Tread Carefully: The Proper Care of Tires

Hello, Chapter 430. My name is Rick Vaux, and the newsletter editor asked me to be our newsletter technical person. To get started, I would like to rerun some articles I wrote for Chapter 7 in Long Beach, CA many years ago. I will pick ones that are still valid until y’all come up with more questions for me!

This month I’d like to discuss Aircraft Tires including construction, inspection and a little about care.

There are two basic types of aircraft tires: Bias-ply, which are popular for durability and ease of retreading and Radial-ply, which feature decreased rolling resistance and increased landings due to rigid belts used in their construction. Both of these types have some features in common:

• (1) Tread - Commonly ribbed to provide good traction under varying runway conditions.
• (2) Sidewall - Rubber covering outer casing ply. Extends from tread edge to bead area.
• (3) Bead - High strength steel wire that secures casing plies and provides a wheel mounting surface.
• (4) Tread Reinforcing Ply - One or more fabric layers that strengthen and stabilize tread for high speed operation. This component is part of tread and therefore is replaced when the tire is recapped.
• (5) Buff line cushion - A rubber compound layer which improves the adhesion between tread reinforce ing plies and breakers or casing plies. This is thick enough to allow tread removal when retreading.
• (6) Breakers (Bias-ply) - Rubber coated fabric under the buff line cushion which protects casing plies, strengthens and stabilizes tread area. Breakers are part the tire casing and can not be repaired by recapping.
• (7) Overlay (Radial-ply) - Rubber coated fabric placed on top of belts to aid high speed operation.

There are many other components to tire construction, but, for our purposes, these are enough. Let’s press on to inspection.

I’ll start with a couple cautions. Never probe cracks, cuts, or embedded objects while the tire is inflated, and all defects should be marked with a crayon before deflation.

OK….Let’s check:

• (1) Tread wear - Tires should be changed when the tread is worn to the base of any groove (at any spot)

or to the minimum depth specified in the aircraft maintenance manual.

• (2) Tread cuts - if no specific information is available in the maintenance e manual, use the following rejection criteria:

a) Any cut which extends into casing plies on bias ply tires.

b) Any cut into the belt of radial ply tires.

c) Any cut that extends across one or more tread ribs to the fabric. (Tread reinforcing ply)

d) Rib undercutting at the base of any cut or tread splice or tread cap.

• (3) Sidewall damage - Replace tire if cracking, weather check, cuts, or snags extend to casing ply side wall or bead areas.
• (4) Bulges - Remove from service with bulge in any area.
• (5) Groove cracking - Remove tire from service if groove cracking exposes any fabric or undercuts tread ribs.
• (6) Flat spots - Unless fabric is exposed, flat spots are not cause for rejection. However, they can cause imbalance problems or wheel shimmy and may need to be replaced for that reason.
• (7) Sidewall indentation (Radial ply) Reject any tire with 3mm or greater sidewall indentation.
• (8) Bead - Inspect for heat damage next to the wheel flange, especially if subject to brake drag or heavy braking. Now a few last items to cover:
• (1) Tire inflation - Ideally tire inflation should be checked before each flight. Over inflation can damage tires by causing reduced traction, uneven tread wear, increased susceptibility to cuts and increased wheel stress. As bad as over inflation is, under inflation is much worse. It produces uneven wear and shortens tire life due to flex heating. The bead area of an under inflated tire can be 50% hotter than a properly serviced one. Nothing can destroy a tire faster than heat.
• (2) Contamination - Keep all oils, greases, and cleaning compounds off of tires.
• (3) Sun - Cover tires when left in the sun. This is probably not as important as it was in SoCal, where a combination of sun and ozone is tough on tires. Still, it makes sense to protect your investment and quite possibly your continued health.

Remember to take care of your tires, Troopers. Axles don’t roll worth a hoot without them.

Rick