sizes

[Moyoni]

Dear yurt-lovers and builders!
I'm just about to build my yurt but still on the level of collecting basic information... I would be glad getting some good advices here! I'm planning the diameter of 6m (about 20ft?) and not sure what size of roof wheel the roof poles can carry without support of middle poles. Is 140cm (4.5ft) too big?
Someone told me better to increase the middle height to 2,80m (9,1ft) instead of 2,40 which was the original idea.
Any suggestions to that?

thanks in advance!