Stop in for a cup of coffee

Using string from under rear of the car around rear tire and measure rear of tire to string, then same for front. Had plates that rest against the tires and measure across front and back but was missing something. Maybe all the sun exposure, hangover or ????
You know me, I'll have to draw a picture to understand. LOL.
But Chrysler used a narrower rear track than front. So if you're counting on the rear tire widths to be same as front (to get parallel strings), that would explain why reality is diverging.