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Old 03-18-2015, 01:33 PM   #1
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Question New tires on TV ? on tire pressure

Just had new Michelin M+S Lt275/65/R18 tires on my 2013 Ford F150 4x4 crew cab. Will be towing a 2015 FC twin. My question is what is the appropriate air pressure in the truck tires? The side wall says max load 80psi, the Ford dealer says 40psi is what most people use and the data on the truck says 35psi.

I previously owned a motor home and there was a scale for tire inflation based on over the axile weights.

40psi compared to 80psi would be 50% difference. Is there a happy medium or do you all change the pressure when towing to higher and lower it for everyday driving not towing?

appreciate the help
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Old 03-18-2015, 01:47 PM   #2
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What load range are your new tires? I'm guessing that they are E's based upon the the max psi on the tire is 80. We have Michelin E's on both our tow vehicles. We run 80 rear 70 front.

If the person at the dealership who told you to use 40 psi is a salesman, there is a fair chance that he doesn't know what he is talking about.

As far what it says on the door of the truck, it applies only to the OEM tires. On a Ford 150, it very likely came with load range C tires. Hence, the 35 psi.

Brian
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Old 03-18-2015, 02:05 PM   #3
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40psi is not enough pressure when towing, but would be fine when not.

The more pressure you run in the TV tires when towing, the more stability you have unless you go too high in the front for the load. If you go too high in the front, the TV will exhibit oversteer, and if too low, understeer, or sluggishness.

It's best to weigh the rig when hitched and ready to travel to see how much weight is actually on each axle to determine the pressure needed.
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Old 03-18-2015, 02:44 PM   #4
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Unless you have a tire pressure load chart that came with your tires you can't be sure what load is for each range of pressure. I would go with the recommendations that Brian made. If 80psi is too hash of a ride reduce the pressure at little. At 80 psi you have 3415lbs load on each tire according to Michelin.

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Old 03-18-2015, 05:48 PM   #5
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See previous post on using driveway dust to view contact patch and determine proper tire inflation pressure:

http://www.airforums.com/forums/f463...ml#post1278419

Note: This method only applies to tow vehicle tires. Our Airstream tires are inflated to the "maximum pressure" printed on sidewalls, which is 80 psi.
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Old 03-18-2015, 06:00 PM   #6
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I don't like to get beat up. I start with the air pressure on the door frame. If the handling is spongy, pressure can always be increased.
I would have purchased load range C tires as they were the original equipment load rating for the vehicle.
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Old 03-19-2015, 12:19 PM   #7
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1) While towing, we run 80 in rears and 70 in fronts of TV...side wall=80psi. ( confirmed by experienced dealership)
2) When not towing, revert to recommendations on driver's side door label 0f TV..
3) On our AS..we run 80 cold, ( of course, as all of above) on Michelins: side wall = 80.
4) Propride Hitch. Evaluate front axle hitched and unhitched! WD hitch a must for stability.
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Old 03-19-2015, 01:23 PM   #8
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Tire pressure guides

Escapees provides links for the manufacturers inflation pressures based on the weight the tire (or axle) is expected to carry.
https://www.escapees.com/SmartWeigh/TireInfo.aspx
To utilize this you need a fairly accurate read on individual tire or axle weights.

Based on the sidewall max PSI, I had been running our Michelins at 80 PSI, but discovered I could run 65 PSI and still have a 10% margin over actual fully loaded weights. The ride difference is like night and day.
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Old 03-19-2015, 02:03 PM   #9
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With the TT hooked up and loaded get BOTH the TV & TT on a set of scales and learn the FACTS on the actual load on each axle.
While at the scale un-hook the TT and get the "empty axle loads on the TV.

Do the math to learn the MINIMUM inflation needed to carry the actual tire loads.
I would add at least 10% to the loaded and unloaded inflation pressure to be run.
Confirm that when the TT tires are at the tire sidewall pressure the actual load is at least 15% below the tire capacity. Multi-axle trailers should always run the pressure on the tire sidewall to lower Interply shear (force trying to tear the tire apart)
You can Google RV tire Interply Shear if you want the technical stuff.

You will probably find a significant difference for the TV inflations loaded vs unloaded. If you drop the pressure when not towing just be sure to re-inflate them when hooking up or you are just asking for future tire problems.

Remember all the pressures are "Cold" inflation which means not in Sun or not driven on for at least 2 hours with 3 hours better. Use a good digital pressure gauge. Get a TPMS for the TT so you learn when there is a puncture not 10 miles later when someone flags you down to point out your holding tank was destroyed when the tire let go.
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Old 03-19-2015, 02:36 PM   #10
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RMA chart

I follow the Rubber Manufacturers' Association charts for psi for each size of tire. I weigh each axle of the tow vehicle, and use the psi listed in the chart. For a 3/4 ton diesel Ram towing a 5400 pound Excella, the charts say 55 psi on all four wheels, and pressure reduced to 45 on the rears when not towing. That's worked well for 15 years, and the tires wear evenly across the tread. The RMA chart is reproduced here:
Tire info for M37
I use the bottom table LT-1R (single) for radial tires.
Nick.
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Old 03-19-2015, 04:11 PM   #11
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A thin line between what the EPA wants us to run and what;s good for the truck.. My Dodge just hammers the humans,, and the shocks pumped over 60psi..

Same tires your running and not towing I have found 40psi a happy balance between breaking teeth off and gas mileage. Towing I bump up the rear;s to 60psi,, on the rear only..

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Old 03-19-2015, 08:46 PM   #12
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Michelin Load E .....75 frt 80 rear when towing, 70 all around solo.

Bob
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Old 03-23-2015, 09:43 AM   #13
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Quote:
Originally Posted by nickcrowhurst View Post
I follow the Rubber Manufacturers' Association charts for psi for each size of tire. I weigh each axle of the tow vehicle, and use the psi listed in the chart. For a 3/4 ton diesel Ram towing a 5400 pound Excella, the charts say 55 psi on all four wheels, and pressure reduced to 45 on the rears when not towing. That's worked well for 15 years, and the tires wear evenly across the tread. The RMA chart is reproduced here:
Tire info for M37
I use the bottom table LT-1R (single) for radial tires.
Nick.
Couple of comments.
The tables are fro Tire & rim Association yearbook not Rubber Manufacturers Association but this is minor point.
Also not sure if those are relatively current tables or not.

Second the tables shown only apply to the specific tire sizes shown and the numbers should not be used unless you have the specific size and Load Range shown. Most tire companies publish Load/Inflation tables for the tires they sell and occasionally there are some minor differences or some additional information (speed restrictions or other) that might apply to your specific application.
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Old 03-23-2015, 10:02 AM   #14
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[QUOTE=Tireman9;1597372]Couple of comments.
The tables are fro Tire & rim Association yearbook not Rubber Manufacturers Association but this is minor point.
QUOTE]

You will note that I carefully said that "The RMA chart is reproduced here:"
I have the original RMA table, and it is identical to the earlier one from the Tire and Rim Association to which I linked.

At the top of each chart, including the one I use, table LT-1R (single) for radial tires, is the statement:

"The following chart has basic load information for various tire air pressures and vehicle speeds for radial ply tires. Always consult the tire manufacturer's specific information for the tire you have fitted for confirmation of these values."

Nick.
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