Tire cord

[Jim Peace]

I fly a Grumman Yankee at times and just came across tire cord on a part of the tire that does not make contact with the ground. At least it appears it shouldn’t. 

what do you make of this picture? Front of tire looking aft..
 

 

[dan nephin]

Mis alignment on that tire. Toed out I believe. 

[EricJ]

Agreed, likely an alignment issue.   IIRC, there's a procedure in the Yankee MM for checking and setting alignment.   We had two of them in the shop at our A&P school and had to do a bunch of stuff like that.

Bummer that that chewed up an otherwise good tire, but it'll keep doing it until corrected.

[RLCarter]

looks like the outside of the tire is wearing too, that would eliminate toe in or out (cant have both on the same wheel) leaving under inflation as a possible cause

[jaylw314]

4 hours ago, Jim Peace said:

I fly a Grumman Yankee at times and just came across tire cord on a part of the tire that does not make contact with the ground. At least it appears it shouldn’t. 

what do you make of this picture? Front of tire looking aft..
 

Not a tire expert, but I suspect that is a few (or one) hard landing.  On a hard landing, the tire deforms, and rides more on the sidewalls.  On a spring landing gear, the wheel also deflects and rotates up and out on a hard landing , so the tire rides more on the inner half.

I suppose it could also have been a really hard turn, but you'd see the outside tread worn on the opposite tire

[RJBrown]

1 hour ago, RLCarter said:

looks like the outside of the tire is wearing too, that would eliminate toe in or out (cant have both on the same wheel) leaving under inflation as a possible cause

Yes,

tires need air. Too little air and they wear on both sides.

time for a new tire for the plane and a tire pressure gauge for you.

[carusoam]

+1 on landing issues...

Weight of the plane will compress the spring gear and rotate the tire out on its edge...

Its possible the landing gear can be set up better... see if the owner has a maintenance manual for that...

The toe angle probably has some form of adjustment...

Or could be a training issue... land a little lighter...  put less weight in the plane...

Great opportunity to set up a go pro and see what is really going on...

A lesson on spring gear will probably be the result...

Springs physically lose their springiness with temp, time, and number of uses...

See what a new spring costs...

Expect that when you put a square next to both tires... the tires are probably splayed out without any weight in the plane...

Take a video as the pilot gets in the plane... you will probably see the spring getting floppy and the tire moving around towards that edge...

Best regards,

-a-

From the automotive world...

Same thing happens when springs wear out in cars...  plenty of adjustments there...

[RJBrown]

Toe scuffs tires and leaves a feathered edge. This wear is not toe. 
this wear is caused by sever under inflation. 
the concave area where the cords show was flat on the ground. The difference between the inner edge and the outer edge is due to camber.

 

[RLCarter]

Actually isn’t when a wheel “leans” in or out, it’s “camber”?

[RJBrown]

Quit guessing the wear pattern was caused by under inflation with a bit of camber to increase wear towards the center and decrease at the outer edge.

no technique would cause this. This one is very very obvious. Guesses only serve to confuse the issue.
if the tire was aired up properly the camber issue would be insignificant. 
BUY A TIRE GAUGE AND USE IT.

PERIOD NOTHING ELSE.

I don’t want to be rude but this is very simple and obvious to anyone who has been around tires at all.

yes Robert camber is as you describe. It accounts for the uneven side to side wear.

[RJBrown]

For a simple explanation of alignment look here,

https://townfairtire.com/information/wheel-alignment/caster-camber-and-toe-alignments/index.shtml

Toe in self corrects and keeps a vehicle going straight. Each tire turn the vehicle toward the other tire. Wears from outside in in a feathered pattern.

Toe out causes a pull to the side that has the most traction. The tires are turning away from each other. Not self correcting, heads you toward the weeds, car or plane. Wears tires from the inside out in a feathered pattern.

Even negative camber creates higher traction in turns and tends to be self correctin directionally. It wears the inside edge of the tire.

Even positive camber causes a directional pull is not self correcting and wears the outside edge of the tire.

a car set up with 1/8” toe in and 1/4 degree negative camber will be stable and won’t wear tires excessively.

Caster is a bit more esoteric and hard to describe.

Think of a shopping cart the center of the wheel is behind the turning point of the suspension. It makes the wheel follow. It is what centers the wheel when you release the steering wheel. Caster does Not cause tire wear but if uneven it causes a pull to the side with more caster. A shopping cart has 15 degrees of caster while a car has about 1 1/2 to 2 1/2 degrees. Too much caster causes the wheel to wobble with increased speed. If you run with a shopping cart you will see them wobble.

Here most roads are crowned. A crowned road will cause a car to pull to the right side. (Gravity sucks) A slight amount more caster on the left tire can compensate for the crown. 
as steering components wear additional toe in will help compensate for the looseness.

When loading and unloading a trailing landing gear like a Mooney the suspension absorbs the load by changing caster. The tire points straight forward on our Mooneys no toe in. The tire sits vertically, no camber. This is why our tires wear more evenly than Cessna aircraft. 
Spring gear is used on Cessna, the above mentioned Grumman, Vans kit planes, and Cubs etc.

Spring gear uses the flex of the landing gear arm to absorb the weight of landing. As the gear arm flexes the alignment angle of the tire changes. The unloaded gear will have positive camber. As the gear arm flexes the tire will be pulled to negative camber. Toe also pulls out as weight is added. To maintain directional control they need to be toed in further to begin with. This effect is worse on a tail dragger. If a tail dragger is toed out it will be hard to keep on the runway.

The slight camber wear on the above Grumman is normal. The under inflation is the wear problem.

 

 

Edited March 4, 2021 by RJBrown

[MARZ]

I vote for excessive side loading - does your airport have consistent cross winds?  

[EricJ]

I'd have thought that being underinflated enough to cause wear like that would be pretty obvious both in appearance and handling.   Did the tire have pants on it or was it easy to inspect?   Were any handling issues noted on takeoff or landing?

It could also be a bearing or hub issue if there's a lot of play in the wheel, but I'd think that'd have to be pretty extreme to result in wear as bad as that shown.

I still think it's worth checking the toe alignment.   There's a two-minute vid online with about forty seconds of relative content once you get past the intro screens and credits.
 

 

[carusoam]

@Jim Peace

Check out the Grumman video posted by Eric above...

See if your Grumman has any shims, or needs any...

Best regards,

-a-

[Jim Peace]

great info thanks guys