Reprogramming PSOM for tires ISSUE
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Elder User
Joined: Jul 2004
Posts: 620
Likes: 1
From: Toronto, ON
Reprogramming PSOM for tires ISSUE
Hey,
OK, so I'm stuck with having to do this, and seems quite simple. One major problem is that i seem to have found a major discrepancy with which some people are reporting the conversion constants.
For example, one online calculator I used and the chart in the article located on this site stated that for a 33" tire, the conversion constant should be in the 8.6 ball park.
But, using a formula provided, I calculate my conversion ratio to be (for 33") to be in the 8.29 ball park, and there are some charts that acknowledge this number as well.
So I don't know what to do or which one to use!
OK, so I'm stuck with having to do this, and seems quite simple. One major problem is that i seem to have found a major discrepancy with which some people are reporting the conversion constants.
For example, one online calculator I used and the chart in the article located on this site stated that for a 33" tire, the conversion constant should be in the 8.6 ball park.
But, using a formula provided, I calculate my conversion ratio to be (for 33") to be in the 8.29 ball park, and there are some charts that acknowledge this number as well.
So I don't know what to do or which one to use!
Cargo Master
Joined: Jun 2002
Posts: 2,033
Likes: 32
From: Aurora,Colorado
I would calculate what your original tires were--and see how close the PROM setting was. I suspect that it wasnt right on even from the factory.
If I remember correctly--the PROM will allow 6 changes before it is locked in.
The published circumference of the tire isnt important in these calculations--only the loaded and mounted radius of the tire is important--and it will be smaller than the published manufacturer radius.
If I remember correctly--the PROM will allow 6 changes before it is locked in.
The published circumference of the tire isnt important in these calculations--only the loaded and mounted radius of the tire is important--and it will be smaller than the published manufacturer radius.
Cargo Master
Joined: Jun 2002
Posts: 2,033
Likes: 32
From: Aurora,Colorado
Originally Posted by MustangGT221
I think you also need the revs per mile, I got mine from the manufacturers website.
Hopefully we can get a solid answer on this, I am in need of calibrating mine for 35s.
Hopefully we can get a solid answer on this, I am in need of calibrating mine for 35s.
Elder User
Joined: Jan 2006
Posts: 544
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Don't go by the circumference of the tire. The best and most accurate way is to measure the rolling diamater. First check and if needed adjust the air pressure in the rear tires, then on flat cement/pavement mark the tire and the ground and roll the truck so the tire makes one full turn and mark the ground again. Then measure how many inches the tire rolled.
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Cargo Master
Joined: Jun 2002
Posts: 2,033
Likes: 32
From: Aurora,Colorado
Originally Posted by DaveBowman
Don't go by the circumference of the tire. The best and most accurate way is to measure the rolling diamater. First check and if needed adjust the air pressure in the rear tires, then on flat cement/pavement mark the tire and the ground and roll the truck so the tire makes one full turn and mark the ground again. Then measure how many inches the tire rolled.
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Thread Starter
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Elder User
Joined: Jul 2004
Posts: 620
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From: Toronto, ON
yeah, that's no problem 
(using the loaded radius rather than published radius/diameter)
but, what formula do i use afterwards? obviously, with the one formula, I will come out close to the conversion constant of 8.29 i got using a diameter of 32.8. but there are still charts i see out there that contradict that number, and show that the conversion constant is actually near 8.6 for 33" tires. there's a big difference between 8.3 and 8.6 :P
my PSOM is programmed currently for 9.72, which is perfect for the tire size it has (29" tires approx, 235/75/15).
(using the loaded radius rather than published radius/diameter)but, what formula do i use afterwards? obviously, with the one formula, I will come out close to the conversion constant of 8.29 i got using a diameter of 32.8. but there are still charts i see out there that contradict that number, and show that the conversion constant is actually near 8.6 for 33" tires. there's a big difference between 8.3 and 8.6 :P
my PSOM is programmed currently for 9.72, which is perfect for the tire size it has (29" tires approx, 235/75/15).
Cargo Master
Joined: Jun 2002
Posts: 2,033
Likes: 32
From: Aurora,Colorado
Originally Posted by Roushians
yeah, that's no problem (using the loaded radius rather than published radius/diameter)
but, what formula do i use afterwards? obviously, with the one formula, I will come out close to the conversion constant of 8.29 i got using a diameter of 32.8. but there are still charts i see out there that contradict that number, and show that the conversion constant is actually near 8.6 for 33" tires. there's a big difference between 8.3 and 8.6 :P
my PSOM is programmed currently for 9.72, which is perfect for the tire size it has (29" tires approx, 235/75/15).
(using the loaded radius rather than published radius/diameter)but, what formula do i use afterwards? obviously, with the one formula, I will come out close to the conversion constant of 8.29 i got using a diameter of 32.8. but there are still charts i see out there that contradict that number, and show that the conversion constant is actually near 8.6 for 33" tires. there's a big difference between 8.3 and 8.6 :P
my PSOM is programmed currently for 9.72, which is perfect for the tire size it has (29" tires approx, 235/75/15).
And 235/75 x 15 are not 29 inches high--not the ones that I have measured. They are actually shorter than that. More like 28 and 1/2 inches or less.
