woom 4 Bike Review

From neighborhood sidewalks to basic dirt trails, the woom 4 is an exceptional 20 inch kids’ bike that can tackle it all. With a lightweight frame and a low center-of-gravity, the woom 4 is designed for easy balancing and maneuvering, providing a natural transition for kids moving up from their 16″ bikes.

Seven speeds offer a wide range of gears, and the grip shifters make mastering shifting as simple as possible. A cleverly designed handlebar can be raised or lowered according to child preference and growth.

Whether your child is still a timid rider, or a little speed demon, woom has thought of everything to make your child’s riding experience as fun and carefree as possible. In our review, we put the woom 4 to the test with several 5, 6 and 7-year-olds to see how it compares with other top brands.

Child standing over woom 4 20" kids bike on a bridge

woom 4 Overview

RATING: Exceptional


BEST FOR: Beginning to intermediate riders on a wide range of terrains and distances – from longer paved trails to basic single-track.


SEAT HEIGHT: 22.1″ – 28″
WEIGHT: 17.9 lb. (with included kickstand and pedals)
GEARS/SHIFTERS: 7-speed/Microshift Grip
GAIN RATIO: 2.3/5.9


  • Low center-of-gravity geometry for easier balance and better maneuverability
  • Insanely lightweight
  • Unique handlebar/stem design allows for adjustments for a better fit as your child grows
  • Low minimum seat height for a 20″ bike allows kids to ride at a younger age
  • Wide range of gears (7-speed) suitable for long paved rides to basic trail riding
  • Ergonomic grips to ease wrist strain
  • High-quality v-brakes easy to engage and offer great stopping power
  • Variety of colors available


  • Microshift grip shifter is more difficult to twist than previous SRAM shifter

woom 4 Video Review

Want to see the woom 4 in action? Check out the video below to learn why we love the woom 4 and how it compares in size to the larger woom 5. The woom 4 shown in this video is not the most current 2021 model, but all the information provided about the woom 4 is still accurate.

woom 4 Bike Review – Results of our Test Rides

Buying your child’s first 20″ bike is akin to buying them their first car. Somewhere between reading about shifters, geometry, and gear-ratios, you think, “How did they get this old?” With gentle rides in the park gone for good, speed, power, and performance now top your list… as should the woom 4.

7 year old girl riding woom 4 in her driveway


While the woom 4 is great for riding around the neighborhood, is it soooo much more than your basic neighborhood bike.  Over the last four years, we’ve tested the woom 4 with over ten different kids (ages 5 to 8) with various levels of ability and they all gave the woom 4 two enthusiastic thumbs up!

young boy riding woom 4 on a mountain trail

Our team of little testers demonstrated that the woom 4 excels on different terrains for many different types of riders. From young riders who are a little hesitant to move up to a 20″ bike,  to confident trail riders and aggressive riders ready to tackle every curb, jump, or dirt mound they see, you really can’t go wrong with the woom.

Its lightweight build (17.9 lb.), adjustable-height handlebars (more about that below), and low center-of-gravity frame work in unison to create a comfortable, confidence-building ride that kids love. About the only thing we wouldn’t recommend the woom 4 for is aggressive mountain bike riding!

Boy riding woom 4 down gravel road

What size child fits on the woom 4?

At 22.1″ the woom 4 has one of the lowest minimum seat heights for a 20″ bike. With the seat height maxing out at 28″, the woom 4 is generally a good fit for kids ages 5 to 8 (or kids 45″ to 51″ in height).  Shorter kids under 45″ are usually a better fit on the 16 inch woom 3, while the 24 inch woom 5 provides more room for growth for kids taller than 49″.

A child’s inseam, however, is truly king when it comes to making sure you’re buying the right size bike.  In order to allow for proper leverage on the pedals, an experienced rider should only be able to touch the ground with their tip toes while sitting on the bike’s seat. 

The seat height should be set to 2″ to 3″ ABOVE their inseam to allow for ideal leg extension while pedaling.  As a result, the woom 4 is best for experienced riders with an inseam ranging from 19″ to 26″ (regardless of age).

To give you an idea of how your rider might fit on the woom 4, we’ll show you riders on the low, high, and mid-range of that inseam range. Looking through these images you’ll see how the woom’s unique design allows kids on the very low and very high range to still comfortably ride the bike. The woom 4 has a much wider “good fit” range than most bikes.

Small Riders

Here is our very tall youngest tester, not yet 5-years-old. Her inseam is 19.5″ and she is 44″ tall with shoes on. Because she is a confident, advanced rider, she can get away with the 22.1″ minimum seat height being almost 3″ taller than her inseam. (When sitting on the saddle she can touch the ground with high tiptoes.)

Child with 19 inch inseam riding woom 4 20 inch bike

If your child is this size and is currently riding a woom 3, they could certainly continue to comfortably ride that smaller bike for several more months, or until they are about 45″ tall. This is especially true for timid riders who may find the transition to a larger bike more intimidating.

Mid-Range Riders

Our primary 6-year-old tester is just over 46.5″ tall with a 21″ inseam and was an ideal fit on the woom 4. 

young boy riding a purple woom bikes 4

Older, Taller Riders

And lastly, our 9-year-old tester who is 52″ tall. With the saddle set to its max at 28″, she’s about to grow out of the woom 4, but can still happily ride it.

52 inch tall girl riding woom 4 at maximum seat height

Adjustable Handlebar Stem – Better Fit as Kids Grow

So how is the woom 4 able to fit such a wide range of kids so well? One of the main reasons is its adjustable handlebar stem, which is unique for a threadless headset. The stem allows parents to easily raise the height of the handlebars on the bike almost 2″ as the child grows in height. How low or high the handlebars are set can also just be a personal preference of the rider.

What the Adjustable Stem Does

The handlebars rotate on an axis, so adjusting them affects both their height and reach. Raising the handlebars also pushes them farther away from a child – great for taller kids. Lowering the handlebars also brings them closer to the child – great for shorter kids.

Handlebars in Low vs High Position

adjustable stem of woom bike

Younger, Shorter Riders

Here you can see how the position of the handlebars affects the position of a child’s body on the bike. Our first little rider is 43.5″ tall, but with a 19″ inseam is the shortest rider that can safely and comfortably ride the woom 4. The seat is set to its lowest height (22.1″).

With the handlebars lowered and rotated closest to the her (left image), she can sit naturally without stretching out too much to reach the handlebars.

Short Rider – Handlebars in Low vs. Raised Position

4 year old girl rider on woom 4 with the handlebars at their lowest and then highest point. The seat is set to its minimum.

Older, Taller Riders

On the tall end, raising the handlebars and extending the reach will extend the “comfortable fit” life of the bike. Raising the handlebars accommodates a taller rider’s longer torso, while pushing the handlebars away will prevent the child from being too cramped in the cockpit.

Here is our 52″ tall test rider who is about to grow out of the woom 4 and is ready for a woom 5. With the seat set to its maximum, the low handlebars (image on the left) make her look too big for the bike. By raising the handlebars (image on the right) her slight change in body position looks more relaxed and natural.

Tall Rider – Handlebars in Low vs. Raised Position

9 year old girl rider on woom 4 with the handlebars at their lowest and then highest point. The seat is set to its maximum.

Riders in the Middle

What about somewhere in the middle? The middle position is upright enough to allow the majority of a child’s weight to rest on the saddle (kids naturally prefer to have their weight centered on their hips), while leaned forward enough to allow the rider to shift their weight through turns and while tackling hills. If you’re unsure where to start, begin somewhere in the middle and adjust from there based on your child’s feedback.

How it Works

Woom’s Vario stem is comprised of three metal pieces. The white base is connected to two black pieces that are shaped like number 8’s.  One side of the 8 is attached to the round portion of the white stem base while the other side has the handlebars threaded through them.

When raised, the black “8s” rotate to point upwards instead of back towards the rider. This rotation raises the handlebars almost two inches, but can be fixed in place at any point in-between.

image showing the adjustable stem height on a woom bike

Raising the handlebars is quick and easy. Simply loosen the two Allen bolts that hold the black 8s in place, and pull up or down on the handlebars.  Once the handlebars are at the desired height, rotate the handlebars to ensure the grips, brakes, and shifter are correctly positioned. The front of the handlebars has a “horizontal” marking on them to make sure they are correctly positioned. When the handlebars are in place, retighten the bolts.

image showing the allen bolts on the adjustable stem as well as the horizontal marker on the front on the woom's handlebars

Updated Stem for Fall 2021

Starting in the fall/winter 2021, the Vario stem system was upgraded slightly to include a top bolt on the white portion of the headset with a corresponding star nut inside the headtube. This top bolt/star nut combo is commonplace on most bikes and therefore greatly simplifies any potential headset maintenance.

2021 update of the woom 4 vario stem with top bolt

Frame & Geometry of the woom 4

Designed specifically for kids (not just “small adults”), the woom 4 frame is built narrower and shorter than the average 20″ bike. To properly fit under a child’s body, woom frames are built with smaller components to prevent kids from having to splay their legs out while pedaling.

Differences in Q-factor

The “width” of the bike (the distance between the inside of the pedals) is known as the q-factor in the bike world. The q-factor width is equal to the distance kids must spread their feet to pedal.

A bike with a lower q-factor provides more efficient pedaling as kids are able to focus more of their physical effort on pushing directly down on the pedal versus down and to the side.   As shown below with our 6-year-old tester, the woom 4 is narrower than typical 20″ bikes, making it more efficient and easier to pedal.

Narrow Q-factor on woom 4

image showing the difference in the q factor of the woom 4 versus a novara 20 inch

Low Bottom Bracket

Where the pedals are attached to the frame of the bike also plays a significant role in a child’s ability to balance and maneuver a bike. Pedals are attached to crank arms, which are attached to the bottom bracket of the bike frame. The lower the bottom bracket of a bike, the lower a child can sit in relation to the bike tires, and the lower the overall center-of-gravity of the bike will be.

Low Bottom Bracket Height on the woom 4

image showing the bottom bracket height on a purple woom 4 bike

The lower bottom bracket also creates more distance between the seat and the pedals, which provides more space for kids to properly extend their legs and to get more power out of every pedal stroke.

This is especially important when kids are riding a bike at its lowest seat height. While the woom 4 is vastly superior to cheap bikes you’ll find at Walmart, it’s even a standout amongst some of its higher-end 20 inch bike peers.

Here you can see the woom 4 and the Cleary Owl 20″ bikes set to 22″ seat height. At the highest point of the pedal stroke, the more relaxed knee bend angle of the woom 4 makes it easier for a child to push down on the pedal.

Side by side comparison of knee bend of child on the woom 4 vs the Cleary 20 inch bike. The woom 4 knee bend is more relaxed.

woom 4’s Components

Front Fork and Tires

In addition to being a lightweight and nimble bike, the woom 4’s tires and fork help it excel in various riding conditions. The rigid aluminum fork helps to significantly keep the weight down on the bike without affecting performance. While front suspension can be extremely helpful for kids hitting the single-track, for the majority of kids, it is more advantageous to skip the “cool shock” to help save on added weight.

In fact, most suspension forks on kids’ bikes are pretty worthless and act merely as eye candy. But for those high-adventure kids looking for a front suspension bike for true mountain biking, the woom 4 OFF AIR is an exceptional option.

Whether on paved or packed dirt trails, the woom 4’s 1.4″ wide Schwalbe Little Joe tires help provide plenty of traction for dirt, yet are thin enough to prevent a significant increase in rolling resistance caused by thicker tires. 

Front wheel and tire of woom 4

Wrapped around woom’s super lightweight Soopa-Doopa-Hoops aluminum rims, the woom 4’s wheels are well-prepared for a variety of surfaces.  For added visibility bonus, each tire also has a white reflective strip.

Grips, Gearing and Shifting (Gain Ratio)

The latest woom 4 model comes with ergonomic grips to help ease the strain on the wrist. While a seemingly small detail, this can make a huge difference in the comfort of your rider, especially on longer rides.

7 speed Microshift grip shifter on the woom 4

With a wide range of seven gears and a 2.3 to a 5.9 gain ratio, the woom 4 is ready to tackle hills as well as easily gain speed on flat rides. With one chainring in the front and a cassette of seven cogs in the rear, shifting is done via a single grip shift on the right hand.

For riders just getting acquainted with gears on a bike, we’ve found grip shifters to be the easiest and most intuitive to use. For more advanced kids who ride aggressively on mountain bike trails, trigger shifters are generally better, and are found on the woom OFF AIR 4.

In Fall of 2022, the woom 4 transitioned from an 8-speed SRAM SX4 system to a 7-speed Microshift system. The switch was primarily due to lingering supply chain issues from COVID. In fact, we have seen many of our favorite brands switch to Microshift in the last year. (Prevelo, Guardian, and Specialized kids bikes also use Microshift now.)

This Microshift shifter, however, is not as easy to use as the SRAM shifter was (woom’s website will tell you this as well). Our experienced, almost 5-year-old rider was at first unable to shift all the way down to 1st gear on the Microshift shifter.

After a few coaching sessions, she was able to shift into 1st gear, but it requires significant effort on her part and is not something she would attempt to do without me asking her to. On the previous SRAM shifter, our rider could easily shift through all of the gears.

Realistically, the amount of time a child needs to spend in that super low gear is minimal. Our test rider never complained about only being able to shift down to 2nd gear, which effectively makes the gain ratio range 2.7 to 5.9 for those kids not yet strong enough to shift into 1st gear.

woom is aware of this issue and is working with Microshift to come up with a solve.

Narrow-Wide Chainring – 2021 update

For fewer hassles with the chain, the woom 4 now comes with a narrow-wide chainring to minimize chain slippage. Narrow-wide chainrings alternate the size of the teeth on the ring to match the narrow and then wide links on the chain. This helps keep the chain smoothly rolling along without skipping or missing a link.

More details about the benefits of narrow-wide chainrings are available on the drivetrain portion of our woom 5 review.

narrow-wide chainring on geared woom bikes


Kickstands can be lifesavers for kids’ bikes, but they can also be a pain.  The vast majority of kickstands are mounted right behind the crank arms of the bike.  As a result, if kids don’t remember to put up the kickstand before they pedal, the crank arm of the bike will get jammed in the kickstand.

woom 4’s included kickstand is unique in that it mounts on the rear of the bike, away from the crank arms.  As a result, if a child forgets to put up the kickstand, they can still pedal their bike without a problem.  The kickstand will then bounce up and out of the way whenever it comes into contact with the sidewalk, grass, or anything in its path.

rear placed kickstand on a woom bike

woom 4 Comparisons

The woom 4 is comparable to several other higher-end bikes, including the Prevelo Alpha Three and the geared Cleary Owl. While each bike has its specific strengths, the woom 4 is our top pick for all-around riding. 

The Prevelo Alpha has trigger shifters and a more aggressive body position best suited for ambitious riders.  The Clearly Owl positions the rider similarly to the woom. However, it only has three speeds and its trigger shifting mechanism was trickier to use compared to the woom’s grip shifter.

woom 4Prevelo Alpha ThreeCleary Owl (3 sp)
Weight17.9 lb.18.4 lb.20.3 lb.
Seat Height22.1″ – 28″21″ – 26″20.5″ – 26.1″
Shifters8sp, SRAM Grip8sp, MicroShift Trigger3sp, Sturmey Archer Trigger
Gain Ratio2.3/5.91.9/6.7

woom 4 Review Bottom Line

The woom 4 is the best all-around 20″ bike we’ve tested. Rugged and nimble enough for moderate single-track riding, yet comfortable enough for street riding, the woom 4 is perfectly versatile to take your all-terrain rider anywhere they want to go. We especially appreciate woom’s unique handlebar design that allows the woom 4 to be a good fit for a longer period of time.

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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