Guardian 20 Inch Bike Review – ETHOS and AIROS

Faster, safer, “funner” braking? Yes! The Guardian ETHOS 20 and AIROS 20 kids bikes feature patented SureStop braking technology that won the admiration of Mark Cuban on Shark Tank. And while investors, parents and kids love the additional level of safety and confidence that SureStop brings to the table, fantastic brakes are just one of many impressive features of these 20 inch Guardian Bikes.

Available in two different sizes, with gears or without, in traditional boy, girl and gender-neutral colors, as well as two different price points, you’ve got a lot of options! There is sure to be a Guardian that fits your child, your budget, and your neighborhood biking needs. In this review, we’ve put all sizes and models to the test to help you determine which Guardian 20 inch model is best for you.

boy jumping off a curb riding a guardian ethos 20 bike

Guardian 20 inch Overview

RATING: Exceptional (AIROS), Highly Recommended (ETHOS)

MSRP:  $339 – $499

BEST FOR: Neighborhood riders who want an easy-to-use bike with great quality and performance. Guardian bikes are especially beneficial for kids who like to ride fast or those who live near hills and need reliable and fast brakes.


SEAT HEIGHT: Small: 21.3″ – 26.8″, Large: 22.5″ – 28.5″
WEIGHT: Varies by model – Between 20.3 lb. and 22.9 lb.
GEARS: Small: Single Speed, Large: 6-speed
BRAKES: Surestop Dual Hand, no coaster
FRAME: Aluminum Alloy (AIROS), Steel (ETHOS)


  • Patented SureStop braking system for faster and more controlled braking
  • No coaster brake!
  • Low center-of-gravity design for better balance and maneuverability
  • Single-speed 20″ small size – a great size for those in-between 16″ and 20″
  • Great quality build for the price
  • Fun, kid-approved designs
  • Easy assembly


  • SureStop brakes not ideal for all-terrain riding, but Guardian is clear that their bikes are made for city riding

Guardian 20 Inch Bike Video Review

Want to see Guardian bikes in action? Check out our video review to learn the 3 reasons why kids and parents love Guardian bikes. Detailed video descriptions of Guardian’s SureStop braking technology are also included. Please note that the “AIROS” line is referred to as the Original line in this video, but all other content is still current.

Guardian ETHOS 20 and AIROS 20 Put to the Test

Guardians were designed and built with one goal in mind – make biking safer for kids by revolutionizing how kids stop a bike. While these bikes have many great features – such as lightweight frames and child-specific geometry – their proprietary SureStop braking system is their main selling point. 

4 year old riding Guardian 20 inch small bike on a farm

Simpler, Safer Braking

The SureStop system simplifies the braking process, and also allows riders to stop faster and with more control. By pulling just one braking lever, the rear and then the front brake are activated sequentially. That’s right… kids have to pull only one brake lever to get the stopping power of dual hand brakes! 

Over many years of testing Guardian bikes, we’ve seen this simple (and genius!) design gives kids a huge boost in confidence. With less anxiety about stopping the bike, many kids are more willing to ride more adventurously. 

We’ve witnessed timid and once hesitant riders learn to love biking as a result of the confidence the SureStop braking system provides them. We’ve also seen confident, aggressive riders enjoy these brakes just as much!

The Advantage of Dual Braking Power with a Single Brake Lever

Child riding Guardian 20" bike down a ramp at the skatepark

Dual-hand brakes work great for advanced riders and are essential for technical youth riders (such as mountain bikers), but can be confusing for the average child rider.  With a brake lever on the right and left hand, which one should they pull?

If a child accidentally brakes with just the front brake, the front tire can lock up, which causes the rear tire to come off the ground and potentially throw the child off the bike.  Yes, this can happen – we have seen this happen several times. 

On a Guardian 20 Ethos or Airos bike, a child cannot accidentally brake incorrectly.  They simply squeeze one brake lever and the SureStop system takes care of the rest.

Single brake lever on Guardian bikes 20 inch kid's bike

Braking is more fun on a Guardian 20 inch bike!

Not only is Guardian’s SureStop system safe, it makes braking more fun!  Every time we put a new tester on a Guardian, a HUGE smile quickly spreads over their face as they experience SureStop brakes for the first time. 

Curious about what the big deal could be, we’ve taken these bikes for a spin ourselves. We quickly found ourselves grinning as big as the kids, and immediately understood their perspective.

Braking with SureStop brakes provides a similar feeling to braking in a new car with an advanced braking system versus an older car with a standard braking system.  Not only is it easier to brake faster, you feel MUCH more in control of the car.  As a result, you’re a more confident driver in a car with advanced brakes, and driving is more fun as well.

How Does the SureStop System Work?

Girl riding 20 inch Guardian kid's bike down the sidewalk. (Turquoise)

So how is it possible for one brake lever to activate the brakes on both the front and rear wheels? The SureStop system uses standard brake calipers, so upon first glance, this braking system looks very similar to most dual-hand brake bikes.  But the difference lies in the rear brake’s ability to activate the front brake.

Guardian’s SureStop Braking Technology

Graphic showing three steps to Guardian's SureStop braking system. Step One: Child activates brake lever, Step Two: Rear Brake Engages, Step Three: Rear brake activates front brake.

Guardian’s proprietary rear brake pad responds to the friction created between the brake pad and the wheel’s rim when the rear brake engages.  This friction between the rim and the brake pad pushes the pad slightly forward.  When the pad slides forward, it pulls on an attached wire that then triggers the front brake to engage.

On Guardian kids bikes, the rear brake pad slides slightly forward due to friction from the rim, and then the wire on brake is pulled which triggers the front brake.

Is the SureStop System for Everyone?

Almost everyone! The SureStop system is amazing for everyday kid riders but is not recommend for technical riding.  If your child is planning on mainly hitting the mountain bike trails, the Guardian system isn’t ideal because technical trail riders need to brake the front and rear wheels independently.  The SureStop system is designed for the average child rider who mainly rides on paved surfaces or dirt paths.

Is the SureStop System Safe?

Yes!  The SureStop system uses high-quality brake calipers like those found on many other higher-end bikes.  The only difference between the SureStop system and a regular dual-hand brake system is that the brake pad on the rear brake engages the front brake.  If for some reason the SureStop system were to fail (which we have never seen in our years of testing), the rear brake on the bike would still work, just not the front brake.

Guardian ETHOS 20 vs. AIROS 20

Airos and Ethos. What’s the difference? Which one is best for your needs?

Guardian’s Airos line is the premium line and features higher-end components than the more budget-friendly Ethos line. Available in the same sizes and with the same basic features, the Airos and Ethos line of bikes are essentially like different models of the same car.  Both models feature the same SureStop braking system.

Premium “AIROS” Line: Designed for those who simply want the best. The Airos models feature an upgraded lightweight aluminum frame, responsive threadless headset, and a high-count spoke count.

Budget “ETHOS” Line: Priced at $100 less than the Airos, the Ethos offers great quality for the price. The Ethos line features a slightly heavier steel frame (instead of aluminum), a threaded headset, and more basic graphics designs.

Guardian ETHOS 20 vs. AIROS 20

Pricing and Sizing
MSRP Sm: $339
Lg: $399
Sm: $439
Lg: $499
Seat Height Sm: 21.3″ – 26.8″
Lg: 22.5" - 28.5"
Sm: 21.3″ – 26.8″
Lg: 22.5" - 28.5"
Weight Sm: 21.3 lb.
Lg: 22.9 lb.
Sm: 20.3 lb.
Lg: 21.2 lb.
Frame Steel Aluminum
Headset Threaded Threadless
Decals Water Transfer Graphics Upgraded Heat Bonded Graphics
Shifters Sm: Single speed
Lg: 6 speed/Grip
Sm: Single speed
Lg: 6 speed/Grip
Spoke Count Average High

Weight Differences Between Models

The frame construction of the Airos vs. the Ethos plays a major role in weight differences between the two lines.  The Airos line is made out of aluminum while the Ethos is steel.  To help keep the weight down as much as possible on the Ethos, a narrower steel tubing was used.

As outlined in the chart above, the steel-constructed Guardian ETHOS 20 Small weighs about 1.0 lb. more than the aluminum AIROS 20 Small model.

The weight difference in slightly more for the 20 inch large models. The Guardian ETHOS 20 large weighs 1.7 lb. more than the Guardian AIROS 20 Large model.

Guardian AIROS aluminum tubing (left) vs. ETHOS tubing (right)

Geometric designs on Guardian bikes are popular with kids

Headset Difference

To help keep the handlebars properly aligned (even in the event of a fall), the Airos models come with a threadless headset. Threadless headsets provide a much stronger hold on the handlebars and as a result, are used exclusively on adult mountain and road bikes.

The Ethos models are equipped with a threaded headset. Threaded headsets are typically found on casual or comfort bikes. They don’t provide as strong as a hold but have no problems keep the handlebars aligned in standard neighborhood or city riding. Threaded headsets are very common on budget-friendly bikes.

Guardian’s AIROS threadless headset vs. ETHOS threaded

Guardian Airos threadless headset vs. Ethos threaded

Rims and Wheel Spoke Count

The spoke count of a wheel plays a role in the overall quality and durability of a bike’s wheel. When paired with a strong double-walled rim, a wheel with a higher spoke count will be stronger and is much less likely to get out of true (a true wheel rolls straight and isn’t crooked or “warped”) than a wheel with a lower spoke count.

When it comes to really aggressive riders who love to ride down stairs and fly over jump or curbs, strong rims and a high spoke count are particularly important to help keep the wheels true. A wheel with a lower spoke count can bend as a result of a heavy hit (from going down stairs or landing a jump) and begin to wobble as you ride as a result (i.e. become out of true).

Built for riders ready to take on anything in front of them, the Guardian Airos 20 features a double-walled rim with 35 spokes. Most 20 inch bikes have 28 spokes per wheel. As a result, the Airos’s wheels are extremely durable compared to the average kid’s bike and much less likely to get out of true.

To keep the price down, the Guardian Ethos 20 has the same high-quality rim, but sticks to the average 28 spokes per wheel. This makes the Ethos wheels more durable than your average 20 inch wheel, but not quite as strong as the Airos’ wheels.

Guardian AIROS 20 vs. ETHOS 20 Wheel

The added spoke count and beefy rims do add additional weight to the AIROS. While still lightweight, the Guardian Airos line is slightly heavier than other aluminum bikes, partially due to its stronger wheels.

For example, the Guardian Airos 20 Large has 35 spokes per wheel and weighs 21.2 lb. While the Polygon Ultralight Premier 20 has 28 spokes per wheel and weighs 20.75 lb.

Guardian’s Child-Friendly Shifter

One of the major differences between the Guardian 20 small and large models is gearing. The Guardian Ethos 20 and Airos 20 SMALL bikes are single-speed bikes, while the Ethos 20 and Airos 20 LARGE models are 6-speed.

Both the Airos and Ethos 20 large models come with a fun and unique Microshift grip shifter that kids love. In addition to displaying the number of the gear the bike is in, there’s an orange “man in the window” who moves to help kids visualize how shifting will affect their riding.

Guardian 20 inch bike grip shifter

When shifting to a lower gear (for when riding up hills), the orange man’s bike rotates to appear that it is riding uphill. When shifting to a higher gear (for when riding downhill), the orange man’s bike rotates to appear that it is moving downhill. Super fun and super effective.

If you look closely in the image, you can also see a turtle at the top of the shifter window and a hare towards the bottom. For those not necessarily tackling hills, this helps them know which direction to shift when they want to ride faster or slower.

If the man points towards the turtle, the bike will go into a lower gear which which has a lower maximum speed. When the man is pointed towards the hare, the bike goes into a higher gear, which allows the bike to reach a higher maximum speed.

The Microshift grip shifter is also paired with a Microshift derailleur that was specifically selected for its quality and durability. Unlike previous version of Guardian bikes, the Airos and Ethos models now feature the same shifter and derailleur.

Does My Child Need a Large or Small?

Guardian 20 inch bikes are suitable for kids ages 5 to 8, depending on their height. To better meets the needs of shorter kids, tall kids, and every size in between, Guardian offers two different sizes of 20″ bikes.

The Guardian 20″ Small comes in only single-speed, while the Guardian 20″ Large (for slightly older and taller kids) is only available with gears. 

Guardian’s 20″ Large is similar in size to standard 20″ bikes, while the 20″ Small is a much needed in-between size between a standard 16″ and 20″ bike.

Guardian AIROS 20 Inch Large

Boy riding Guardian Airos 20 inch bike in black, green, and blue

The 20″ Small is designed to ease the jump from a 16″ to a 20″ bike which is often challenging for timid or lightweight riders (as well as younger riders who are tall for their age). With wheels that are 4″ larger than a 16″ bike, a frame that is several inches longer, and with a significant increase in weight, standard 20″ bikes are often too big for some riders who have outgrown their 16″ bike.

Guardian ETHOS 20 Inch Small

Boy riding Guardian Airos 20 inch Small bike in black and red

While the wheel size of the 20″ Small is the same as the Large, the wheelbase and the minimum seat height are both about 2″ shorter than the Guardian 20″ Large frame, thereby creating a smaller, more manageable bike.  As a result, Guardian recommends the 20″ Small for ages 5+ and the 20″ Large for ages 6+.

If you really want gears for your child, but aren’t sure they are big enough for the 20″ large, here’s another size reference. Our 43″ tall 4-year-old tester shown below, can fit on both the Guardian 16″ and 20″ small.

Guardian 16 vs Guardian 20 Small

Side by side comparison of 4 year old girl on Guardian 16 and Guardian 20 small

As a confident rider, she fits on the 20″ small at its minimum seat height, but she’s about as short a rider as we would recommend. She can touch the ground with her tiptoes, and while the bike is manageable for her, it’s still a lot of bike for a child her size.

For example, with the handlebars higher in proportion to her body, the 20″ will be a bit more difficult for her to manuever. She could definitely not stretch to fit on the 20″ large at this point.

If you’re feeling overwhelmed about sizing, we can walk you through a few easy steps to find the best size bike for your child in our Kids Bike Sizes Guide.

Guardian Frame Sizes

SizeEst. AgeChild HeightSeat Height
16″4+40″ – 46″18.25″ – 22.6″
20″ Small5+43″ – 51″21.3″ – 27.1″
20″ Large6+45″ – 53″22.5″ – 28.5″
24″8+49″ – 61″25″ – 33″

Guardian’s Virtual Bike Sizer

To help parents determine the perfect size Guardian for their child, Guardian created a unique and clever RideSizer tool

Upon entering your child’s height, inseam, birthday, and answering questions about their riding ability, RideSizer will display an avatar of your child on whichever size bike Guardian recommends for them.  The tool will also tell you about how long the bike will be a good fit for your child.

Based on our experience, the RideSizer tool works great, but if your child is right on the edge between two sizes, be sure to compare their inseam to the bike seat height to ensure a perfect fit.

Insanely Easy Assembly

To ensure quality and ease of assembly, every Guardian bike is checked, tuned, and re-packaged by Guardian’s own mechanics in California BEFORE they are shipped out to customers.  Bikes are NEVER shipped straight from the factory to the consumer. Both 20 inch bikes we received from Guardian were ridiculously easy to assemble, were put together in less than 10 minutes, and required no additional tuning once assembled.

To keep the assembly process as simple as possible, Guardian bikes feature peel-off stickers on the handlebars, stem, and crank arms. These stickers take the guess-work out of lining parts up and tightening them correctly. It’s a small addition that makes a HUGE difference while assembling the bike. We’ve assembled hundreds of bikes, and we still found the stickers helpful!

Stickers on Guardian 20 stem, handlebars, and crank arms provide assembly instructions for parents

Guardian ETHOS 20 and AIROS 20 Bottom Line

Safe, lightweight, and fun to ride, Guardian’s line of bikes is simply exceptional. Whether cruising the neighborhood or enjoying extended family bike rides, your child will be in good hands with a Guardian. 

The Guardian Airos 20 is ideal for lighter-weight kids who would benefit from a lightweight bike as well as higher-end components such as stronger-build wheels and a threadless headset. The Guardian Ethos 20 is a high-quality but budget-friendly choice for the average child rider who wants the benefits of those impressive SureStop brakes, but needs to save $100.

FTC Disclosure: Affiliate links are included in this review.  No monetary compensation was provided for this review, however, the reviewed product was supplied by the manufacturer or distributor to help facilitate this review. All opinions and images are that of Two Wheeling Tots LLC.  All content and images are copyrighted and should not be used or replicated in any way. View our Terms of Use.

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