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Old 08-18-2013, 11:27 AM   #1
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Tag axle tire pressure

I understand the concept of axle weights and tire pressure. However, I now have a tag axle and not sure how to determine the correct tire pressure. If I weigh at a CAT scale I can get the front weight but the rear weight will be both the drive and tag together. Do I use the total rear weight and use the dual chart for the drive axle tires and then what chart do I use for the tag axle tires?

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Old 08-18-2013, 03:50 PM   #2
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I can only tell you what our tag axel is set at... per the factory recommendation, the tags and the drive axel are the same at 85 PSI.

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Old 08-18-2013, 04:01 PM   #3
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To set tag axle tire pressure you would need the tag axle weight which would mean 3 different weights. On our Newmar Essex the tag axle weight can be adjusted to determine the weight you want on the tag axle which would then determine the air pressure to put in tag axle tires. When you adjust tag weight by adjusting air pressure in air bags on tag axle this would also change weights on front and drive axle. Should only be done by person who knows what they are doing and have all scales needed. Usually have around 6 to 7000 pounds on tag axle which means without scale should be between 80 to 90 psi. Tom 04 Essex
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Old 08-18-2013, 04:36 PM   #4
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Our coach has a label inside, behind the captain chair. It lists the TAG at 80 P.S.I. Since the other wheel PSI #s assume a max. axle load I share in your fustration.

I use the chart in the manual to adjust down based on my actual axle weights (drive and steer) and just keep the TAG at 80.
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Old 08-18-2013, 05:03 PM   #5
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Here are my pressures (52000 GVWR)
Steer axle: 130 pounds
Rear Dual Drives: 95 pounds
Tag Axle: 110 pounds
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Old 08-18-2013, 07:53 PM   #6
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I drive onto the truck scales backwards. This gives me individual weights for each of the 3 axles. I don't know if you can do that on a Cat scale though. You really need the three weights so you can adjust the load on the tag. After doing this and getting the weight of each axle, you'll know the correct tire pressures.
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Old 08-18-2013, 08:00 PM   #7
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Start with this info and then use the charts for tire pressures. Untitled Document
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Old 08-18-2013, 08:58 PM   #8
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This is gonna sound complicated (it sorta is if you are math challenged) but Here is what I do at a CAT scale...

1. get full axle weight of each axle the first time around. I have someone spot me so that I can split pad 2 and 3 with the drive & tag.

2. I go back and put one set of wheels on the scale and the other on the side apron. I put the center line of the MH on the crack between the pad and apron. The steerer goes on pad 2 and the drive & tag combo go on pad 3 (trailer).

Now, lets say the full drive weight (Pad 2) was 18,000# & the tag (Pad 3) was 7,000#. You will need that information a bit later.

Now the math...

1. Subtract the second weighing pad 2 from the first pad one (steerer) and you now have separate steerer tire weights. DONE WITH STEERER!

Now the hard part...

2. Add together the full axle weights of both the drive and tag axles from the first weight and then subtract the pad 3 weight. You can use this to approximate the ratio of left vs right. As an example, if the total weight of the full axle weights equals 25,000# and the combined weight of the rights wheels on the second weighing was 12,300# the left side would be 12,700#.

NOW...convert that to a %. In the above example the right side is 49.2% (12,300/25,000)

So...I use that ratio to APPROXIMATE the weights.

Based on the above:

Right Drive = 8856#
Left drive = 9144#
Right Tag = 3444#
Left Tag = 3556#

It isn't perfect but it is reasonable.

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