The frame is the heart and soul of the bicycle. It binds all the components together into one cohesive machine. It is the identity of any particular bike. Without it, a bike is nothing. So it’s no surprise that choosing the right bike often comes down to choosing the correct frame, and when it comes to frames, material matters.
Most bike frames will be made of either steel, titanium, aluminum, or carbon fiber. Steel and titanium are the most popular options for custom and handmade bike building. The vast majority of modern bikes, however, will be made from aluminum or carbon fiber.
How do you choose between the two? Let's compare the key differences
Comfort is completely objective and it's largely rooted in your perception. The conventional wisdom in cycling has been that aluminum is stiff and harsh, while carbon is compliant and smooth. Now, however, this thinking is a bit outdated. It was true 20 years ago when aluminum frames were unrefined. Aluminum is actually a fairly soft metal, so in the early days, builders used thick, oversized tubing for strength and durability. This made aluminum frames super-stiff, which was fine for racers but too harsh for everyday riders.
Ride quality has long been a claimed benefit of carbon frames. Carbon can be engineered to be stiff in certain directions and compliant in other directions. This means a carbon frame can be comfortable over bumps and rough roads while simultaneously being stiff enough in key areas for efficient pedaling. You’ll often hear this sort of magical ride quality being described by marketers as being “laterally stiff and vertically compliant.” Carbon intrinsically tends to dampen vibration better than aluminum, simply because of its material properties.
Over the last couple of decades, improved technology has narrowed the comfort gap between aluminum and carbon. The process of hydroforming aluminum now allows manufacturers to vary the shape of aluminum tubing throughout its length to achieve laterally stiff and vertically compliant ride characteristics. It can be formed thinner — sometimes as thin as a soda can — in areas where compliance is desired and thicker where stiffness and strength are necessary. All this means that a modern aluminum frame isn’t significantly less comfortable on regular roads than its carbon counterparts.
With most modern bikes, objectively quantifying the difference in comfort between two similar bikes is incredibly hard. Bike design has a huge influence over comfort. Obviously, a road race bike is going to feel less comfortable than a touring bike, regardless of frame material.
The two things that really influence how comfortable your bike feels are your tires and touchpoints. If your bike feels harsh, wider tires with more supple casings and lower air pressure will likely make the greatest perceptible difference. Things like more compliant handlebars, seatposts, and thicker bar tape can make noticeable improvements too.
The bottom line: Carbon has a slight edge, but if comfort is your biggest concern, frame material is often secondary to other more important factors. Is the bike intended for road racing or endurance riding? Look at things like tire clearance, fit, and geometry. Ultimately, no matter the frame material, comfort is something that can always be fine-tuned or improved.
Weight is a primary concern for many riders. Even if you’re not a “weight weenie,” a lighter bike can improve the riding experience. It’s possible to build very light and capable bikes out of either aluminum or carbon. Carbon, however, rules supreme in this area. A carbon frame will almost always be lighter than an aluminum equivalent. When it comes to the strength-to-weight ratio, few materials can come close to carbon fiber.
Not all carbon, however, is created equal. Carbon comes in various grades. Lower-grade (or modulus) carbon has more fillers, which reduces the cost but adds weight. It is entirely possible for a lower-modulus carbon frame to weigh more than a high-end aluminum frame. In this case, you get what you pay for. For the lightest frames in production, though, carbon is the best option.
Using high-modulus carbon and clever engineering, designers are able to produce carbon bikes that are very strong, while being ludicrously light. Many major manufacturers now produce carbon road bikes that weigh less than 15 lbs complete, and cross-country mountain bikes weighing in around 20 lbs.
It’s worth noting that the frame only contributes to a portion of the bike's total weight. Components are the other half of the equation. A carbon frame with low-end components can end up weighing the same or more than a nice aluminum frame with high-end components. Wheels, in particular, will make a huge difference in bike weight and how heavy it actually feels when riding.
The bottom line: With the right components, aluminum frames can still be competitively light, but if you’re looking for the ultimate in lightweight performance, carbon is unbeatable. Lightness isn’t cheap, however, and it will likely only matter most to those who compete at a high level or simply want the best.
Responsiveness and stiffness
One of the impressive things about modern bikes is how they are able to be stiff and responsive without feeling punishingly harsh. This is the lateral component of “laterally stiff and vertically compliant.” When you push hard on the pedals or dive into a corner, a good frame needs stiffness to resist the torsional forces that rob you of power or derail your bike's handling.
Does one material do this better than another? Technically, carbon would come out on top. With aluminum frames, manufacturers can make a competitive bike using different tube shapes and varying thicknesses to control the ride characteristics. But as a material, Carbon fiber simply has far greater leeway for engineers to tune ride quality. By simply changing the carbon layup or direction that carbon fibers are oriented, it can be made stiff in one specific direction, and in one specific area.
The differences might be marginal to most riders, however. We all become accustomed to how our bikes ride, and that’s fine. If you had the same model bike in carbon and aluminum, you’d likely only be able to tell the difference if you were immediately switching back and forth between them.
The bottom line: Both carbon and aluminum frames can be made to be responsive and stiff. The responsiveness and stiffness of carbon frames can be engineered and tuned to a higher level and it can be finely controlled, giving carbon a slight edge over aluminum. Most average riders, however, will be just as fast on either.
Many riders are afraid of damaging an expensive carbon frame. Carbon fiber's strength to weight ratio is higher than steel. This is why it enjoys widespread use in the aerospace industry and motorsport. Carbon has infinite fatigue life, but it is also susceptible to damage from direct impact, as you'd experience in a big crash.
Fortunately, carbon can be easily repaired, and when done correctly, the repaired frame is as good as new. That's something that can't be said for aluminum.
That's why every Certified Pre-Owned carbon fiber bike sold by The Pro's Closet comes with a 1-year Carbon Frame warranty. If it breaks, we'll fix it, and you can keep on riding.
While aluminum frames cannot typically be repaired, they are less expensive to replace. Alumimum can also withstand some crashes and impacts and still be okay to ride. However, make sure you have your local bike shop check out your frame, if you're concerned it might be damaged. Dents in key areas can compromise an aluminum frame. Cracks can appear in welds that can eventually lead to frame failure.
While carbon fiber has an infinite fatigue life, aluminum frames won't last forever. Sometimes riders will talk about how they can notice how an old aluminum frame feels "softer" after years of riding.
No matter your frame material, it's important to regularly inspect it to ensure it is safe. The simplest way to tell if carbon is cracked is to run a clean rag along the tubes to see if it snags on loose fibers. You can also tap on an area that's been impacted and listen to the sound — a dull "thwack" is a bad sign, but a clean, crisp "tick" might mean you're okay. Again, check with your friendly, local pro mechanic before assuming your bike is safe to ride.
Aluminum dents can vary from shallow cosmetic blemishes to deep dents. Ultimately, it’s always best to get your bike inspected by a trusted professional.
The bottom line: Modern frames, in general, are fairly durable. Any frame that’s properly cared for can last a long time. Bad luck and crashes can happen to anyone and in these cases, aluminum might be more durable, but it's certainly cheaper to replace. Carbon might get damaged by impacts, but it can be repaired.
There’s no real contest here. Carbon is more expensive. There is more engineering required, the manufacturing process is more labor-intensive, and every frame requires a dedicated mold that further increases the cost. It's possible for aluminum frames to be built by machine, but carbon fiber layup is still done by hand.
When considering bikes at an equal price point, an aluminum bike will generally have a nicer component spec than a carbon bike. The components factor greatly into how well a bike performs. It is a balancing act between paying for frame quality and component quality. Remember, components are always easier to upgrade than frames.
The bottom line: Aluminum is cheaper. Whether or not that makes it better or worse can be a matter of taste. Good bikes are made at every price point. The lower cost of aluminum frames may free up your budget for higher-end components.
Carbon fiber opened up new possibilities in bicycle design. The smooth curves and swooping shapes of today’s bikes were unimaginable in the era of steel and titanium.
Aluminum bike manufacturing has also gotten good enough to produce bikes that look a lot like their carbon counterparts. Hydroforming allows manufacturers to form aluminum frames into smooth aerodynamic shapes. Seamless welds can add to that smooth appearance, making some new aluminum frames almost indistinguishable from carbon at a distance.
For some, welds can also be a mark of beauty. Perfect, clean, and even welds represent excellent craftsmanship. They can give a bike a utilitarian, workhorse sort of look. For some mountain bikers, thick, beefy welds can make a bike feel tough and ready for gnarly riding.
Ultimately, a good looking bike could be made out of anything if it’s done right. It's up to the rider, and if you're happy, that's all that matters.
The bottom line: Beauty is in the eye of the beholder. Ride what you like and be happy!
Based on this info, ask yourself questions when deciding on a new bike. What's your budget? Are you a competitive rider or are you more casual? How much does weight matter? Are you planning to crash a lot? Some riders simply don’t need carbon. Some can’t stand the thought of riding aluminum.
Remember, though, that the most important part of a bike — even more so than the frame — is the rider. Pick the frame that you think can make you the happiest. That’s the best way to enjoy the ride.