So I picked up a nail in my inside sidewall, that I'm pretty sure can't be repaired. Tire is a non-directional Bridgestone Protenza RE760 and I have around 8-10K? on the set. I was wondering what you guys thought about running a new tire with 3 older tires. Will a slight circumference/rotational difference give any problems to the flat tire sensor, or differential if run as front tire?

The tires are actually in pretty good shape, I'm guessing around 75% remaining life. Just for comparison, I found this picture of someone else's RE760, and mine has just lost all of the shallow sipes.... in other words, in comparison to the below picture, half of the yellow marks would be scrubbed away.

 

were it me I'd buy the one tire . . .

yes, what you have there is not to be repaired - a puncture in the sidewall....not even CLOSE to the debatable area.

 

When I had my puncture the price for the runflat Dunlap was $324.00 plus tax & shipping.

I decided to get a complete set of Michelin non runflats for a total of $829.00 total with a $70.00 rebate back from Michelin.

I did not really like the runflats and I'm happy with the way I went. I did sell my Dunlaps on Creigs list and got $120.00 for them. Not bad considering one has a plug in it. I did show the guy that bought them the plug.

$829.00 less $70.00 Less the $120.00 = $639.00 for all four one size larger Michelin 215/45/17 Exalta PE2 tires.

If you were planing to dump the runflats, now is the time to look into it.

 

These are actually my second set of non-runflats.... I sold my original RF tires for $100 a piece (w/50 mile on them, no rims). Having said that, this kind of sidewall puncture is the type of thing that sometimes makes you reconsider.

 

That's a miracle! I'd like to see how that happened in extreme slo-mo. Save the photo as evidence of a sidewall puncture in the extreme.

From the looks of the tread depth, I agree that you probably need to replace only that one tire. It still looks almost new with 8-10k miles on it (thus, probably a rear).