Most BMX and mountain bikes were not used for racing, (or riding in the mountains) but were used for putting around town, sometimes with friends. Just like Stingrays.
And yes, Stingrays were the first production Muscle bike. Here's a '68 Orange Krate (first year for the Krate) I restored and had a lot of fun with. I sold it in 2019 at substantial profit thanks to the vehement following these bikes still have today.
