BFG KM3 recommended tire pressure

[SiRaDuDe]

Hi Guys,
Just upgraded from KM2 315/75R16 to KM3 same size.

I noticed that the KM2 were D Load Rated with a max air pressure of 50psi, i keped them at about 40psi for road and they lasted over 7 years with much thread left but due to drying of tire I upgraded.

Now the KM3 are E load rated and max air pressure of 75psi with a much higher load capacity.

I originally inflated to 50psi and while ride was rough, they rolled much faster and a much less strain on my power steering pump! But Im concearned thia might be to high for daily use.

Anyone have any info on this tire and recomendations using the weight parameter of an 80? (4.5” lift, front bumper and winch)

BFG say to email them with the stock tire size and stock airpressure, and they would recommend the correct air pressure for new tire, im just not sure if they would just be pulling this info from a averaged street car table.

I may just lower to 40psi for testing
Thanks in avanced for any contribution to this topic

 

[NV1971FJ40]

I run 40psi in my nittos with zero issues

 

[Bear80]

Tire size and or load rating has NOTHING to do with proper pressure. ONLY THE AIR PRESSURE SUPPORTS THE WEIGHT OF THE VEHICLE. Follow the vehicle manufacture's recommendations. In this case 32psi or 35psi towing (also interpreted as fully loaded). I personally run 33 in my 345/75's and prior 36" radial swampers.

As a side note, load rating is simply the strength of the tire in the TREAD not the sidewall.

 

[baldilocks]

Load rating dictates approved max psi and the psi carries the load.

Load capacity is a function of air pressure times air volume. So, we should be able to run lower psi in our larger tires with similar results as a stock tire running 32psi.

Factors to consider are the type of roads you drive on mostly and how much payload is on your axles. If you drive a lot of curvy roads you may want to run higher psi to keep the tires from wearing at the outside edges prematurely.

I usually run my 37” SS TRXuS , on the factory wheels, at 30. I’m always paying attention to how they are wearing for signs that more or less psi is called for.

Running a large tire at 40 would produce a rough ride and faster wear toward the center of the tread.

 

[SiRaDuDe]

Thanks for the info,

I live in Puerto Rico and our roads are poorly maintained. So lots of pot holes and many curves and hills, even the highways are infected with hazzards

I dont drive much, but i do also use dirt roads on occasion.

I will lower the pressure for a smoother ride, worried so many pot holes might damage a tire that is so high in psi

Im also tryng 8oz of Commercial Off-Road Dyna-Beads since i had problems keeping the KM2s balanced

 

[Bear80]

Load capacity is a function of air pressure times air volume. So, we should be able to run lower psi in our larger tires with similar results as a stock tire running 32psi.

Sounds like you are mis-applying Boyle's Law. I'm no chemist or tire engineer but I do not believe your interpretation is correct. I present the following static example of a 275/70r16 vs 347/75r16 tire.

Diameter: 31.2 vs 36.5, Width: 10.8 vs 13.6: Volume of each 6,082 in^3 vs 11,411 in^3. That is a 88% change in volume

No way will 88% lower pressure in a 345/75 support the vehicle.

Tire Rack has some great tech articles:

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=72

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35

 

[Chrisw023]

chaulk test them is the best way to make sure you get even wear. in my e rated ko2's i run 40psi

 

[baldilocks]

Sounds like you are mis-applying Boyle's Law. I'm no chemist or tire engineer but I do not believe your interpretation is correct. I present the following static example of a 275/70r16 vs 347/75r16 tire.

Diameter: 31.2 vs 36.5, Width: 10.8 vs 13.6: Volume of each 6,082 in^3 vs 11,411 in^3. That is a 88% change in volume

No way will 88% lower pressure in a 345/75 support the vehicle.

Tire Rack has some great tech articles:

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=72

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35

Don’t get too scientific but answer this question. How can a 285/70R17 load range D have the same load capacity at 65psi as that of a 265/70R17 at 80psi? It does. Please explain?

 

[JOHN OF LONDON]

It's really not so complicated. The weight on the tire is spread over the number of square inches of tire touching the road so 10 inch wide tire witha contact patch 5 inches long at 40 psi will hold up 2000lbs. Higher pressure shortens the contract patch. Lower pressure lengthens it.

 

[Rifleman]

Here is a link to a good thread by another Mud member, that just may help you answer your tire pressure question.
Tire pressure question?

 

[JeepinPete]

I run a 365/75R16 KM2. The tires are rated at 3200 lb @35psi. Two tires will hold the weight of the truck. I run them at 25psi, even wear, no issues in the 30k miles they have been on the truck.

 

[Bear80]

Don’t get too scientific but answer this question. How can a 285/70R17 load range D have the same load capacity at 65psi as that of a 265/70R17 at 80psi? It does. Please explain?

1. I am not a tire engineer.
2. Most information I have sourced, indicates that sidewall stated max load and max psi are not intended to be used as a linear relation to determine correct pressure for the corner weight on each tire. From one of the Tire Rack links I provided:

"Because of the weight they bear, pneumatic tires' sidewalls bulge and their treads flatten as they roll into contact with the road. This results in dimensional difference between the tire's "unloaded" radius (i.e., between the center of the axle and the top of the tire) and its "loaded" radius (between the center of the axle and the road). The engineers call the difference between the two radii "deflection." Increasing vehicle speed will cause the tires to deflect quicker, and increasing vehicle load will cause the tires to deflect farther (if tire pressure isn't increased)."

Focusing on the last sentence, I infer that the need to increase pressure is to reduce the deflection factor due to increased load. However, as mentioned in another of the links explaining load range and ply ratings, the construction of the tire will dictate how much pressure the tire will safely hold. So max psi is NOT indicating that the psi MUST be at that level to support the max load indicated.

3. Increased deflection builds heat in the rubber of the tire. This leads to a tire failure ie. "a blow out."
4. SO proper psi will support the load without excessive deflection and heat buildup.

Here is a link to a good thread by another Mud member, that just may help you answer your tire pressure question.
Tire pressure question?

I respect LC Phil but from my research and personal enthusiasm for tires, I would NEVER endorse starting near the max psi stated on the sidewall.

 

[nukegoat]

I would run about 31 psi

 

[Rifleman]

I respect LC Phil but from my research and personal enthusiasm for tires, I would NEVER endorse starting near the max psi stated on the sidewall.

When you read Land Cruiser Phils entire thread, with him stating you should start at "Max pressure" was just one of 4 different methods he offers in his thread.

When i installed my new (factory stock tire size) load range E tires (80 PSI max on the sidewall) i went with his "let the chalk tell you" method to set my new tire pressure. As it turned out using his method my "new tire" pressure wasn't to far off from whats listed on my trucks factory door sticker, IIRR factory pressure was 32 PSI. and i ended up at 35 PSI. Cheers

 

[baldilocks]

1. I am not a tire engineer.
2. Most information I have sourced, indicates that sidewall stated max load and max psi are not intended to be used as a linear relation to determine correct pressure for the corner weight on each tire. From one of the Tire Rack links I provided:

"Because of the weight they bear, pneumatic tires' sidewalls bulge and their treads flatten as they roll into contact with the road. This results in dimensional difference between the tire's "unloaded" radius (i.e., between the center of the axle and the top of the tire) and its "loaded" radius (between the center of the axle and the road). The engineers call the difference between the two radii "deflection." Increasing vehicle speed will cause the tires to deflect quicker, and increasing vehicle load will cause the tires to deflect farther (if tire pressure isn't increased)."

Focusing on the last sentence, I infer that the need to increase pressure is to reduce the deflection factor due to increased load. However, as mentioned in another of the links explaining load range and ply ratings, the construction of the tire will dictate how much pressure the tire will safely hold. So max psi is NOT indicating that the psi MUST be at that level to support the max load indicated.

3. Increased deflection builds heat in the rubber of the tire. This leads to a tire failure ie. "a blow out."
4. SO proper psi will support the load without excessive deflection and heat buildup.



I respect LC Phil but from my research and personal enthusiasm for tires, I would NEVER endorse starting near the max psi stated on the sidewall.

Thank you but I knew the answer to my own question. The post you quoted me on was directed toward a single participant who was obviously uninformed; the member I quoted.

 

[baldilocks]

I would run about 31 psi

42’s would probably be happy at 21 all the time. Do you drive in the street very much? Yes, I know your were being snarky.

 

[nukegoat]

42’s would probably be happy at 21 all the time. Do you drive in the street very much? Yes, I know your were being snarky.

I said 31, not 21. And I drive to all trails I run. The hammers is about 400 miles away

 

[baldilocks]

I said 31, not 21. And I drive to all trails I run. The hammers is about 400 miles away

Driving to trails and traversing crappy roads on a daily basis don’t compare. Thanks for the clarification though.

 

[nukegoat]

Driving to trails and traversing crappy roads on a daily basis don’t compare. Thanks for the clarification though.

Not sure where youre going with all this

 

[baldilocks]

Not sure where youre going with all this

Nowhere really.