yeah looking at 45mm wheels with 22mm gears so that takes me up to 87mm then I will be supporting it with a bearing at the far side that's about 10-15mm wide so that's me up to 102mm call it 105mm to be safe.

Should be fine with a collar will also make changing wheels a bit easier :-) Will do some more design work then try and get an order in once stock of the 85A controllers goes up again.