Originally Posted by dbworld4k
I fully and respectfully disagree with regards to the setup being impractical.
1) If you need a bubbly tire to protect your rim from curb rash, then you probably shouldn't park so close to curbs to begin with.
2) False. I always ran OEM inflation specifications. Never had any issues due to tire pressures.
3) It's possible, but not all that probable. Unless of course it is a VERY extreme stretch that is put under stressful conditions, then yeah.
I have had everything from 235/35/19 all the way to 275/30/19 on my old 9.5" wide wheels. Each setup (235, 245, 255, 265, and 275) was at some point thrashed without remorse on the track (mostly at TMP Cayuga). Not once did the tire size ever have a detrimental effect attributable to the stretch. I did burnouts, peel outs, drifts, anything and everything imaginable to stress the tires to their absolute limits and never experienced any failures or concerns whatsoever. Some might consider the 235 on a 9.5" to be an extreme stretch, or my 235 on a 10" - others may consider it mild. Depends where you fall on the spectrum. Regardless, the impracticality claims that are rampant online are purely based off wild conjecture and perpetuating hearsay than actual experience, even if anecdotal.
But, as I said before, to each his own.
Speaking in general, assuming that all tires are the same brand and compound, the tire size that gives you the fastest lap time (assuming optimized tire pressures) is the best, and by that definition any other tire size will have a detrimental effect, regardless of whether or not it's stretch or meat.
I'd have a hard time believing that if you were to put the stig on Cayuga with a 330ci with 235 tires and then again with 275 tires on the same day that there would be no discernible difference in lap times.
Also, depending on the aspect ratio of the tire, 9.5" is the upper end of the rim width range for some 235 tires, so it's not exactly extreme stretch.