Well we ran 12 nights at Flamboro this year on 2 sets of tires. We changed after six nights, and not really because we thought they were worn out, but because my brother ran about 8 on his first set and they totally went away, and we wanted to avoid that. So we split the season six nights on each set, and won 4 features doing that. My brother ran probably 16 nights on his two sets plus a few of mine i gave him at the end of the year, and he won 6 features.
Some guys are changing them a lot more frequently than that, but i've never felt at a disadvantage with a bunch of nights on my tires.
With the 7 inch tires we ran just as many nights or more too.
Linkback: https://www.canadianracingonline.com/smf/index.php?topic=16769.msg106099#msg106099