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Tag axle switch confusion and axle weights
#1
I have access to a truck scale. I know this is not the preferred way to measure axle weights. I can confirm that its not, by the facts below. My confusion comes from the switch on my dash that says "tag axle" and the light that says "Dcres weight" or something like that.  While checking axles on the scale, I left only the 3rd axle on the scale, the drive and steer were off the scale. 

with out the "tag axle" switch I read #17,140
with the "tag axle" swicthed and the light reading "dcres weight" I get #20,760

why ?

has somebody mis wired my switch ?

#20,760 seem too much on the tag axle.

Back to the scale, it is not level going off one of the ends, so I choose the better end of the 2 to measure from. Also as I park the front axle on with tag and drive axles just off the end. I get different reading from going on the scale from a different direction. In other words, trying to get as close to the middle of a 80' scale. #20,800 facing west, #18,900 facing east.

Totals for Going west
Steer only                    #20,800
steer and drive only      #43,240
All 3 axles                    #57,070
drive and tag only         #37,920
Tag only not measures because the ramp going off would add weight to the Tag.

Totals for going east 
Steer only                   #18,900
Steer and Drive only    #32,740     (ramp or bump at this end may throw this measurement off)
all 3 axles                   #57,460
Drive and tag only       #39,380
Tag down (?) #17,140
Tag Up (?)     #20,760

 Are scales not accurate when not loaded evenly across the "plate" ?  Crappy scale ?


It's has to be the scales....partially. Right?

I want the correct weights, Where have you folks found to get this accurate information

Thoughts????
Dave, Karen and buddy. 
06 Newell #784 towing a 05' Featherlight enclosed  trailer for toys and tools
A bunch of stuff on wheels (46 wheels, too many according to the wife) including 59' Nash metropolitan conv., KTM 250 dual sport. 

Carpe Diem. 
Tomorrow is not guaranteed.

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#2
If all the tires aren't on the same level, you will get weird results.

Set up cribbing so all tires are at the level plane & move the scale to the different spots to get better results.

I took mine to a truck stop & used their scale - it was about $10 for the first weigh & about $3 for the next weigh (so you can change the tag axle setting)
1987 classic #159
8V92 MUI , Allison 740
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#3
I have also experienced issues with the area around some truck scales not being level and messing up the weights. The best way to get wheel weights is to find someone with portable truck scales so you can find a level spot and drive up on the individual scales. Newell has that type of scales and I found a man in Kerrville, TX that would come to your site and bring his scales. At regular truck stop scales such as CAT scales at Pilot/Flying J, the best I was able to do was get the tag axle and drive axle combined and the front axle separate by asking for a split weight. I found some moving company scales would allow me to do what you did but the area around the scale was not flat since they always expected the entire truck/trailer to be on the scale at one time so the measurements were not repeatable.

The 17,000 tag weight is high even assuming you have a 63,300 GVWR. The axle weight ratings for the 63,300 coaches are 20,000 front, 28,000 drive and 16,000 tag.

Not sure how the ZF suspension tag switch functions. Prior to the ZF suspension, Newell used first a switch that dumped the tag, then in later years a switch that either removed pressure from the tag or ADDED pressure to the tag to decrease weight on the DRIVE AXLE. Decreasing weight on the DRIVE axle would be consistent with what you were seeing.

IF the weights were in the ballpark, the front looks like it is close to the weight limit, the tag over the rated capacity with extra capacity remaining on the drive axle.
Michael Day
1992 Newell 43.5' #281
NewellOwner.com
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#4
(09-23-2018, 11:05 AM)DK on the road Wrote: I have access to a truck scale. I know this is not the preferred way to measure axle weights. I can confirm that its not, by the facts below. My confusion comes from the switch on my dash that says "tag axle" and the light that says "Dcres weight" or something like that.  While checking axles on the scale, I left only the 3rd axle on the scale, the drive and steer were off the scale. 

with out the "tag axle" switch I read #17,140
with the "tag axle" swicthed and the light reading "dcres weight" I get #20,760

why ?

has somebody mis wired my switch ?

#20,760 seem too much on the tag axle.

Back to the scale, it is not level going off one of the ends, so I choose the better end of the 2 to measure from. Also as I park the front axle on with tag and drive axles just off the end. I get different reading from going on the scale from a different direction. In other words, trying to get as close to the middle of a 80' scale. #20,800 facing west, #18,900 facing east.

Totals for Going west
Steer only                    #20,800
steer and drive only      #43,240
All 3 axles                    #57,070
drive and tag only         #37,920
Tag only not measures because the ramp going off would add weight to the Tag.

Totals for going east 
Steer only                   #18,900
Steer and Drive only    #32,740     (ramp or bump at this end may throw this measurement off)
all 3 axles                   #57,460
Drive and tag only       #39,380
Tag down (?) #17,140
Tag Up (?)     #20,760

 Are scales not accurate when not loaded evenly across the "plate" ?  Crappy scale ?


It's has to be the scales....partially. Right?

I want the correct weights, Where have you folks found to get this accurate information

Thoughts????

To answer your question, scales frequently are not accurate when part of a vehicle is on and part is off.  That is referred to as "split weighing" which is illegal in most States for commercial purposes.  There are many variables involved which can introduce error.  FYI as a rule of thumb a legal vehicle skill may be off 160 pounds when 80,000 pounds are applied and be in tolerance.  Again there are many variables which come into play which affects the allowed tolerance, that is why I said rule of thumb.

FYI I am the weights and measures director for KS.

Your best bet would be a "cat" style scale.  These are actually multiple scales which give a summed total.  The trick is finding one where each axle sits on it's own platform simultaneously.  For a class A RV you'll need to drive on from the opposite direction that a semi and trailer does to make this work.  And even then it may not depending on the deck size of the individual scales in the system.
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