• No products in the cart.
View Cart
Subtotal: $0.00
  • No products in the cart.
View Cart
Subtotal: $0.00

Avoiding bike flats on fat bikes

Bike flats, fat bikes, and Flatbike. To the newcomer, it’s a random bunch of overlapping word salad; but to the fat bike owner in goathead thorn land, it’s frustrating and personal—especially if you’re pushing a heavy e-bike with flat tires! Can Flatbike help? Now???

Indeed we can, with a high-performance insert that is tested against flat tires for both remote-terrain ruggedness and elite MTB event performance.

Tannus Armour

Tannus Armour (shown in red) is a molded tire insert that fits around your (smaller) inner tube to solve several common MTB biking problems.

Fixing common bike flat tire problems.

There are two distinctly different types of flat tires, and Tannus Armour protects against both of them, while also offering a third benefit.

Puncture protection.

In rural areas, tire threats are typically thorn-related—goathead and cactus thorns in the south, and Himalayan blackberry thorns in the north. In cities, you’re more likely dealing with broken glass, nails, and screws.

Puncture threats without ArmourTannus Armour

It’s all the same to Tannus Armour. Anything that goes through your tire embeds in your insert and avoids your tube. You can either pull it out later after dodging a flat tire–as often happens with nails and screws–or leave it in as if the threat never existed, a common approach with thorns. Either way, your tube is safe.

Pinch flat protection.

With a pinch flat, you actually create your own tire threat inside the tire. Maybe it’s been a while since you pumped up your tires, or maybe you intentionally let air out for more traction on a particularly technical ride. In both cases, your rim pinches a hole in your insufficiently inflated inner tube, and you get a flat without any indication on your tire.

Pinch flats without Armour

Whether it’s a little hole that progressively takes the air out of your trip or a sudden blowout that stops you in your tracks, the result is the same; your cycling trip is over until you can get this fixed.

With Tannus Armour, low inflation now means that your inner tube is squeezed between foam and foam. Zero risk. In fact, many professional MTB riders take advantage of this fact, riding at insanely low tire pressures for maximum grip with no fear of a pinch flat.

No pinch flats with Armour

This leads to our third common problem solved.

Impact protection.

If you ride a bike with flat tires, you’re going to damage your rims. Put dents or gashes in your rims with an impact or road grinding while riding flat, and they’ll return the favor by giving you spontaneous flats at any tire pressure, like a rock inside your sock giving you blisters.

But in underinflation with Armour, there are actually two layers of foam between your rim and the pavement. So even if you get a flat, you can ride home from it with no damage to your rims.

Impact protection with Armour

And it gets better. Suppose you’re an aggressive MTB rider who likes to catch air or jump off of small buildings. That’s a lot of force coming down on your tube, squeezed between a rock (the ground) and a hard place (a metal rim). Armour acts as a shock absorber, splitting and dispersing that compressed force for a safer, more comfortable ride.

But…what about tubeless to avoid flat tires?

Tubeless tires, on the other hand, are built around the idea that you remove your tube and replace it with some liquid “slime” that sloshes around inside your tire, extruding and blocking any thorn holes in your tire. A self-healing tire!

It’s a common practice, but it isn’t maintenance-free. It requires special equipment, often including tubeless-compatible rims and tires and an air compressor to get the tire inflated quickly enough for the seal to hold. Problems with the seal? It helps to use a little bit of soapy water to boost the seal. Got that on your ride too?

And don’t forget the slime. Just put it in and leave it…for a year or so until it hardens and becomes useless. You’d better remove it before that, so you don’t go out on a thorny ride, thinking you’re protected and suddenly realize that your protection is so last year. And even in the best of conditions, slime seals a hole up to 3 mm across–any bigger, and you’re headed for a sudden and memorable deflation and sealant blowout.

slimy blowout

Oops. Now what?                              [Credit: https://www.renehersecycles.com/the-trouble-with-road-tubeless/]

What riders are saying about Armour

Probably the best perspective about Armour is from actual, everyday riders. Here are some thoughts from riders who took the time to explain why they chose Armour over other options:

Out of the box, the Armour’s are made of tough material, soft and sponge-y and strong and light as air and were easy to install. I had no issues with their fitment at all, it’s really not much different than changing a tube. In fact, I had to do one of them twice (I realized I got the tread on the first tire backwards). So after having installed THREE I can honestly say it wasn’t any big deal at all.

And my bike doesn’t feel noticeably different than before, weight or ride. I’m just glad I have that protection now. The reduction of flat anxiety is worth the investment and effort. Glad I did this instead of pumping stupid, messy, expensive slime in my tires, something that has a lower success rate and requires regular refills. The Armours are a smart, one-time investment and are maintenance-free. What’s the problem?


Decided to give Tannus Armour a shot after struggling with the mess of tubeless, and not having a compressor to seat the tire. They have been great, albeit a bit heavier than tubeless but the vibration dampening and the rim protection have made up for that!

I sliced my tire on a rock on my race run this earlier this season and the Tannus Armour Protected my rim so i could finish the run.(Granted I was riding it well above the recommended run flat speed.)

Overall I would recommend Tannus Armour if you want your bike to be quieter smoother and still have flat protection, without the fuss of tubeless.


If there’s another Rambo sequel they’ll be naming it “Armour.” I live on gravel roads in Kansas (relatively close to the Dirty Kanza route for you gravel racing nuts.) Out here “gravel” actually means 0.5 – 1.5″ rocks. On top of the gravel, my setup sporting the inserts is a ridiculously heavy electric bicycle I run at high speeds (30mph+) continuously. The inserts are running inside Schwalbe “Fat Frank” tires with kevlar sidewall protection.

With all the abuse I’ve thrown at them they just won’t die. 5,000 miles deep and not a single flat. The only tire pressure adjustment the bike has seen is due to cold weather. I’m quite certain I’ve violated nearly all of Tannus’ recommendations and even so they still keep coming back for more.

I’m not sure I even remember how to change a fat tire now and I’d like to keep it that way.
If I had another one, I’d give these inserts 3 thumbs up.

Bike flats, fat bikes, and Flatbike. What’s the connection?

Fat bikes have tires ranging from about 3.7″ wide to 5.2″ (at the high end, probably pushed by a big motor, so pretty close to a motorcycle!). You can take a fat bike anywhere other folks don’t even ride. Snowy/muddy places? Rocky places? Thorny places? No problem… except you’ve got more tire, more tire threats, and more flats.
Flatbike? At first, we had nothing to do with flat tires. We sell add-on components to make it easier than ever to store your fat bike, like folding stems and pop-off pedals to make your bike fit conveniently (and flat) against a wall.

Bars in the way? Not with a THINstem

But we do focus on solving common problems in the biking world, and bike flats are a big one. We originally introduced Tannus Armour just on our own line of CHANGE folding mountain bikes (that never need a car rack) as a way of making our convenient bikes even more useful. Then our Convenient Cyclist blog article about tires went viral, and fat bike owners descended up our site, asking for Armour inserts sold separately for tires we didn’t even have on our bikes. Hmm. Okay…
As a public service, we started carrying Tannus Armour at Flatbike for the most common size of fat bike tires: 26″ wheels, 4.0-4.8″ tires. We keep our stock light, but go through it rapidly, so we are constantly getting Tannus Armour resupply.

Three installation tips.

For the best experience, take a few minutes to check out what you’ll be doing before you order.

1. You’ll need a smaller tube.

While it’s perhaps possible to reuse your existing tube, it will be really difficult, and any reviews about difficulty reflect that. For a 4.0-4.8″ Armour, we recommend a 3.0″ width inner tube, which will go together really easy. We don’t carry it, but you can get it really easily on Amazon. (Order these tubes at the same time as your Armour, or even first, as the Armour will arrive faster.)

2. Your installation will be in a different order.

When changing a tire, we all know the routine: stuff the tube in the tire, mount one tire bead side, then the other. That’s not what you’ll be doing here. Instead, you will:
  1. Mount one bead side
  2. Insert the Armour
  3. Insert the tube
  4. Mount the other bead

3. If a picture says a 1,000 words, this video should say everything you need to hear.


See you out on the trails… but not kneeling in the dirt with another flat tire! Got Armour?


Bob Forgrave's Signature

Bob Forgrave is president of Flatbike, an
ecommerce company offering full-size folding bikes
and kits to make any bike take up half the space.



  1. Michael says:

    How much does this thing weigh exactly? Going tubeless on a fatbike is also intended to be a significant weight savings. A 26×3″ tube plus your product adds how many grams per wheel?

    1. Bob Forgrave says:

      Good question, Michael. Going tubeless for weight savings alone is an interesting goal, but you’re not just subtracting the weight of the tube. You’re trading the X grams of the tube for Y grams of fluid (Slime, Stan’s NoTubes, etc) to slosh around in your tire to plug any tire punctures. How big is Y? It depends on the tire size–as does X, I suppose. On a 26×4 fat tire, the recommendation is 130mL of sealant, which converts to 110 grams of added weight (using the mL/g density of water). A Fatbike tube can weigh 260g (Q-tube) to nearly 500g (Surly), so yes…that’s a weight savings of at least 120 grams.

      We don’t have a fat bike Tannus Armour in stock right now to me to weigh, but it weighs less than the shipping box. Let’s generously call it 1 lb (450 grams). With that as flat protection, you can use a lighter tube, saving 250 grams. And you can use a lighter tire, saving another 200 grams. Di you lose weight? No. You possibly stayed the same, while increasing your protection against thorns, burps, sidewall tears, and walking your bike home. Read these comments from a pro racer: https://tannus.com/armour/pro-riders/roger-vieira/.

  2. Erick Jamieson says:

    How long before the Tannus itself flattens down to where inflating the smaller tube is not enough? I’ve heard that this can be an issue.

    1. bob says:

      When left in a continuously inflated tire, Tannus Armour will eventually flatten down. We know of one customer where this happened after 9 months (and 1,200 miles). We have not heard about this issue affecting tube size, but it could affect long-term flat protection.

      If this is a concern, one solution is to reduce the pressure when the bike is not being used for a while. This allows the Armour to spring back to full thickness.

  3. Dalton says:

    While cycling, I noticed that my wheels wobbled. I checked and the tire was flat. I tried to fix it for the next ride, but the same thing happened. This time, I started to wonder “why does my bike tire keep going flat?”

    1. Dalton says:

      It could be something sharp stuck in the tire of the bike that I can’t see. I realize worn tires are also a cause. Old tires are prone to cracking and breaking, and their tubes often expand beyond their average size. Another reason to consider is that the sharp corners of the spokes can poke into the bike’s tubes, eventually causing a puncture if they are not adequately covered with duct tape.

      1. Bob Forgrave says:

        If the tire (I’m assuming it’s just one) gets flat every time, regardless of where you ride, then the tire is probably never fully fixed for a slow leak. The culprit may be something stuck inside the tire, as you note, such as the tip of a thorn. Nowadays, most wheels have a rim strip to cover up the spoke heads, so I wouldn’t expect anything there. But do look for the tell-tale signs of a pinch-flat—two side-by-side mini-holes like a snake bit your tube; these are evidence of a bike ridden with too low a tire pressure, squeezing the tube between road and rim.

        Best way to check? Pump some air into your tube outside of the tire and run the tube slowly through a sink full of water. The location of the stream of bubbles tells you where your issue is.

  4. Katy says:

    I just bought a new G-Force T42 fat tubed E bike. Is there anything I can do to prevent these tee ninesy thorns that are everywhere in Texas from flattening my tire? I don’t recall having nearly this problem with my regular road bike tires. Anyway, to me the tire itself seems pourous. I am wondering if I can tape the inside of the tire itself, as I haven’t seen anything else that sounds like it will fix the problem. Is there a shield of some sort that is made for 4 inch fat tires on E bikes….I’m miserable…and I LOVE this bike otherwise. But don’t want to push it home, so only ridden on my property.:(

    1. Bob Forgrave says:

      Absolutely, Katy. E-bikes are fabulous for going greater distances, but flat tires on them are the WORST! Heavy, and you just went a really long distance.

      Tape won’t protect you. But Tannus Armour is a custom designed layer of semi-rigid foam that fits between your tire and tube, protecting it from everything–large thorns, small thorns, nails…everything. And yes, we’ve got it in 4″ fat tire, both for 20″ wheels and 26″ wheels. You can finally get off your property : )

Leave a Reply

Your email address will not be published. Required fields are marked *

Scroll to top