First a lil background... I >was< compiling a pretty massive spreadsheet of all the tire rack test track results. I wanted to see how the various categories compare to each other because tire rack almost always compares category to category. I found many places where numbers for the same tire were different. Same test car, but different days... shrugs... It did kinda take the wind outta my sails for that little project tho.
Now, to these tires and their differences...
1. The specs tire rack lists say "max pressure", not what they actually set the tire at. Is it set to the specs of their BMW test vehicle? Some arbitrary number (IE 30 PSI)? Is every tire set to the same number? How precise are they at making sure these pressures are the same?
1.a. - Are they measuring loaded or unloaded? This page seems to show unloaded: https://www.tirerack.com/tires/tiret...jsp?techid=201
Also, even looking at the picture they show that they are not measuring every last bit of tread. They're measuring the amount that's touched by their tool. That may or many not be a great measure for every style of driving, let alone every tire pressure or unloaded versus loaded.
2. The measured rim sizes are different for the two sizes you're comparing. Meaning... if you put the 225's on the same 8" rims, you will get different numbers than what TR has measured. They even talk about this: https://www.tirerack.com/tires/tiret...jsp?techid=200
And then there are the other unknowns... When did they measure each tire? How tall is each technician (point of view changes EVERYTHING)? Is every tech super diligent?
There's just something wayyyy off about that S-04 225 showing more tread width than the S-04 245. Hell, it shows 1.5" more tread than the SAME SIZE (225) RE-71R?!?!? Sorry, gotta call BS on that one.
Oh, and the 245 S-04 has .7" more tread than the RE-71? I'm pretty sure that HAS to be a result of shoulder design and other variables (pressure, tires not loaded, etc...)
It's the same kind of weird variance that took the wind out of my massive tire comparison spreadsheet.