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Carbon XS Mad 6 20″ Mountain Bike Review

Author: Kristen Bonkoski


Haven’t heard of the Carbon XS Mad 6? Let’s remedy that oversight.

This 20-inch mountain bike from the Australian boutique bike company “Carbon XS Cycles” is unlike anything else on the market. Designed for FAST cross-country riding, the Mad 6 has full-suspension, a full-carbon build, and an adjustable frame that can grow with your child.

carbon xs mad 6 review

It weighs in at a crazy-light 17.5 pounds (with pedals), climbs like a dream, and is comfortable in rocky and technical terrain. This bike is SO awesome, in fact, that it’s the first bike we’ve been able to convince our son to ride for any length of time since he got his Trailcraft Blue Sky 20. I didn’t think another mountain bike would be able to usurp that throne.

carbon xs action shot

Review In A Nutshell


  • Adjustable frame that grows with your child
  • Carbon build is crazy light (17.5 lbs)
  • Full suspension offers a comfortable ride
  • High-quality Shimano ZEE drivetrain
  • Shimano XT hydraulic disc brakes
  • Tubeless setup upon request


  • No quick-release seatpost collar
  • Long crank arms for younger children
  • No thru-axles on the wheels

Price: $3,450 (with shipping) USD

Carbon XS Mad 6 Video Review

Unique Adjustable Frame Grows With Your Child

The high price of the Mad 6 is far more digestible when you consider the lifespan of the bike. Its unusual adjustable frame grows with your child and fits kids between 4 and 7 years old. That means your child could potentially ride the bike for 4 YEARS–that’s unheard of with kids bikes!

carbon xs mad 6 rear shock

Of course, an even better indicator of appropriate fit is your child’s height and inseam. The Mad 6 will provide the best fit for kids with an inseam between 15″ and 25.5″. As a reference point, my son is 7 years old, 48″ tall and still has quite a bit of room to grow on the bike.

mad 6 sizing

As you adjust the frame, the standover height raises. Consequently, the head tube angle also changes when adjusting the shock into a new frame mount setting. When the bike is in it’s lowest standover position, the headtube angle is a nice slack 65 degrees. In the highest standover position, the head angle is a more aggressive 69 degrees.

Unlike some mountain bikes that have been designed to grow with your child by converting from 16″ wheels to 20″ wheels, the Mad 6 sticks with 20″ wheels in both it’s smallest and largest positions. This makes the bike attractive for parents who recognize the benefits of bigger 20″ wheels but who’s child has an inseam too short for the typical 20″ bike.

The one drawback of the bike is that while the frame adjusts sizes as your child grows, the components do not. The cranks, for instance, are 135mm which are too long for your average 4 or 5-year-old. As a frame of reference, the Prevelo Zulu Two (which is also designed for kids this age) has cranks that are 95mm.

Other components you might want to swap out for younger riders include a shorter stem and narrower handlebars.

50mm of Front and Rear Suspension Provide A Comfortable Ride

Unlike other full-suspension 20 inch bikes (the Spawn Rokkusuta and Norco FS 1 Fluid 20 for instance), the Carbon XS Mad 6 is intended as a xc/trail bike rather than a downhill machine.

We used it on a variety of trails around Utah–both rocky and buff–and found that the bike provided a much more comfortable ride for our son than the hardtail bikes he’s used to. On rocky sections of trail, where he might usually complain, he was able to comfortably cruise along. This is likely due to the carbon build as much as the 50mm of front and rear travel.

The front fork is the ever-present Spinner 20 Air Grind suspension fork. It’s quite common on mid-range 20″ mountain bikes including the Pello Rover and the Kona Honzo 20. It’s not quite as plush as the Manitou Junit or other custom forks like those on the Spawn or Trailcraft, but it’s perfectly adequate for cross-country riding.

The fork (which has been customized by Carbon XS) has 50mm of travel, adjustable air pressure, and a lockout switch. We did use the lockout on the fork fairly often for big climbs (as well as the rear shock).

Speaking of the rear shock, it’s a DNM dual air, adjustable 50mm shock. As I just mentioned, it has a lockout, which is nice for the climbs. DNM is a lower-end budget option when compared to Fox, for example, but has performed well for our son (at least in the short-term).

All Carbon Build Makes For An Extremely Lightweight Bike

The bike’s superior climbing ability is largely due to its low weight. At 17.5 pounds the Mad 6 is on par with fully rigid bikes like the Woom OFF 4 and lighter than high-quality hardtails like the Trailcraft Blue Sky 20.

Carbon XS has achieved this impressive weight by using carbon everything — carbon frame, carbon wheels, carbon handlebars, carbon seatpost, and even a carbon saddle. (We should note that the bike also comes with a padded comfort saddle in case a rigid carbon saddle seems like overkill).

High-Quality Drivetrain Will Have Kids Shifting Smoothly

We’ve been really happy with the Shimano ZEE drivetrain on our Prevelo Zulu Three HEIR, so we were excited to see it on the Carbon XS Mad 6 as well.

The Shimano ZEE rear derraileur has a short cage (to provide extra clearance on the trail) as well as a clutch that does a great job of reducing chatter.

We also have been pleased with the ZEE trigger shifter. Compared to a grip shifter, it performs much better and makes nice clean shifts. (It is a bit more difficult to operate than the more expensive Shimano Deore trigger shifter).

The only issue might be for younger kids (4 and 5 year olds) who haven’t already learned to shift. There’s no display so it’s not terribly intuitive for little kids and they may struggle with the thumb strength required to operate the trigger. My 7 year old, who already knows how to shift is rocking and rolling with the ZEE shifter.

carbon xs chainring and crank

The front chainring is–you guessed it–carbon, and has 30T. The Shimano XT 10-speed cassette ranges from 11-34 teeth.

As far as gearing goes, the bike has a gear ratio between 0.88 and 2.73 and a gain ration between 1.83 and 5.67. (Bike nerds, feel free to check my math)! In practical terms, this means that the gearing is well suited for climbing, which we found to be true.

Tire DiameterTire radiusWheel diameterWheel radiusfront chainringrear cassette rear cassette gear ratiogear ratiocrank length (mm)crank length (inches)gain ratiogain ratio
carbon xs mad 6 in action

Shimano XT Hydraulic Disc Brakes Offer Superior Stopping Power

Remember when you got your first set of hydraulic disc brakes? It was life changing, right? The same thing will happen to your child if they are upgrading from v-brakes.

Also, the Shimano XT hydraulic disc brakes aren’t just and hydro brakes. They are a step above the Tektro hydraulic brakes found on most good kids mountain bikes.

They offer significant stopping power, especially when you consider that your child is likely sub-50 pounds.

The brake levers are easy to reach and easy to pull. Your child’s hands won’t get fatigued like they would with v-brakes or even mechanical disc brakes.

Carbon Wheels Are Lightweight and Fast Rolling (But No Thru Axles)

We all know that rotational weight is the most important factor on a bike, and the Mad 6 has taken this to heart. The carbon rims are built up with Colony stainless steel spokes (16 count), Sapim nipples, and a lightweight hub.

The only thing we aren’t crazy about is the lack of a thru-axle. Like most modern adult mountain bikes, more and more kids mountain bikes are also being offered with front and rear thru-axles for increased stability and safety.

The Mad 6 is rocking Kenda Small Block Eight (2.1) tires. These tires are a good old standby I’m sure you’ve run at some point, and which again, are well suited to the cross-country nature of the bike. Carbon XS can set them up tubeless, upon request, which we appreciate.

No Quick-Release Seatpost Collar

At the risk of sounding like a broken record (I’ve been complaining about this on a lot of bikes lately), I thought it was a bummer that the bike lacks a quick-release seatpost collar. Because we ride a lot of mountainous terrain in Utah, we are constantly raising and lowering our son’s seat. With the Mad 6 I had to keep getting out a mini-tool to adjust the seat height. Not ideal. But, of course, this is an easy and cheap thing to upgrade.

carbon xs seatpost collar

Of note, there also isn’t routing for a dropper post, so if you want to go that route you’ll have to use an external option like the PNW Pine.

Internal Cable Routing Keeps Things Clean and Tidy

While there isn’t routing for a dropper, there is internal routing for both the derraileur and brakes which we appreciated. Internal routing keeps things clean and tidy, especially when riding dusty or muddy trails.

bottom bracket

You Won’t Need to Replace the Stock Pedals

Unlike adults, who usually have a preferred pedal they already ride, kids generally ride whatever comes stock on their bike. That’s why we appreciated that Carbon XS but high-quality platform pedals on the Mad 6 that don’t require updating.

carbon xs pedals

The pedals are lightweight, have a slim profile, and include 7 metal pins on each side. But here’s the cool part: the metal pins are smooth and rounded on top and are less likely to inflict a shin wound than a traditional metal pin. With a pair of Five Ten Freeriders, they provided plenty of traction and I never noticed my son slipping off his pedals even on rocky downhills.

Boutique Brand Equals Highly Customizable Bike

Carbon XS is a small boutique brand. So the drawback is that you can’t go down the street to your LBS to buy it this weekend, but the upside is that each bike is made to order. They are willing to work with customers to customize the bike for your unique child and situation.

Each bike also comes with a custom name engraving (that looks sweet by the way). Our bike was engraved with the name “Mad Rascal” which was quite appropriate.


Carbon XS Mad 6 Vs The Competition

It’s almost difficult to compare the Mad 6 to other 20 inch bikes because it’s so unique. That said we’ll give it a shot.

It’s not the most expensive 20″ mountain bike that we’re aware of (that honor belongs to the Meekboyz Mini Beast). In terms of price, the Lil Shredder Prodigy (a more DH oriented full-suspension bike) is probably closest . The Lil Shredder is also designed to grow with your child, but accomplishes this by converting from 16″ to 20″ wheels, whereas the Mad 6 only accepts 20″ wheels.

There are a couple of other bikes that rival the Carbon XS Mad 6 in terms of weight (the Woom OFF 4, the Early Rider Trail 20) but they are fully rigid. The lightest hardtail mountain bikes are a couple of pounds more, and the more downhill-oriented full-suspension 20″ bikes are even heavier.

It’s also the only 20″ mountain bike we know of that has a carbon frame.

For more information, check out our 20″ MTB comparison chart.

Bottom-Line: A Top Choice For Parents Who Prioritize Weight

I’m always a huge advocate of going as light as possible on kids bikes, and Carbon XS has taken the prize in terms of weight. At 17.5 pounds (with pedals), there just isn’t another 20-inch bike out there that compete. It climbs well, is comfortable in rocky terrain, and let’s kids go FAST.

While it isn’t cheap (in fact it’s mind-bogglingly expensive), the fact that your child can get YEARS of use out of it helps lessen the sting a bit. If budget isn’t a serious constraint for you, you probably can’t beat the Carbon XS Mad 6.

carbon xs 20 inch mountain bike

More Resources To Help You Make An Informed Decision

About Us

The Rascals are a family of three. Kristen (mom), Blair (dad), and Parker (kiddo). We started Rascal Rides when Parker was born and we didn’t want to give up our passion for biking. As we learned, we shared. Over the years, we’ve tested hundreds of kids bikes, helmets, bike trailers, and more.

Kristen is a USA Cycling certified coach and loves to share her passion for biking with other families. Blair is a bike geek, mechanic, and mountain bike junkie. Parker is our resident tester and inspiration.

If you see us out on the trail, make sure to say hi!

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