . Max load
---- . ----------
35 . 1770
40 . 1945
45 . 2110
50 . 2270
55 . 2430
60 . 2595
65 . 2755
70 . 2900
75 . 3050
80 . 3195

Unless you overload your pickup, you will probably never have enough weight on you rear axle to require more than 40 PSI, so maybe pump them up to 45 PSI just for grins. But don't pump them up to anywhere near the 80 PSI they can handle, else you'll wear out the center of the tire tread and the truck will ride "rough".
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 3.5L EcoBoost SuperCrew.
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Old 05-09-2015, 09:19 PM   #7
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When I pulled a trailer I always inflated the rear tires to the maximum.

That was for sway control. The firmer my rear tires were the steadier the combination was, especially when trucks passed me.

So my vote is to follow the suggestion of maximum air pressure while towing.
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Old 05-09-2015, 10:11 PM   #8
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Have to agree with those that use the tire size to load calculator. Seems that the charts are getting harder to find though. I went through that this week as I upgraded from a 10 ply ST tire to a ST F (12ply) tire. The E tire had a max pressure of 80 (3520#) and the up grade had a max pressure of 95# (3960). Also, I noticed that all tires aren't created equal. Used to be, if you had a tire of a certain size, ply rating or load rating, it was the same throughout the industry. Not now. The oem tires on the 5'er were Road Rider ST235/80R16 had a max load rating of 3520 @80 psi. Had a blow out earlier this spring and got a Hercules tire of the same size and ply. It has , as I just noticed, a max load of 3420. This surprised me. 100# isn't a lot, but as the trailer weight is running close to max for the tires, a 100 # difference isn't good. Had thought about an LT tire but from all available infro, the ST tire has a heavier sidewall that will , or should, give more stability and not flex as badly when cornering. The summer is young so it will give ample time to see how my choice works out. Can't "I hope" be worse that the tires that came on it.
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Old 05-10-2015, 08:55 AM   #9
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Use the weight/ inflation chart for your tire. Weigh your truck with and without a load. Add 5psi to what the chart says.

80psi will beat you to death.
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Old 05-10-2015, 09:28 AM   #10
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When I had my 2010 F150 I changed out the P tires for E rated Michelins. The tire guy at Discount tire told me I only needed 44psi to reach the trucks max payload. I ran 50psi when towing and aired own to 35 psi when empty. No need to run 80 psi as you'll have a rough ride and where the center of the tire out too fast.
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Old 05-10-2015, 02:11 PM   #11
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Originally Posted by SDCOToyhaul View Post
Seems that the charts are getting harder to find though.
Yeah, the big boys Goodyear, B.F.Goodrich, Firestone/Bridgestone and Michelin no longer publish load/inflation tables for their smaller tires for pickups and SUV tow vehicles. But thankfully you can still get them for both P-Series and LT tires from Toyo. The TRA tables apply to all brands of tires sold in the USA and Canada in that size, so you can use the Toyo tables for any other brand of tires.

And the TRA load/inflation tables for special trailer (ST) tires are well hidden. Perhaps because most RV trailer manufacturers mount only trailer tires that will be overloaded unless pumped up to the max PSI on the sidewall? The only place I've found them is on the Maxxis website:
Trailer Tire Load/Inflation Chart | Maxxis USA
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Old 05-11-2015, 02:25 AM   #12
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Also here there is an absolute trust in the information of the tire-makers.
But because of wrong conversing from KG and kPa to LBS and PSI, and the different curselive the different tire -organisations have put themselfes in, there has been done a lot wrong conversing wich is corrected afterward.

Worldwide tires are first calculated in maxload using kPa( 100kpa=1bar=14.5psi) and KG. Then for the about 500.000.000 costumers that still use PSI and LBS that maxload and pressure is conversed .
in that proces first KG is rounded down to LI steps, then conversed to LBS, and again rounded. Also kPa is conversed to psi and rounded. Also in pressure loadcapacity lists this is done.

Then the system of EUR ETRTO is somewhat different then USA TRA ,and more exeptions are allowed. C-load/6PR for instance has largest difference USA 50 psi and EUR 55psi, this also has lead to wrong conversions in time. Then for instance keeping maxload for 55psi and print AT 50 psi wich would overload the tire if you follow the advice list

The 3520 and 3420 that SDCOToyhaul mentiones I already saw in other topic and is because that tire is set in the market by different tire-makers for 80 psi /85psi and 90 psi . The 3520 then is originally for 85 psi and other tire maker yust combined 3520 to 80 psi.
That is why you have to search the internet for different maxload/AT-pressure combinations of same tire for same maximum speed, and always pick the lowert maxload for the same AT-pressure.

SmokeyWren gives Pressure/loadcapacity list for LT tire in wich the formula has been used for diagonal tires, also a wrong thing that you still can find on the internet.
People who do the logical calculation even do it better , and that is part of the AT-pressure is part of the load, so linear calculation , wich is even easy and quick. 40 psi gives 1945 lbs loadcapacity, linear calculation would give 40/80*3195 = 1597.5 lbs. I use my own calculation that gives slightly higher loadcapacity, and comes closest to the ever to be constructed ideal formula, laws of nature are the same around the world.

Will give picture of different calculations that are done for calculation pressure of a sertain load. If you use them best is still , even if you look in a list , to first add 10% for reserve, so if pressure drops a little , or yudging of the load is to low,etc etc, you still wont damage your tires by to much heatproduction.

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Old 05-11-2015, 04:00 AM   #13
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Consider this, you brought (E) rated tires for the extra load carrying capacity, not the ride quality. I've learned from experience using (E) rated tires on civilian type APC's, you should not run less than 65 PSI in them due to their stiffer sidewall developing early cracking because they do get hot when flexed under inflated.
I'm not claiming any of the other responses are not correct as far as load charted information, you have to start somewhere.
I would not run less than 65 PSI if I where planning for a long lasting tire, and compromise just a little on the ride. If you're operating a truck similar to the Ford F350 capacity class, you'll very seldom need to run the pressure up to the max (80) PSI. On a trailer I always use the max pressure.
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Old 05-11-2015, 04:50 AM   #14
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Thanks All

Did not realize i was opening suck a mathamatic question here's why i choose to put E rated LT tires on my 2013 Ram 1500 5.7

1. Need new rear tires
2. For the slight increase in cost, for a increase in load capacity ( not that i need it)
3. Want a more AT tread if needed.
4. Possible reduction in the slight amount of sway without buying a new anti-sway LDH

I was told by Discount Tire Direct to run them at 45 psi for normal street, and max when towing. I not much on using max ( except if i want the most sway control, any proplem in using max. pres. ) i'm thinking 70 psi while towing.

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