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Aluminium or carbon frame? This is one of the biggest decisions you’ll make when considering your next bike and - as always with buying a bike - there’s a lot to think about. In this blog, we’ll talk about the main differences between the two and help you to come to a decision about which might be best for you.
The way Trek names its bikes tells you what its frame is made from and where it sits in the weight range. For road and gravel bikes, the hierarchy goes AL for aluminium, ALR for lighter aluminium and then SL for carbon and SLR for the lightest carbon. For mountain bikes, any product name with a number from 9 and below will be an aluminium frame, while 9.5 and above has a carbon frame.
The most talked-about topic in this debate is weight. Although there are some exceptions, carbon fibre generally weighs less than aluminium and certainly the lightest carbon frame will weigh less than the lightest aluminium.
How much less does a carbon frame weigh? As an example, the Trek Emonda SLR 9 AXS, top of the range for this lightweight climbing road bike, weighs 6.75kg while the mid-range SL 7 weighs 7.97kg and the entry level ALR 4 weighs 9.33kg. The 800 Series OCLV Emonda frame used in SLR models weighs an incredible 760g (frame only) while the 300 Series Aluminium frame used in ALR models weighs 1.91kg. All of these comparisons use a size 56 frame.
X-Caliber 9
Procaliber 9.8
For the Fuel EX trail bike, the 9.9 XX1 AXS weighs 14.11kg and the entry level Fuel EX 5 weighs 15.7kg. When it comes to cross country hardtails, the X-Caliber 9 tips the scales at 12.75kg whereas the carbon-framed Procaliber 9.8 comes in at 10.26kg. These comparisons use a medium frame.
The choice between carbon and aluminium often comes down to budget. Carbon is more expensive because the manufacturing process is more complex and labour-intensive, and the cost of a top carbon bike is usually into five figures, though the entry level carbon Domane and Emonda are both less than £2,500. The decision will usually come down to how important weight is to the riding you want to do.
If you compete in a discipline where there’s a lot of climbing such as road or cross country racing, you might want to invest in carbon because carrying more weight uphill obviously saps your energy faster. For downhill and enduro racing, where weight can be a good thing and a stronger frame is a must, carbon is less value for money.
If you compare carbon and aluminium bikes at the same price point, the latter will generally have better components because less of the cost has gone on the frame. If better componentry is more important to you than weight savings, this might prompt you to go for aluminium.
Carbon frames are widely considered to offer better ride quality than aluminium, providing a slight flex that makes them more comfortable. Carbon frames can be made to be stiff in one direction and compliant in another so the frame can be comfortable over bumps while simultaneously efficient when pedalling.
Aluminium is actually a fairly soft metal so these frames were initially made with thicker tubing, causing frames to be really stiff, which was great for racing but not for everyday riding. As technology has developed, the gap in ride quality between the two materials has reduced as bike manufacturers can now vary the shape and thickness of tubing so it can, for example, be thicker at the ends where the joints are and incredibly thin in the middle.
Comfort is, of course, a matter of personal preference and frame material is probably not the most important consideration here, when things like tyre choice, saddle, bike fit, suspension, handlebars and seatpost are a factor too.
To the uninitiated, a carbon frame might seem to be more fragile and delicate than its aluminium counterpart. However, that’s simply not true and, typically, it’s more complex than that.
Carbon fibre's strength to weight ratio is actually higher than steel but it can be cracked by the kinds of direct impacts sustained in a big crash. Aluminium is better at withstanding that kind of punishment. What’s surprising is that carbon can actually be easily repaired whereas that’s not the case with aluminium. Also, carbon fibre experiences almost no fatigue over time whereas an aluminium frame might feel slightly soft after many years of use, though that’s longer than most people will keep a bike for.
So it’s clear that a lot of concern around damaging carbon frames is related to the cost of replacing it rather than any particular flaw in the material. But with Trek’s lifetime frame warranty, which protects the original buyer against crashes, imperfections and so on, it needn’t be a worry. Look after your bike and Trek will look after you.
Fuel EXe 9.9 XX1 AXS
Fuel EXe 8 GX AXS
The emergence of carbon fibre in the late 90s and early 2000s made possible curves and shapes that were previously out of reach. However, aluminium manufacturing has certainly made a lot of headway since then and the hydroforming process means that bike makers can now create these in smooth aerodynamic shapes.
That leaves welds as one of the easiest ways of distinguishing between aluminium and carbon visually. Even higher-end aluminium bikes will have these tell-tale weld beads at the joints. You’re unlikely to notice them as a rider zooms past but on closer inspection they’re fairly easy to spot. See above the welds on the Matte Keswick Green alloy Fuel EXe compared to the smooth Baja Yellow carbon Fuel EXe.
Does it matter? Again, that’s up to each individual rider. Aesthetics are a personal choice and one cyclist’s must-have could be irrelevant to another.
As with pretty much all the considerations involved in choosing a bike, whether you go for a carbon or aluminium frame is down to your own preferences, circumstances and the type of riding you want to do.
Aluminium is probably best if your budget is lower to mid-range and you want low weight and good stiffness on a bike you’ll use for everyday riding, weekend blasts and less serious competition. If you have a more generous budget, weight savings are important and you want that extra edge in competition, then a carbon frame is for you.
Come and feel the difference between these two frame types at Big Bear Bikes in Southgate, Pickering. Our friendly, experienced team will talk you through the options and you can even go for a test ride.
