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-   -   Safe margin of tread wear (https://vansairforce.net/community/showthread.php?t=149798)

kevinsrv7.com 05-25-2017 04:32 PM

Hours?
 
Brian, How many hours are on these tires?

rzbill 05-25-2017 04:37 PM

Quote:

Originally Posted by Blain (Post 1175487)
Alright, In my defense, lets analyze what happens when we flip-I'm not alleging its wrong, just setting up an understanding.

Do we agree that some wear happens across the face, with more on the outside? If so, then flipping the tire in my picture some wear will occur on the already bald side? Back to my original question-how far can it go?

If flipping is going to be the plan, than the tire should be flipped before the tread depth is gone. Ideally estimating how much it will take to get "Even" with the high side.

We agree so far?

If so, the tire in question, in my estimation, was too far gone to justify flipping.

The question of flipping demonstrates the old adage "How was copper wire invented"? Answer;2 pilots fighting over a penny. My choice as I'm sure many others would be a time vs. value decision.

Jeez, I just wondered how many landings I could squeeze out of a tire.....

Why not flip them and watch for yourself? Learn. The tire wear is trully assymetrical so the portion of tire that is missing tread may last in its current state until the fresh tread is worn down considerably. You could certainly look at the good tread that is there at the moment. How much do you think it has worn down from new? On my first set of tires, I kicked myself for flipping too early.

I think this is a matter of personal tolerance. Each of us will choose differently. If it bugs you, put new donuts on it and watch for a better time (in your own mind) to flip them.

Blain 05-25-2017 05:38 PM

Quote:

Originally Posted by Carl Froehlich (Post 1175495)
While taking the tire off the wheel and flipping will buy more time, for the time it takes to do all that work I'd rather just put a new tire.
Carl

Thank you. My thoughts exactly.

Quote:

Originally Posted by kevinsrv7.com (Post 1175531)
Brian, How many hours are on these tires?

Should be right at 60 hours now. And as I said before over 100+ landings, 7 hours of low and high speed taxi. I just went to Google Earth and measured from the hangar to the runup area 1.13 miles. So a lot of ground ops.

Plummit 05-25-2017 06:07 PM

It seems to me that if you flip your tires and install new tubes (as recommended), the increased savings will be at least partially offset by the cost of your parts, materials and labor.

I don't know that I'll flip my tires (Flight Custom III). I may just leave them on until they have been used up, then buy new. They aren't that
expensive...

~Marc

strahler13 05-25-2017 07:45 PM

Quote:

Originally Posted by Plummit (Post 1175546)
It seems to me that if you flip your tires and install new tubes (as recommended), the increased savings will be at least partially offset by the cost of your parts, materials and labor.

I don't know that I'll flip my tires (Flight Custom III). I may just leave them on until they have been used up, then buy knew. They aren't that
expensive...

~Marc

Flip tires and install new tubes? One of my current tubes has been on the plane since the day I bought it--13 years ago and over 1,000 fight hours.

Flying again! 05-25-2017 08:12 PM

Quote:

Originally Posted by RV8JD (Post 1175534)
I was surprised also! We were Flight Flutter Testing a new large commercial transport near the turn of the Century and using the Company T-38 for high speed chase. Between flights we were walking the flight line, admiring the sleek looking, well maintained T-38. We noticed that one of the mains had cord showing and were quite surprised by that. We talked to one of the mechanics on duty and he said that the tire didn't have to be replaced yet, as not enough cord was showing. We were quite surprised by that given the high TO and landing speeds of the T-38, but they are 14-ply tires, IIRC.

The T-38 tires have a red cord, when that shows it is time to replace them.

My project at Test Pilot School was to modify a T-38 with a larger speed brake and use it to decrease the L/D to simulate the X-24B lifting body approach ( about a 24 degree glide slope). When I briefed the Flight Safety Board one of their requirements was to use old tires instead of new. The thought was that old tires had been heat cycled many times and new tires had too much tread for the high speeds we were touching down, increasing the chance of tread separation due to centrifical force. We crossed the threshold at 230-250 knots as I recall.

After the last approach when at Bingo fuel the closed pattern and normal 3 degree approach seemed way too low:D

ludgater 05-31-2017 11:25 PM

If you are doing circuits go to a grass strip, stay off the seal as much as possible, rotate the tires and there will be plenty of life in them yet

DanH 07-06-2017 09:17 AM

Since I was about to swap tires anyway, I sectioned one for the cause. These are common Aero Classics. Measurements may vary given a different tire.

I ran this set somewhat past the point where tread grooves had disappeared from the primary wear area. They were not flipped. I inflate to 50 psi nominal.

Need a wear indicator? At the bottom of the tread groove, you have 1/8" of wear rubber before you'll see cord. Total carcass thickness from the bottom of the groove is 3/16".



The section looks like this:



Below, 10x magnification, taken at the thinnest point. Wear rubber is 1/16" to cord. Looks like four cord plies, with three in the rubber and one merely lining the inside of the carcass. The cord layers total another 1/16". Might get a little more life by flipping them, but not a lot. Going forward, I'll run 'em until one tread groove remains (first photo), then just replace them.


Blain 07-06-2017 08:15 PM

When 1 remains? Wouldn't that assume consistent wear pattern?

At the bottom of groove there will only be 3/16" between me and running off the side of the runway- if lucky. Think I'll pull them when tread disappears.

I would have thought the carcass to be a bit more substantial. Thanks for the visual, Dan.

DanH 07-07-2017 07:37 AM

Quote:

Originally Posted by Blain (Post 1185851)
When 1 (groove) remains? Wouldn't that assume consistent wear pattern?

Safe enough assumption for repeated sets on the same airplane, but the wear pattern shown here many not be true for another airplane.

Quote:

At the bottom of groove there will only be 3/16" between me and running off the side of the runway
The "run 'em until you see cord" camp is down to 1/16". However, we have no direct correlation between tire carcass thickness and the chance of a flat tire. Offhand, it does not appear that carcass thickness alone is an issue given a clean running surface. When we worry about flats due to thin tires, I think we're really talking about foreign object damage...and then the size and shape of the object becomes an entirely random factor.

Same category as primer, really ;)


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