I didn't know...

You're doing a pretty great job there with those colorizations! These two pictures could easily pass as natively coloured images that where aesthetically stylized in post processing for use in high gloss fashion magazines.

I think the result is fine. But I still prefer the black and white original and I'm not sure if this picture gains anything from colours.

This looks like magic to me.  I like it better than the original. 

Thank you R-Man. Here is some real magic (not mine) with a picture of The Mamas & the Papas.

It's really good but did they forget the tire?

Yes, but this particular area looks entirely untouched and all the bright areas like the rims on the tire or the chrome sparkles look too greyish / unsaturated. In fact I would say the chrome parts in the other areas look a little unnatural too but since they are at least less greyish, it can be perceived as an intentional artistic choice. To make it look authentic, I guess it would work wonders to have it reflect a speckle of color, like greenery from the roadside or blue from the sky. And maybe give the rims on the tires a slight tint of dirty yellow. Another thing is the eye of Michelle Phillips. Should be greenish but here it's grey-blueish.

I know zero about colourization but aren't you limited to the shades of gray that you start with?  For example if you think the rims should be reflecting the blue in the sky or something wouldn't you see a gradient of gray shades that appear brighter for some reason, indicating that there ought to be a reflection there?  If the shading is flat and not indicative of a reflection, wouldn't it be wrong to add one?  I'm just commenting in general of course, not saying anything about this particular image, but it seems to me that you are stuck with the pixel brightnesses you start with and have to interpolate within that information alone.

Yeah, unless you're recolouring work requires historic correctness, there's a bit of artistic license involved. Quite a few people take this way too far, basically guessing colours that would be easily researched. Another common problem is sepiafication. Since brown is kind of every colour people tend to recolour in tans and browns, resulting in a perception of the past as this dreary brown time long ago. Looking at early colour photos is a good cure against that. https://en.wikipedia.org/wiki/Sergey_Prokudin-Gorsky