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Unfortunately after purchasing these 8.5 X 19" and 11 X 19" wheels on Ebay, I have come to realize the tire companies absolutely refuse to produce tires in the appropriate size for the 11 X 19" rear wheel (315/25/19). It's well documented the 315/25/19 is the closest 19" option to keep with the 25.2 dia./800 Rev/mile OEM tire at 295/30/18.
Without the 315/25/19 option available for what appears to be several months, what's the consensus of listers on an alternative option? I have read a few threads on various forums and it seems some people are running 235/35/19 & 305/30/19 without AWD/front differential issues. When comparing the specs for the Hankook Ventus V12, this combination nets 816 & 791 Revs/mile respectively, or ~3% difference.
The optimum match, if the front tires would fit (big if) would be 225/40/19 & 295/30/19, for resulting in 773 & 777 Revs/Mile. This results in the speedo reading 2.5 mph below actual @ 65 mph, but oddly enough the stock 18" wheels make the speedo 2.5 mph optimistic so it may actually be more accurate with the larger overall diameter at 26" as opposed to 25".
By the way, I'm basing my speedo being ~2.5 optimistic on readings from 2 different GPS systems that are consistantly lower by 2-2.5 mph than the speedo at 65mph.
I'm also a little miffed that Discount Tire Direct would lead me to believe the 315/25/19 Falken 452's I "special" ordered would be here on the 20th of August when clearly there hasn't been a 315/25/19 available from any tire manufacturer for several months according to numerous 996TT forums/threads.
I was forced to run 305 30 19's in the back, when my 315 25's wore out Still running the 235 35 fronts that are 50% tread. Porsche dealer put them on and said it will not have any affect on the PCM or viscous coupler. I now have 2,000 miles and no problem or PCM error.
Here's the update: After much searching I found a new set of 2 Pirelli P-Zero Rosso tires on Ebay, 305/25/19 for $364. I was using a few of the online tire calculators and found all calculators to agree that a 225/35/19 has almost identical rev/mile as the 305/25. With tire calculators being a generic thumb in the wind type deal, I looked at Tirerack's mfg. specs for the Pirelli P-Zero Rosso in the 225/35 size and intended to compare them with the 305/25 size but soon realized Tirerack doesn't carry the 305 (discontinued) and therefore does not have the specs for that size listed. After a quick chat with Ross at Tirerack i had the answer. 822 vs. 826 Rev/mile for the 225 and 305 respectively.
At the end of the day the the 305/25/19 works with the 225/35/19 and is still available in short supply (Ebay).
If you're concerned about as close to a perfect match of diameter as possible, go with the 245s (25.7") and 295s (26.0").
Any combo of the four sizes above is safe though.
08-21-2012, 09:11 PM
315/25/19 Tires????
