Where the Rubber Meets the Runway — Part 1

By Vic Syracuse, EAA Lifetime 180848

This piece originally ran in Vic’s Checkpoints column in the January 2021 issue of EAA Sport Aviation magazine.

I’m always amazed at the condition of some of the tires we see when an airplane comes to our shop for a condition inspection. Sometimes, they are downright scary and close to a catastrophic failure, as you can see in some of the pictures. For those of you who are performing formation takeoffs and landings with your fellow pilot friends, checking your tires should be a routine part of your preflight. Many of our amateur-built airplanes have wheelpants, which admittedly make it difficult to check the whole tire. One good practice is to roll the airplane on the ground while looking at the tires. This sometimes requires two people. Another trick is to pour some water in front of the tires, or taxi through a water puddle, and then check the tracks left by the tires. You will quickly be able to discern any unusual tire wear or missing tread.

For the new, nonbuilder owners, since lots of takeoffs and landings usually happen during early ownership, having the tires and brakes in good shape is paramount to keeping the fun factor alive!

Don’t be like the owner who asked me to pick up his airplane for the condition inspection, telling me to go ahead and replace the tires. Yep, they looked horrible, and I mistakenly thought I could get at least one more landing out of them. The right tire proceeded to go flat after landing on a GRASS runway. Boy, was I lucky — except for having to fix it on a grass runway. Ever try to jack an aircraft on grass?

I know many of us grew up with car tires that routinely went flat, especially while on vacation with a fully loaded car. When checking the air in the tires, you always checked the air in the spare, knowing there was a good chance it would be used. Oftentimes, those tires would sing really loudly prior to failing, so at least there was an audible warning once in a while. Today, we are so used to the reliability of steel-belted radial tires we never even check them. Most cars have a pressure-alert sensor that tells you when they aren’t properly inflated. Some cars no longer even come with a spare tire. So, it’s understandable that we have built up a lackadaisical attitude toward car tires, which is not really transferable to aircraft tires. Plus, our aircraft tires are much, much smaller than the typical car tire, requiring them to spin much faster, which translates to faster wear.

About the only sound you will hear in an airplane when the tire goes flat is the thumping of the tire and perhaps all of the noise from the wheelpant being torn apart. By then it is too late. The damage has already been done, and hopefully you haven’t veered off the runway.

Aircraft tires are subject to much different forces than car tires. While car tires spin up slowly at every start and stop of the car (racing excluded), aircraft tires are expected to spin up from a dead stop to landing speeds in fractions of a second upon contacting the runway. The loss of rubber during this phase of operation is starkly visible as black streaks on every runway in the touchdown zone. Some commercial runways are so black they look to be painted.

Another common cause of rubber loss is that most aircraft do not have carefully aligned axles, and the flex of the landing gear usually causes a toe-out condition at landing, further exacerbating the loss of rubber due to the misalignment of the tire to the travel direction. Any friction in the wheel bearings due to improperly tightened wheel nuts or improper wheel bearing grease will delay the wheel spin-up at touchdown, causing even more rubber loss. Some aircraft have axles that are able to be aligned through the use of axle shims. The shims themselves are somewhat pricey, usually allowing corrections in half degrees, but over time are worth it for the decrease in tire wear and the improved ground handling.

The bottom line is that the wear of aircraft tires is not usually even, with everything from flat spots to uneven inside/outside groove wear, so it really does behoove one to regularly check the tire throughout at least one rotation during a preflight. Some owners will reverse the tire on the same wheel once during the lifetime of the tire to extend the life when the wear is only on the inside or outside of the tire. Frankly, I find tire changing not worth this effort and just replace the tire when this occurs.

Yes, changing the tires is usually a dirty, grimy job, but it beats having to repair wheelpants, losing an airplane, or potentially getting hurt with an off-runway excursion. Most tires can be removed, changed, balanced, and reinstalled in about two hours or less per tire, including replacing the brake pads, if you are prepared and have all of the right tools. Or, you could just have your local, friendly A&P mechanic change them. At some airports, the amateur-built community is so large now that there is usually a cadre of tools such as jacks and specialty tools that can be borrowed. Don’t hesitate to check with the local EAA chapter as well.

For those who wish to learn something new, and are willing to give it a try, I thought I would put together a short, step-by-step procedure over the next two columns. As with any repair project, making sure you have the right selection of tools will save a lot of time. Some you may have, but some you may just want to borrow. So here’s a quick list of tools and parts you may want to start gathering up between now and next month:

  • Wing jack or axle jack
  • Sockets and wrenches (usually 7/16 inch for the wheel bolts and brake caliper bolts on most light aircraft)
  • Diagonal cutters
  • Safety wire or Nord-Lock washers
  • Wheel bearing grease
  • Solvents to clean the wheel bearings, brake calipers, brake discs, and wheels
  • Talcum powder or baby powder
  • Wheel weights
  • Wheel balancer
  • Tie bead breaker
  • Screwdrivers
  • Valve stem removal tool
  • Brake pads
  • Drill with an 1/8-inch drill bit
  • Brake rivet set
  • Compressor
  • Tire pressure gauge
  • 2-by-1/8-inch cotter key (one for each axle nut)
  • Nitrile gloves
  • New tires and tubes (90-degree valve stem and air stop/leak guard tubes preferred)
  • Brake fluid and brake bleeder (not always needed)

For some of you, we are now in the winter months as you read this, so flying may have slowed down and you can get to some of the dirty maintenance. However, if you happen to check your tires between now and next month and they look like any of the pictures here, either ground the airplane or have them replaced. It will keep the fun factor alive!

Vic Syracuse, EAA Lifetime 180848 and chair of EAA’s Homebuilt Aircraft Council, is a commercial pilot, A&P/IA, DAR, and EAA flight advisor and technical counselor. He has built 11 aircraft and has logged more 9,500 hours in 72 different types. Vic also founded Base Leg Aviation and volunteers as a Young Eagles pilot and an Angel Flight pilot.

No excuse for flying with a tire such as this. We received a call one afternoon asking if we could replace tires the following day. Three hours later, the aircraft was being towed off the runway to our shop.
Wheelpants can hide tire problems, but there are tricks that can be done during the preflight to avert failures. The uneven wear shown here can sometimes be corrected by the use of shims between the axle and the gear leg.
A motorcycle wheel balancer is the perfect tool for balancing aircraft wheels and can be purchased for less than $100. There’s even a good chance that one of your cycle-riding buddies already has one. The stick-on wheel weights are usually 1/4 ounce each.
Here’s the reason for the brake fluid being listed in the tools: Sometimes the brake caliper O-ring can be leaking and will be discovered when the brake calipers are removed in order to remove the wheel. Replacing the O-ring will cause a loss of brake fluid in the system and require rebleeding the brake system with fresh brake fluid. Be sure to use 5606 or equivalent and not automotive brake fluid.

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