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Old 10-22-2021, 07:57 PM   #1
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CAT scales seem inaccurate

Have any of you ever found CAT scales to be slightly inaccurate? In my quest to get my new Flagstaff 526RK to ride the smoothest I made a trip to a nearby CAT scale at Love's. I weighed my rig, then unhooked and weighed the truck, then rehooked and made some adjustments and got 2 more reweighs. The first gross weight was 18320, the second two were 18260. That's 60 lbs. lighter and nothing was removed from the rig. Not a big deal but it changed my pin weight by about 1/2% point. Just wondering how consistent these scales are?
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Old 10-22-2021, 08:36 PM   #2
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According to the laws, scales must be accurate to 1/10 of 1% of the capacity of the scale. Back to that in a moment. Highways scales in most locations are either 200 or 300,000 pounds capacity. So multiply that capacity by the accuracy and it means the scale is only accurate within 200 lbs.

Also, did you set your parking brake when you were on the scale? If you stay on the brake pedal before the scale settles and reads, it will shift the weight to other axles.
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Old 10-22-2021, 09:22 PM   #3
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Good enough for gov'n work

After all they are intended for Semi tractor trailer combos

Us light weight 5th wheelers can get close enough weigh tickets for checking axle weights
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Old 10-22-2021, 11:08 PM   #4
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Sometimes wind can be a factor .
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Old 10-23-2021, 05:08 AM   #5
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Please explain. The only thing I can think of is a tornado lifting it off of the scale.
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Old 10-23-2021, 06:46 AM   #6
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Please explain. The only thing I can think of is a tornado lifting it off of the scale.
High sided vehicle catch the wind which pushes against the truck/trailer causing the scale readings to change , depending on wind direction against the vehicle.
Thats why dot will sometimes shut a scale house down when winds get gusty or above a certain wind speed.
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Old 10-23-2021, 07:30 AM   #7
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Interesting conversation. Learn something new everyday.
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Old 10-23-2021, 04:17 PM   #8
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Also, did you set your parking brake when you were on the scale? If you stay on the brake pedal before the scale settles and reads, it will shift the weight to other axles.
I think if you've properly stopped moving it makes no difference whether you're on the service brake or the emergency/parking brake.
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Old 10-23-2021, 08:00 PM   #9
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I think if you've properly stopped moving it makes no difference whether you're on the service brake or the emergency/parking brake.
Yeah it makes a difference with a auto tranny left in gear with a foot on the service brakes.
First lesson learned is shift the auto tranny to neutral then apply a brake or with a std tranny shift to neutral.
Generally scale are level to the world and applying a brake may not be necessary.

Oh yeah....don't make jack rabbit starts and don't make jerky stops.
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Old 10-23-2021, 09:34 PM   #10
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Right after I bought my truck I went to the CAT scales and the ticket was 4K for a 2018 F-350. The manager scratched his head and said to go reweigh and it was 7,200. Yes, they can be wrong.
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Old 10-23-2021, 09:43 PM   #11
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Right after I bought my truck I went to the CAT scales and the ticket was 4K for a 2018 F-350. The manager scratched his head and said to go reweigh and it was 7,200. Yes, they can be wrong.
OP is questioning a 60# difference not 3200#
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Old 10-24-2021, 07:53 AM   #12
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Originally Posted by rollondown View Post
According to the laws, scales must be accurate to 1/10 of 1% of the capacity of the scale.
I havenít been able to verify that, but I did find discussion of CAT scales where they claim +/- 0.2% accuracy, applied to the load being weighed. Mettler Toledo also claims the same, with the usual verbiage about striving to narrow that to a smaller tolerance. That would mean the OPís rig should weigh 18,000 lb +/- 36 lb.

I could not find actual truck scale accuracy tolerances by state or by any other standard.
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Old 10-24-2021, 08:43 AM   #13
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I havenít been able to verify that, but I did find discussion of CAT scales where they claim +/- 0.2% accuracy, applied to the load being weighed. Mettler Toledo also claims the same, with the usual verbiage about striving to narrow that to a smaller tolerance. That would mean the OPís rig should weigh 18,000 lb +/- 36 lb.

I could not find actual truck scale accuracy tolerances by state or by any other standard.

Well if at 18,000# combined one is worried about 36#, you already have an issue!
I have always weighed at ODOT (Oregon DOT) closed weight stations, the displays are always left on. The display only displays in 50# increments, so they must not get into the nity grity of a couple pounds.


Interesting that our 2016 Ram Laramie 3500 DRW had a curb weight of 8,589# when it left the factory, and the last couple times we scaled it at a weigh station with full fuel and DEF, and ready to tow scaled 10,000#. This is the part that many when looking at yellow sticker payloads forget, that is the deductions before hooking up the trailer.
Wife and I are not skinny, but also not obese, I do have a standard 5th wheel hitch and picture frame adapter, and an in bed tool box with stuff in it, seems some heavy stuff.
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Old 10-25-2021, 10:53 AM   #14
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Also, did you set your parking brake when you were on the scale? If you stay on the brake pedal before the scale settles and reads, it will shift the weight to other axles.
Can you explain how the brakes change the weight? That doesn't make sense to me.
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