Whatever the topic , this is what happens here . Most days I'm just here for the entertainment .All this over tire pressure? Imagine if these guys took flying lessons!
What air pressure for new tires
- Thread starter nickaluch
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I run 10 ply tires because I use my truck AS a truck. I haul things...sometimes heavy things. I pull trailers...sometimes heavy trailers. I go offroad fairly often. I have even drag raced it. But it's still my daily driver. I run 285/75's because of added ground clearance...I also have a 3" leveling kit. 285/75's are next to impossible to find that AREN'T E-rated.
When I haul a heavy load, I bump up the inflation to a pressure suitable to the load...like you're supposed to do. When I'm not hauling anything, I run them @ 35psi. I don't haul loads often enough to warrant having to buy a bigger truck, but often enough to warrant a tire that will handle it...plus I like the mpg I'm getting with mine. I'm right at 20mpg on the hwy. Also, the 10 ply tires last longer in an apples to apples use comparison for what I'm doing vs a SL, C or D rated tire.
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*double post*
OVERKILL
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I mean, I use my truck as a truck too, but still run P-rated tires, because their limits align with the limits of the truck
The statement that one needs LT tires to use a truck "as a truck" is like the personification of "truck nuts". The fact that many guys doing it aren't running proper air pressure because they aren't aware of the existence of the load tables is just the icing on the cake. I think we can avoid taking this conversation down that road.And yes, the size you've chosen does limit you to LT tires, though I do see one that isn't E rated (Toyo Open Country A/T III), but most seem to be.
But you aren't "supposed to" on a 1/2 ton, that's why the placard doesn't contain entries for loaded/unloaded. On a 3/4 or 1-ton, they'll often give multiple pressures on the placard for loaded/unloaded, my old F-250 did. However, these come with LT tires on them factory and the placard directly applies, while 1/2 tons don't, which is why one is required to derive the appropriate pressure from the load tables as indicated. For your truck, 45psi is appropriate for the stock load carrying capacity of the vehicle, assuming the numbers I used to derive that were correct, based on the sizes given.
Again, the loads your truck is rated to carry are well within the limits of the stock tires, a 1/2 ton doesn't need an E-rated tire to "handle" a load and as already discussed, needs higher pressure in order to handle the same load; have the same load carrying capacity.
Yes, they typically employ a harder compound, due to their intended application and operating profile, and subsequently have longer tread life. The downside of course is that, at the proper pressure, they provide a poorer ride that some may object to.
It's probably the most common tire "swap" in North America, the fitment of LT's to 1/2 tons that spec P-Metric. I've got no issue with it, heck, our Expedition came with LT's on it when we bought it (it spec'd P-Metric) and I went down the rabbit hole of having to determine the appropriate pressure after learning from @CapriRacer's data that running them at placard was wrong. However, most people doing it aren't doing it correctly. Tire pressure is one of the most misunderstood and hotly contested subjects on this forum!
I'm also curious why you didn't mention that you "adjusted" your pressure in any of your previous responses? Clearly, that's germane to this discussion
One would have assumed you'd bring this up right out of the gate, given the context of the discourse thus far and the fact that these last few responses have specifically referenced pressure on LT tires needing to be higher than a comparable P-Metric in order to have the same load carrying capacity.
Yeah, my truck isn't "supposed" to run over 99mph, but it does. My truck isn't "supposed" to haul a 1 ton load in the bed, but it does. My truck isn't supposed to tow over 5000lbs, but it does. You aren't supposed to use a screw driver as a prying tool or chisel...but people do it all the time. Pushing my truck past what it's engineered limits supposedly are certainly have never hurt it, or me, or anybody else.I mean, I use my truck as a truck too, but still run P-rated tires, because their limits align with the limits of the truck
And yes, the size you've chosen does limit you to LT tires, though I do see one that isn't E rated (Toyo Open Country A/T III), but most seem to be.
But you aren't "supposed to" on a 1/2 ton, that's why the placard doesn't contain entries for loaded/unloaded. On a 3/4 or 1-ton, they'll often give multiple pressures on the placard for loaded/unloaded, my old F-250 did. However, these come with LT tires on them factory and the placard directly applies, while 1/2 tons don't, which is why one is required to derive the appropriate pressure from the load tables as indicated. For your truck, 45psi is appropriate for the stock load carrying capacity of the vehicle, assuming the numbers I used to derive that were correct, based on the sizes given.
Again, the loads your truck is rated to carry are well within the limits of the stock tires, a 1/2 ton doesn't need an E-rated tire to "handle" a load and as already discussed, needs higher pressure in order to handle the same load; have the same load carrying capacity.
Yes, they typically employ a harder compound, due to their intended application and operating profile, and subsequently have longer tread life. The downside of course is that, at the proper pressure, they provide a poorer ride that some may object to.
It's probably the most common tire "swap" in North America, the fitment of LT's to 1/2 tons that spec P-Metric. I've got no issue with it, heck, our Expedition came with LT's on it when we bought it (it spec'd P-Metric) and I went down the rabbit hole of having to determine the appropriate pressure after learning from @CapriRacer's data that running them at placard was wrong. However, most people doing it aren't doing it correctly. Tire pressure is one of the most misunderstood and hotly contested subjects on this forum!
I'm also curious why you didn't mention that you "adjusted" your pressure in any of your previous responses? Clearly, that's germane to this discussion
Plain and simple, the factory P-metric Firestone tires that were on my truck from the factory lasted about 20K miles. I thought it must have been just bad quality tires. So I put on the same factory spec tire in a Michelin AT (the best of the best, right?). They too lasted ~20K miles.
Moved up to D rated when I lifted the truck and went with the bigger tire. Got ~40K miles out of those. The trend seemed obvious. So...I went with the E-rated....been getting consistent 65-75k miles out of them ever since. Never seen any evidence of a safety issue or premature wear or any type of failure running them @ 35 psi. On my truck, they ride better, they handle better, wear better AND they last longer at that pressure.
Why didn't I mention adjusting air pressure when hauling heavy stuff? Well I guess since I'm a truck driver who deals with heavy loads and logistics, I assumed it was common knowledge that it's people adjust air to accommodate heavy loads. I guess it's not?
My question to YOU is...why does it matter to you if I run E-rated tires @ 35 psi on my 1/2 ton truck on a normal basis? It's not a danger to anybody...not me as an operator and not anybody else on the road.
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The tires aren't the weak link in over-loading a truck (which you are admitting to doing here). The frame, brakes, axles, and other components are simply not designed to handle that kind of weight, that's why they make bigger trucks, with heavier components in all of those departments.
As long as you aren't doing that on the road, I don't care if you do it, but if you are driving on public infrastructure with an overloaded vehicle and think you can do so because you have E rated tires on it, you are sadly mistaken and a rolling hazard.
BTW, that's a remarkably low towing capacity.
I also had awful luck with the factory tires on our RAM (Goodyear Eagle). They lasted about 40,000Km and were close to bald. The pictures are on here. We replaced them with Conti's, was going to go LTX's, as I've had fantastic service out of those on other vehicles, but the price break on the Conti's made the gamble worthwhile. Can't comment on wear yet, but they seem to do well in other important metrics like wet performance, stability while towing...etc.
Again, it's not about wear or likely anything visible, the tire simply isn't rated to carry the same weight at 35psi as the stock tires. How close you are coming to the "lower than factory" limit you've created during daily operation? I don't know, would depend on what you regularly have in the vehicle, but the fact is that it's lower than the OE tires at the same pressure and that's why it was brought up.
No, not with 1/2 ton trucks, that have a single pressure spec on the placard, and this thread, and most of the discussion, revolves around placard pressure and its appropriateness, including the posts you've been responding to, that's why I don't get it. There was a clear segue into this conversation in mentioning it, but instead, you just sarcastically quoted Michelin and completely avoided it, that's why I made it a point to break that out specifically as an item of interest.
As I noted, 3/4 and 1 ton trucks have unloaded/loaded pressures, but your 1/2 ton clearly doesn't, neither does mine, so that assumption doesn't really fit in with the conversation that has thus far transpired and in fact its omission seems totally out of place, given its relevance to the topic. Worded differently, given what had been discussed in the thread so far, one would expect that you would have led with this point, not add it significantly after the fact.
Again, back to the subject, an E-rated tire at 35psi does not have the same load carrying capacity as the factory P-Metric ones and typically the placard isn't updated with the correct pressure when an LT is fitted to a P-Metric application. This creates a hazard if the owner isn't cognizant of the fact that the placard pressure is no longer correct and in order to use the vehicle safely within its limits, they will need to significantly increase that pressure beyond what is on the placard, using the load tables.
Your initial contribution to this thread was to indicate that you run LT's at 35psi, not that you run LT's at 35, but will add air if you put weight in the truck, based on the load tables (which you also haven't indicated whether you use or not). That's what resulted in my commenting. You then responded about wear and how the tire looks, again, not mentioning that you manipulate the pressure with load, that's what resulted in the conversation going as far as it has.
Consider the audience and the reason for the concern should be self-evident, particularly given the exchange up to the point where you mentioned pressure manipulation for load handling. Of course now you've indicated that you over-load the truck, but I don't think we need to beat that horse any further, my position on that should already be abundantly clear.
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I'll be abundantly clear then, too. You do you...and I'll do me...and every body lives in harmony.
Yes it is- because when you have a tire failure and lose control, you risk the lives of others around you.
Except your approach is clearly incorrect. Multiple posters have proven this using industry-standard reference materials and guidelines. Just because someone is experienced in their area does not mean their experience is valid and correct.
Don't bet on it.Golddot immediately went out and bumped his load range E tires up to 45 psi after reading the exchange. We’ve all learned new things on the internet.
A tire failure? Explain how from an engineering standpoint it would cause a tire failure.
Something I've been doing for 25 years with this truck and others I've owned...that has never caused an issue for me or anybody around me is "incorrect"? A man isn't "just lucky" for 25 years. I have well over 200K miles of uneventful use on E-rated tires running them @35 psi. It's not hurting-a-thing. Those "industry standards" is not an exact science nor is it a once size fits all. It is simply a recommendation.
Underinflation increases the risk of tire failure.
In my day job, I have reviewed hundreds of accounts over the years that have "never had a loss" despite their lack of proper operational controls. However, if you look at how a book of these risks perform, the losses are severe when they do happen....and statistically, the losses do happen over time. You might get lucky, but not everyone following your advice will.
Then first about the loadindex of the 285/75R17. 121/118
Its stangely low.
A 225/75R16 tire in LT has 115 AT 80 psi loadindex.
European C-tyre in same sise LI 118 AT 77psi and LI 121 AT 83 psi.
Seached with google, but only saw LT.
I think in Europe the 285/75R17 is not an interesting sise in C-tire, did not even found it in normal car or XL tyre.
So a smaller tire but same loadindex.
So I expect a 285 , if it was available in Europa , it would have a higher loadindex AT 80 psi ( or 77 or 83psi).
285-225 = 6 x10 + 1 step for 17" against 16" gives aloadindex of 121+7= 128.
LT 115 +7= 122, so that is pretty much in line with the 121 given for 285.
New calculations:
Front GAWR 3700lbs +10% reserve=4070.lbs.
LI 121 / 3200lbsx2tires= 6400lbs.
LI 128/ 3970lbs x 2 tires= 7940lbs.
(4070lbs/6400lb)^1,25 x 80psi= 45.43psi ,
Make it 45 or 46 psi front.
But if 128LI
(4070lbs/7940lbs)^1.25 x 80psi= 34.69 psi , make it 35 psi.
So the one that used 35psi all around for almost empty driving, probably did not destoy his ( or her) tires by it.
Because empty driving weigt on rear axle is about the same or lower as front axle.
All general , RV and towing is a different story. no overheating depends on laws of mother nature, wich not always follows the rules and systems the ( tire) organisations agreed on , and EUR and USA system not always agree with each other.
EDIT
Looked back the topic and saw the list you gave . Not only GAWR's are given there , but also base weigh, and comfirms my only driver axleloads of front about 3000 lbs and rear about 2200 lbs. So the 99% normal driving most do ( no towing , RV , transporting heavy loads or many persons) next pressures for that
Front 3200lbs+10% = 3520 lbs .
Rear 2400lbs + 10%= 2640 lbs
Only the 120LI AT 80 psi.
Front (3520lbs/ 6400lbs)^1.25 x 80 psi = 37.89psi rounded 38psi.
Rear ( 2640lbs=6400lbs)^1.25 x80psi= 26.44psi, rounded 27 psi, make it 30 psi.
And this is for max speed 99mph, for lower speed lower pressure would not give overheating.
So still for most normal used 35psi will still not give overheating.
Again : determining the weights in your use , stays the most tricky part in this.
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Allow me to tell you a story about Isambard Kingdom Brunel, a British civil engineer. He was investigating a railway accident where a shaft on one of the axles failed. He determined it to be caused by fatigue and the result of too sharp of a radius in the machining of the shaft.
Can you imagine how many shafts were made before this was discovered? How many years this problem existed? How many people died?
That's why we engineers pay attention to history. We don't publish load limits to have them ignored by people who know better.
Can you imagine how many shafts were made before this was discovered? How many years this problem existed? How many people died?
That's why we engineers pay attention to history. We don't publish load limits to have them ignored by people who know better.
The same sharp machining of the jet engine shaft was responsible for Soviet made, Polish LOT operated Il-62M crash. The shaft disintegrated at stress focusing point.
The worse part was that Soviets had improved engine with smooth transition but it was more expensive to produce and was only for Soviet party dignitaries flights.
Krzyś
The worse part was that Soviets had improved engine with smooth transition but it was more expensive to produce and was only for Soviet party dignitaries flights.
Krzyś
OVERKILL
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@CapriRacer noted earlier in the thread that LI for Euro tires is a bit different than for American ones:
That may be relevant here with respect to your calculations.
Also, for the sake of providing as much info as possible, here's the link to the tires on TireRack, all of the E tires have the LI of 121. The lone C rated tire has an LI of 117.
As noted though, these are indeed LI121, which is 3,195lbs @ 80psi.
Regarding empty weight: With a half-ton, in the context of placard pressure, they only give the single value, and the load tables aren't provided with the vehicle. The placard pressure is supposed to align with the capacities of the vehicle, loaded or non. That works fine for the factory P-Metric tires, but is clearly not the case for LT's. If you buy a heavier truck (2500/250, 3500/350) it comes with LT's and will have loaded and unloaded pressures on the placard.
Yes, as I noted above, it appears LI is different as well, according to CapriRacer.
Yes, now base weight will be a bit variable here. My truck on that table has the following specs:
GVWR: 7,100lbs
Payload: 1,840lbs
Base weight: 5,260lbs
BW front: 3,093lbs
BW rear: 2,167lbs
GAWR Front: 3,900lbs
GAWR Rear: 4,100lbs
GCWR: 17,000lbs
Max trailer: 11,340lbs
With just my son and I in the truck on the dump scales we are ~5,800lbs and the pair of us are about 300lbs. Often we are 5 people in the truck however. Typical 1/2-ton use, we'll often be the whole family, cooler, guns and a trailer. If we are only taking the one ATV, that's 1,000lbs in the bed. No change to tire pressure for any of this, as I have OE sized tires on it so placard applies, with E's at 35psi we'd be well past the load carrying capacity of the tire on the rear and you've already shown that at base weight we are over on the front. That's why this is such a good conversation, because there are so many people out there running LT's on half tons and SUV's with no idea as to what pressure they need to be running.
I see you have a verry variable use of the truck, so my generalisation dont go for you.
But you can also choose , to drive at lesser speed , when using high weights on axle ( ends)
Rule of tumb , tiremakers also use is for every speedcodestep= 10 kmph= 6.3mph different 1 loadindex step different, higher speed/ lower loadinddex, lower speed/ higher loadindex.
The calculate pressure for normal use + 10% and 99mph ( speedcode Q and higher 160kmph) , this gives highest reserve with still acceptable comfort ( on asphalt roads comfort even with 20% added still OK.
Then if you have some occacional high weights to transport, reduce the max speed to for instance 100kmph/62mph, and you can add 160-100=60/10=6 LI steps and gives higher load to carry at same pressure, without overheating tires.
And then when going on a tripp with TT behind its better to highen up the pressure, but then OK for the whole tripp.
Saves you manically pumping up and letting off air all the time.
Then about the different loadindexes for same sise and loadrange.
The P-tires and eurometric normal car tyres, it gives marginal differences, and only other pressure used for the calculation, but for the E- loads I mentioned, there is an important difference in what the different tiremakers think what is still save for the tire.
As European guy, I trust the european tyremakers, to have determined the higher loadindexes for E-load , so it wont compromise the tire when using to the max, but you as American shall think the american tiremakers use the lower LI , because its needed for savety, and the euros use a to high loadindex.
Time will tell who is in line with laws of mother nature.
But you can also choose , to drive at lesser speed , when using high weights on axle ( ends)
Rule of tumb , tiremakers also use is for every speedcodestep= 10 kmph= 6.3mph different 1 loadindex step different, higher speed/ lower loadinddex, lower speed/ higher loadindex.
The calculate pressure for normal use + 10% and 99mph ( speedcode Q and higher 160kmph) , this gives highest reserve with still acceptable comfort ( on asphalt roads comfort even with 20% added still OK.
Then if you have some occacional high weights to transport, reduce the max speed to for instance 100kmph/62mph, and you can add 160-100=60/10=6 LI steps and gives higher load to carry at same pressure, without overheating tires.
And then when going on a tripp with TT behind its better to highen up the pressure, but then OK for the whole tripp.
Saves you manically pumping up and letting off air all the time.
Then about the different loadindexes for same sise and loadrange.
The P-tires and eurometric normal car tyres, it gives marginal differences, and only other pressure used for the calculation, but for the E- loads I mentioned, there is an important difference in what the different tiremakers think what is still save for the tire.
As European guy, I trust the european tyremakers, to have determined the higher loadindexes for E-load , so it wont compromise the tire when using to the max, but you as American shall think the american tiremakers use the lower LI , because its needed for savety, and the euros use a to high loadindex.
Time will tell who is in line with laws of mother nature.
Still waiting for somebody to explain...from an engineering view...why they think my E rated tires are under inflated WITHOUT a chart saying so. I will remind you folks that I drive for a living. I am approaching 2 million incident/accident free miles in an 18 wheeler alone...not counting my personal vehicles. I know a thing or 3 about tires.
Under inflated tires cause more sidewall flex and extra friction within the tread contact which creates excessive heat in the tire...that excess heat is what starts breaking down the tire's construction and results in a blowout. (ANYBODY CARE TO DISPUTE THAT?) My tires have near sidewall zero bulge or distortion.
Passenger vehicle and truck tires typically are good up to 195°F before the tread compound begins to deteriorate rapidly. Into the 225-250°F range is when they structurally begin to disintegrate....regardless of their temperature rating.
I've gauaged my tires with my infrared thermometer on a 95°F (ambient) temp day during a 160 mile trip running 65-70 mph. All 4 tires were 160-162°F with the asphalt right around 155°F. They run way cooler on cooler days. Using that as a rule, I'm well within the safe zone with my tire pressure.
My daughter was following me in her car with the factory size and spec tire running the pressure on her door placard which is 35 psi. Her tires were 5° warmer than mine. I assume the difference is because my 33" tall tire is turning way less revolutions than her 25.7" tire in the same distance.
So...let's hear why I'm wrong with my tire pressure again?
Under inflated tires cause more sidewall flex and extra friction within the tread contact which creates excessive heat in the tire...that excess heat is what starts breaking down the tire's construction and results in a blowout. (ANYBODY CARE TO DISPUTE THAT?) My tires have near sidewall zero bulge or distortion.
Passenger vehicle and truck tires typically are good up to 195°F before the tread compound begins to deteriorate rapidly. Into the 225-250°F range is when they structurally begin to disintegrate....regardless of their temperature rating.
I've gauaged my tires with my infrared thermometer on a 95°F (ambient) temp day during a 160 mile trip running 65-70 mph. All 4 tires were 160-162°F with the asphalt right around 155°F. They run way cooler on cooler days. Using that as a rule, I'm well within the safe zone with my tire pressure.
My daughter was following me in her car with the factory size and spec tire running the pressure on her door placard which is 35 psi. Her tires were 5° warmer than mine. I assume the difference is because my 33" tall tire is turning way less revolutions than her 25.7" tire in the same distance.
So...let's hear why I'm wrong with my tire pressure again?
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