This came back in an inspection for a tailwheel Maule:

"Left main wheel shows wear on inside of tire."

The seller had already advised me of some wear on the tires, so it wasn't a surprise, but now I'm wondering about tracking. Anything else anyone's seen which might cause wear on the inside of one tire, but not another?

Gear can get bent with vigorous off airport use.
The technique for straitening Maule gear is unsettling at first, but quite straightforward.
There are multiple post about the procedure over on the Maule forum.
Calling Jeremy.......

I would say that IF it were wearing on the inside, the angle of the tire would be really obvious and the aircraft would be setting very uneven. I would also think that if it were alignment, that it would handle terribly in taxi. Since you've only had it a while, could it be that the previous owner dismantled the wheel and rotated the tire from outside in inside to leverage some more life out of it? Also, if the opposite main has less obvious wear to it, it may be a newer tire? A photo on flat ground directly from the front would reveal any of this.

Thanks ChazDevil, Delta Romeo. The A&P shop got right back to me with an explanation of the wear & photos, it is not due to a bent frame but to lack of correct spacers for those tires:

"...rubbing was caused by the oversized tires on the airplane without the proper spacer on the spindle to provide clearance and the corner of the brake assembly would rub. The tire would only rub if the tire pressure was low or the tire flexed excessively so it was not a constant rub."

Issue has since been fixed with installation of appropriate spacers.

Got me...

I came away that we were talking about tread wear, not inside sidewall rubbing by the caliper.

Ah, so this isn’t treadwear, but something rubbing on the sidewall. Sounds like you tracked down the rubbing.

It’s been said that moving the brake calipers from the aft side of the Maule landing gear/axle to the front will all but eliminate that rubbing with larger tires in most cases. Not sure whether yours is configured that way or if yours is on the back side. Mine was moved to the front. My largest tire is an 850x6, though, not a 31” or larger.

Actually the main reason to have the caliper mounted on the front not rear is for safety and also for better braking traction.
If a tyre is soft or is squeezed inward as in a crosswind one main wheel landing, when the brake caliper is on the rear, the tyre is moving rearward and can catch on the caliper especially on the bleed nipple. If the caliper is on the front, the tyre is rotating forward and downward and will not catch the caliper as the tyre is not squashed.
If the braking force is on the front it is pulling the tyre onto the ground for better braking traction versus with caliper on rear it is pulling tyre away from the ground.

maules.com wrote:Actually the main reason to have the caliper mounted on the front not rear is for safety and also for better braking traction.
If a tyre is soft or is squeezed inward as in a crosswind one main wheel landing, when the brake caliper is on the rear, the tyre is moving rearward and can catch on the caliper especially on the bleed nipple. If the caliper is on the front, the tyre is rotating forward and downward and will not catch the caliper as the tyre is not squashed.
If the braking force is on the front it is pulling the tyre onto the ground for better braking traction versus with caliper on rear it is pulling tyre away from the ground.

Thanks for that extra bit of info. It clarifies the reasons greatly. Nice to hear it from the expert.

Several things to think about when mounting calipers on disk brakes. Clearance from tire, skis, mud flaps, and wheel fairings should be considered. Proper brake line routing, prevention of damage from rocks, brush, and pilots. Brake line material allowing caliper flotation. Location of bleed nipple and understanding air entrapment in caliper and brake lines all have a role in good brake operation.
From what I have seen most all of the old stuff we fly has issues and many are made worse by people meaning well but not thinking it through. In the days of covered gear and small tires you ran the line under the fabric as it came out the bottom it was aerodynamic, tidy, and clean to just hang caliper upside down or at bottom of wheel to clear fairing and connect line. It worked fine on nice strips. So now when we strip the gear, add big tires, and want to move caliper up to clear brush, rocks everybody says the bleed nipple came from the factory pointing up so that must be the way it should be. Then they figure out the line is also in danger so swap the caliper so nipple is down. Instead of replacing the entire line on the gear leg just add a short pice of flared copper to the line creating a big arch for air bubble to get trapped. So when you look at how brakes are set up most will work but many can also be made better.
On most big wheel stuff 10 o'clock position, nipple down, seems to work, easy to bleed, and clear extra stuff. Use a 45 degree not the old 90 degree fitting out of the top to avoid creating a loop to trap air. Next use single flex line from caliper to fuselage bulkhead fitting in a continuous uphill slant. On a cub do not take line to top of leg and make a big loop down below middle of belly bulkhead exit gear leg early. If you are building a cub run bulkhead out side above gear. Hard lines to calipers work but, in todays world we have better stuff. I don,t think the rotor cares where the caliper grabs it front/rear/bottom/top all positions will lift the tail if you brake hard enough.
All of the above is complicated by price point, parts availability and wrench turners understanding of what is legal or not.
DENNY