A roof tent looks like eighty kilos. On a side slope it behaves like a great deal more, and that is the number that matters.
Roof loads are the most commonly ignored figure on a built truck, partly because there are two of them and people only ever read one. Static capacity is what the roof can hold parked. Dynamic capacity is what it can hold moving, and it is usually less than half.
A roof tent that weighs 70 kg with two adults in it is a static load of maybe 230 kg, which most roofs will happily take because nothing is moving. The same tent driving is a dynamic load of 70 kg plus whatever the suspension throws at it — and dynamic ratings on a Defender roof are often around 75 kg. You are usually at the limit before you have packed anything else.
Weight on the roof raises the centre of gravity, and the effect is not linear — it is the height that hurts. Eighty kilos two metres up changes the angle at which a Defender tips considerably more than two hundred kilos in the load bay does. Anyone who has felt a loaded truck get light on a rutted side slope knows the feeling.
Pack the heavy things low and between the axles, and put only bulky light things on the roof. If it is heavy and it is on the roof, ask honestly whether it needs to come at all.
On a gutter-mounted rack the load path is the gutter, which is a folded lip of thin steel spot-welded to the roof. Full-length racks spread that across many feet; a short rack with four feet concentrates it. Check the feet regularly, because gutter cracks start small and they start where you cannot see them.
Everything you put on the roof, you also put on the outside of the corner.
Dimitar Kolev · Off-Road Build Lead
Book it into the Ram Parts workshop, or order the parts and do it yourself — either way you get the same advice.
