Outer Limits 4x4 Board

i am building a flat bed tandem axel trailer, to use as a car trailer and work trailer

bed approx 5m long x 2.4 wide draw bar ???

??? is does any body no the correct mathmetics to set up the lenght of the draw bar and where to position the center of axels, i am sure there would have to be a formula,

thought it would be easier to ask than to keep moving until it was o.k

any help much appreciated

the law for the axles is the centre line between the two axles has to be closer to the rear of the tray then the front, do not include drawbar in the calc. Personally for a car trailer 50 -100mm should be fine. The draw bar doesn't really matter, given it's a car trailer the distance from the ball/hitch to this imaginary centre line(tandem trailer) will be long enough for even long wheelbase vehicles to manuover. Just make sure it's long enough so that the front of the trailer won't hit the tow vehicle when trying to reverse I would go for about 1.5m depends on if you want to fit a tool box spare tyre etc to the draw bar.

For a tandem axle trailer the relative axle position is half way in between the two axles. If like on some buses with two rear axles where the drive axle has dual tyres and the bogey one the relative axle position is one third the distance between the axles closer to the dual tyres, all has to do with load carring capacity and the dynamics of the turning vehicle.