Jack, good historical info.
There is also a benefit to going smaller on a given wheel width, stretching the tire a small amount. This promotes better sidewall action especially with modern performance tires using stiff sidewall construction.
My experiment with a 235/50-15 Toyo R888R on a 15”x10” wheel yielded some good benefits in transition speed due to the stiff sidewalls being at a more desirable angle in relation to the wheel bead.
Is ultimate overall lateral grip lower? Possibly. Is the reduced overall grip offset by more transition speed in mid corner performance? Possibly.
I have yet to perform instrumented testing back to back with a wider tire. That would prove challenging since same model tires in different, but appropriate tires sizes aren’t easy to come by in the 15” diameter.
I can only comment on track testing which proved to be excellent. The 235 R888R performed superbly on the 10” wheel. Ultimate lateral grip was stupendous and transitioning was much better than a “too wide” tire would have provided.
Another thing to consider is that published tire sizes are often guides rather than actual measurements. Case in point, the 235 R888R is actually 9.7” in width, which predicted its favourable performance and fit on an otherwise unadvisable 10” wide wheel.
Other 225 or 245 mm tires are often much narrower than their published widths may suggest.
However, for looks on the street, it may not be an aesthetic choice for most.
I was hoping to hear from someone who is running these new P7s at higher speed (over 100mph) extended to get their impressions versus the existing TB5/15, P7 Corsa Classic, P Zero, Avon and Yokohama AVS options that have been available.
The Get Out Of Jail Free card sure sounds good!