these kids must have been pretty thrilled to get their first gravity racer, 1959 to 1962 or so, in Sears and Harrison catalogs, thanks Billy O and Steve!

I'm guessing this was a kit that was built at home.

Did you wear out the knees in your pants too, and sew on, or iron on patches? I sure did, from the first day I got a bike (no training wheels! We die like men! lol) until about a year later, there was no reason to get new pants just because I scraped my knees all the time. 

https://www.jalopyjournal.com/forum/threads/vintage-shots-from-days-gone-by-part-2.1154030/page-878#post-13843419

Billy O sent me a link to a recent Barrett Jackson auction of one:

From a 2017 auction https://barrett-jackson.com/Events/Event/Details/1960s-childs-ride-on-Hot-Rod-Racer-209109

thanks Steve!