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Mongoose

Mongoose Flatrock

  • Based on 383 reviews
Condition: Used - Very Good
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$363.16 Why this price?
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Color: Red


Size: 18-Inch Frame/29-Inch Wheels


Features

  • ADULT MOUNTAIN BIKE: Get ready to explore new trails on the Flatrock by Mongoose. Featuring 29-inch wheels, this bike is perfect for riders from 5'4" - 6'2" tall. Roll over difficult terrain with ease.
  • BORN IN DIRT: Lightweight yet durable with a 6061 aluminum hardtail frame, this womens and mens mountain bike is ready to explore off the bike path and keep up with adventurous riders.
  • BUILT FOR ADVENTURE: This Mongoose mountain bike is ready to roll with knobby mountain tires and double wall alloy rims for durable traction. The suspension fork absorbs bumps and uneven terrain, ensuring a smooth, controlled ride.
  • SHIFT INTO GEAR: This 21-speed bike boasts twist shifters and a rear derailleur for smooth shifting and the right gear for your ride. Mechanical disc brakes provide reliable stopping power in varied conditions, giving riders control on rough terrain.
  • KNOW YOUR ROOTS: As one of the OGs in BMX and action sports, Mongoose has helped bring this 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

Explore rad new trails with the Flatrock mountain bike by Mongoose. The Flatrock comes equipped with a lightweight aluminum hardtail frame and Element suspension fork that are ready to tear down the trail. 21-speed twist shifters and rear derailleur provide effortless gear changes, while alloy v-brakes deliver reliable stopping power. Plus, double wall alloy rims offer lightweight durability. Get out there and explore with the Mongoose Flatrock.

Bike Type: Mountain Bike


Age Range (Description): Adult


Brand: Mongoose


Number of Speeds: 21


Color: Red


Wheel Size: 29 Inches


Frame Material: Aluminum


Suspension Type: Front


Special Feature: Adjustable Seat, Dual Disc Brake, Durable, Lightweight, Quick Release Seat


Included Components: Flatrock Bike


Bike Type: Mountain Bike


Number Of Speeds: 21


Suspension Type: Front


Additional Features: Adjustable Seat, Dual Disc Brake, Durable, Lightweight, Quick Release Seat


Brake Style: Disc


Specific Uses For Product: Trail


Power Source: Pedal power


Bicycle Gear Shifter Type: Twist Grip


Skill Level: Intermediate


Derailleur Configuration: Front and Rear


Bicycle Drivetrain Type: Derailleur


Is Autographed: No


Number of Handles: 21


Color: Red


Style Name: Bike


Frame Material Type: Aluminum


Wheel Material: Aluminum


Seat Material: Plastic or synthetic material


Age Range Description: Adult


Brand Name: Mongoose


Included Components: Flatrock Bike


Model Number: R5864


Model Name: Flatrock


Model Year: 2021


UPC: 038675236325


Manufacturer: Pacific Cycle, Inc


Warranty Description: Limited Lifetime


Item Type Name: Mountain Bike


Wheel Size: 29 Inches


Size: 18-Inch Frame/29-Inch Wheels


Wheel Width: 2.3 Inches


Item Weight: 16.8 Kilograms


Warranty Type: Limited


Maximum Weight Recommendation: 300 Pounds


Is Assembly Required: Yes


Minimum User Height: 65 Inches


Frequently asked questions

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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.

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Top Amazon Reviews

    • The kiddo likes it. The kiddo likes it.
Review Image by Rin B.
I had a little bit of trouble getting the breaks set correctly but that was definitely my own incompetence. I watched a YouTube video & was eventually able figure it out. Overall it's a great kid's bike and very pretty!
Reviewed in the United States on February 11, 2024 Reviewed in the United States on February 11, 2024 by Rin B.
    • Great present!
Color: Mint Size: 14.5-Inch Frame/24-Inch Wheels
Purchased as present for my great grandson. He loves it. So great purchase all around . I paid for an Amazon technician to assemble it at my home, and was extremely pleased with his service. He was on time and quick and efficient. He also cleaned up and hauled off the box and packing material. Highly recommend using this service! ... show more
Reviewed in the United States on May 15, 2026 by ssf
    • "You Get What You Pay For" Should be the Title for Every Bike Purchased in this Price Range
It's a really heavy Mongoose but .. I knew that when I pressed the "add to cart" button. The hardware on the bike is mediocre but .. knew that. The bike does everything you need it to do .. unless you're a "bike person". If you ride this too hard .. it breaks. If you use it for transportation, or if you need a good beater for your kid who will be throwing this at the ground repeatedly until they move out of your house chasing some dream job in cosmetology or whatever nightmare they're dreaming of .. this is the bike for you. Assembly was complicated by the fact that it's just an okay bike. The tools they include are enough to assemble the bike with but, you can cut your assembly time in half if you just have some basic tools lying around the house. The bike rides and feels fine. With some fine tuning on the brakes and shifter mechanism, the bike would stop and shift fine. Solid "bang for the buck" on this but, if you spend another couple hundred bucks, there are better choices that would be worth much more than the extra investment. All in all .. this is okay and it's fine unless you're really trying to do anything outside the realm of "commuting". ... show more
Reviewed in the United States on July 27, 2023 by Sean C.
    • Great size for a 10yo
Color: Mint Size: 14.5-Inch Frame/24-Inch Wheels
We just gave this to our 10yo son for his birthday and we are very happy with it. I was torn between purchasing a 24inch or 26th inch, but the 24inch is perfect. The frame size coupled with the 24inch wheels is the ideal size for him, the larger size would have been too big. For reference he stands at approximately 4ft 8in, and he still has lots of room to grow with it. I am 5ft 3in and can also ride it. Walmart advertises this size as being suitable for 10-14yo and I think that is pretty accurate. The bike is not the lightest compared to higher end mountain bikes, but this will be used for neighborhood riding and going on park trails. And for the price, I was expecting a solid feeling frame. First impressions tell us the quality is good, comparable to any other bike. It was very simple to assemble. We did take it to a local bike store to have the gears checked and brakes tightened, but it was ridable out of the box. Overall for the price, we are really happy with the size and quality of this bike, and our son loves it! ... show more
Reviewed in the United States on March 15, 2026 by Ashley Kelly
    • Not well made, parts already braking, no customer support
Color: Red Size: 18-Inch Frame/29-Inch Wheels
My husband and I recently bought the above bike on Amazon for our son for his birthday. We studied reviews and felt good about this being a good bike for a big kid--he's almost 6' and a stout guy. He loved the look of the bike; however, after a couple weeks of use, we've been very disappointed in the quality and functions of the bike. Here are several items of note: 1) The handle bar--this bar, although sleek looking, does not offer much room for adjustment and it is very uncomfortable, even painful, to ride for our son, me (5'8") and my husband (6'1"). We all experienced pinched shoulders and neck even after riding it just around the block. A neighbor helped us put a different handlebar in to raise the grip a bit, and although it helps, it's not quite the right size for the bike, the overall grip is still pretty narrow. Which means we will have to keep shopping around to make adjustments. 2) The handle grips and gear shift--these are entirely too small and spaced too close together! My son's hand, if he grips with a standard 4 finger grip, overlaps with the gear shift, so gears are shifting when he's just holding on to the handlebars and not meaning to shift gears. 3) The pedal/crank set--there is a decent amount of wiggle room in this. As I understand, this should be a pretty sturdy feel, but it jiggles. It doesn't appear that this is anything we can adjust, it is as it came. We had the bike professionally put together, and the mechanic noted this right away. 4) The kickstand--it has already bent and bends forward with the weight of the bike and no longer works. Overall, we are extremely disappointed in this bike. We feel that for the money, we shouldn't be having all these issues right away with it. We reached out to the manufacturer, and have not heard any response back. I'd shop for a different bike! ... show more
Reviewed in the United States on August 2, 2023 by Joe Wilkins
    • chain issues
Color: Red Size: 18-Inch Frame/29-Inch Wheels
nice bike but had constant problems with the chain snagging
Reviewed in the United States on November 15, 2025 by Phaidra
    • My Go-To for Fun and Adventure!
If you're looking for a bike that's ready for anything, whether it's cruising around the neighborhood or hitting some easy trails, the Mongoose Flatrock is an awesome choice. I've been riding mine, and it's just a fantastic, reliable bike that makes getting out and about a joy. First off, it's really comfortable to ride. The front suspension (that's the "hardtail" part, meaning suspension in the front fork) does a great job soaking up bumps and uneven paths, so your arms and body don't take a beating. This makes longer rides or slightly rougher terrain much more enjoyable. Changing gears is super easy with the 21-speed twist shifters. Whether you're going uphill and need a lower gear, or flying downhill and want to pick up speed, a simple twist of the wrist gets you where you need to be. It shifts smoothly, so you're never struggling to find the right gear. I also really appreciate how lightweight yet sturdy it feels. It's easy to maneuver, which is great for weaving through paths or even just getting it on and off a bike rack. And when you need to stop, the brakes are reliable and give you plenty of stopping power. Overall, the Mongoose Flatrock is a fantastic bike for anyone who wants to enjoy the outdoors. It's built tough, rides smoothly, and is just a lot of fun. Whether you're a casual rider or looking to explore a bit more, this bike is a great companion! ... show more
Reviewed in the United States on May 22, 2025 by Burning Man
    • Great quality 👍 would highly recommend
Color: Grey Size: 17-Inch Frame/26-Inch Wheels
Really nice bike 👍 easy to put together 😊 will last a really long time 👍I highly recommend if you go biking a lot ❣️ it's expensive but worth it
Reviewed in the United States on October 25, 2025 by amber

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