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Allied BC40 Mountain Bike Review: This Ultra-Light Bike Is a Lightweight XC Ripper

If you’re in the market for a light, ultra-fast cross country mountain bike, you should add Allied’s BC40 to your cart.

allied bc40 mountain bike on grass
Chase Pellerin

When I visited the Allied Cycle Works factory in 2017 for Issue Five of the Gear Patrol Magazine, it had only been in operation for a little over a year. It was located in Little Rock, Arkansas, and even though it was really only producing two types of frames, Allied was gaining traction among those in the know of the cycling industry.

Fast forward to today, and the brand has relocated nearly 216 miles away, outside the town of Bentonville, and has added another three frames to its arsenal, the latest of which marks a departure from its road and gravel roots. The Allied BC40 is the brand’s first mountain bike, and while it can certainly get rowdy, it holds Allied’s speed and gravel racing pedigree close at hand. Here's what I thought of the bike after taking it out for testing this year.

What's Great About the Allied BC40

It's incredibly quick

Before I got on the BC40, it had been nearly a year since I thought about Strava. I had decided I wasn’t going to worry about how fast or how far I went this summer, only whether or not I had fun riding my bike. The second I started turning the cranks on the BC40 though, I couldn’t get the mega-popular tracking app out of my head. How many KOMs ("King of the Mountain", the fastest rider for a given segment) could I knock off? How many of my local circuits could I set personal bests at? Am I too old to pursue World Cup XC racing? The bike was fast.

That’s thanks to a number of thoughtful aspects singing in concert, under the direction of maestro Sam Pickman, Allied’s Director of Product and Engineering. Before joining the team that launched Allied, he spent eight years in the trenches at Specialized, engineering some of the fastest bikes on the road.

It’s no wonder that the BC40 has a distinctly quick character to it. But the nuts and bolts of it aren’t as simple. There's tons of time and engineering that goes into creating a bike like this, pouring over the geometry numbers, suspension kinematics and even the parts list. That time and effort shows.

The rear end is super snappy

Part of what makes the BC40 so quick and lively are the flex stays on the rear triangle. Traditionally, a full suspension XC mountain bike with a four bar linkage like this would run a split pivot design, where there are two pivot points on the seat tube and one in line with the rear axle. The BC40 makes use of flex stays, which is a fairly new technology in the mountain bike industry — in the past two years, it's been more widely used, but is still considered emerging tech.

back view of an allied bc40 bike
Chase Pellerin
back tire of an allied bc40 bike
Chase Pellerin

These flex stays work by having a certain degree of flex worked into the rear seatstays and chainstays. The BC40 is engineered around a 120mm rear shock and a 120mm front fork. With that amount of travel, it’s possible to allow the stays to flex just enough where you can forgo a pivot at the axle. Not only does it cut down on weight, but it offers a lively, snappy ride that’s nothing short of addicting.

It’s a little disconcerting at first, though. How long before the carbon fatigues? What if I really send it off of something? Having seen the black magic of Allied’s layup department first hand, it’s worthy of your trust. And having ridden the BC40 off more than a handful of features stretching its capabilities, I can say for certain that you’d have a very hard time breaking any carbon.

One more quick note about the suspension that's worth mentioning before moving on — the alloy rear linkage is fabricated in-house, along with the rest of the frame in Allied’s factory. How’s that for made in USA?

interior close up image of the allied bc40 bike frame
Chase Pellerin

You can build it however you want it

For $5,590, you can pick up a frameset and build the bike to your ideal spec — a great option if you’re as exacting as we are when it comes to bike components. But even if you choose the Shimano XTR build of the Allied BC40, or any of the other available build kits, you can still tweak and swap parts to your heart’s content. Want a different headset? Go for it. Another suspension setup? Fire away. You can even choose your frame color from the plethora of Allied’s “standard” paint options.

What's Not So Great About the Allied BC40

It's expensive

The price of the BC40 is undoubtedly the elephant in the room here. For the frameset alone, you’re looking at $5,590. Heck, you can get into a Canyon Lux Trail in an XT build for less than that. The cheapest you can pick up a BC40 complete bike is $7,625 — that’s a lot of pennies.

In regards to price, this bike isn’t for everyone. But if you can afford it, and are in the market for a zippy, what the kids are calling “downcountry”, bike, you’d be hard pressed to find an option that will bring a wider smile to your face.

You may find yourself in some spicy situations

It’s easy to forget how much travel the BC40 has, which is simultaneously good, and challenging. With 120mm of travel in the front and rear, it’s super efficient on the climbs and the flats. You can rip along like you’re on a hardtail — no problem.

front of the allied bc40 bike
Chase Pellerin
side view of the allied bc40 bike
Chase Pellerin

That over-confidence also quickly transitions into downhill segments, which, depending on where you live, can lead to you finding yourself in a bit of trouble. Not so much trouble where you feel like you’re riding a gravel bike where it doesn’t belong, but enough to get the heart pumping and start creeping into that underbiked feeling.

The parts spec

This is admittedly a tough critique, given that as stated above, you can build your Allied however you want, and the feedback I have is hyper specific to the build that I tested. It may sound crazy, but I’d skip the Sram XO1 AXS shifting and Sram G2 RS brakes. I find wireless shifting on mountain bikes to be a bit finicky and definitely overkill, and as far as brakes are concerned, you’re pretty much team Sram or team Shimano — and I prefer the snappy bite of Shimano brakes (although the modulation on the Srams is better). If I had my pick of the litter, this frame is calling out for Shimano XTR derailleur and brakes.

allied bc40 bike back tire
Chase Pellerin

Final thoughts on the Allied BC40

The Allied BC40 is the fastest mountain bike I’ve ridden since I tested Yeti’s SB100 aways back. The BC40 immediately had me stomping on the pedals and hammering through the rolling singletrack of my local trail networks. It almost has a placebo effect, with its feathery weight giving you the confidence to power up your favorite climb, full speed ahead.

But second to that, it’s a full-suspension carbon fiber mountain bike made right here in the USA. The number of companies doing that can be counted on one hand (by my estimation there are only five total — Trek Project One, Guerilla Gravity, Alchemy, Ellsworth and now Allied — though I’m sure there are more). That’s worth making note of, as bringing manufacturing of carbon fiber bikes stateside is a good thing for both local economies and cyclists.

For what it's worth, if you're looking for a speedy, lightweight mountain-ready ripper, the Allied BC40 has my vote.

Chase Pellerin
Allied BC40 XT M8100 Complete Bike
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