Calculating tire size
 

Okay, A 225/50/16 tire should measure 24.858" using the formula
right?
I measured mine to be 24.125" .
What gives?
The tires are pep boys futura cheapos so maybe they're off but
I sorta doubt it, I would think quality standards on any tire manufacturer are pretty tight.
Which measurment do I use??

If you haven't already done so, you might try tirerack.com. They have all the spec's on every tire they sell. I did notice though, that their spec's and real world spec's can vary slightly. Depends on lots of things like tire pressure, tread wear, rim width, etc.
But I was able to decide on exactly what size tire I wanted when I was changing tire sizes for my other car.

There will alway be a difference in what a tire measures and what it actually will measure. have to take in account the pressure and also did you measure it on the car or off??

well I did measure on the car, wasn't thinking about the wieght
of the car. But still thats almost 3/4".
I guess I'll go with my actual measurments