Fun with a truck scale

[HMS_Beagle]

I bought a truck scale off of eBay.

These are frequently advertised as wheel scales, axle scales, wheel weighers, etc. Most of them these days are electronic, but the MD400 is a mechanical one that you see from time to time. I paid less than $200, they are heavy and it cost about $50 to ship. It is readable to 20 lbs, claimed absolute accuracy is 50 lbs to 5000 lb load, then 1% of applied load to max capacity of 20,000 lbs.



With only one scale you need a wheel shim of the same thickness so that the axle being weighed is level. There will be a very small error if the other axle is not also blocked to the same height, but that can be safely ignored.



The results for my '99 F350 DRW 4x2 with Bigfoot 10.4E:

LF 1930 RF 2160 total 4090 GAWF 4550
LR 3500 RR 3640 total 7140 GAWR 7460
total 11,230
GVWR 11000



This is with nearly full tanks (fresh water, propane, diesel), full owner's outfit, but no clothes, food, people. As you can see I am just under on each axle (but will be over on the front with 2 people and the cat), and over on GVWR. This is a relatively light camper, no slides, no air conditioner, no genset. The "owner's outfit" I transferred from the old camper, about 4 armloads worth - I doubt it was more than 100 lbs.

I remain truly amazed at those who can put a 2 slide camper on a 3/4T pickup and keep in under GVWR - filled with helium maybe?

You can weigh the camper directly with the scale. By measuring the weighing points, you can calculate the CG too.

[mkirsch]

Nobody ever said they were putting 2-slide units on 3/4 ton trucks and keeping them under GVWR. Most are blissfully ignorant of the fact and the rest just don't care.

[HMS_Beagle]

I Fish 2 wrote:
HMS, you show a picture of the camper setting on the scale. What did it weigh?

I weighed both the old (1998 Bigfoot 9.6) and new (2008 Bigfoot 10.4E) camper.

2500C9.6 front 1550 rear 1200 total 2750
Water and propane, nothing else in it

2500C10.4E front 1830 rear 1740 total 3570
1/2 water, propane, gear but no groceries.

The campers are not that different in size, I'm a little surprised at the weight difference, but those weights more or less match the documentation.

Front was right near the front end as shown in the picture, rear was approximately end of bed. I took actual measurements, it is sitting on a 3x6 so a little bit approximate, from that the CG aft of the camper front bulkhead calculates to 42 inches for the 9.6 and 52 inches for the 10.4.

Part of why I did this is to understand why the 10.4 feels so much better driving than the 9.6. I made some changes to the truck right before I picked up the 10.4, clearly those are responsible for the improvement, not the weight or CG. I had recently changed tires from the original OEM Goodyears to Michelins and inflated them to the same pressure (55 lbs) as called for by the tire chart. However the Michelins are a true 0 deg radial and the sidewalls are squishy, truck drove noticeably worse loaded or empty. Consensus here seemed to be pump them up hard, so I inflated them to 70 and also set the front shocks (Rancho 9000) up a couple notches. So those two changes made the 3600 lb camper feel better than the 2800 lb camper. Now I have 1.5 inch front and rear antisway bars and it feels better still. I never put the 9.6 back on the truck and now it is sold.

There are some other subtleties I would like to understand better. I had to run 40 psi in the air bags with the old light camper to get level. I run minimum (like 5 psi) in them now with the new camper and it is level. There is a lot less pitching with the new camper, part of that must be due to the front shock settings. Two things about the old camper: the tanks were at each end, water in front, propane right in back, batteries up high and back. I also had a toolbox and some heavy steps mounted on the 18" hitch extension, whole affair might have weighed 200 lbs right at the back. On the new camper I can't use that arrangement, and the tanks, propane, and batteries are right at the front and all together. So, worse weight distribution? higher polar moment of inertial? I don't understand it, new camper CG is further back and heavier....

[I_Fish_2]

HMS, you show a picture of the camper setting on the scale. What did it weigh?

[Raften]

Good idea Wheel. Don't have to go to the truck stop as there is a scale I always drive across when going to the dump. Free, and I am out there most every day flying RC. Next time I load up the TC. It does not get me just the TC weight ratio but will do just fine. Thanks

[Wheelholder]

Raften, you could go to a truck stop and when you get on the scale, put one side of your truck off on the edge, but not on the scale. Then you can tell them you want a reweigh and do it for the other side.

That would be the most accurate method I can think of to weigh side to side.

[Ski_Pro_3]

That scale is exactly how I measured vehicles I loaded onto C5 aircraft while in the Air National Guard for the Load Master. One wheel at a time. If it's accurate enough to load a plane for stable load, I'd think it would be accurate enough.

[Raften]

I keep looking for a racer that has four scales. My TC is very unbalanced, heavy on the slide side. I have to add twice as much air pressure in the air bag on that side to get it to level out. Got a plan to shim things up next time I start crawling around under the truck. A shim under the slide side Timbern might help.

[HMS_Beagle]

The total travel of the scale table is approximately 0.050" at 20,000 lbs - I think I will ignore that! The shim goes under the opposite wheel, not the other dual wheel on the same side. I have put a couple of known heavy objects on the scale, it seems accurate. For my purposes, +/- 100 lbs it fine.

On my BF, the fridge, galley, and propane are on the right, but the head, furnace, and water heater are left, fresh water offset to the right a little. I haven't weighed the truck empty on each wheel, it may start that way for all I know.

[Led_67]

Not to be a nit picker but...You do realize that you will get inacurate weight from using that shim because it will support part of the weight because the scale has a floating table whereas the shim is fixed. I would at least get a Cat Scale to verify those numbers before I would trust them

[Butch50]

HMS Beagle wrote:
It would be a little hard to get accurate numbers on the jacks with just one scale. By weighing the rear tires you can get an idea of which side is heavy and how much - notice in my figures the right side is about 300 more than the left, not sure why.

My NL is heavier on the right side also. What side is the fridge on, batteries and propane? Mine is on the right pulse my propane and batteries on all on the right side so this is probably the reason mine is heavier on the curb side.

[HMS_Beagle]

It would be a little hard to get accurate numbers on the jacks with just one scale. By weighing the rear tires you can get an idea of which side is heavy and how much - notice in my figures the right side is about 300 more than the left, not sure why.

[Raften]

I need to find someone with one of those so I can get the numbers on how much each jack supports. I know the slide side is heavy but it would be nice to know just how much.

[AYRTIME]

Interesting to see the scales again. I used those in Ag Extension work for weighing loads of hay/grain/silage etc.

[HMS_Beagle]

Yep, in 2005 they raised the GVWR to 12,800 for the DRW (1800 more than '99). Now (2013) you can get optionally 14,000. I think my camper weighs about 3500, if I had another 3000 in GVWR I'd be well under. A post 2005 F250 has a maximum payload of 3100 or less depending on configuration so I would be way over on that.