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Old 08-04-2015, 09:58 AM   #11
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Location: Michigan
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I run my tires at max pressure all the time. 80 for the truck , 42 for the car. My ride suffers but I can get 70k miles out of a e rated tire (firestone) before I am looking for new ones. Someone might not agree but i am not going to Change my ways

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2012 Wildcat 344QB

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Old 08-04-2015, 12:34 PM   #12
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Originally Posted by jadatis View Post
I will give a copy of text I used for different fora and topics, and saved so I dont have to write it again and again.
For you the weights must be determined as accurate a possible for the 2 situations , towing and not towing. These weights are the most tricky parts in determining the needed pressure. But If you only give the tires specifications I can also make a Pressure/loadcapacity list for them with use of my extra save formula , the american lists lead to to much loadcapacity for the pressure.

Tirepressure advice is all about load on tire and speed ( and sometimes about alighnment - camber angle).

So if you can give details of car and tires , I can calculate an advice pressure with some reserve for things like, pressure-loss in time, unequall loading R/L, incidental extra load, misreadings of pressure scales,and misyudging of weight, etc.

This is from tires next and can be read from sidewall:
Maximum load or loadindex.
Kind of tire to determine the AT-pressure/pressure needed for the maximum load up to maximum speed of tire, or if lower 160km/99m/h/reference-pressure, wich is not the maximum pressure of tire.
Maximum speed of tire, most given as letter ( Q=160km/99m/h,N=140km/86m/h fi)

If you have offroad or tires looking like that , with large profile blocs that cover a part of sidewall, also mention, they are allowed lesser deflection then a normal road tire, then the tire maker used to determine the maximum load (to my conclusion the case for the Bridgestone tires on Ford Explorer in the Ford/Firestone affaire).

If you cant find all of it give sises of tire and Loadkind, then I will google for it.

From car next and mostly can be found on same plate as the original pressure advices:
GAWR and GVWR ( Gross Axle/Vehicle Weight Rating)
But best would be to determine the real weights in your use on seperate tires or estimate it as acurate as possible, by weighing per wheel(pair) or axle.
Maximum speed , you dont go over for even a minute in your use, eventually different for different situations, for instance when towing or fully loaded.

This apart from trafic regulations, if you drive faster then allowed give that speed. Nature punnisches with tire-failure, police only with a penalty.

Give all that and I will calculate and give a picture of one of my filled in spreadsheets in my answer.

If other then original tires, indead as is already answered other advice is needed, a stiffer tire ( fi C-load instead of P-tire) needs a higher pressure for the same load, or the other way around, has lower loadcapacity for the same pressure.

Greatings from a Dutch pigheaded self-declared tire-pressure-specialist.
My tires are LT 275/65R18 E rear axle load right at 4000lb (eazlift) or 4100 with a andersen hitch. ( yeah I know truck is rated for 3850 ) Front axle is right at 3250lb when loaded with eaz lift or 3200 with andersen.

Unloaded the truck is 3400lb front and 3000lb rear.

I would like to swap to an equalizer with 1400lb bars and maybe get that weight in check. I suppose I could pull off my canopy but that's such a PITA.

2015 Vibe 268RKS
2014 F150 Supercrew 4x4 3.5L EB 3:31 axle
1999 F350 Supercab V10 4x4 3.73 LS
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Old 08-05-2015, 04:54 AM   #13
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That you give real weights , knowing rear is overloaded is a good thing.
Laws of nature always rule above rules and regulations of tire and car makers and law.

First found the tires with google from Michelin R speedrated ( 170km/106m/h maxspeed of tires) , and filled the loadindex of that of 123/1550kg/3417 kg in.
Can be that your tires are N speedrated with 125 Loadindex but I use nowadays the maxload for 99m/h /160km/h and R can be compared to that.
Then add 10% for reserve and determined that to give no discomfort or bumping and acceptable gripp.

So this gives highest pressure with no bumpin and maximum reserve.

The for your front of 3250 most weight 40 psi cold pressure advice .
And for you rear of 4100 lbs max weight 51 psi cold pressure advice.
More is not needed.

If in time pressure might dropp to F35psi R 45psi you would still do no damage to tires if your speed is below 75m/120km/h , even included a weightdifference R/L on the axles. A 47/53% loadivision would then still be covered. This ofcource asuming your measuring devices for pressure and load are 100% accurate wich they never are.

If you are scared to go that low , then realise that your P-tires 55 psi maximum pressure is not the pressure at wich the maximum load is carried up to 99m/h with no overheating the tires . Thats called the AT/pressure /maxloadpressure /referencepressure, and is always 35 psi( cold for P tires Standard load .
For XL/reinforced/Extraload P-tires its always 41 psi in American TRA system and I expect your P-tires where XL because of the given max cold pressure of 55 psi, Standard load mostly max pressure (cold) of 51 psi max, often even 44 psi.
From C-load they give ATpressure// on sidewall , P tires maximum cold pressure.
But if you still are scared the start at F50/R60 psi , but then already some bumping, but this is subjective and depends on your sensibility. Never bad for the tires, central wear does not happen that fast at radial tires.

Here a picture of the advice.
For 75m/h I highened up the Loadindex by 4 to 127 .
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pressure, tire

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