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After thinking about what might be behind some occasional "odd" handling characteristics, I measured my tires regularly this last season. I wish I hadn't. If you are compulsive about trying to get your car well-balanced on the scales, you don't really want to know how inconsistent our tires really are. They grow after use, but not always consistently, so measuring them before you run them will catch some of the mismatches, but not all of them. I've taken back to Goodyear the new occasional really small or really big tire, and not had any push back, but I've never tried to bring back a used tire...

I measure circumference and don't worry much about a difference, side to side, of 3/8" or less. Anything over that and I pump up the small one(s) and, rather than leave them overnight, leave them to bake in the sun. I've been able to stretch a tire about a 1/4", although some tires don't seem to stretch at all (not sure what that is about. Maybe 'cause they've already gotten hot and taken a set?).

Michael Hausknecht (NE#60)

I took what Bob had recomended and then made it more involved and complicated! (An engineer's job is to make the simple complex, the complex impossible, and the impossible possible!)

All of these measurements were on the pair of 5 cycle tires that had the worst size difference.

Starting point at 30 psi, circumference: LF 70 1/16" RF 71 11/16" (Difference in calculated diameter: 0.52")

Inflate to 50 psi: LF 70 9/16" RF 72 1/16" (Difference in calculated diameter: 0.48")

Wait 24 hours, 50 psi: LF 71 1/8" RF 72 3/16" (Difference in calculated diameter: 0.34")

Deflate to 30 psi: LF 70 3/4" RF 71 3/4" (Difference in calculated diameter: 0.32")

Wait an additional 24 hours, 30 psi: LF 70 9/16" RF 71 11/16" (Difference in calculated diameter: 0.36")

Wait an additional 24 hours, 30 psi: LF 70 1/2" RF 71 5/8" (Difference in calculated diameter: 0.36")

Clearly, the cycle of overinflating, waiting, and then deflating significantly reduced the size difference between the tires. Does this suggest that I should overinflate my tires the day before racing and then deflate to my target pressure before going on-track? Or, perhaps I need to repeat this "overinflate, wait, deflate" cycle several times to see if they continue to get closer to the same size? That was rhetorical, since there's no reason not to just give it a go. Update to follow in a few days!

Ed

Two more cycles of pressure-up to 50 psi, wait 24 hours (or more), deflate to 30 psi, wait 24 hours (or more), then measure:

After cycle 2, the difference in calculated diameter: 0.32"
After cycle 3, the difference was 0.34"

There doesn't appear to be any significant benefit from additional pressure cycles.

M.Hausknecht wrote:After thinking about what might be behind some occasional "odd" handling characteristics, I measured my tires regularly this last season. I wish I hadn't. If you are compulsive about trying to get your car well-balanced on the scales, you don't really want to know how inconsistent our tires really are.
Michael Hausknecht (NE#60)

I'm going to use the same data to convince myself that it's just not worth the trouble to try to perfect corner weights and stagger since tire size and expansion will make that fruitless.

Or as any good crew member will tell a driver moaning about handling - "Shut up, and drive!"

breton wrote:Or as any good crew member will tell a driver moaning about handling - "Shut up, and drive!"

The converse, as provided by Louis Hamilton several times last season, "Don't talk to me while I'm racing". I wish one of his crew would have replied, "You call that racing?".

breton wrote:Or as any good crew member will tell a driver moaning about handling - "Shut up, and drive!"

I don't know Bob, when Fred said that it usually meant a big piece was about to fall off my car.

We are taking Hal's method to the next level by reducing diameter by locking them up.

Dave