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mowermech

Billings, MT

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Posted: 10/11/20 07:20am Link  |  Quote  |  Print  |  Notify Moderator

There is always the tried and true "chalk mark" method. Get some chalk, and draw a line across the tread of the tires. Drive for 100 yards or so. If the chalk mark is gone on the edges, but not in the middle, the tire is under inflated. Add air.
If the chalk mark is gone in the middle, but not on the edges, the tire is over inflated. Decrease the pressure.
If the chalk is gone clear across the tread, the tire is properly inflated for the current load.
If the chalk is gone on one side of the tire, there is an alignment problem that needs to be fixed ASAP!

Under inflated or over inflated results in a small contact patch, which results in poor grip on the highway. We need all the rubber on the road we can get!


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Posted: 10/11/20 10:42am Link  |  Quote  |  Print  |  Notify Moderator

Btw, the “tried n true “ chalk mark test is about the worst way to figure it out unless one can’t envision what gross over or under inflation looks like.
Either go hit a truck scale or do a little math based on Uvw, anticipated axle loads and a good guesstimate of how much ccc you’re using. And what your tire load capacities are.
Not rocket surgery and not that difficult.
You’ll find 65 is probably right for little tires under a big van steer axle.
The right rear pressure could be all over the board. But higher than necessary is safer than lower than necessary.

But you have to do your own math. We can’t invent the math without the numbers


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

Cummins12V98

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Posted: 10/11/20 10:44am Link  |  Quote  |  Print  |  Notify Moderator

wa8yxm wrote:

Till you scale it go with the maker's mark (No not the booze) The manfacturer's recommendation.

Then get it weighed and use the Tire Maker's inflation chart.

I say that because there are a few inflation pressures all but guaranteed to be wrong

1: The number on the sidewall (Actually it's right but you need to read the full sentence: Maximum load of xxxxx pounds at maximum pressure of yy PSI)

2: the pressure on the sticker (They do not know know much STUFF you have)

3: The pressure the tire dealer puts in.

On my rig.. turns out the sidewall is correct as loaded.


I agree but I will add by saying to add 10 psi to the front chart spec and 5psi to the rears.


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IAMICHABOD

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Posted: 10/11/20 12:34pm Link  |  Quote  |  Print  |  Notify Moderator

Cummins12V98 wrote:


I agree but I will add by saying to add 10 psi to the front chart spec and 5psi to the rears.


That is ludicrous the very reason of the spec chart is to give you the BEST INFORMATION why use it at all if you choose to ignore it...[emoticon]


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dedmiston

The West

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Posted: 10/11/20 12:35pm Link  |  Quote  |  Print  |  Notify Moderator

Moved from General RVing.


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DrewE

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Posted: 10/11/20 01:37pm Link  |  Quote  |  Print  |  Notify Moderator

Cummins12V98 wrote:


I agree but I will add by saying to add 10 psi to the front chart spec and 5psi to the rears.


For most class C's, adding 5 psi to the rear tires over the chassis manufacturer's recommendations (i.e. the door sticker) will put the tires exactly 5 psi over their maximum inflation pressure. The rear axle weight rating is the maximum for the standard tires at their maximum pressure of 80 psi. It's fairly likely the wheels are also rated for a maximum of 80 psi.

Would 5 psi higher than the rating be dangerous in practice? Probably not...but still it's hardly a good idea.





Jack Spratt

Maine

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Posted: 10/11/20 03:27pm Link  |  Quote  |  Print  |  Notify Moderator

We have a 2019 260DSF
Front 70# Rear 75#
Airbags at 50#
These #’s work great for us. Gusty 35 + blowing the semi’s around
and we had a steady ride.
I might try 75# on the front tires on our next trip, but think the handling
and ride quality might suffer.
The door sticker calls for 75 and 80.


Leprechaun 260 DSF
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Cummins12V98

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Posted: 10/11/20 03:30pm Link  |  Quote  |  Print  |  Notify Moderator

IAMICHABOD wrote:

Cummins12V98 wrote:


I agree but I will add by saying to add 10 psi to the front chart spec and 5psi to the rears.


That is ludicrous the very reason of the spec chart is to give you the BEST INFORMATION why use it at all if you choose to ignore it...[emoticon]


Gee thanks

Have you ever gotten over 100k on LT tires on a 4x4 2500 RAM diesel? I have and more.

Also thanks for the name calling.

Cummins12V98

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Posted: 10/11/20 03:32pm Link  |  Quote  |  Print  |  Notify Moderator

DrewE wrote:

Cummins12V98 wrote:


I agree but I will add by saying to add 10 psi to the front chart spec and 5psi to the rears.


For most class C's, adding 5 psi to the rear tires over the chassis manufacturer's recommendations (i.e. the door sticker) will put the tires exactly 5 psi over their maximum inflation pressure. The rear axle weight rating is the maximum for the standard tires at their maximum pressure of 80 psi. It's fairly likely the wheels are also rated for a maximum of 80 psi.

Would 5 psi higher than the rating be dangerous in practice? Probably not...but still it's hardly a good idea.


Don’t most have dual rear wheels with “E” tires???

Cummins12V98

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Posted: 10/11/20 03:37pm Link  |  Quote  |  Print  |  Notify Moderator

DrewE wrote:

Cummins12V98 wrote:


I agree but I will add by saying to add 10 psi to the front chart spec and 5psi to the rears.


For most class C's, adding 5 psi to the rear tires over the chassis manufacturer's recommendations (i.e. the door sticker) will put the tires exactly 5 psi over their maximum inflation pressure. The rear axle weight rating is the maximum for the standard tires at their maximum pressure of 80 psi. It's fairly likely the wheels are also rated for a maximum of 80 psi.

Would 5 psi higher than the rating be dangerous in practice? Probably not...but still it's hardly a good idea.


Please show me a class C rear tire inflation of 80psi. Do you understand that will add up to at least 11,000#.

Like I said weigh your rig LOADED. Use chart, it ain’t gonna be 80psi front or rear.

I run full rear axle rating of 9,750#. Ram says 65psi rear.

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