My 18M ASH 26 E Cobra trailer has the 1300 kg (2870 pounds) Al-Ko axle,
which is adequate for even an Open Class motorglider like the Nimbus 4M
a friend has. Al-Ko offers the same style axles up to 8000 pound
capacity, but I don't know what capacities Cobra offers. I suspect the
major reason for choosing the dual axle trailer is for more stability.

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I have a big heavy trailer for a vintage two place. The trailer had
dual axles and would sway at normal cruise speeds. Add a lot of weight
in front and it made no difference. Increase tyre pressure and still
no improvement.
Converted to single axle and problem is solved.
GA