Backcountry tire overview

by Jon Battson

Contributing author

One of the most discussed topics in backcountry aviation is tires. People often ask which tires are best suited to a particular mission or aircraft. The answer varies greatly depending on many things. In this guide, we will cover the range of tires available, different sizes, how to choose a tire or combination of tires to suit your aircraft, and touch on some common questions. There is no one "right tire" for any given aircraft, it depends on a range of factors and we will discuss them here.

Let’s start by covering the range of specialized backcountry aircraft tires available, the sizes they come in, and their specifications. There is a lot of choice, both in tire design and tire size. We will organize the tires by size. The smaller sizes common on most aircraft are often described by their width, while the larger sizes are usually described by their diameter or height, measured without the weight of the aircraft resting upon them.

Photos featured in this guide were sourced from the community in this forum thread. Feel free to add your photos there.

8.00s and smaller

Eight inch wide tires or "8.00s" or "800's" can be used in the backcountry with great success, provided the risks are managed. The same applies to some smaller size tires too. This is particularly true for tricycle undercarriage, where the nose wheel is normally no wider than 8.50 inches. Given these smaller tire sizes are usually the default tires found on the aircraft, this article will not cover them any detail.

8.50s

Before specialized backcountry tires were developed, 8.50 tires were a mainstay for off-airport flying. They are still commonly used today. Large enough to deal with rough surfaces, 8.50s are normally treaded and used with an inner tube, run at slightly reduced air pressure.

Skywagon running the Desser Aero Clasic 8.50, a smooth tire without grooves that is affordably priced and less likely to pick up rocks and throw them into the tail. Photo: Asa Darnell

A host of Skywagons on what are considered the smaller end of the tire spectrum nowadays. From L to R: 180A on 8.50 (unknown brand), 180A on 8.00 Condor, 180B on 8.50 Desser (smooth), 180B on 26" Goodyear Photo: Asa Darnell

8.50 tires available

A Cessna 170B rolling on 8.50x6s.

Desser 8.50x6 at left, Goodyear 26" on right Photo: Robw56

26 inch

The 26 inch tire is popular among those with who want to go off-airport, but who also want to preserve as much airspeed as possible. There are a range of options in this size bracket. At one end there are sealed tires made of soft rubber, suitable for running at very low pressure on LSA aircraft or microlights, At the other end, there are stiff-walled 6 ply tires which can handle extensive use on tarmac, and suit heavier aircraft over 3,000 lbs. Tires this size and above need some serious brakes to match.

The 26" Airstreak is the perfect size for offroading without taking too much of a cruise airspeed hit. Photo: S7Paco

Battle of the 26's: Skywagon on Goodyear 26" and 170 on 26" Alaskan Bushwheels. Photo: Robw56

26" tires available

Alaskan Bushwheel 31" left, Alaskan Bushwheel 26" right Photo: Robw56

Relative comparison: L to R: Goodyear 8.50, Goodyear 26", Alaskan Bushwheel 26" Photo: Wingnut185

29 inch

The 29" tire represents a big step up in off-airport capability, but also an increase in weight and drag. Though the diameter has increased, the width tends to be similar to a 26" tire. These tires still have a stiff enough sidewall to suit heavier aircraft, such as a Cessna 185.

Size eligibility: The 29" is the most popular Bushwheel among the 185 Skywagon crowd, as it is the max allowable size per the STC for many later serial numbers. However, some early 185s are eligible for 31", perhaps due to a lower max gross weight. Photo: Z.Jacobson

A popular setup in the 29" range, especially on tricycle-gear aircraft, is the 29x11x10. This uses a conventional tire with tube, but is a stiffer and more substantial tire than the Bushwheel. It's a good compromise between tire diameter and something that can be used on paved surfaces without wearing too quickly. It doesn't provide the same level of rough terrain cushioning though that the soft Bushwheels do, and is subject to issues inherent to inner tubes.

The 29x11x10 can be achieved by two avenues: The Airframes Alaska "Air Hawk" 29" run on their 10x10 wheel, or from Alaska Tundra Tires (formerly Gar-Aero) using 10" adapters on 6" wheels. The Air Hawk can be had "buffed," where they turn the tire to cut it down below the grooves, effectively removing the rock-chucking grooves.

STC availability may determine what's available for your model aircraft. Check the List of Backcountry Aircraft for your machine, then click on that aircraft's Modifications tab to find wheel/tire STCs.

29" tires available

The 29" Airstreak, a lighter weight/lighter duty version of the 29" Bushwheel, is popular among the LSA bush plane crowd. It gives the same advantages but doesn't have to support a 2700 lb aircraft.

This J-3 enjoys a little more offroadability with the large 29" Airstreak. Photo: Felix

It does give the J-3 a decidedly tougher look. Photo: Felix

31 inch

Perhaps the most common choice for bush pilots, 31" tires are more commonly associated with pickup trucks than single engine aircraft. Provided you can tolerate the extra weight and limited top end speed, this tire has the capability of landing most places. These tires are the most popular choices for Maule and Super Cub aircraft.

Maule MX-7-180C on 31" Alaskan Bushwheels Photo: JDW

31" tires available

Cessna 170B on 31" Alaskan Bushwheels Photo: Z.Jacobson

Piper Pacer on 31" Alaskan Bushwheels Photo: Z.Jacobson

The 31" Bushwheel is the most popular and well-known in the size, but in 2015, Desser released the 31x11x10, a smooth conventional tire that uses an inner tube, but the potential was clear for tubeless use. The limiting factor was available 10" wheels. At the time of this writing, certified use of the 31x11x10 is via field approval. There is talk of approval via STC from several wheel manufacturers.

The tire was also initially attractive because of the relatively low price at its introduction, but that has steadily crept upward as it becomes more popular.

Even the Cessna 150 works well on Bushwheels (after a few minor modifications.) Photo: Z.Jacobson

35 inch

These tires were originally developed for very large backcountry aircraft like the Pilatus Porter, de Havilland Beaver and Otter. The design has been modified to shave off some weight and better suit light aircraft, though they all require a 10" wheel. These tires come with a sharp increase in weight, airspeed loss, and expense, but are nearly upstoppable on rough off-airport terrain. Run at approximately 4 psi, the 35" Alaskan Bushwheel can easily roll over 6+" rocks.

Easily as tall as an average man's head and torso, the 35" Bushwheel makes quick work of true, rough off-airport surface. Photo: Z.Jacobson

35" tires available

The modern classic Alaskan Super Cub running 35's. Photo: Taj Shoemaker

Choosing a tire

This section discusses how to choose a tire for your aircraft. We will summarize the range of options available and the benefits and disadvantages of each, depending on the circumstances. There is no one tire which has all upsides without any downside.

The best way to choose a tire starts with evaluating your mission, then reviewing the tires applicable to your aircraft type, considering your budget, and determining which tire is the best match.

Your mission is how you want to use the aircraft. This includes what kind of surfaces you want to land on and how far you will normally travel. For example, if you often fly long distance, is losing airspeed is a big deal? Before you can make a good decision about tires, you need to have a clear vision of your mission.

Before we start, it’s important to understand which tires are eligible for your aircraft. For aircraft manufactured under a type certificate, an STC or field approval may be required. This can limit the list of choices you have available. The best source of this information is the manufacturer of the tire.

Your existing wheels are also worth considering upfront. While most tires fit a 6" wheel, some require an 8" or 10" wheel. Some tires need a special sealed wheel to run tubeless. Adding a new set of wheels and brakes into the equation can increase the total purchase price considerably.

Where to land

Where you want to land is an important consideration. How frequently the tires will see pavement also needs to be considered. Be honest here; focus on the kind of landing place you will go regularly. Bigger tires will take you more places, but there are weight and airspeed penalties associated with the larger tires.

Soft surfaces can make surprisingly good landing places. Beaches, gravel bars, and dry lake or river beds can all offer enough room to land a plane. On these surfaces, larger tires with a greater footprint are preferable in case of soft spots. A larger or wider tire provides more flotation on a soft surface. This reduces the chance of the main landing gear sinking in and becoming stuck, or worse, overturning the aircraft.

A Cessna 206 Stationair running the popular 29x11x10 setup to smooth out the 4" river rock. Photo: A.Remboldt

Riverbeds are also commonplace for backcountry aircraft. Landing on these gravelly surfaces with treaded tires can throw extra debris into the empennage, or worst, the propeller. Smooth tires are better suited to gravel bars and river beds, although still scuff up some debris when touching down. River beds also contain large rocks, driftwood, and soft spots. Because of the risk of running over those things, larger tires are generally preferred for riverbed landings. Although running over driftwood with an aircraft is not recommended, no matter what tires are installed.

Slippery surfaces including wet grass and muddy fields suit treaded/grooved tires, because of their superior grip and improved braking action. Smooth tires provide almost no braking action on slippery surfaces, which can drastically increase the landing roll and reduce control in a crosswind too. However, smooth tires are less likely to grip rocks and chuck them into tail surfaces like a baseball pitching machine.

Tundra, coarse riverbeds, and the roughest rocky ground demand the most specialised tires. These tires are normally 31 inches or more in diameter. The large overall diameter increases the maximum sized obstacle which the tires can roll over successfully. These larger tires have taller sidewalls, which allow greater flexibility. Greater flexibility means more suspension and cushioning on rough ground. This protects the airframe and its occupants from the vibration and stresses. Small wheels and large tires are the best combination to get the biggest possible sidewall and thus the greatest suspension effect. Softer compound tires are also preferable. A tire’s softness can be judged crudely from its ply rating. Smaller ply numbers are generally softer.

Pilots may want to spend a lot of time landing on steep off-camber hillsides, sloped beaches, and other angled or curved landing places. To resist the unusual forces during a turning take-off and while taxiing on sloping ground, the weight of the aircraft and strength of the tires sidewall are both important considerations. One common example is a Cessna 185. This heavy aircraft needs a stiff sidewall tire to tackle sloping ground without the tire folding over sideways.

Pavement is a common surface at many public airports. Generally speaking, the softest tires will not wear well on pavement. Given the high cost of large backcountry aircraft tires, continuous pavement operations with soft tires should be avoided. If your home airport only offers paved runways, you should limit your selection to higher ply tires only.

In Alaska, trikes are used to their potential and many are equipped with the largest wheel combo possible. In this case, a Cessna 336 on 29"x11"x10" Airhawks. Photo: Z.Jacobson

A Cessna 207 Stationair, more commonly known as a "sled," on 29s. Photo: Taj Shoemaker

Tube or tubeless

Inner tubes are common in aircraft tires. In the backcountry scene, they are met with mixed opinions because they rely on high air pressure to keep the tire’s bead locked on the rim. Running tires at low pressure is advantageous in the backcountry. It provides more cushioning and a bigger footprint. This is contrary to what an inner tube needs.

The Alaskan Bushwheel (26,29,31,35) is a uniquely-designed self-contained unit that requires no separate tube, and the inflator valve stem does not route through the wheel.

Running an inner tube at low pressure creates a risk of flat tires. Because tires rely on high pressure to remain seated properly on the rim, typically about 15 psi is needed. When the pilot applies heavy braking during a landing, if the tire pressure is too low then the tire can slip around the rim. Braking heavily is often necessary when landing in the backcountry. As the tire moves or "creeps" around the rim, the inner tube moves with it. This causes the inner tube's valve stem, which pokes through a hole in the wheel, to bend over sideways as the tube moves against the wheel. Eventually the valve will be sheared off by the wheel, causing an instant flat tire. Best case, this leaves the pilot and aircraft stranded in the backcountry. Worst case, it can lead to a bent airplane.

There are a few ways to address this rim creep problem. One option is to simply keep the tire pressure well above 15 psi, and forego the benefits of soft tires. Alternatively, the pilot can mark their tires with a witness line and keep a close eye on the valve stems for movement. Once the tires have crept around the rim they need to be removed, disassembled, and re-seated. This can become annoying, particularly if you need help from someone with the necessary tools and license to maintain your aircraft. If the aircraft is homebuilt or experimental, other options are available. Gluing the tire to the rim, or better yet installing removable bead-lockers may be an option.

Having read this far, it’s clear why tubeless tires are an advantage in the backcountry. Tubeless tires come in two varieties, sealed tubeless tires and regular tires which can be used tubeless when combined with a sealed wheel. Let’s discuss both.

Sealed wheels have an o-ring between the two halves of the wheel, making the wheel airtight. A valve is installed in the wheel, separate from the tire. Once a tire is installed, it can be inflated without an inner tube. These tires can slip on the rim without risking damage. However, they still rely on air pressure to maintain an airtight seal between the bead and rim. If the pressure drops too low or if the tire spins excessively on the rim, then air escapes and the tire can go flat.

Sealed tubeless tires are like a big hollow donut. They are completely airtight except for the valve, which is mounted into the side of the tire. These tires can run at the lowest pressure of all, because they are completely independent of the wheel. It is basically a big inner tube that acts as a tire.

Typically the manufacturer recommends about 8 psi or more, however some people prefer to run them as low as 3 or 4 psi for maximum cushioning. Note that very low tire pressure can lead to premature tire wear, especially on hard surfaces like tarmac. These tires are best suited to the roughest landing places.

Gabe from Airframes Alaska explains the hand-layup process for an Alaskan Bushwheel.

The raw ingredients for the outer layer begin as rubber granules which get baked on in a hot press.

Airspeed

Airspeed loss is one of the most common questions about increasing tire size. The answer varies with the size and shape of the tire, cruising speed of the aircraft, throttle and mixture settings, even the cruising altitude in flight can make a small difference. It even seems to vary from one aircraft to the next. A desire to preserve cruise speed might limit the size of tire you install. Alternatively, running the engine at a higher power setting can offset the cruise speed loss, provided the engine does not overheat. To try and answer this question, we’ll have to generalize.

Generally, a modest increase in tire size will hardly be noticeable on a slow aircraft. A fast backcountry aircraft will probably lose more than 10 knots when upgrading to very large tires. An average aircraft cruising about 100 kts might lose around 5 to 8 knots after installing tires about the 30 inch mark. When installing 35 inch tires, it is best not to worry about cruise speed at all.

Cruising a few knots slower may not be a consideration for those who only fly near their home airport. For instance, this table shows how a five (5) knot cruise speed loss affects different aircraft.

Price

Some tires are very expensive. Price could be one of the main considerations when selecting a tire to suit your aircraft and mission. This article avoids listing the price of tires because they are subject to change, but we can say price varies greatly across the range. Tires can cost anything from a few hundred to a few thousand per tire. Generally speaking, two things affect the price. Larger tires need more rubber and cord, which makes them more expensive to produce. More specialized tire designs are also more expensive to produce, such as fully sealed tubeless tires with have an inbuilt valve, such as the Alaskan Bushwheel. These are handmade.

Normally the wheels, wheel adapters, oversize brakes, and tubes (if required) are all extra costs in addition to the tires.

Maintenance

All tires wear out over time and have to be replaced. Some things like normal wear can be slowed by rotating tires and maintaining proper inflation. Other things like the rubber vulcanizing over time are harder to prevent. While this still applies to backcountry tires, they do have some special considerations all their own.

Soft tires are worth a special mention here. If used solely on grass even the softest tire should last well over a thousand hours of flying, perhaps even two thousand hours or more provided you take proper care of them. Conversely, abuse on pavement can wear soft tires to the cords in as little as a hundred hours, rendering them unairworthy. Many manufacturers are now offering thicker rubber to combat this problem, although this extra rubber adds weight and cost. Experimental aircraft can address this problem by coating the tires in hard rubber-like compounds such as spray-on truck bedliner. One quart is plenty for an application on Bushwheels up to 31". This practice effectively achieves the same thing as heavy duty Bushwheels by adding weight, cost, and inconvenience of dealing with nasty goo, but some models of Bushwheel aren't available in a heavy duty version. And, the bedliner can be applied over and over again.

The distinct appearance of bedliner applied to Bushwheels; it actually works quite well. 29" Airstreaks. Photo: Av8r3400

Larger tires can create more maintenance. They can often lead to accelerated brake wear, because heavier braking is required with larger tires. We’ll explain this in the FAQ. Larger tires may put increased stress on parts like the axles during landing because of their increased weight and bending forces. Although they also reduce impact stresses so the added stress may not be a big consideration.

UV rays are also incredibly hard on soft rubber compounds, and can check and crack them in a surprisingly short time. For aircraft stored outside, it's recommended to use tire/wheel covers, and periodically coat the rubber with a special protectant like Aerospace 303.

Wheel and hardware FAQ

What about the tailwheel?

The tailwheel is often the first wheel to sink in on a soft surface. This can be irritating and good cause for a larger tailwheel, or it can be an early warning not to taxi any higher up the beach, depending what size your main wheels are. On particularly rough surfaces a large tailwheel can reduce the stresses on the back of the airframe, the tail spring, and on the tailwheel itself. It can also improve ride comfort while taxiing. Of course there is no free lunch; a large tailwheel creates more drag during cruise. There a couple of options for larger tailwheels in the market, but the current standard is the Airframes Alaska baby Bushwheel. It is literally a baby bushwheel, made using the same techniques as its larger, main-mounted brethren.

ABI Baby Bushwheel 3400 for stinger spring.

Traditional Scott 3200 setup.

What about the nose wheel?

The Airglas fork is an STC modification for larger nose wheels. It accepts nosewheel tires up to 8.50. Read more about the fork and the install process on a Cessna 172.

The Airglas nosewheel fork and STC that allows 8.50s all around is popular mod on the Cessna 172. Photo: 88Echo

Will a more flexible sidewall get damaged by the brake caliper when there isn't much clearance?

For large sidewalls, as in the case of the Alaskan Bushweels 31x6, or any tire that is run at a lower pressure where the sidewall can push outward, a minimum gap should be achieved between the tire sidewall and the brake caliper to avoid the rotating tire from being cleaved like it's on a lathe. This is usually as easy as adding a spacer between the wheel and brake disc to move the caliper away from the tire. Call the folks at Airframes Alaska for guidance and parts.

Do I need heavy duty brakes?

Here’s a general rule of thumb. If the tire is called by its diameter, then you are going to need heavy duty brakes. Heavy duty brake calipers become necessary as the tire size increases. The larger diameter of the tire compared to the unchanged diameter of the brake disc, means a lot more force is required to dissipate the landing aircraft’s kinetic energy. The weight of the aircraft is a key factor here too, because this affects kinetic energy. Normally more braking power comes from installing double piston AKA double-puck brake calipers. Homebuilt aircraft may also be able to install two normal-sized brake calipers, to achieve the same result. Larger diameter wheels and brake discs may also be an option.

Some tires need 10 inch rims, do I need new wheels?

Gar Aero adapters are 6 to 10 inch wheel adapters. They fit a standard 6 inch wheel from common manufacturers like Cleveland or Grove, and covert it into a 10 inch rim diameter wheel. Airframes Alaska 10 inch wheels are another option, no adapter required.

A Super Cub running the 31" Desser setup on 10" wheels Photo: TVATIVAK71