It is simple linear math.
If you’re at 50 mph at 2500 rpm w/ a 26” tire and want to know the rpm with a 27” tire, multiply 2500 by 26 and divide by 27.
If you’re at 50 mph at 2500 rpm and want to know your rpm at 80 mph, multiply 2500 by 80 and divide by 50.
Makes perfect math logic. BUT, hardly as much as fulfilling as factoring through a polynomial equation…
Ok, ok its not actually polynomial. But I did get that rare chance to use the abacus again.
In all seriousness, mainly for giggles I’m solving for the rare chance the stock 3.23 gears have been swapped out. No solid reason to suspect. Just a brand new car to me and I expected lower revs at highway speeds. Again, just curiosity.