Tires: 35's, 37's and beyond . PSI TP

[Ole Cowboy]

The proper contact patch will be achieved when the tire is mounted on the design rim width, and inflated according to the manufacturers load and inflation chart.

Yes you need to know what each axle weighs, that is a given.

Load and inflation charts BEGIN at a specific pressure, not because the union chart writer is a lazy bastard, but because highway operation below that pressure or exceeding the approved load at that pressure is detrimental to the construction of the tire.

Using the Mk1 mod 0 optical comparator (eyeball) while useful does not tell the whole story. I'm not disparaging you, but the contact patch in a static position is an incomplete representation of what is occurring at speed and/or during lateral loading.

Best answer is use both. Let measurable data points be your friend, and back it up with the Mk1 mod 0.

As tires have developed over the course of the last 4 decades they have become far more reliable, longer lasting, better ride quality, less prone to leakage and punctures both. But with that has come technological changes that require more careful monitoring of pressures, and most importantly that those pressures are correct.

Modern radial tires are highly engineered components you simply cannot treat them like we used to and expect a positive outcome.

1) I am talking about outside the OEM parameters... there is NO manufacturers load and inflation chart for a set of 37x12.50 BFG KM2's mounted on a set of 18x8.5 Walker Evans Bead Locks
2) Load and inflation charts as published only provide data points at SPECIFIC tires (Toyota, etc) max weight carrying at specific inflation pressures.
"This guide is intended to provide assistance in utilizing load and inflation tables when replacing tires with optional tire sizes including “plus sizes” that may not be listed on the vehicle’s tire information placard (T.I.P.) or in the owner’s manual. For inflation pressure recommendations for the original equipment (OE) size, refer to the tire information placard (T.I.P.) or owner’s manual."
From https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf found at post #22 this thread.

I apologize for the redundancy:

I have been doing this for over 60 years on ranch trucks, tractors and assorted vehicles that you have no idea what the TP should be. Much of that stuff the tires have been changed out many times and different sizes mostly on whatever was in stock that was a close fit. I did this in my racing days and I would bet $$$ racers still do it today on everything from AA Fuel to C stock, contract patch or some magic chart from Goodyear for AA fuelies?

Somehow, someway you need to ascertain TIP outside the OEM parameters of tires, wheels, Load rating, radial or bias ply or ply rating. There is NO MAGIC CHART! Look on most any tire and you will find the Max load carrying capacity and the Max PSI. IIRC I think my BFG KM2's it was like 3250 lbs at 65 psi, guess I could have driven around on just 2 tires on my Jeep...I tried that and it sure caused a lot of sparks as I drove.

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[Renegade]

The proper contact patch provides performance envelope which contains safety, driving performance, comfort, tire mileage, braking, life of the tire and handling.

Your tires carry the weight of your automobile and the contact patch provides the OPTIMAL coefficient of friction to obtain the above results.

WHY do we air down when we go off road? To INCREASE the size of the contact patch in order to distribute the weight of the vehicle over a larger area and gain more traction points.

Door jamb psi I have found to be very accurate, of course, it does not apply when going to other sizes of tires so you have to find what does. The only way is visual observation of the contact patch.

Given your response to my 2nd question, I’ll argue that you are wrong that 16 psi would put a vehicle in a safe state of on-road handling/performance. Having not received a reply on my first question, I shall ask it again, “What’s the math on cost savings of correct contact patch vs. higher pressure and fuel economy over the life of a tire? Would you save more on tires by airing down, or save more on gas by airing up?”

 

[Ole Cowboy]

Given your response to my 2nd question, I’ll argue that you are wrong that 16 psi would put a vehicle in a safe state of on-road handling/performance. Having not received a reply on my first question, I shall ask it again, “What’s the math on cost savings of correct contact patch vs. higher pressure and fuel economy over the life of a tire? Would you save more on tires by airing down, or save more on gas by airing up?”

I apologize! Email is a bit of a struggle, between fone conferences and other business calls, workers here on the ranch, company business its a never-ending struggle to get an email out at all. There are times it takes 2 days to finish a reply, in fact, this morning around 5:45 I finished an email I started yesterday...PLEASE, if I do not reply, ask again!

1) over 60, 000 mi of driving from Dallas and or Scottsdale thru the US Southwest. That said I did go thru 3 sets of KM2's and 3 sets of GY MTRs, not due to miles, but due to trails.

2) My MTRs required more psi (24-26 IIRC), forgot how much but more than my KM2s (which on the highway I ran a higher pressure, IIRC 24 psi??) But in town, it was 16-18. WHY? First I was amazed they needed so little psi vs my same size MTRs???

Lets look at the KM2 specs:
LT 37X12.50R17: Load Range D, Max load capacity 3525 lbs @50 psi

Here is what BFG says about the tire: "BFGoodrich Mud-Terrain T/A KM2 is a tire designed for off-road. It is made so tough that it resists most off-road hazards including bruises and cuts because of its 3-ply construction and sidewall compound. The Mud-Terrain T/A KM2 can overcome most obstacles and hazards. When aired-down the tire will conform and flex to be able to grab obstacles with ease."

I was on a run in heavy "Shale". It was an overnight run and by 3 in the afternoon on day 1 they had to call it due to sliced open tires, I was the only guy with KM2's and the only guy with all 4 tires holding air and I drove home them...POINT: KM2's one TOUGH tire, remember I run the harder trails. I had lots of slices and cuts but nothing penetrated the sidewalls.

I remember when got my first set. I had gotr a call from one of my wheeling buddies who was an Executive at Discount Tire HQ and he told me about the KM2's and asked if I would like to try them out on a special price deal. I did and they outperformed the MTRs by a significant margin in all areas. Both on and offroad!

So I removed my wheels, took off the beadlock ring and hauled them down to Discount Tire. Got them back, put my beadlock ring back on and went to find the sweet spot on psi. I started around 28 or so. Finally arriving at 16-18 psi, WOW was I surprised!

As your math question: Simply not enough data poins to compute. Optimal mileage and performance will be with a full contact patch. NOTE: I arrive at FCP for the STREET when my adjusting psi gives me full lateral contact and I stop. For offroad I air down until the front and rear tire tread edges no longer increase with less psi. Now you know max width and length of the CP and what psi to run to obtain it offroad.

Why so low vs MTR? I surmised this: Stronger less flexible sidewalls for their D rated tire. Off road I ran them at 3-5 lbs psi my MTRs was more like around 10 psi.

The KM2 was meant and sold to be a true Off Road tire, it was tough as hell and to get an edge to edge contact patch I had to run 16-18 psi to do so. Bear in mind albeit my Jeep was a daily driver, I did not go to work everyday like most, fighting freeway traffic. The almost 100k mi I put on my Jeep were mostly trips out to the SW US, then a week, 2 or 3 running trails and driving back home. I wheeled all the time somewhere, many of my trips were alone as most of my wheeling buddies were just weekenders and they could not travel as far.

MPG was never a concern any more than it is a concern in my F 350 diesel haling loads, it is what is, no more, no less...FYI my Jeep got in the 12's day in, day out, hwy or in town.

 

[bgenlvtex]

1) I am talking about outside the OEM parameters... there is NO manufacturers load and inflation chart for a set of 37x12.50 BFG KM2's mounted on a set of 18x8.5 Walker Evans Bead Locks
2) Load and inflation charts as published only provide data points at SPECIFIC tires (Toyota, etc) max weight carrying at specific inflation pressures.
"This guide is intended to provide assistance in utilizing load and inflation tables when replacing tires with optional tire sizes including “plus sizes” that may not be listed on the vehicle’s tire information placard (T.I.P.) or in the owner’s manual. For inflation pressure recommendations for the original equipment (OE) size, refer to the tire information placard (T.I.P.) or owner’s manual."
From https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf found at post #22 this thread.

I apologize for the redundancy:

I have been doing this for over 60 years on ranch trucks, tractors and assorted vehicles that you have no idea what the TP should be. Much of that stuff the tires have been changed out many times and different sizes mostly on whatever was in stock that was a close fit. I did this in my racing days and I would bet $$$ racers still do it today on everything from AA Fuel to C stock, contract patch or some magic chart from Goodyear for AA fuelies?

Somehow, someway you need to ascertain TIP outside the OEM parameters of tires, wheels, Load rating, radial or bias ply or ply rating. There is NO MAGIC CHART! Look on most any tire and you will find the Max load carrying capacity and the Max PSI. IIRC I think my BFG KM2's it was like 3250 lbs at 65 psi, guess I could have driven around on just 2 tires on my Jeep...I tried that and it sure caused a lot of sparks as I drove.

Load capacity is purely a function of inflation pressure, and absolutely not dependent on whether it is an OEM application.

There actually is a "magic chart" and you (ironically) posted a link to one.

If you know the load, and the tire is mounted on the appropriate wheel, you absolutely can determine the correct air pressure using the manufacturers load inflation chart. I WILL say that some manufacturers don't make this information easily accessible for passenger and light truck tires (not the case for commercial applications).

Load capacity is a function of the volume of air at a specific pressure. Below a specified pressure the air volume ceases to perform its necessary function and damage to the tire will occur.

Why is it on this site when you try to inject some reason everyone gets puffy eyed and starts swinging their unimpeachable experience/degree around?

If you have a tire mounted on the wrong wheel, and you have no idea what your vehicle weighs, then by all means, do what you have to do to make to make it work.

If you are not working in the dark, with a cobbled together bunch of shit and would like to operate safely and economically then by all means reference known data points. If you are unable to locate load inflation data online, contact the manufacturer of your tire and provide a tire size, wheel dimensions, and individual axle weight and they will provide you with an acceptable inflation range of pressures.

 

[Renegade]

The problem with the original post is that it fails to account for the need to resist lateral forces when cornering at speed. Tire deflection needs to be considered, and 16 psi does not provide enough pressure for a tire to maintain structural integrity during on-road cornering.

 

[steffen707]

nope, all good

wow, even with the 37s? killer!

 

[Ole Cowboy]

bgenlvtex, Reneagde

1) Reading comprehension is NOT your strong suit.
2) Your spinning and fabricating
3) END of discussion!


BFG KM2's 16-18 lbs street

 

[steffen707]

bgenlvtex, Reneagde

1) Reading comprehension is NOT your strong suit.
2) Your spinning and fabricating
3) END of discussion!


BFG KM2's 16-18 lbs street

Badass stinger!

 

[Renegade]

bgenlvtex, Reneagde

1) Reading comprehension is NOT your strong suit.
2) Your spinning and fabricating
3) END of discussion!


BFG KM2's 16-18 lbs street

Is it the end? Who's to say? Do photos of your well equipped Jeep prove that 16 psi is sufficient pressure to maintain structural integrity of a tire during emergency maneuvers at highways speed? Maybe we should set up a timed slalom course...
My concern is that someone reads your recommendation of 16 psi for on road use, then takes off down the highway at 70 mph in a Jeep that is incapable of safely avoiding unforeseen traffic situations, resulting in injury or death.

 

[TennesseePA]

You can talk till you are blue in the face but you will never convince me that 16 PSI on the highway is safe or smart. You mentioned that load charts are just data points but they are NOT just data points for a tire. They are data points that have been tested and verified by the manufacturer. Did it never cross your mind to ask why there are no data points below 25 PSI? Probably because you’re not supposed to be running on the highway at that low pressure. That is my opinion and I have nothing but good ole common sense to back it up.

 

[Ole Cowboy]

You can talk till you are blue in the face but you will never convince me that 16 PSI on the highway is safe or smart. You mentioned that load charts are just data points but they are NOT just data points for a tire. They are data points that have been tested and verified by the manufacturer. Did it never cross your mind to ask why there are no data points below 25 PSI? Probably because you’re not supposed to be running on the highway at that low pressure. That is my opinion and I have nothing but good ole common sense to back it up.

I have NEVER said I ran 16 psi on the highway, in FACT I say in more than one post that was my street pressure, in fact 16-18 lbs. ON BFG KM2's 37 x 17, Gy MTR 37 x 17 were different I was running mid 20's usually around 24 psi.

I also ran BEAD LOCKS, that changes the whole dynamic.

This is how its been done for a 100 years, I do it on my 3 tractors, the ranch trucks you name it and have been using it for nearly 60 years of driving. When you leave OEM tires behind and or cross the curb the game changes.

Failure to establish your lateral contact patch will lead to premature tire failure and or poor tire wear. Too wide (low psi) and the tire wears out on the out edges, to narrow (high psi) the tire will wear in the center of the tread.

The charts: Provide a set of data points for THAT tire and its ability to carry X weight at Y psi. You might note that as the weight load increases so does the psi and at all data points, you have a full lateral contact patch. I accomplish EXATCLY the same thing the charts do with one exception my way is far more accurate because to takes in to account the weight as DRIVEN! The chart does NOT weigh your vehicle. MY runs out to Death Valley or down into the Sonoran Desert in Mexico were anywhere between 1 week to almost a month in duration, often I pulled a trailer...what CHART are you gonna use????



On the beach Sea of Cortez, Sonoran Desert, Mexico...wheres my chart?

 

[steffen707]

I have NEVER said I ran 16 psi on the highway, in FACT I say in more than one post that was my street pressure, in fact 16-18 lbs. ON BFG KM2's 37 x 17, Gy MTR 37 x 17 were different I was running mid 20's usually around 24 psi.

I also ran BEAD LOCKS, that changes the whole dynamic.

This is how its been done for a 100 years, I do it on my 3 tractors, the ranch trucks you name it and have been using it for nearly 60 years of driving. When you leave OEM tires behind and or cross the curb the game changes.

Failure to establish your lateral contact patch will lead to premature tire failure and or poor tire wear. Too wide (low psi) and the tire wears out on the out edges, to narrow (high psi) the tire will wear in the center of the tread.

The charts: Provide a set of data points for THAT tire and its ability to carry X weight at Y psi. You might note that as the weight load increases so does the psi and at all data points, you have a full lateral contact patch. I accomplish EXATCLY the same thing the charts do with one exception my way is far more accurate because to takes in to account the weight as DRIVEN! The chart does NOT weigh your vehicle. MY runs out to Death Valley or down into the Sonoran Desert in Mexico were anywhere between 1 week to almost a month in duration, often I pulled a trailer...what CHART are you gonna use????



On the beach Sea of Cortez, Sonoran Desert, Mexico...wheres my chart?

wish i was in Mexico with a drink in my hand. =)

 

[Renegade]

I have NEVER said I ran 16 psi on the highway, in FACT I say in more than one post that was my street pressure, in fact 16-18 lbs. ON BFG KM2's 37 x 17, Gy MTR 37 x 17 were different I was running mid 20's usually around 24 psi.

I also ran BEAD LOCKS, that changes the whole dynamic.

This is how its been done for a 100 years, I do it on my 3 tractors, the ranch trucks you name it and have been using it for nearly 60 years of driving. When you leave OEM tires behind and or cross the curb the game changes.

Failure to establish your lateral contact patch will lead to premature tire failure and or poor tire wear. Too wide (low psi) and the tire wears out on the out edges, to narrow (high psi) the tire will wear in the center of the tread.

The charts: Provide a set of data points for THAT tire and its ability to carry X weight at Y psi. You might note that as the weight load increases so does the psi and at all data points, you have a full lateral contact patch. I accomplish EXATCLY the same thing the charts do with one exception my way is far more accurate because to takes in to account the weight as DRIVEN! The chart does NOT weigh your vehicle. MY runs out to Death Valley or down into the Sonoran Desert in Mexico were anywhere between 1 week to almost a month in duration, often I pulled a trailer...what CHART are you gonna use????



On the beach Sea of Cortez, Sonoran Desert, Mexico...wheres my chart?

Throwing in cool pictures of your awesome Jeep does not make your argument correct. We might just have to agree to disagree on this issue. If your "street pressure" and your "highway pressure" are two different driving circumstances altogether, you might have clarified what they mean to you up front, because to most people these are the same thing...
Whatever. Hopefully this issue can rest.

 

[HectoRome]

I Hate It When Mommy And Daddy Fight !!!

Would One Of My Uncles PLEASE TELL Me What PSI to run my 35s ???

 

[Ole Cowboy]

Hecto,

Its a 2 step process:

1). Get the Mfg chart on you tire and it will provide psi <> weight. In example you Jeep weights 3850 lbs, you look the chart closest to 3850 lbs and it says 32 psi. This your starting point.

2) Look at your contact patch. In the tire business FULL CONTACT patch is the objective at that point in time you have optimizes your CoF (Coefficient of Friction) this gives max: Braking, acceleration, lateral performance and tire wear-mileage.

I learned this was I was 14 and dad would send me out to fix flats on our ranch trucks and tractors. We did not have any tire gages or air compressor except my arms and a hand pump.

I gave the answer to your question, told how or you can use their solution but its YOUR Jeep, your wallet, your pride of ride you do it as you see fit.

Here is the data sheet on my OEM tires on my truck. I run 70 psi on the street but when I am loaded I run 80 on the front and rear. The pic of my tires on my F 450 truck when I picked it up. The dealer had put in 90 psi but the door jam calls for 80. At 80 I get full contact patch but at 90 the outer tread does not touch the pavement, note how white it is vs the black where the tire rides. Without adjusting to contact patch you will wear out your tire faster, simple as that.

You are welcome to follow the experts on here...

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