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Availability:
In Stock.
Arrives
Sep 14 – Sep 27
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Size: 20-Inch Wheels/MX
Color: Black
Features
- BMX STARTS HERE: Built for riders 4' 10" to 5' 6" tall, this 20-inch beginner BMX bike has everything needed to learn first tricks, rip around the block, and make the transition from the sidewalk to the skatepark.
- READY TO ROLL: Strong, lightweight 48-spoke aluminum rims help handle the abuse that comes with learning BMX. Designed for durability and consistent performance, they're ready for session after session.
- BUILT FOR PROGRESSION: A durable 1-piece crank helps keep pedaling smooth and reliable while developing strength, balance, and bike control through every stage of learning.
- RIDE WITH CONFIDENCE: A 4-bolt alloy stem helps keep handlebars secure while an aluminum linear-pull brake and alloy lever provide dependable speed control when it's time to slow things down.
- KNOW YOUR ROOTS: As one of the OGs in action sports, Mongoose has helped bring the BMX movement to the world. For over 50 years, we've been all about epic rides and pushing limits and we're just getting started.
Description
For 45 years, Mongoose has been in the dirt, down the trails, and on the ramps. With the Legion Series, Mongoose offers a full line of freestyle BMX bikes for riders of all ages and ability levels. The Legion L20 was designed to be a fully park, street and dirt worthy BMX bike. The Legion L20 features a Hi-Ten steel frame (20.25” top tube), tapered headtube, and removable brake mounts. The L20 Hi-Ten steel 8” rise handlebar and 48mm stem are designed for precision riding, while the wide aluminum single wall 36H rims and 2.3” BMX tires offer grip and durability. The 25x9T gearing with one-piece tubular chromoly 170mm hollow spindle cranks and American loose ball bottom bracket offer a clean, reliable drivetrains. An alloy U-brake with alloy brake levers provide speed control, while the Hi-Ten Steel BMX fork with 1-1/8" threadless steerer and taper leg helps maximize performance. This bike ships ready to be assembled and comes with a 5-year limited warranty on the frame and a 1-year limited warranty on parts.
Bike Type: BMX Bike, Kids Bike
Age Range (Description): Youth
Brand: Mongoose
Number of Speeds: 1
Color: Black
Wheel Size: 20 inches
Frame Material: High Tensile Steel
Suspension Type: Rigid
Special Feature: Adjustable Seat
Included Components: Reflectors, User Manual
Bike Type: BMX Bike, Kids Bike
Number Of Speeds: 1
Suspension Type: Rigid
Additional Features: Adjustable Seat
Brake Style: Linear Pull
Specific Uses For Product: Freestyle
Power Source: Manual
Intended Riding Terrain: BMX Terrain, Paved Roads, Urban Terrain
Bicycle Drivetrain Type: Chain Drive
Color: Black
Wheel Size: 20 inches
Size: 20-Inch Wheels/MX
Wheel Width: 2.1 inches
Item Weight: 29.2 pounds
Warranty Type: Limited
Maximum Weight Recommendation: 200 pounds
Minimum User Height: 48 inches
Age Range Description: Youth
Brand Name: Mongoose
Included Components: Reflectors, User Manual
Model Number: M4105G27U1OS11
Model Name: Legion MX
Model Year: 2026
UPC: 038675293694
Manufacturer: Mongoose
Unit Count: 1 Count
Item Type Name: BMX Bicycle
Warranty Description: Limited lifetime warranty on frame. 1 year limited warranty on parts. 30 day limited warranty on wearable parts.
Frame Material Type: High Tensile Steel
Wheel Material: Aluminum
Seat Material: Polyvinyl Chloride (PVC)
Frequently asked questions
If you place your order now, the estimated arrival date for this product is:
Sep 14 – Sep 27
Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
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Similar Products
Top Amazon Reviews
Size: 20-Inch Wheels/MAG
Color: Orange
The bike from the pictures looked pretty cool. I didn't realize how beautiful this bike would be until it came in the mail. I purchased the Legion Mag in orange for my 8 year old. It was great to see his reaction on Christmas when receiving this bike. He was so excited. I read some other reviews from reviewers who had complaints on the difficulty of assembling the bike and in my opinion the people having trouble assembling the bike must be blatantly ignorant or illiterate. The instructions for assembly are written so a teenager could assemble this bike, with clearly labeled diagrams and more in depth explanations than what is necessary for assembly. The instructions on assembly are excellent and I had almost no trouble assembling the bike without them until it came to adjusting the brakes. I assembled the entire bike without instructions except for the brakes because it is just self explanatory. I was also able to assemble the brakes without any trouble or needing the instructions although I did refer to them for proper adjustment and alignment protocols. The only issue I had when assembling the bike is when I got to the point of attaching the handlebars to the handlebar binder assembly attached to the stem. The four socket cap screws that tighten down on the handlebar binder bracket would not thread easily. I felt as though I would break the screws or destroy the threads if I attempted to tighten them down far enough to grip the handlebars. There was too much paint in the threaded holes and also the tolerances on the machining of the threads was not great. I have included some pictures showing just how much paint was removed from tapping and also chips from burs in the threaded holes from poor tolerance drilling and tapping at the factory. In order to fix this problem I grabbed a tap handle and a M8x1.25 normal thread tap and tapped the holes. I would give this bike a 4.9 out of 5 if I could just because I needed to tap these holes and a tap was not listed as a required tool. I don't think many people will have problems assembling the bike even if they have this issue and need to tap the four holes as these are the only holes that need anything to be screwed into. Honestly if you don't at the very least know how to use a tap and die set you probably shouldn't be assembling a bike as it's not safe to do so if you're not familiar with basic tools. You could wind up hurting your child from pure negligence if you don't know how to use basic hand tools to assemble this bike properly. My suggestion is that you take it to a local bike shop and pay $30-$40 to have them assemble the bike and adjust the brakes if you don't know what you are doing. I assume some people who buy this bike will do just that with the majority of people knowing how basic hand tools work and them being able to assemble it themselves. Overall the bike is amazing, my son loves it, it was extremely easy to assemble, and I recommend you tap the holes on the handlebar binder even if it doesn't need it as it will allow you to make a more secure connection. Please don't listen to people complaining about difficult assembly as it was extremely easy even the detangler brakes something of which I've never seen or dealt with on a bike before. The instructions are very clear on how to hook the brakes up and how to adjust them properly and I was actually surprised how easy it was to assemble the brakes because I was expecting something very difficult based on the reviews but it turns out these brakes are easier to assemble than normal brakes.
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Reviewed in the United States on December 30, 2020 by Dave
Size: 18-Inch Wheels/L18
Color: Silver/L18
My son, absolutely loved this bike when he received it, and it was put together, the bike was perfect for his size. It rode very smooth and I feel like I got what I paid for unfortunately after moving into our new place, the bike was stolen from our backyard
Reviewed in the United States on May 29, 2026 by Latisha
Size: 20-Inch Wheels/MAG
Color: Orange
Great Bike for a beginner and a leap above Huffy and Walmart bikes. I remember Mongoose being a Good recognizable brand decades ago. This bike was easy to assemble. I think it took an hour to unbox and put together. Box was damaged heavily, but bike was packed so well with foam and wrapping that there wasn't a single scratch. The most important part is the kid is happily surprised and liked the color.
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Reviewed in the United States on March 2, 2026 by The Real Hughleys
My 5 ½ year old boy is a little bit taller & thicker than most of his peers & the bike is almost too big for him but that was kind of the goal when deciding to upgrade his BMX. He was way to big for his first peddle BMX bicycle, so it's nice he'll grow into this one & he really seems to be enjoying it. I did throw a front brake on there just because I had one laying around that fit perfectly but tbh I adjust that to where it barely grabs because we're not too keen on him doing an indo & knocking his teeth out. There's no peddle brake on this bike, so if you're going from a bigginner bike, that almost always have the rear peddle brake, just be aware this has a hand brake, it does require large enough hands to reach it, & a bit of strength to get the brake to engage. All in all, so far, it's a nice BMX for a 5 ½ to say up to about 7 or 8 years old depending on how big a kid. I wouldn't consider this a beginner bicycle, it's more of a 2nd or 3rd bicycle not a 1st IMO.
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Reviewed in the United States on October 17, 2024 by JJ47
Bike is beautiful, my 8 year olds reaction was priceless. He has a little difficulty with the hand breaks which I adjusted up to make them easier to use. The pedals have little raised teeth for grip, not as sharp as other pedals but they have already made a few scratches on my young riders legs but we are only in his 2nd of riding without me holding the seat and he is still learning. Was deciding between the Legion Freestyle and the Walmart mongoose bike for $50 less and I’m so glad I went with the Legion Freestyle as I believe assembly would have been incredibly more difficult on the Mongoose bike sold at Walmart. Look forward to buying again for my 2 other kids as soon as they are ready.
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Reviewed in the United States on August 3, 2019 by J Younger
Size: 20-Inch Wheels/MAG
Color: Orange
Mya nephew was very happy......
Reviewed in the United States on May 3, 2026 by Imanuel Hodges
Size: 20-Inch Wheels/MAG
Color: Orange
With all of the four and five star ratings, I must be the problem, right? The bike came partially dissembled for shipping purposes. I expected that. What I did not expect was: 1. Missing parts. One of the nuts and both of the washers were missing from the front wheel. Ok. A shipping problem. But what kind of washers do I need to go find? Should be simple. Just read the instructions. 2. Horrible Instructions: For example, to attach the front wheel, I need to follow the appropriate set of instructions depending if my bike's wheel is, "nutted with step retaining washer, nutted with clip retaining washer or quick release". But I don't know which one my bike is; the nut and both washers are missing. Every section is just like this; follow the set of instructions that pertain to your bike. But where does it say if the bike I purchased has a quill stem, a threadless stem, a front load stem or a top load stem? I have no idea. Mongoose has been around for a while. So there are plenty of videos on YouTube. But there are so many configurations for Mongoose bikes, good luck finding the right one. I watched a bunch of videos, went to Wal-Mart (twice) and got $30 worth of nuts, washers, hex drivers and, no I didn't go out and buy the lithium gel they recommended! Then I paid a bike shop $45 to put the thing together because I still couldn't figure it out. The bike shop wouldn't do the brakes because of liability purposes. But they showed me that I needed to loosen a nut and put the brake cable out some. Should be easy, except... 3. CHEAP parts!: I stripped a nut and two screws trying to tighten the brakes just enough to barely work. It's Christmas Eve and I'm soooo frustrated. Should I be worried? Every single step in the instruction book says that if I don't do this step correctly, someone could get seriously injured or killed. Here ya' go son. Have fun! Merry Christmas. I could call Mongoose Customer Support. They are open Monday through Friday 8 to 5; because that's when dads assemble bikes right? Sorry for all of the venting. I've had the bike for a week and I have to say, I have NEVER had this much trouble assembling something that came in a box. I've got $250 invested into a $170 bike and I don't feel safe letting my son ride it. I am not a happy customer.
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Reviewed in the United States on December 25, 2020 by Jared D.
Size: 20-Inch Wheels/MAG
Color: Orange
Let me preface this by mentioning I've assembled a number of kids' bikes and have rebuilt my own (mountain) bikes. This is a solid bike I purchased for my 12 year-old (<5') that my 9 year-old is also able to ride as am I (6'). It was pretty easy to assemble (directions were clear) and all parts included; nothing broken/damaged. This model bike, per specs and picture, only has a rear brake which works as expected. My kids are not riding ramps or rails or performing tricks; riding in the street and occasionally off-road at the bmx park (dirt) and if this is what you're using it for, this is a good value in terms of it being the last bike of this type I suspect my kid will own. The one thing I'd mention is that the seat post is bmx-height (low since you're rarely sitting on it); if you plan on using this more for just biking around, invest in a longer seat post (I used a 25.4 x 350mm available elsewhere on the site) -- you can keep the seat and just switch this out. The bike came in an undamaged box; I presume this is the way they all leave the factory -- if yours is damaged on receipt, that's on the delivery company.
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Reviewed in the United States on February 3, 2020 by fells77