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#4545523 - 10/16/17 08:10 PM Tire Pressure adjustment
itguy08 Offline


Registered: 09/15/11
Posts: 3150
Loc: Somewhere
Just got the new shoes for the truck installed today - Cooper Discoverer AT3. Quite the upgrade from the junk Hankook Dynapro HT's that were on there. However, have a question on determining the best inflation pressure, especially when towing our trailer.

The truck is a 2011 F150 Ecoboost with the Max Tow package and 1820 lbs of payload. It specifies a 114T tire @ 35 PSI.
We wow a 9900 lb GVWR travel trailer with probably 1100-1200 lbs of tongue weight (875 "from the factory") so we're near the max when we tow.
The Coopers are Load range 116T so I gained a little more capacity.

With the previous Hankooks I'd air up to 40 PSI all around as we found the ride too bouncy at 35 PSI. They had a max pressure of 51 PSI.

The Coopers' max is 44 PSI. So I'm wondering if it would be good to go to 40 or shoot straight to 44 PSI?

Thoughts?

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#4545541 - 10/16/17 08:31 PM Re: Tire Pressure adjustment [Re: itguy08]
Alex_V Offline


Registered: 04/10/16
Posts: 1117
Loc: Campbellsville, KY
What's the max. weight capacity of the tire?
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#4545630 - 10/16/17 09:29 PM Re: Tire Pressure adjustment [Re: itguy08]
itguy08 Offline


Registered: 09/15/11
Posts: 3150
Loc: Somewhere
2756lbs @ 44 PSI

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#4545728 - 10/17/17 12:12 AM Re: Tire Pressure adjustment [Re: itguy08]
rubberchicken Offline


Registered: 07/07/08
Posts: 399
Loc: Maryland USA
I would have to fall back and say "go with what the manufacturer specs". My 97 Suburban has 2 specs: for comfort and non-towing, use 40 in the front tires and 50 in the rear. For towing, use 50 in the front and 80 in the rear. 2500 4x4.

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#4545740 - 10/17/17 12:55 AM Re: Tire Pressure adjustment [Re: itguy08]
FZ1 Offline


Registered: 02/07/08
Posts: 4727
Loc: Texas
Try the door placard 35 psi and see how it tows. Auto tires are not supposed to be run at the max pressure on the sidewall. Tires will heat up when towing and the hot pressure will increase. You run the tires at 44 max and they will exceed the max when towing. Stay safe.

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#4545777 - 10/17/17 04:15 AM Re: Tire Pressure adjustment [Re: FZ1]
Ducked Offline


Registered: 10/25/12
Posts: 4074
Loc: Taiwan
Originally Posted By: FZ1
You run the tires at 44 max and they will exceed the max when towing. Stay safe.


I think "A tire's maximum inflation pressure is the highest "cold" inflation pressure that the tire is designed to contain", so this seems to be irrelevant. If they are designed to take that pressure cold, they'll take the corresponding hot pressure too. May not be optimal for the particular vehicle and service though.

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=196


Edited by Ducked (10/17/17 04:18 AM)

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#4545830 - 10/17/17 06:08 AM Re: Tire Pressure adjustment [Re: itguy08]
itguy08 Offline


Registered: 09/15/11
Posts: 3150
Loc: Somewhere
Problem is Ford just specifies 1 pressure. With the previous tires it was a little bouncy when hooking up the trailer. Adding some extra air not only made the tires look better but seemed to lessen the bounciness. Seems that with a large load you'd want to air them up a little bit to restore some of the shape to the tire.

I'm picking up the trailer today and they're at 35 so we'll see how it goes and up to 40 if need be.

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#4545848 - 10/17/17 06:41 AM Re: Tire Pressure adjustment [Re: itguy08]
Kuato Offline


Registered: 10/23/05
Posts: 7094
Loc: Colorado
On my F150 the rated psi on the tires is also 44; I run 42 front and 40 rear unloaded; for towing, the rear goes to 44.

Nice, even wear all around and no stability issues towing ~6000# trailer.

Tires are Michelin LTX 2.
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Thick vs Thin test: 15k / 43k miles complete

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#4545915 - 10/17/17 08:13 AM Re: Tire Pressure adjustment [Re: itguy08]
zeng Offline


Registered: 09/01/15
Posts: 2095
Loc: Malaysia
itguy08,
Is the tire you referred to of standard load rating or extra-load rating ?

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#4546102 - 10/17/17 10:50 AM Re: Tire Pressure adjustment [Re: zeng]
itguy08 Offline


Registered: 09/15/11
Posts: 3150
Loc: Somewhere
Originally Posted By: zeng
itguy08,
Is the tire you referred to of standard load rating or extra-load rating ?


Standard 116T load rating.

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#4546176 - 10/17/17 11:55 AM Re: Tire Pressure adjustment [Re: itguy08]
zeng Offline


Registered: 09/01/15
Posts: 2095
Loc: Malaysia
Originally Posted By: itguy08
Originally Posted By: zeng
itguy08,
Is the tire you referred to of standard load rating or extra-load rating ?


Standard 116T load rating.


116T tire at 32 psi carries equivalent load as 114T tire at 35 psi.

At 32 psi, you could travel upto 62 mph at designed vehicle load.
At 40 psi, you could travel upto 74 mph .
If you wish, you could go for max 44 psi with no further advantage as you are still limited to the same max load at 74 mph max.


Edited by zeng (10/17/17 11:56 AM)

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#4546344 - 10/17/17 03:12 PM Re: Tire Pressure adjustment [Re: zeng]
CapriRacer Offline


Registered: 02/22/03
Posts: 3344
Loc: Somewhere in the US
Originally Posted By: zeng
Originally Posted By: itguy08
Originally Posted By: zeng
itguy08,
Is the tire you referred to of standard load rating or extra-load rating ?


Standard 116T load rating.


116T tire at 32 psi carries equivalent load as 114T tire at 35 psi.

At 32 psi, you could travel upto 62 mph at designed vehicle load.
At 40 psi, you could travel upto 74 mph .
If you wish, you could go for max 44 psi with no further advantage as you are still limited to the same max load at 74 mph max.


Whoa, whoa, whoa!! You have to be very careful here.

First, do we know what the tire size is? (OK, I did some research and the only 2011 Ford F150's that have a 114T Service Description come with P275/65R18's.)

So I looked up the Cooper Discoverer A/T3 - and the tire is a 275/65R18 116T - NO P !! That means it is either a Eurometric or .... ah ..... Let's call it a Japanese metric.

Looking up a Eurometric 275/65R18 IN ETRTO, I find it has a Load Index of 116 - and the rated pressure on that tire is 250 kPa ~ 36 psi. At 240 kPa (~ 35 psi), the load carrying capacity is 1210 kg ~ 2668#.

Oh, and a P275/65R18 114T has a load carrying capacity of 2601# at 35 psi. (I don't know how the other value was obtained, but it is wrong.)

Those 2 values are very close and with rounding, they could be considered the same.

So use 35 psi just like the placard says.


Edited by CapriRacer (10/17/17 03:14 PM)
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CapriRacer

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#4546617 - 10/17/17 08:06 PM Re: Tire Pressure adjustment [Re: itguy08]
itguy08 Offline


Registered: 09/15/11
Posts: 3150
Loc: Somewhere
Thanks for the tips. Yes, it's the 275/65R18 116T.

I towed the camper home tonight and it did good @ 35PSI. Seemed to handle the highway and getting passed by semis just fine. But the ride did feel a little bouncy. And when I got home the tires looked like they were carrying a good load.

Still thinking of bumping to 40 for the trip - would it necessarily hurt anything?

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#4546692 - 10/17/17 09:41 PM Re: Tire Pressure adjustment [Re: itguy08]
zeng Offline


Registered: 09/01/15
Posts: 2095
Loc: Malaysia
Originally Posted By: CapriRacer
Originally Posted By: zeng
116T tire at 32 psi carries equivalent load as 114T tire at 35 psi.
At 32 psi, you could travel upto 62 mph at designed vehicle load.
At 40 psi, you could travel upto 74 mph .
If you wish, you could go for max 44 psi with no further advantage as you are still limited to the same max load at 74 mph max.

Whoa, whoa, whoa!!
Looking up a Eurometric 275/65R18 IN ETRTO, I find it has a Load Index of 116 - and the rated pressure on that tire is 250 kPa ~ 36 psi. At 240 kPa (~ 35 psi), the load carrying capacity is 1210 kg ~ 2668#.
Oh, and a P275/65R18 114T has a load carrying capacity of 2601# at 35 psi. (I don't know how the other value was obtained, but it is wrong.)
Those 2 values are very close and with rounding, they could be considered the same.


Each OEM spec'ed P275/65R18 114T at 35 psi carries 2513 lbs (1140 kg) load.
This is the load requirement per tire from vehicle OEM (Ford).

Now, Cooper Discoverer AT3 275/65R18 116T with a similar load of 2513 lbs (1140 kg) load requires only 32.26 psi tire pressure , rounding off to 32 psi., and not 35 psi....... at OEM designed load per tire .Not that one cannot exceed 32 psi on an AT3.
Hence my statement quoted above, after rounding off!

This AT3 275/65R18 116T at a tire pressure of 35 psi would each carry a load of 2667 lbs (1210 kg) i.e 154 lbs more than OEM designed load 2513 lbs per tire .
This AT3 has a maximum load of 2756 lbs (1250 kg) per tire , btw.

Note: 1 kg = 2.2046 lbs.
Originally Posted By: itguy08
Still thinking of bumping to 40 for the trip - would it necessarily hurt anything?


Yes, bump up to 40 psi.
No, it won't hurt anything ..... other than a 'harsher' ride whilst gaining better FE.

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#4546745 - 10/17/17 11:45 PM Re: Tire Pressure adjustment [Re: itguy08]
zeng Offline


Registered: 09/01/15
Posts: 2095
Loc: Malaysia
Oops, 160 km/hr = 100 mph, not 62 mph (100 km/hr) .Hence 62 mph in previous post #4546176 should read 100 mph.
190 km/hr = 119 mph, not 74 mph (62mph/160 kmh x 190 kmh).Hence 74 mph in previous post #4546176 should read 119 mph.
Apologies for wrong conversion from metric > imperial.


Edited by zeng (10/17/17 11:50 PM)

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