BFG KO2 LT285/70R/17 Tire Pressure (once and for all)

[mmatthie]

Currently, I'm running 33s on my Sport S JT. I bought them at Costco and 3 times now the shop there said I should keep them
inflated to 48-50...I'm asking WHY???

Researching on here and on Google, I'm reading that 50 is a MAX inflation for these. I've read just the normal day to day driver
should run these around 35-36 (aka like the front door sticker states)

Can (once and for all) someone help me with this?

Thanks

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[stingrey]

You have it right. KO2 are one of a few standard Jeep options so using the door sticker should steer you right. Just note that that is cold tire pressure and its not unusual for the pressure to increase into the low to mid 40's depending on how warm the air inside gets when driving.

Edit: in Scuba we know it as Charles' Law

 

[JTBurns]

I'm running the Falken MTs in the same size and keep them at 36. 48-50 seems really high so not sure why they're telling you to run them at that. I think I've read you may want to up the PSI when towing so maybe that's the confusion? Anyway I think running 34-36 for daily driving should suit you well.

 

[smlobx]

You have it right. KO2 are one of a few standard Jeep options so using the door sticker should steer you right. Just note that that is cold tire pressure and its not unusual for the pressure to increase into the low to mid 40's depending on how warm the air inside gets when driving.

This is absolutely correct.

 

[mmatthie]

Thanks everyone. It's so frustrating...3 separate occasions they said that. I went yesterday since my WARM pressure was at 58!!! They only lowered it to 48.

They said KO2s, specifically, need to be close to that 50 psi mark. I told them I've researched and have always thought that was high.

They are Load Class C, and I would think door sticker is the way to go. I was told since it's a Light Truck...you need that high pressure.

I'll just air them down myself...I just hope I didn't lose any tread life.

 

[CerOf]

Your Costco guy is an idiot.

There isnt a single reputable tire shop that will tell you to run near/at max inflation for every day driving.

I bought tires at Costco once, long time ago and will never do it again.

I get no kick backs, but I recommend you find the best price for the tire you want, then go to discount tire. They actually have a clue as to what they are doing.

PS good luck getting Costco to sell/mount a tire larger than factory. They’ll tell you it’s dangerous and not recommended.

 

[KVJ]

I run mine at 40 Psi. Every time I've had my oil changed on the Jeep Wave program I get it back lowered to 36.

 

[Renegade]

This is applicable for any comparable tire. Find your tire’s specs, then reference the recommendation.
https://www.toyotires.com/tires-101/tire-load-and-inflation-tables

 

[Mr._Bill]

Thanks everyone. It's so frustrating...3 separate occasions they said that. I went yesterday since my WARM pressure was at 58!!! They only lowered it to 48.

They said KO2s, specifically, need to be close to that 50 psi mark. I told them I've researched and have always thought that was high.

They are Load Class C, and I would think door sticker is the way to go. I was told since it's a Light Truck...you need that high pressure.

I'll just air them down myself...I just hope I didn't lose any tread life.

The MAX PSI for the tire is imprinted on it. Rarely do you want to run them at that pressure. Look at the wear on the tires. If they are over-inflated, the center wears faster than the edges. Too much pressure also affects the ride and the steering.

A chalk test can be used to determine the pressure that should be in the tires for optimal ride and wear. You can also try to get a weight/psi chart from the tire manufacturer and set the pressure based on the amount of weight on the tires.

I also recommend Discount Tire. Costco and Sam's Club are good for inexpensive tires, if you are using the factory recommended size.

 

[ShadowsPapa]

I asked an engineer - literally. I contacted General tire about my tires.
I gave them the weight of my truck, the max gross vehicle weight, and my stock tire size and what the door sticker says (38 psi on the door sticker in my case)
38 psi is for the Bridgestone Dueler H/T 255/70R18 diameter 32.1", width 10.2"

Keeping in mind any time you increase diameter or width, you increase the footprint on the pavement. Since it's the PSI - air pressure in the tire that holds the truck up, science and logic say that if you increase the footprint, you decrease the pressure to hold the same weight.
The General engineer did some calculating, figuring the SL load rating of the tires I bought, curb weight, maximum truck weight and came back and said for my truck weight and the new size tire 275/65R18 I should run 33 psi.
The new tire is a wider tire than the Duelers by about .7-.8" so logic dictates lower psi from 38.
The engineer was going by my truck's posted curb weight of course. I found that a bit on the light side because my truck's curb weight is a bit more as I have added the winch, bumper, skid plate so I increased up to 34-35 psi. Now it appears to sit nice and flat across the face now where after the dealer aired the new tires up to 40, I could slip a putty knife under the edges of the tire in about 1"

The rule is - the wider and taller the tire, the lower the pressure to maintain the same weight of truck. PSI working against a given number of square inches. Increasing tire size increases the square inches that pressure is working against, so you can lower the air pressure and support the same weight.
Weight supported = pressure in psi x contact patch tire to pavement in square inches.
Increase one you need to decrease the other to maintain the same weight.

 

[Higher_Ground]

This is applicable for any comparable tire. Find your tire’s specs, then reference the recommendation.
https://www.toyotires.com/tires-101/tire-load-and-inflation-tables

I tried to use that chart when I was researching new tires. The funny thing is, despite buying Toyo tires and that link providing 37 pages of tables.... it doesn't have the size I bought (P285/75/r17).

The closest they have is P285/70/r17 and the table only shows values from 26 to 35 PSI.

The stock tires size, P245/75/r17, only has values listed up to 35 PSI as well. But my door sticker is 36 PSI. I can extrapolate but it's pretty close. Either way, if you take the 35PSI value you get a tire load limit of 2337 lbs.

If you were to try and find that same load limit at the size I first mentioned, good luck. The lowest they show is 26 PSI and the tire load limit is still 2480 lbs. Granted, the load index went from 110 to 117 - another potential factor to consider. I suppose this is all to say that from a "loading" standpoint the tires could be aired down below 26 PSI to maintain the same loading characteristics.

I'm not an expert, but I think at that low of PSI you're going to have sidewall deformation that leads to lower overall lifespan - or maybe not since most tires will not fail at the sidewall unless punctured.

I did a chalk test or two but seemed to get about the same result at 33, 35, & 38 PSI. Maybe not all that surprising because that's not a big difference IMO.

I have had to let air out of them as the days have gotten hotter. I have them at 33 cold in the morning, which heat up to 36+ driving or during the day.

I feel like we over analyze tire pressure about as badly as we do MPGs.

edit: I should have check back a little closer - I had the sizes all wrong (mixed up my P's and LT's, metric and all that)

 

[Terry]

I ALWAYS buy Michelin Tires and only from America's Tires. From what's on the Volvo to my heavy duty work truck, they have stood me well. And NEVER run any tire at max inflation. Ever.

 

[ShadowsPapa]

I ALWAYS buy Michelin Tires and only from America's Tires. From what's on the Volvo to my heavy duty work truck, they have stood me well. And NEVER run any tire at max inflation. Ever.

Amen. Like said, that is the inflation for MAXIMUM load on the tire. If you run the truck fully loaded and come close to the rated tire load, then yes, but not for curb weight trucks.
You want the contact patch to stay the same on a given tire - to do that you adjust PSI up for more load, down for less load.
If you get bigger tires, it takes less air pressure, if you get smaller tires, it takes more air to hold the truck up.

This is sort of an explanation - heavy truck tires change things because at lower pressures the sidewall starts to help support the vehicle, and short sidewalled performance tires also change things drastically, but for something like my wife's WK2, it should work pretty well. Standard load range, not heave sidewalls, highway tires.
https://www.exploratorium.edu/snacks/tired-weight

 

[19JTRubiconEcoDiesel]

Chalk testing will allow you to identify the proper tire pressure you need for your setup.

 

[mmatthie]

Thanks everyone...I must say, I'm even more pissed at Costco.

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