Weighing my trailer using the tire patch method.

[Honda03842]

I've weighed the trailer after all modifications and loading. I use the tire patch method to approximate the weight. I did this on my Motorhome and after checking its weight on truck scales found it a relatively accurate method.

The trailer should be level and the tires on somthing flat like a board or concrete.

I measure the length of the tire patch with no jacks down by placing a piece of paper under the front and rear of the tread, pushing it right up to the tread's contact with the wood and measure the distance between the paper (6.25 inches in my case).

I measure the width of the tread by placing a piece of paper on each side of the tire and again measure the distance between them (4.25 inches in my case).

I estimate the amount of the tire patch that is represented by tire groves (in my case 1").

I measure air pressure (42 pounds) using a digital gauge.

I multiply patch length x (patch width - groves) X air pressure.
6.25 x (4.25-1) 42 = 853 pounds per tire.

I measured the hitch weight with a bathroom scales at 155 pounds.

This gave me a trailer weight of 1861 pounds. Normally we travel with an additional 250 pounds of gear giving me a weight of 2111 pounds.

I did not measure the tries separately which is always a good idea.

Though it's hard to use this technique on big trailers to get the hitch weight it is really good at detecting side to side inbalances in tire loading and lets you see the percentage of loading on the tires. My tires are rated for 1480 pounds and each carry about 1000 pounds of load when fully loaded.

Norm Milliard
1982 Sunline 15.5SB
2004 Honda CRV

[purplesuebug]

That's too cool.........I just saw that on Beakman's World last Saturday Morning. They were measuring a car's weight with extreme accuracy!! In case you don't know Beakman's World, It's a science show for teens and GEEKS like Sue & I. Sorta like Bill Nye the Science Guy............Anyway, It's a neat trick and a cool tool!!!! I really like the way you meausered the footprint of your tire. I was still trying to figure that one out. Thanks.........Marshall

[Honda03842]

The first time I used this method was to reduce my weight concerns before our trip to Alaska in our Bounder.

I placed a piece of plywood under each wheel and sprayed around the tires with black spray paint,measured the area, deducted for the grooves and multiplied by the air pressure. Overkill I think but one is often clumbsy on first trys.

Norm Milliard

[PTHutch]

Ok guys, here’s a question.

If you use this method to take 2 measurements. 1st measure all tow vehicle & trailer wheels with trailer hitched & WD bars set and then measure all tow vehicle & trailer wheels with the trailer unhitch can you come up with the trailer’s tongue weight and also the tongue weight transferred to tow vehicle front axle, tow vehicle rear axle, and trailer axles and also informatin to compare with tow vehicles GCWR and GVWR?

Here are the formulas I came up with:
For both loaded/hitched and unloaded/unhitched.

TV Frt Left Tire + TV Frt Right Tire = TV Frt Axle weight (loaded/hitched & unloaded/unhitched)

TV Rr Left Tire + TV Rr Right Tire = TV Rr Axle weight (loaded/hitched & unloaded/unhitched)

Sum of all TT Tires = TT Axle weight (loaded/hitch & unloaded/unhitched)

To compare with TV’s GCWR – sum loaded/hitched values.
To compare with TV’s GVWR – sum loaded/hitched TV Axle weights (Frt + Rr)
To get TT tongue weight & WD values:
Loaded TV Frt Axle – Unloaded TV Frt Axle = Tongue weight xfer to Frt Axle
Loaded TV Rr Axle – Unloaded TV Rr Axle = Tongue weight on Rr Axle
Loaded TT Axles – Unloaded TT Axles = Tongue weight xfer to TT Axles

TT Tongue weight = sum of the 3 tongue weights above.

Does this make any sense?

Sometime I'll have to try this to see how the values compare to the weights I got at the scale.

[Honda03842]

Without doing the details, checking the weight of the tow vehicle with the hitch connected and unconnected will tell you the hitch weight.

Norm

[PTHutch]

I estimated the weights of our tow vehicle and trailer using the patch method and compared these estimate weights to the weights obtained at the scale. The weights from the patch method were about 10% greater than the weights obtained from the scale.

The patch method seems to be a convenient way to estimate weights. I would rather have estimates that are higher than actual, it adds a built in safety factor.

[Honda03842]

I found three potential sources of error when I measured.

Inaccurate measurement of air pressure.

Under estimating the percentage of the tire that does not contact the ground due to grooves, i.e. the tire pattern.

Over estimating the tire patch.

I don't know why your estiamte came out so high but that's some of the potential error. For example on my tire the grooves require a deduction of about 20% from the tire patch.

Thanks for trying the method.

I haven't put my trailer on a scale and won't until next year but when I do I'll report on the accuracy.

Best,

Norm Milliard

[PTHutch]

Norm,

You’re right, wrt potential sources of errors.
FYI - I estimated the tire groove reduction at 1½” (~27% reduction of Patch) and it truly was an estimate. Also I have an analog tire gauge which is not the most accurate.

Here are some impacts of source error that you mentioned that I came up with from my calculation:
Air Pressure: ±1 PSI – impacts output by ±2% error
Groove Est. or Patch measurements: ±¼” – impacts output by ±4% error

I think the patch method is a valid way to obtain weight estimates at home, but I’m still a strong advocate for going to a scale to get accurate weights of TV and TT. If you’re interested here’s a link to when I posted my tow vehicle and trailer weights and how I measured them at a scale.

Hutch