I've been playing around with the trailer balance spreadsheet a bit this week, and had a question about using a Dexter torflex axle. The spreadsheet requires a measurement from the back of the trailer to the axle, and of course with leaf springs it is also the wheel center. But with a torflex the wheel center is approx 6" behind the axle center, and I'm not sure which measurement to use in the spreadsheet.
I'm planning on using a #9 Dexter torflex with 14" wheels/tires on a customized NT 5x8. I plan on extending the tongue similar to how Zach did it on the X-Cubed, then extend the frame at the back end. I'm planning to extend the trailer frame by using 2 of the 5' cross rails to extend the side rails, overlapping by approx 2' to achieve 11' total. I was figuring on centering the Dexter axle mounting brackets on that overlapped area. This would leave only the wide cross member on the frame, but the torflex should add some rigidity. If necessary I can add a couple of pieces of angle iron as new cross members.
This would put the axle center about 48" (36%) from the back of the frame, but the wheel center would be about 42" (32%) from the back. Using some very rough estimates I've found that the tongue weight will be a bit high ... somewhere around 250 lbs ... when using the actual wheel center as the distance from the back of the frame.
So which should I use ... axle center, or wheel center? My intuition is to use wheel center, and my reasoning is this: Imagine that the axle location is the perfect balance point of the trailer when it is raised off the ground ... the resulting tongue weight would be zero. Then lower it to the ground ... the wheels are 6" behind the balance point, so the tongue weight would increase considerably.
Any thoughts on this?