CARBON VS. ALLOY: How to Choose the Right Frame Material

Is there a perfect frame material? We'll help you decide and choose the right bike frame for you.

With carbon fiber bikes topping podiums and packing sales racks, you’d be forgiven for thinking that it’s the only viable choice in mountain bikes. But that’s hardly the case.

In 2022, aluminum accounted for more than 36 percent of all bikes sold in the US, while steel came a close second. That leaves carbon in a distant third place for market share. Still, carbon is seeing faster market growth than any other material out there, and it has come to dominate the top tier of the market, casting the impression that it is unquestionably the ultimate choice.

At Thunder Mountain, we ride, rent, and sell both carbon and alloy bikes. Each makes sense for their own reasons. To help make that point, we reached out to a number of our favorite bike manufacturers to talk us through some of their top models and why you would choose one material or the other.

“As Keith Bontrager said many years ago, ‘Cheap, light, strong—choose any two.’ This is still true to this day,” says Ibis Cycles founder Scot Nicol.

Ibis is a perfect test case for the question: They dived into high-performance carbon fiber early (the 2005 Mojo was legendary) and now make one of TMB’s top-selling Sedona bikes in both carbon (Ripmo) and alloy (Ripmo AF).

“But,” continues Nicols, “it’s not the 90’s anymore, meaning the strong part is non-negotiable.”

In other words, the heart of the debate is a choice between strong and light on one hand (i.e. carbon) and strong and less expensive on the other (e.g. aluminum). But that’s just the beginning of the story.

Strong, a.k.a Durability

When bike manufacturers began building with carbon—some 30 years ago—it was a new medium in the industry, and lots of experimentation led to notable, if infrequent failures. Right or wrong, carbon gained a bit of infamy as brittle and subject to damage, especially fractured frames and snapped wheels caused by impact.

But times have changed. Most manufacturers say warranty claims for carbon frames are no more frequent than for alloy ones. And wheel manufacturers are so confident of the strength of carbon that they offer generous guarantees: lifetime, no-questions-asked warranties in the case of Reserve and We Are One; liberal replacement programs from the likes of Industry Nine and Enve.

“A lot of people worry about the durability of carbon. But it’s just not an issue anymore,” says TMB owner Mike Raney, who has personally been shredding carbon frames and wheels in Sedona for over a decade. In that time, he says, his carbon bikes and components have been just as reliable as the alloy ones he’s owned.

Still, because it is more flexible than carbon, aluminum can often deform with no real structural implications. You see this a lot on wheels, where a misshapen rim can continue functioning for years. Even small frame dents can cause no real effect on the ride. On the other hand, carbon is more rigid than aluminum, so it can fracture or splinter with a hard enough impact.

“I think people tend to want an alloy bike for the added durability,” says Ryan Anger, assistant mountain bike product manager at Trek. “In the case of a big crash, aluminum will generally have a better chance of making it through unscathed.”

Of course, the company builds both alloy and carbon iterations of its long-travel enduro sled, the Slash. With 160mm of rear travel and a 170mm fork, this is a bike that’s built for abuse. Which is to say, the company has plenty of faith in its carbon.

Carbon breakage is less common than a decade or two again given the refinement in lay-ups and construction methods. And an entire cottage industry has grown up to fix broken carbon, meaning composite frames are, in a way, longer lasting.

“While it’s true that alloy can take more abuse, it’s also true that often you can repair carbon when you can’t repair aluminum,” says Raney.

The bottom line is that both materials are exceedingly strong and tough. For normal use, carbon is equally as durable as alloy. If you are someone who smashes your bike into rocks regularly or worries about big crashes, it might be worth leaning toward aluminum. (Or perhaps just stop smashing your bike into rocks.)

Ride Quality

This is another realm where outdated attitudes continue to falsely color perceptions.

Back in the early days of bike building, when aluminum bikes were built from straight, unimproved tubes, the material had a reputation for a sharp, stiff, uncomfortable ride. But manufacturers have long since learned to mold the tubes, first with butting, where the tubes taper in places where less material is needed for strength, then with hydroforming, where water is used to shape the tubes into unique structures. Both of these techniques are today used to not only tune ride quality, but also to hone aesthetics and trim weight.

A similar thing has happened with carbon fiber. To grasp how, it’s first useful to understand that these bikes are built by laying sheets of carbon into a metal mold, injecting the whole with resin, then baking it so it sets. When manufacturers first started using carbon, there was little consideration for different weights and directions of carbon fiber sheets or the types and amounts of epoxy resin used to cure them. But now it’s understood that by jigsawing different shapes of carbon sheets with careful attention to direction and choosing and using resins judiciously, builders can tweak the stiffness, flexion, and weight of a frame.

Both techniques yield far superior ride qualities to what was possible a decade or two ago.

“With aluminum, you're limited to the capabilities of tube extrusion, hydroforming, and forged parts to make a frame look and feel like you want. With carbon there are nearly infinite ways to create shapes and surfaces, so you have a lot more freedom as a frame designer,” says Lars Sternberg, Product Specialist at Transition Bikes.

The Smuggler, Transition’s 130mm/140mm trail bike, another of TMB’s most popular all-around Sedona models, illustrates just how far materials engineering has come. Other than the welds on the alloy bike versus some subtle creases on the down tube and shaping around the bottom bracket area on the carbon fiber model, the two frames are almost indistinguishable. Sternberg calls the difference in ride quality between the two, “subtle.”

Finally, the things you attach to the frame can make more difference in how a bike feels than the frame material. Carbon wheels and handlebars can add damping over alloy counterparts. Skinny, faster-rolling tires will feel harder-edged than fatter, softer-durometer models, and the ride will feel harsher or smoother on either depending on air pressure. And touch points including saddle, grips, and pedals can add performance and comfort.

In short, there are nuanced differences between how a carbon and alloy bike will ride and feel. But in terms of modern trail bikes, this shouldn’t be the decisive factor.

Weight

If there’s one characteristic where carbon and alloy definitively diverge, it’s weight. Aluminum isn’t just heavier than carbon by volume, it also takes more of the material to hit the same performance benchmarks.

“It’s not the ‘90s, where light aluminum race frames were only expected to last a few years,” says Nicol. “To pass rigorous testing standards, our aluminum bikes are going to be about 2.5 pounds heavier than carbon.” That might not sound like much, but it can stack up. Says Nicol, “Add the modern features people want in a mountain bike, including longer geometry, more travel, frame storage, flip chips, rubber chain slap and rock protection, and we’re talking about an overall frame weigh difference of like 7.5 pounds for carbon and 10 for alloy.”

Since alloy bikes are also significantly less expensive to produce than carbon (more on that below), manufacturers often spec them with more budget-conscious components to appeal to a broader range of riders. Lower-tier parts add still more weight, so it’s not uncommon for an alloy bike to weigh 5-10 pounds more than it’s carbon counterpart.

For perspective, a top-of-the-line, size large Ripmo with Industry Nine carbon wheels tips the scales at TK, while the least expensive Ripmo AF with SRAM GX is TK. If you are a frequent racer, that’s a big deal. And even if you don’t race, that much extra weight—let’s call it something in the neighborhood of 15-20 percent depending on models—will definitely change the ride experience. The weight difference would be much more noticeable than the minor differences in ride feel between carbon and alloy.

So weight is definitely an important consideration when choosing a frame. The only perhaps more decisive is price.

Cost

When considering builds and specs across a specific model, weight and cost are directly related: The less a bike costs, generally the heavier it is. The lighter the bike, the more money you’ll spend.

That partly comes down to the frame: Alloy bikes, which are made of tubing extruded by machines, are simply less costly to produce than carbon ones, which are largely built by human hands. (You can find examples of automated carbon bike production, but the price is generally even higher since the scale is so small.)

“Aluminum has cheaper raw materials and only requires about 10 man-hours of labor. In Asia, a carbon frame takes about 40 to 60 man-hours,” says Nicol. “Our US frame factory has got the labor time on carbon much closer to aluminum, but we’re paying a higher labor rate so the cost ends up being pretty close.”

So carbon becomes the “strong” and “light” option—but not cheap.

And because the alloy frames are already less expensive to build, manufacturers tend to build them out with less expensive parts in order to hit lower price points. While you can get that Ripmo AF for $2,999, a carbon Ripmo starts at $4,999 and the goes for an eyewatering $9,899.

To be clear, much of that extra cost isn’t about the frame. It’s paying for niceties including wireless electronic shifting, carbon cockpit and wheels, more powerful and reliable brakes, and as lightweight of bits and pieces as possible. In an exquisitely designed platform like the Ripmo—any modern full-suspension bike, really—these upgrades will make a bigger improvement in the ride quality than the differences between a carbon and alloy frame ever could.

Last Word

If you are like most consumers, the choice will largely come down to price: how much can you afford, and how much do you value riding? If you race or even ride every day, you may find more value in an expensive carbon frame with lightweight parts. For more recreational and occasional riders, a bit heavier but still awesome bike and more money in the pocket may be the better choice. These are personal decisions.

If you have the resources, there’s no arguing that the top-shelf, no-expenses-barred carbon bikes will provide an excellent ride. Having said that, once you’ve settled on an alloy frame or a carbon one, it starts to get into nuance and personal choice whether it’s worth an extra grand or two to upgrade from SRAM GX to Shimano SLX or from Shimano XT to SRAM XO AXS.

The good news is that no matter what you pick, frames—both alloy and carbon—offer a higher quality, more refined ride than ever before. “

We have a good ratio of Transition employees opting to ride both carbon and aluminum bikes,” says Sternberg. “There are differences in material, ride feel, weight, and price. And decision making can fall on a spectrum between budget-driven and purely emotional.”

If there’s one thing we pine for at Thunder Mountain Bikes, it might be the alloy frame bike with a high-end build kit. The extra pounds in the alloy frame would be offset by the lightweight components and, especially, carbon wheels, while the lower frame cost would counterbalance the expense of the top-shelf parts. You’d get a relatively light bike at a relatively low cost. And truth told, if you want to go that direction, TMB can always source a bare frame and help build it up to your exact specs.

On the other hand, bike brands have gotten so good about offering a wide range of builds—8 options between the two Ripmo frames, 5 for the Smuggler, and a whopping 10 for the Fuel EX—that it’s just as easy and generally more economical to pick something off the shelf. That can feel like a lot of decision making. If you need help wading through it all, stop by Thunder Mountain Bikes or give us a call at 928-282-1106. We’d love to help set you up.