Why is Rupa (not) Ultimate Reality? When we see "a car' then there is the "seeing of the car formation" and that is mind or "nama". At the same time there is the rupa car formation that is not a concept from our mind. I always thought rupa was "the experience or hardness , softness, roughness ect.. but I guess this is wrong because rupa is it's own ultimate reality?
According to the Abhidhamma, we don't "see a car". It is a bit more complicated :-)

According to the Abhidhamma, sensing involves seeing a small patch of colour. The small patch of colour is rūpa, an ultimate reality.

How small is this patch of colour? Extend your arm and hold out your thumb. Scientists say that the size of your thumbnail as compared to your entire field of vision is what that retina can process at one instant. The rods and cones of the retina respond to specific colours.

Once this small patch of colour (the ultimate reality) has been seen, it becomes a concept (the tadanuvattikā manodvāravīthi process). Sensing is finished and now thinking takes over. The first thing that thinking does is the “grasp the object as a whole” (samudāyagāhikā); in other words, thinking builds up the entire field of vision from these “thumbnail-sized” patches of colour.

How is this done? It is not in the linear mechanical way that a TV screen image is built up. Scientists say that the eye focuses first on areas of high contrast, on faces and on movement before filling in the rest of the scene.

Once the entire scene has been built up, the thinking mind recognizes colours (vaṇṇasallakkhaṇā). Next, a shape or “entity” is extracted from the pattern of colours (vatthugāhikā). Next is the thinking process of recognizing the share or “entity” (vatthusallakkhaṇā). Next is a thinking process of gasping the name (car in the example you gave) (nāmagāhikā) and the thinking process of recognizing the name (nāmasallakkhaṇā).

Scientists explain that the activity in the brain extends from the visual cortex to involve memory.

Of course, next comes the idea of the car, judgements and associations regarding the car, obsessions and fantasies about the car. 

What we see is the ultimate reality of a small patch of colour. Once seeing of this small patch of colour is complete, then thinking of concepts takes over.

This is explained in Bhikkhu Bodhi's "Comprehensive Manual of Abhidhamma" (page 164).