Just been out to measure clearance on the +4 - best I can get is approx. 95 mm to the cross-member, approx. 100 mm to the bottom of the thread of the gearbox mounting bolts, approx. 105 mm to the bottom of bell housing and approx. 111 mm to the bottom of the forward exhaust mounting bolts.
From the snappily titled 'The Highways (Road Humps) Regulations 1999' it seems to me that road humps should be no less than 25mm or more than 100 mm high. This makes the ground clearance of my +4 very tight indeed even on correctly installed humps.
I'm sure some humps are more than 100 mm though ....
