Does a portal axle system mean a lift?

A YouTube commenter suggested that portal axles mean a vehicle is taller than the equivalent without. While it’s true that vehicles modified with portals are often taller than the original, it doesn’t need to be that way because the modified vehicles aren’t designed for portals from the start, and often have taller tyre plus a suspension lift as part of the modifications.

A diagram in Part 2 of my Unimog U1700L video (linked below) showed these three examples:

This shows the portal axle version having the same roofline as the non-portal. Why so? Well, the fundamental point is that the wheel size hasn’t changed, so the room required for a wheelwell for suspension travel and wheel turning doesn’t change, unlike a physically larger tyre. You could perhaps argue that as a portal axle pivots a bit differently on the suspension compared to non-portal that is a change, but not one that is significant in this case.

There are two ways in which a portal axle need not require a taller body:

Shorter springs – could simply fit shorter springs which take up less vertical room that the originals.
Redesign the spring mount clearance – steal some space above the axle for the spring.

The diagram below demonstrates:

On a related note, do portal axles increase unsprung mass? Yes, and maybe not so much.

Yes, because of course the portals and gears add mass. Maybe not, as the alternative is larger wheels, so in a way you need to compare the mass of a portal system against the equivalent sized taller tyres. However, that’s not quite a fair advantage as a portal-axled vehicle with say 400mm of ground clearance will be less capable than a vehicle with 400mm of ground clearance and no portals, as those huge tyres will offer fantastic obstalce-climbing capability and of course lift the entire vehicle improving approach, ramp and departure angles. All portals offer is improved ground clearance.

This isn’t exact, but if the Unimog gets another 100mm of ground clearance from its portals, it’d need tyres 200mm taller, so 1.4m not 1.2m, or 55″ tyres not 46″. And while larger tyres are good for offroad, they have a whole lot of disadvantages such as rolling mass, raising the tray height, making the turning circle larger, complicating the spare wheel location, reducing handling and other negative effects.

The gears in the portal axles will also increase fuel consumption, but again, a fairer comparison would be against the much larger tyres which would also definitely increase consumption. I wonder if anyone has done the maths or testing to come up with principles as to which is better in a given scenario?

This comparison photo shows a 70 Series with stock axles, and Marks 4WD portals, courtesy Adam Craze.