Cadillac SRX Second Generation Forum - 2010+ Discussion, Incorrect Odometer Mileage? in Cadillac SRX Forums; http://www.rimsntires.com/specs.jsp
This site shows a general comparison between tire sizes. However, tire brand variances may differ....
Today I'll run my cruise control at 60 and use a stop watch & compare with odometer. Yesterday I read an article on internet regards auto manufactures:
"Almost every vehicle in the country is purposely made to READ about 5 mph HIGHER THAN actual speed. I say the manufacturers do this to make the vehicle odometer rack up the miles more quickly, which is "Gotcha Capitalism" at work. But, the manufacturers avoid massive class-action lawsuits by claiming they must do this to make absolutely sure that the car isn't going FASTER than speedometer speed so they don't get sued by people who get a ticket".
You can also use the mile markers on the interstate. Use your trip odometer. Zero it in and run 10 miles or so. My 2010 is right on ,some construction zones have radar signs set up always read the same. Sounds like Urban Mythe # 84979600 about speedometer being fast.