Why even use GPS for this, as opposed to a known distance and a clock, or an on-site laser (or whatever electromagnetic wave) based system? Seems like using satellites is unnecessarily complex and error prone(esp. civilian GPS).
GPS (really, multi-constellation GNSS these days) is not only easier to physically set up, it also gives you more data, and likely more accuracy. You don't save the PVT output of the receiver on the vehicle. (I mean, you could save that too, I guess.) You save the raw observables, and post-process along with data gathered at the same time by stationary reference stations. (Either run your own base, or use data from networks like unavco.)
This gives you a remarkably precise picture of the vehicle's position, motion, and acceleration, in 3 dimensions, throughout the entire run. If they want to be transparent about it, they'll publish a multiconstellation RINEX file of the whole shebang, so anyone can analyze it themselves. There might be fewer internet sleuths who know how to sling rtklib or gpstk than youtube-dl and audacity, but the ones who can, will produce a wealth of data.
For bonus points, put two receivers on the car, a few feet apart. This allows moving-baseline so you also get an orientation solution.
Maximum theoretical speed on a dyno, sure.
It's not like the tires can expand in diameter 200% though. I'm sure that Michelin has parameterized tables for the tire's mechanical behavior that they are confident about by now. They aren't exactly new to tire engineering...
Your high school physic teacher is on line 1. Wants to talk to you about what "weight" means...
Weight is the force the earth needs to provide to support the car. Mass remains constant except for burned fuel loss.
Agree re: GPS, on-site laser traps timing an accurately measured distance is obviously preferable. I presume laziness prevails.
The point was really if the mechanical system can only "turn" to a maximum theoretical speed of e.g. 300mph, then they clearly and obviously didn't exceed it, no matter what, unless the car transforms into an airplane at some point.
I don't personally know how much those tires deform at such speeds. My personal experience with sportbikes approaching 200mph has been it's not even enough to make up for the ~5% speedometer error that still indicated higher than actual around 190. But that's a much narrower and lighter tire, and 300mph is a different world.