Does anyone know if the Germans painted the interior of the road-wheels or left them in red oxide.

There are colour photographs of Pz IIIs fording the Bug in 1941 which show red between the wheels. On the other hand the assembly plant images of Panthers show that those wheels were painted (probably by the sub-contractors) in Dunkelgelb.

What and when are you depicting?

I have seen one model by a rather serious model builder and he had left the interior faces of the wheels in red oxide / primer.
I haven't got any photographic or other evidence though ...
/ Robin

Late summer / early fall '44 Stug IV and Panther G. My thoughts were that if they were not reversible it would be wasteful to paint inner wheel.

I have seen that too. Impossible to tell from b&w 70 year old photos.

Darned good question Jerry ! I have wondered that myself.
A good weekend to everybody !

Worn, dark, pitted bare metal from a regular coat of paint. Metal center guides on wheel will wear any paint off as the track goes around. Look at those Panthers with the inner wheel with the bright shine from the track teeth. The more likely the surface is to hit the center guides the more shiny it's likely to be.

One color picture showing the red are actually showing a seal, not primer, and that seal is on top of a clearly dark grey wheel center.

Some things on tanks are just universal and worn metal inside road wheels is one of them. And yes, I have climbed inside of road wheels of various display vehicles. Until recently most never had between the road wheels painted so I got good looks on the worn pitted metal I knew so well from my M60.

Bear in mind that the subcontractor has no idea which way round the wheel will be fitted and that if the orders call for it to be painted all over, then it will be. The Waffenamt inspector will not accept the batch otherwise, in which case the supplier will not be paid. It is not for the supplier to determine whether it is a waste of effort to paint something.