I have a (new to me) triple axle Manning and I am thinking of keeping a 2x8 (the piece would be about 6 inches long with a angle cut edge) in the tow vehicle so that when (not if) I get a flat, I just pull the good tire(s) up on the wood piece and that would lift the bad tire off the ground about 1.5 inches in order to change it out...would this work (or are the axles independently sprung)?

Works great! I have never used a jack on any trailer. Get 17.5 tires and you will never have a flat....

They are independently sprung, and even if you had NO suspension, it still wouldn't work with one 2x thickness since the tires compress too with added weight.

I had a whole trailer tool box filled with multiple lengths of 2x6s that I could puzzle together to lift any of the tires off the ground. (8" to 30" long, and you don't need an angle cut on them)

However, you are not going to make it work with just one thickness of 2x8. The flat tire is going to articulate down, and you will not get a new (inflated) tire on there. And the suspension on two tires that are carrying the weight are going to articulate further up, and those tires are going to compress more; all due to the fact they are taking the weight supported by 3 tires and now only 2.

Try it in your driveway. You have to lift it high enough to get an INFLATED tire off the ground anyway, since you have to get an inflated tire back on there.

Roger that, concept works but I will have to figure out how much thickness I need... agreed?

Bottle jack works pretty easy...

I have (3) 2 x 8's angle cut and screwed together to accomplish what you describe. I also carry a bottle jack. However I replaced tires every 4-5 years and thankfully have never needed to use either!

That depends too.
I always carry a bottle jack as well. However, Myco and perhaps others install the torsion axles so the outside suspended portion of the axle where the spindle mounts to points UP, so the trailer has a lower CoG.
However, you can't snag the end of the axle with the bottle jack due to this. As such, for a torsion axle that points UP, you would have to use the bottle jack to lift the ENTIRE axle and basically the weight of the whole trailer.

Now, if your torsion axle points DOWN, you can use a bottle jack on the edge of the spindle bracket, to pivot the individual axle up.

Follow up:

"Positive Angle" torsion axle, you can use a bottle jack to lift up the spindle end.
"0* Angle" or "Negative Angle", as soon as you try to raise that spindle end up with the bottle jack, the jack is going to kick out (to the right in this diagram).

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https://www.overtons.com/easy-lift-trailer-jack-315931.html?s_kwcid=adwords__&gclid=Cj0KCQjwl6LoBR DqARIsABllMSaSkuJ5qFSNKMLsOiB46TCkUhFhsUsIJ2rrgB23 6seXFQ-PyA5nOlsaAmUXEALw_wcB

But notice, that's really only designed to work on LEAF SPRING axles. IF you try to use it on a torsion axle, you are going to lift the entire trailer.