When to change a tire

[trey kule]

I had a question, but it has been answered. Maybe one of the mods will delete the thread.

[Colonel Sanders]

Actually, it's a very good question. The fur really flew here a few
years back last time we discussed it, when I found a doc from Goodyear
saying that a tire with 2 layers of cord gone was ok for service.

[DonutHole]

Colonel:
Have a thread title I can search up for that? Interested to hear the different perspectives.

I was always surprised at the amount of damage a tire can exhibit and still retain serviceability.

[trey kule]

Just a thought, but rather than the perspectives, I found the B.F. Goodrich website has all sorts of aircraft tire training..Not only wear related, but over under inflation, alignment etc. Worth spending an hour or so on if you are interested.
Which is why I dropped the original question.. I felt I was getting good information. and they answered the question

[Beefitarian]

What brand are they?

[Popol]

I had a question, but it has been answered. Maybe one of the mods will delete the thread.

Why delete a thread after you had an answer... this can be usefull for someone else...

[dashx]

http://www.goodyearaviation.com/resources/tirecare.html

http://www.airmichelin.com/generalcontent.aspx?id=219

Tires are a never ending source of concern to AME's, flight crews, and passengers. Sometimes its amusing, sometimes annoying but it's something I always take seriously.

[Colonel Sanders]

There it is!

In order to return to a maintenance base, Goodyear tires can remain
in service with top ply cord visible, but only as long as the cord is not
worn through or exposed for more than 1/8 of the circumference of
the tire or not more than 1 inch wide at the fastest wearing location.

That is one scummy looking tire, guys. You would be amazed at
how many people would say that such a tire was not legally airworthy.

[GyvAir]

That is one scummy looking tire, guys. You would be amazed at
how many people would say that such a tire was not legally airworthy.

I'd say that's a good thing. Would we rather be amazed at how many people would say that if that threadbare tire's legally good enough to return to base on, then it's good enough to finish out the rest of the week?

[dashx]

All the Bombardier AMM's (Q series and CRJ's) have info on tires.

Classic Dash:

a) Examine the tire for the usual tread wear. After you see the reinforcement cord
in the tread area, you can have a maximum of three more landings. After that
you must replace the tire before the subsequent flight.
(b) Examine the tire for too much tread wear. If the tire is worn through the tread
reinforcing plies to the rubber buff−line cushion, remove the tire from the
aircraft. If the tire is worn to the breakers or casing plies, remove the tire from
the aircraft and discard the tire. It is not permitted to retread this tire.
(c) Make sure that the tread wear is the same across the tire. If the tire has more
tread wear at the center area (over inflation) or more tread wear on the
shoulder areas (under inflation), remove the tire from the aircraft. Too much
tread wear along the center decreases traction and can cause the tread to cut
easily. Too much shoulder area tread wear increases the possibility of
shoulder and side wall bruising and decreases the tire life because of flex
heating.
(d) Make sure that the aircraft tires are replaced before the subsequent flight, if
the landing speed of the aircraft was more than 182 kts with the flaps at the 0°

CRJ200

(a) Examine the tire for normal tread wear. Except as noted in the TREAD
DAMAGE section of this procedure, it is acceptable for the tire to remain in
service until the tread reinforcing ply (also known as the fabric ply) on fully
worn tires is:
– exposed to a maximum of of the circumference of the tire but not worn
through to the rubber buff−line cushion
– exposed to a maximum of 1 inch (2.5 cm) wide at the fastest wearing
location.
NOTE: Tires that reach this wear point on an aircraft at a remote station can
make a return−to−base revenue flight(s) under normal operating
conditions without sacrificing the retreadability of the tire.
NOTE: Some retreads have reinforcing cords that are referred to as spiral
wrap [Refer to Figure 603 (Sheet 1)] that are wound into the tread
which become visible as the tire tread wears. This visible reinforcing
cord is used to reduce chevron cutting and tread chunking of a
retreaded tire and is not a reason for rejection.
(b) Examine the tire for excessive tread wear. If the tire is worn through the tread
reinforcing plies to the rubber buff−line cushion remove the tire from the
aircraft. If the tire is worn to the breakers or casing plies, remove the tire from
the aircraft and discard the tire. It is not acceptable for retreading

Remember you are trying to save money for the company if you can re use the tire...........the more money you save the bigger your bonus will be............

Right then enough of this tirade.

[CpnCrunch]

Here is the info from Michelin, which is a bit clearer:

When the wear level reaches the bottom of any groove
along more than 1/8 of the circumference on any part
of the tread, OR
• If either the protector ply (radial) or the reinforcing
ply (bias) is exposed for more than 1/8 of the circumference
at a given location.

So you can keep using the tire if a small amount of it is worn down to the cords. However you can't keep using it if the entire tire is worn down to the cords and you don't have any tread. So basically you can only have a "spot" that is worn down to the cords.

And if you read the Goodyear document CS posted, you'll notice it also says:

Tires should be removed when tread has worn to the base of any
groove at any spot, or to a minimum depth as specified in aircraft manuals.

The main reason you need tread (and grooves) is for wet-runway braking effectiveness.

[Colonel Sanders]

The main reason you need tread (and grooves) is for wet-runway braking effectiveness.

uh, not sure about that. Hydroplaning speed is pretty
much solely a function of tire pressure, IIRC. If tread
mattered, we'd see MUCH more sophisticated tread
patterns on aircraft tires.

Those radial grooves on aircraft tires are tread wear
indicators, as described above.

that threadbare tire's legally good

When my father was flying F-104's at CEPE and the
OTU, often the tires would be a mess. Several layers
of cord showing. Looked like a fuzzy dog. Didn't matter
because of the incredible number of plies the tire had.
And that's with 170 knots over the threshold.

[photofly]

Fantastic. Does that mean someone can now make me some dimpled tires - like the surface of a golf-ball? Then I can lose 60% of the drag from my un-faired undercarriage.

Airlines that fly twotters on wheels can thank me for the reduced fuel burn my idea will enable, with free tickets for life.

http://www.aerospaceweb.org/question/ae ... 0215.shtml

[GyvAir]

The main reason you need tread (and grooves) is for wet-runway braking effectiveness.

uh, not sure about that. Hydroplaning speed is pretty
much solely a function of tire pressure, IIRC. If tread
mattered, we'd see MUCH more sophisticated tread
patterns on aircraft tires.

Really? I've rarely experienced hydroplaning while driving a vehicle on tires with good tread. I've often experienced varying degrees of hydroplaning when driving on tires worn to the limits and beyond. I can't vouch for exact tire pressure every time of course, but the common shortcoming has always been lack of tread depth. Why would it be different for an aircraft on a wet runway?

I've also wondered why aircraft tires generally have only radial tread grooves and none laterally? Would lateral treading or sipes not aid in wet/snowy condition braking performance? That said, I've noticed that front tires on some highway coaches have only radial grooves.

[CpnCrunch]

From a NASA study:

This investigation has demonstrated the important effects of tire-tread
wear on the wet-runway braking effectiveness of aircraft tires. For the two
types of tread wear that were simulated - that is, uniform and nonuniform wear -
gradual degradation in braking effectiveness was experienced as tread wear pro-
gressed from a new tire, or 0-percent-worn condition, to a 60- to 80-percent-
worn tire. As tread wear passed the 80-percent-worn condition, however, braking
effectiveness dropped markedly. These results indicate that aircraft tires
should be replaced before the tread is worn completely smooth if safety requirements a r e not t o be compromised.

But apparently CS knows better than both NASA and the tyre manufacturers themselves.

I'm surprised that you're allowed to fly the dash8 on bald tires. What is the reasoning behind that? There was an accident where a learjet went off the end of a 10,000 ft runway, and having little tread on the tires (even though it was legal) was cited as a factor.

[Colonel Sanders]

You may have heard of the Federal Aviation Administration,
which publishes a book called the "Pilot's Handbook of
Aeronautical Knowledge". The following is the relevant
excerpt:



The FAA seems to be implying that grooves in the runway
are probably more important than grooves in the tire.

My apologies for offending you by reading that book.

[GyvAir]

I can't find the passage in that handbook that states something to the effect of "the only factor affecting an aircraft's likehood of hydroplaning is tire pressure and the presence or absense of runway grooving"

http://www.nlr-atsi.nl/downloads/hydrop ... -tires.pdf

Quote:

"Dynamic hydroplaning is the result of the hydrodynamic forces developed when a tire rolls on a
water covered surface. This is a direct consequence of the tire impact with the water that
overcomes the fluid inertia. The magnitude of the hydrodynamic force varies with the square of
the tire forward ground speed and with the density of the fluid. Dynamic hydroplaning is
influenced by tire tread, water layer thickness and runway macrotexture. Macrotexture is the
runway roughness formed by the large stones and grooves in the surface of the runway. When
there is sufficient macro texture on the surface and / or the tire has proper tread, total dynamic
hydroplaning will usually not occur. However, hydroplaning can occur when the water depth is
high enough so that both tire tread and runway macro texture cannot drain the water quick
enough."

They also go on to talk about Horne’s dynamic hydroplaning equation as mentioned in the FAA handbook.


I also missed the point in this thread conversation where a transition to belittling sarcasm became appropriate, necessary or in any way beneficial.

[torquey401]

The general rule of thumb is that the aircraft manufacturer's recommendations take precedence over component recommendations. Then when the AMM is mum on a subject, you go to the specific component manuals. I have had to produce the Goodyear and Michelin data more than once to show an owner why I need to replace his tires.

[Colonel Sanders]

Monday morning, I shall inform the Ottawa airport operator
that the resurfacing of runway 07/25 this year was unnecessary
according to the AvCan experts, who maintain that if all the large
aircraft that went off the runway recently had sufficient tread,
it wouldn't have happened.

[CpnCrunch]

I guess in that case then you should also remove reverse thrust from all jets, as you've got brakes that should stop you.

[GyvAir]

Ahh... the age-old forum difficulty of determining if a poster is being wilfully ignorant, genuinely thick, or just idly trolling.

[CpnCrunch]

In all seriousness, you can't keep a bald tire on your plane (if it's Goodyear or Michelin). The tread is required for wet-weather braking performance. If you have no tread, your wet-weather braking performance will be signficantly worse.

Both Michelin and Goodyear say you should change the tire when the tread is gone. AC43.13 says the same, and it applies unless your tire manufacturer says something different.

I think what happened is that CS read the paragraph about it being okay to have cords visible and that stuck in his brain, but he completely missed the paragraph after that which says you ALSO need to change your tire when the tread is gone. You'll see he brought up the very same argument a couple of years ago and we were all shaking our heads back then. Now that the "bald tires are fine" meme is stuck in his brain, it's impossible to shift it. Unfortunately this is just the way the human brain works and further discussion is impossible, hence the lapse into sarcasm rather than hitting your head against the monitor.

Also CS is a little confused about the difference between hydroplaning (which he has a bee in his bonnet about, but nobody mentioned it apart from him) and wet-weather braking. Read the study that NASA did and it will clear some things up.

[Colonel Sanders]

remove reverse thrust from all jets

The jets I fly do not have reverse thrust. I shall
immediately inform Transport Canada and the FAA
of this important fact which renders them inoperable.

[CpnCrunch]

Ah, completely ignoring the discussion.

Now getting back to the topic of when to change your tires. The manufacturers recommend waiting until 100% of the tread is gone. However NASA showed that braking performance reduced markedly after 80% wear. The reason is that it's the grooves on the BOTTOM of the tires that are important for wet weather operation. With the airplane sitting on the tires, the weight results in the grooves disappearing, so effectively you have zero tread on the bottom of the tire when tread wear reaches 80%.

In a light aircraft landing on relatively long runways I guess this isn't really too much of a concern as you can usually get away with minimal or no braking. I'd be more concerned about passenger jets, so it does seem odd that they (or at least Bombardier) seem to let you run their planes with bald tires. I would query the manufacturer to see what the logic behind that is, and whether it's a good idea.

[GyvAir]

I've contacted my favourite NASCAR team and passed on what I've learned here. They are absolutely thrilled to know that they can quit wasting money and precious pit time on changing to rain tires on wet days. Now they know all they really need to do is inflate their regular slicks to 472 PSI and they’ll be just fine on a wet track at 200mph+.

It's too bad, really; internet forums can be great learning tools for all. Unfortunately there tends to be a core group that lurks on every forum that just can't help turning a friendly discussion into a mudslinging put down fest, or an argument for argument's sake, even when they know information and ideas they are putting forward is twisted or inaccurate.