I spent 18 years involved in tire and tire maintenance. I worked from dealing with simple tire situations up to large commercial vehicles and owned and operated a large retread facility and maintenance facilities.
I worked with large commercial aircraft tires. I taught classes in aircraft tire maintenance as well as commercial tires. I was on a national organization committee who addressed tire and tire maintenance problems. I have spent a large amount of time teaching general aviation tire procedures, tire inspection and aviation tire maintenance along with brake and brake maintenance.
What I have learned and what I teach is that the general aviation community is totally out of “sync” on proper tire maintenance. Tires and brakes are one of the most important items on an aircraft next to engines.
Let me start with the general aviation twin Cessna aircraft. Every single aircraft from a Cessna 310 to a Cessna 421C uses a 650 x 10 8 ply RATED main tire. The nose gear is a 600 x 6 6 ply RATED tire. No matter what aircraft from a 5,000 pound 310 to a 7,000 pound 421C the tire is the same. Does this makes sense? Absolutely not.
As an attorney lets first visit on the failure of a tire on the runway on the roll or after landing. If a tire fails from an impact and it is reported by the tower at a controlled field the FAA and NTSB is going to get involved. They will visit with you the pilot and the maintenance staff to determine the quality and installation of the tire. If the tire is a “flat” then the FAA and NTSB will not get involved.
Now we get to the bottom line, or one of them, that I am so adamant about. So you are going to have the same tire on your 340, 414 and 421C.
Let’s talk about tire construction. Tires are constructed as bias, radials and in some cases bias belted. The majority of aviation tires are bias construction which is a model of construction that has been around since the Model T and before. It is layers of a material pressed into unvulcanized rubber and laid in opposing layers. It is then “vulcanized” or cooked in a mold that puts the imprint of the tire and makes the rubber solid. Rubber prior to being cooked is like chewed bubble gum.
Rule One on Tire Maintenance – UP THE AIR PRESSURE
Air pressure is your friend. Low air pressure is your enemy. For instance, tires with low air pressure build up heat on the roll and heat causes tire to separate. Low air pressure causes the tire to face an “X” type of impact that happens on bias tires. Low air pressure causes rolling resistance on takeoff which hampers the roll. Low air pressure causes the plane to “walk” on a landing with cross winds. Low air pressure affects braking performance. Low air pressure can “destroy” your landing trunnions or other gear components. When the tire pressure is low and you make an exit from the runway or on to the runway the gear absorbs the turn as the low air pressure locks the tire in place. This causes damage to gear components.
Rule Two – Raise the ply RATING on your main tires and nose gear.
An 8 ply RATED tire does NOT HAVE 8 PLIES. It has four. The “rating” is an equivalency for the strength of an early real 8 ply tire. Materials are now used in bias tires that were stronger than originally used that set up the original ply material years ago.
So What Do You Do?
First, when you are ready for a tire change on a Twin Cessna up the rating to a 650 x 10 to a 10 ply RATING. Up the nose gear tire to a 600 x 6 8 ply RATING. Raising the ply rating does NOT increase the size of the tire. Tires are molded and not matter what the ply rating is the mold will not let it get bigger in the curing mold.
Second, PUMP UP THE AIR. Large commercial aircraft run up to 200 psi on their tires and the military runs up to 300 psi. IT IS ALL ABOUT THE AIR PRESSURE. Even if you have the 8 ply rated and 6 ply rated nose gear raise the pressure by 10 psi over the POH. Bias tires are NOT suppose to squat. YOU CANNOT HURT A BIAS TIRE BY PUTTING IN MORE AIR. It is the other way around. Too little air is an accident waiting to happen.
In Conclusion
- When you change your tires change your tubes. Do not skip this. New tubes are critical to tire safety and long time tire life.
- Monitor your air pressure prior to every flight. Put a label somewhere near the tire of the POH air pressure and then raise the pressure by at least 10 psi. Buy a quality air gauge. Do not use a cheap pencil gauge. They are not accurate.
- Look for gouges or cuts in the tire. No, they are not safe and they WON’T WAIT UNTIL THE NEXT ANNUAL.
- If you have not upped the PLY RATING, on your next tire change put the next highest ply rating on your plane and again new tubes. Higher ply rating along with 10 psi higher keeps your tires from “squatting.” Bias ply tires should not squat. They should stand up without the bulge. The bulge is a problem waiting to happen. Take your 8 ply RATED tire and make it a 10 ply RATED, Take you 6 ply RATED tire and make it an 8 ply RATED tire.
- Make sure your home airport is taking FOD as a serious problem. Runways and taxiways have to be inspected and checked on a regular basis.
- The nose gear tire is more critical than the main tires. When you start the roll the load is heavy on the nose gear tire until the aircraft builds lift. Most twin Cessna Aircraft sit a little nose down on the ramp so that nose tire is loaded on the initial roll. Up the ply rating to an 8 ply RATED tire with a new tube on change out.
- Think about your gear when you think about doing rolling takeoffs and fast exits. The damage to the gear can be tremendous and expensive. Stop your aircraft to a crawl and make a steady forward speed exit in the turn off the runway. Taxi out from the taxiway to the runway and keep forward momentum while lining up with the runway. Trunions are expensive to replace. The torque from a locked tired pivoting on that tire puts a large load on the trunions as the tire does not move easily while rotating on the tire.
Save your aircraft and passengers. Keep good “shoes” on your plane.