If you took 2 datums one of the angle and one of a fixed point on the shell then it would take rake into account

Does it have to be that accurate?

Could you work it out from a side-on view printed out, and using a protractor from a school maths set?  You could even make paper cutout roll bar and screen frame and move 'em about until you like it/it matches a Mono Manx.

Good point! Will give that a go!

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What wrong with standing back by the side, holding your arm out, thumb up, and squinting as you twist your wrist around?  ..... Yep looks about right to me! 

28 degrees.

[" is that by rule of thumb"]

28 degrees.

Couldn't resist it                 " is that by rule of thumb"      I'll get my coat

Thanks guys got it nailed now

Thanks guys got it nailed now

Suggest to use nuts and bolts - far stronger 

that is  28 degrees + or _  28 degrees 

that is  28 degrees + or _  28 degrees 

28 degrees =  82 degrees Fahrenheit = Bloody Hot, funny, it doesn't feel it though...