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05-25-2017, 06:54 AM
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been here awhile
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Join Date: Dec 2004
Location: North Alabama
Posts: 4,301
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Quote:
Originally Posted by DanH
Time out for a Belief System Alert.
Where is the data connecting tread depth and incidence of flats?
Tread grooves are for liquid escape. Sure, a pointy object (like a nail or thorn) won't reach the tube if the total tire carcass is thicker than the length, but given ordinary objects (pebbles and stones mostly), why should tread depth make a lot of difference?
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That is why I haven't bought into the concept of tread depth being related to tire failure. The strength of the tire is in the carcass, tread just provides traction and water repulsion. As long as the carcass contains air pressure, we have a tire that will keep the rim off the ground.
I don't worry about tread depth because I rarely fly off a wet runway. When the tread wears off of the contact patch I consider that an indication that the cords can't be far below the rubber and it is time to stop depending on that portion of the tire to be the contact patch. But because my RV-6 only wears tires on the outside third of the tire I have safely used tires since 1999 that have little tread on the inside third of the tire. I just don't see the need to toss a tire that still has half of its service life remaining.
The key is to be familiar with the operational characteristics of our particular aircraft and maintain it accordingly. This is a case where one size does not necessarily fit all. 
Last edited by Sam Buchanan : 05-25-2017 at 07:04 AM.
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05-25-2017, 07:17 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by Sam Buchanan
....tread just provides traction and water repulsion.
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To be perfectly accurate, tread grooves and other molded patterns in the surface of a tire reduce paved surface traction. Maximum dry traction is found with a smooth tire, aka a slick. I'm just polishing the pins here. Sam likes sports cars, so he knows that little detail. And maximum grip isn't a big deal in our application anyway.
Again, can anyone present a study of tread wear vs incidence of flats?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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05-25-2017, 07:34 AM
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Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,393
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Tires
I was told that there is a Goodyear document detailing how much cord can be showing and the tire is still airworthy.
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05-25-2017, 07:47 AM
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Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,393
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Tires
Disregard my previous post. I found the Goodyear document online. It allows very limited exposure of cord at bottom of a groove but does not allow flat spotting that exposes cord. Very detailed and interesting article. They call for tire replacement for any wear to bottom of groove.
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05-25-2017, 08:04 AM
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Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,393
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Tires
For many years there were surplus aircraft tires available that probably dated to WWII. A lot of these were smooth tires. On homebuilt airplanes they were commonly run until cord showed. This is in accordance with the Goodyear document and there is absolutely nothing unsafe about it. 500 x 4 wheels tires and brakes were used on the Culver drones and were widely available.
awheels was late Nick D'Appuzzo, designer of the PJ260/Senior Aero Sport Biplanes. He sold surplus Culver wheels probably well into the 70's. In the 60's they were under $100 a set and I think this included tires and tubes. The brakes were Goodrich Cub style and not very good. Smooth tires.
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05-25-2017, 08:22 AM
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Join Date: Oct 2007
Location: In New Braunfels, ist das Leben schön!
Posts: 871
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Goodyear Aviation Tire Care Document
Here is Goodyear Aviation's Tire Care Document. Includes pictures and a clear discussion of tread wear limits including when to flip the tire.
https://www.goodyearaviation.com/res...are_3_2017.pdf
__________________
Larry New
RV-7A - Built, flying 900+ hrs
RV-10 - Built, flying 2.9 hrs
??? - RV-12, Subsonex
48 States in 7 Days!
VAF Paid - Annual Autodraft
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05-25-2017, 08:37 AM
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Join Date: Dec 2005
Location: Ridgecrest, CA
Posts: 432
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Tire Wear II
One "what if" that hasn't been addressed during this interesting thread- What if the wear was uniform across the whole tread? No advantage then to flipping. At what point would you replace the tire?
I would run it down to just before the tread grooves disappear.
By flipping, I'm doing essentially the same thing.
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05-25-2017, 09:02 AM
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Join Date: Oct 2012
Location: Clearwater, FL KCLW
Posts: 1,281
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Quote:
Originally Posted by Walt
Apparently it's just that I have a little different philosophy on aircraft maintenance than some of the folks here. I wonder how many "frugal" folks that flip their tires to get every last mm of rubber off them can say they have had ZERO mechanical break downs, ZERO out of service time, ZERO flat tires and 100% dispatch reliability for the last 12 years and 1500+ hours. I can assure you it has nothing to do with luck and everything to do with my maintenance practices.
If you can't afford new tires what else have you neglected I wonder?
Anyway that's just the way I see it.
Ok I'll take that time out now...
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While your record is certainly a testament to your workmanship, you could put on new tires every flight and also go 15 years without a failure. You could do the same with any number of other parts. Doesn't mean it was necessary.
I thought this was a valid question. The OP was asking at what point tires become less safe, not "how long can I get away with being a cheapskate".
Replacing something more than necessary doesn't make you any safer, and in the case of maintenance-induced-failures, can actually have the opposite effect. Sure, changing tires is a simple, low-risk procedure, but it is another chance to pinch a tube, improperly torque the wheel, etc.
Chris
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Chris Johnson
RV-9A - Done(ish) 4/5/16! Flying 4/7/16
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05-25-2017, 09:15 AM
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been here awhile
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Join Date: Dec 2004
Location: North Alabama
Posts: 4,301
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Quote:
Originally Posted by pvalovich
One "what if" that hasn't been addressed during this interesting thread- What if the wear was uniform across the whole tread? No advantage then to flipping. At what point would you replace the tire?
I would run it down to just before the tread grooves disappear.
By flipping, I'm doing essentially the same thing.
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Agree. It is interesting how the Goodyear document says the same thing.
Last edited by Sam Buchanan : 05-25-2017 at 09:27 AM.
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05-25-2017, 09:24 AM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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In principals, I am in agreement with Walt.
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Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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