painted wheels on drag cars

I have always wondered why back in "the day" some drag cars had some of the wheels painted half black and half white.

 

To visualize wheel spin. "Hooking up" was not so easy in the past.

 

I was told so they could check the amount of wheel spin comming of the line.

 

Like they said--to check wheel spin--we only painted a 1/4 pie white on black wheels