I found panels for this Camel Cigarettes ad from 1940 and pieced it back together in Photoshop. I hesitate to explain the irony of cycling and smoking. The fact that 6-Day Bicycle Racing appeared in national advertising is testament to the popularity of this lost sport.
6-Day Bicycle Racing was a hugely popular spectator sport in the US from 1891 until WW2. Madison Square Garden in NYC was one of the major venues. Click here for a Wikipedia page about the sport.
There’s a terrific documentary film about the history of the 6-Days. Here’s a youtube clip of the intro.