TIRES relation load/pressure/speed - BFG 235/255/265

[kookynet]

Let's say you have to deflate (soft sand :snorkel.
How slow should you drive with such load and such pressure ?

See the relation load / pressure /speed for three sizes in a later post (the attachement below does not work)

LT-255/85R16

LT-265/85R16

LT-235/85R16

I had asked these data for BFG A/T and M/T. I got only one answer so I assume it would apply to both type of tire.

Safe Drive !
Robert

 

[iigs]

I don't see any of the embedded data in that document... Can you export it as a .PDF?

 

[LandCruiserPhil]

I found this article on tire pressure interesting:

I worked for Michelin Tire Corporation for 7 years and Yokohama Tire Corporation for 11 years. I have given numerous tire seminars on tire maintenance and especially how to determine the correct tire pressures. So here goes.
The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph. (The speed can vary somewhat but it is not important for our discussion).
The air pressure is required to support the load that the tire must carry in such a manner that the tire flexes at the designed place on the sidewall of the tire.
If the load on the tire changes then the air pressure should change accordingly to keep the tire flexing at the proper place.
The reason for correct air pressure is to prevent the tire from overheating. It was put together with heat and it will come apart the same way. An under inflated tire will eventually self destruct due to excessive heat build up. An over inflated tire will ride harshly and be more likely to burst upon impact. Sorry for the long explanation but here is the bottom line.
To determine the correct air pressure, check the pressure when the tire is cold. Run the tire for several miles at highway speed. Stop and immediately check the air presser in the tire. It should be higher than we cold but no more than 10% higher.
Now here is the hard to believe part. If the pressure is more than 10% higher you must ADD AIR and test again. For example if you start with 50 psi cold. If the pressure is 60 when hot, you have exceeded the (10%) in this case, 55 psi maximum safe heat build up pressure. You must ADD AIR. In this case I would add 5 psi which would take the tire to 65 psi when hot. After you run the tire again you will find the pressure to actually drop because the tire will run cooler. The heat build up causes the tire pressure to increase when under inflated.
On the other hand, if the 50 psi cold pressure does not change when hot. You have more air than needed. You can remove 5 psi or so and test again when they return to cold. Like the next trip you take.
So a fully loaded rig will require more air in the tires than one with empty tanks and a light load on board. Always error on the side of over inflation. Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed. Each axle has its own requirement based upon the load on that axle.

 

[Redline]

x2, all I see is the tire size at the top of the page, no data.

I don't see any of the embedded data in that document... Can you export it as a .PDF?

 

[Redline]

Thanks for both posting that and listing your credentials, obviously you know what you are talking about. I like the method you describe as a means of setting the proper on-highway, higher speed PSI. It is certainly different than the 'calk test' most people use, or suggest that others use. I assume the calk test is an okay method, though I have never used it.

The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph.

I would add one word here for clarification... 'The pressure on the sidewall of the tire is the maximum pressure at the maximum published load...

I found this article on tire pressure interesting:

I worked for Michelin Tire Corporation for 7 years and Yokohama Tire Corporation for 11 years. I have given numerous tire seminars on tire maintenance and especially how to determine the correct tire pressures. So here goes.
The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph. (The speed can vary somewhat but it is not important for our discussion).
The air pressure is required to support the load that the tire must carry in such a manner that the tire flexes at the designed place on the sidewall of the tire.
If the load on the tire changes then the air pressure should change accordingly to keep the tire flexing at the proper place.
The reason for correct air pressure is to prevent the tire from overheating. It was put together with heat and it will come apart the same way. An under inflated tire will eventually self destruct due to excessive heat build up. An over inflated tire will ride harshly and be more likely to burst upon impact. Sorry for the long explanation but here is the bottom line.
To determine the correct air pressure, check the pressure when the tire is cold. Run the tire for several miles at highway speed. Stop and immediately check the air presser in the tire. It should be higher than we cold but no more than 10% higher.
Now here is the hard to believe part. If the pressure is more than 10% higher you must ADD AIR and test again. For example if you start with 50 psi cold. If the pressure is 60 when hot, you have exceeded the (10%) in this case, 55 psi maximum safe heat build up pressure. You must ADD AIR. In this case I would add 5 psi which would take the tire to 65 psi when hot. After you run the tire again you will find the pressure to actually drop because the tire will run cooler. The heat build up causes the tire pressure to increase when under inflated.
On the other hand, if the 50 psi cold pressure does not change when hot. You have more air than needed. You can remove 5 psi or so and test again when they return to cold. Like the next trip you take.
So a fully loaded rig will require more air in the tires than one with empty tanks and a light load on board. Always error on the side of over inflation. Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed. Each axle has its own requirement based upon the load on that axle.

 

[Antichrist]

Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed.

I assume the person meant the maximum pressure indicated on the sidewall. I've never seen a "sidewall pressure" given on a tire. In any case, doing that would be a good way to get premature wear on the tire.

 

[charlieaarons]

http://www4.mercedes-benz.com/e/unimog/unimog_ugn405/betriebsanleitung/vertiefen/N232D6.html

Look at the very bottom of the linked page. This gives percentages of highway/high speed pressure suggested by Mercedes for various offroad situations.
These are for big Unimog tires, but the percentages give you an idea.
Generally, the higher the aspect ratio the more you can drop the pressure at lower speeds.

Charlie

 

[kookynet]

THREE pics re TIRE / PRESSURE SPEED LOAD

Sorry about the attachement. Pdf was too big.
This time I try to ATTACH three jpg

Very interesting input re adding air above 10%. Thanks.

Robert