the dreaded tire topic...

brulaz wrote:
Thanks John.

Don't recall having seen a CAT scale set up with such a wide flush open area next to the scales. But will keep my eyes open.

EDIT: hmmmm, a bottle jack with gauge may be the way to go ...
Bottle jacks with gauge port
or
Youtube video

Yes, those will work you just have to get a gage in the correct pressure range and figure out the piston diameter. Boy, they have a U tube for everything now a days....

Here are the basic steps, need a hard surface that is flat. Level the camper. Drive up on 4, 2 x 8's or wider


Now set the force jack under the axle seat, use a feeler gage or sheet of paper to "just" be there. You do not want to lift and you do not want to be very much low. I used a 0.001" feeler. Lock the jack


Now jack up the camper at that wheel by the frame and pull the 1 2 x 8.




I also used a bottle jack, easier to control


Very slowly lower the jack to lower the camper onto the force jack. Read the gage




Then jack camper back up, slide 2 x 8 under tire, release force jack and move out from under the axle seat, slowly lower camper back down. Move to the next wheel.

When your done, you need to measure from the jack point at the axle seat to the center of the tire. Then calculate the reduction of force out at the wheel. (summat moments about a point) If you need
help with this let me know.


A link to a bigger image so you can read it.
Larger size

Things that will affect the force.

• Air in the jack, make sure there is none in the hydraulics.
  
• A non solid surface. If the jack base compresses into the ground it changes the load as the entire trailer will shift some and the equalizer can shift a little load.
  
• The gage itself, ideally you are mid range of the pressure gage for best accuracy.
  A rubber equalizer. These "settle". So when you jack up the camper, the rubber uncompresses. When you lower it down, the rubber starts compressing and takes time to settle into it's loaded position. As the rubber is compressing, the spring load if shifting some to the other wheel location. I finally had to measure with a caliper 3 decimal places where the settle in width across the equalizer was to get a repeatable reading. Drove me nuts until I figure this out. And you have to wait a fair amount of time too.

I did not dream this method up, but I did enhance it. Member EX Rocket Scientist dreamed it up with his Sherline tongue weight scale.

Good luck

John