Smart Weigh vs Cat Scales

[Riverbug]

Just sharing some information I recently learned in case it is of interest to anyone...

During a visit to Escapees Smart Weigh to have my truck and travel trailer weighed, I learned that Cat Scales are designed for trucks hauling 80,000# to 120,000# and have a margin of error of 1,000#. I have used Cat Scales to help me understand where weight is distributed in the trailer when the various 4 tanks are empty, full, or partially filled. Before any of my mods, I only had 1,361# of available CCC off the lot. The solar panels, inverter, lithium batteries, cabling, safe, and other misc items I mounted, weighed in the area of 500#. That left 800# for food, new matress, and everything else we put in it. Therefore, if a scale I use to weigh might be off by nearly 1,000 lbs it makes me wonder just how helpful it is other than getting a general idea of how loading shifts weight front to rear. I hadn't really thought about a margin of error on these scales before.

Anyway, Smart Weigh uses scales calibrated and intended for weights within the range of RV's with a margin of 100 lbs.

There's also the advantage of getting each wheel weighed so you also get the side to side weights rather than just front to rear. This was my second truck/trailer I've taken to Smart Weigh and this time I asked lots of questions and learned more than I did the first time around.

 

[Hoopy Frood]

I wonder if that margin of error of 1000 lbs. might not be put into better focus, if the margin of error is a percentage. A percentage of a heavier weight will you a larger possible error than a lesser weight. F'rinstance, a 100,000 lb. trailer/truck with a 1000 lb. error is about 1%, a 1% error on a 20,000 lb. trailer/truck would amount to about 200 lbs.

 

[Riverbug]

I wonder if that margin of error of 1000 lbs. might not be put into better focus, if the margin of error is a percentage. A percentage of a heavier weight will you a larger possible error than a lesser weight. F'rinstance, a 100,000 lb. trailer/truck with a 1000 lb. error is about 1%, a 1% error on a 20,000 lb. trailer/truck would amount to about 200 lbs.

Could be. I'm not really sure. On the surface it makes sense that weighing 120,000# or more might allow for a wider degree of error. But you're point makes sense too.

We are still on the trip where we stopped at Smart Weigh. We were given good advice to note the tank levels, including truck fuel tank, so we had a point of reference for future weighing if we wanted it. If I'm able to put similar percentages into our tanks on the way back North I will try to stop at a Cat Scale and see how the weights compare. That would be interesting.

 

[ajg617]

Interesting read. https://fifthwheelst.com/commercial-truck-scales-vs-portable-scales-for-weighing-rvs.html

 

[Hoopy Frood]

Yeah, kind of looks like it boils down to "Depends..."

 

[Joe1967]

Here in Minnesota, when the DOT scale near my house is not open for business, the scale is still functioning. I have weighed my truck and campers on it several times. There are enough pads that each axle can have it's own weight. The weights on that scale go down to the 10's. I don't know if they are that accurate, but after several weighings, they are quite precise.

 

[Second Chance]

... have a margin of error of 1,000#.

That statement is not true. From CAT themselves:

"The variance of our scales is established in the National Institute of Standards and Technology Handbook 44 Table 6. Class IIIL scales are allowed one division, or a 20 pound variance off zero for each 10,000 pounds of weight applied.

Most calibration tests preformed by either the State Weights and Measures or a licensed scale service company will use a minimum of 20,000 of certified test weights. In the case of a 20,000 pound test, anything beyond a 40 pound error in reading would be a failed test.

In the case of CAT Scale, all of our scales are calibrated at least four times per year by a licensed service company and we require the calibration to be adjusted to zero error."

I'm pretty sure your number for the Smart Weigh program are not correct, as well, and am waiting on a call back from the weighmaster at Escapees.

Rob

 

[Riverbug]

That statement is not true. From CAT themselves:

"The variance of our scales is established in the National Institute of Standards and Technology Handbook 44 Table 6. Class IIIL scales are allowed one division, or a 20 pound variance off zero for each 10,000 pounds of weight applied.

Most calibration tests preformed by either the State Weights and Measures or a licensed scale service company will use a minimum of 20,000 of certified test weights. In the case of a 20,000 pound test, anything beyond a 40 pound error in reading would be a failed test.

In the case of CAT Scale, all of our scales are calibrated at least four times per year by a licensed service company and we require the calibration to be adjusted to zero error."

I'm pretty sure your number for the Smart Weigh program are not correct, as well, and am waiting on a call back from the weighmaster at Escapees.

Rob

Apparently I (and the weighmaster that weighed us and told me this information) stand corrected. If you would like to delete this thread so that nobody receives the wrong information it wouldn't offend me whatsoever. I was just sharing what I was told so would prefer the information not be shared if it is not correct. Thanks.

 

[Second Chance]

Apparently I (and the weighmaster that weighed us and told me this information) stand corrected. If you would like to delete this thread so that nobody receives the wrong information it wouldn't offend me whatsoever. I was just sharing what I was told so would prefer the information not be shared if it is not correct. Thanks.

Thanks for your understanding. I spoke with a weighmaster in Livingston this afternoon. The person who calibrates the Smart Weigh scales is not in but the weighmaster is going to check with him/her as soon as possible and get back with me. I'll leave things in place here until we get it straight from the horse's mouth. I'm confident about the CAT part but want to make sure I'm not the one who's wrong about the Escapees part.

Rob

 

[Wileykid]

I have been to a number of different CAT scales, and accounting for additional or less weight that I know about, the weights have all been within 20-40 lbs. With a margin of up to +/- 30 lbs at my weight, that is pretty good. The CAT scale weight can be used to challenge a DOT weight in court, so they are kept as accurate as possible.

 

[Riverbug]

I can't really understand why we would have been told this. It's possible that we misunderstood but my wife says she heard it the same way I did. Perhaps he didn't explain it the way he meant but anyway... Guess we'll chalk this one up to a "misunderstanding", but I'm still going to try to replicate the tank levels and weigh on the way back North if I get the chance. Since I have SeeLevel monitors it would at least be easy enough to fill them to the same level as when we had the Smart Weigh done.

 

[Captcolour]

Don't forget that CAT scales are 3 individual scales and not one giant one. So the capacity of each scale likely isn't 100,000 lbs but more likely in the 50,000 lb range (could not find this number on-line). For best accuracy, you want to weigh at a minimum around 5% of the scale capacity.

 

[roegs01]

Here in Minnesota, when the DOT scale near my house is not open for business, the scale is still functioning. I have weighed my truck and campers on it several times. There are enough pads that each axle can have it's own weight. The weights on that scale go down to the 10's. I don't know if they are that accurate, but after several weighings, they are quite precise.

On our annual trip to FL we pass many DOT scales in each state both open and closed. I've often wondered if I could pull in as I don't remember ever seeing gates or cables across the off - on ramps. Are all DOT scales available for anyone to use when they are not open for truckers? Also, when they are open and actively weighing trucks, can I get in line and get weighed?

 

[Second Chance]

On our annual trip to FL we pass many DOT scales in each state both open and closed. I've often wondered if I could pull in as I don't remember ever seeing gates or cables across the off - on ramps. Are all DOT scales available for anyone to use when they are not open for truckers? Also, when they are open and actively weighing trucks, can I get in line and get weighed?

Pulling in while the DOT scales are closed is one thing (though maybe not Kosher). If you pull in while they're open and you're not a commercial vehicle, you'll get some dirty looks and be told to get out of their way.

Rob

 

[Joe1967]

I second not visiting a scale open for business. I don't see anything wrong with stopping at one that's closed. I would make sure the scale readout is on before driving on the scale, however.

 

[Second Chance]

OK... information from two people over two days of communication with the Escapees Smart Weigh program and finding the scales on the manufacturer's web site:

"The scales are Haenni WL 101 scales.

Accuracy is:
+ or- 50 lbs up to 2500 lbs
+or - 100 lbs up to 10000 lbs.
The scales are calibrated every year."

Since these scales are single-wheel (or wheel location in the case of dualies)scales, these margins of error could be multiplied by the number of wheels - four for two axle trailers, six for three axle trailers, and four (locations) for the tow vehicle (unless you're towing with a non-singled class 7 or 8 tractor). Though the errors might average out, if the scales are measuring either high or low the error(s) would be additive. It pains me to say it, but my opinion of the Escapees Smart Weigh program just went through the floor and, personally, I don't consider it useful for folks with smaller rigs or who are close to the payload limit on their tow vehicles. Again, my opinion only, but these numbers would be good only for getting a ballpark for tire inflation pressures. No business would ever pay a carrier weight-based freight charges based on scales with this kind of margin of error, either.

There are three scale pads with the CAT scales: steer, drive and trailer which puts multiple wheels on the same scale pad. The CAT scales are also much more accurate.

Rob

 

[JPS350]

I would agree with your assessment above. Only 1 data point here, but I visited 2 cat scales on 2 different days in my area this week. I had to use a second location because the first was closed for service when I got there. I did 2 of the same weighs on day 1 (WDH bars on and off). Exactly the same gcvw on each, so if there were compounding errors on the 3 scales it would have shown up likely.

Day 2 I dumped the approx 30 gal of water I had in the water tank. I did 2 measurements to see the effect of moving my 2 generators around in the trailer. Both the gvcw's were exactly the same and were 220 lbs lighter than the previous day (weight of the water). Also, moving the 2x 50 lbs generators from the garage area to the very back of the trailer (behind the axles) resulted in the tongue weight being reduced by 120 lbs. I'd say these scales are very accurate even for lighter vehicles.

While measuring individual wheels would give you some additional info, if the margin of error is like you stated, I'm not sure you really learn anything, especially when the errors compound.

 

[Hoopy Frood]

I'll have to admit I was surprised at how much error was allowed by the individual wheel weighing scales. But to me their usefulness is the fact you have individual wheel weights. Their total weights may be pretty inaccurate, but IMO, the reason you weigh each wheel is for information on how the wheels/axles are loaded, not necessarily gross weight of the trailer. JMO anyway. Considering how closely the axles tend to run toward their upper limit, on heavier trailers anyway, knowing wheel weights is a good idea, to me anyway.

 

[kb0zke]

Sounds to me like the best isn't either/or but both/and. Smart Weigh will give us individual wheel weights, which will tell us if one wheel is carrying more of the load than it ought. The CAT scales will give good information on how the truck axles are loaded and an overall gross combined weight.

Our situation is perhaps different than what a heavy 5'er would have, since we have eight tires on the ground (four each truck and trailer) and we're about 23,000 gross combined weight. We should have about 2800 pounds on each trailer wheel with about 2000 pounds on the tongue. WDH moves some of that around, of course. I'm figuring the truck at about 10,000 pounds as loaded for travel.

 

[JPS350]

It is a great idea. I'll agree with that. I know this is unlikely, but what if you were interested in tongue weight and did 2 weighs (no load bars truck and trailer, then truck only). If all the truck wheel weights were off by +50 on the first weigh and all the all the truck wheel weights were off -50 on the second weigh, it would all be acceptable (in specs) and the tongue weight would be off 400 lbs.

If you're concerned with balancing side to side and 2 wheels on the right side of the trailer measure +50 lbs over each, and the 2 on the left side measure -50 under each what do you do? All within spec and side to side you start with a 200 lb error you don't know about. Sure, an extreme case but I wouldn't have a lot of faith in the results of their selling point of the need to measure individual wheels rather than axles.