Opinion: Carbon and Aluminum Wheels
A Brief History of StiffnessThis story was worth writing for that sub-heading alone, right? Before we dive much further in here we need to cast a glance back across mountain bike history. What many of you may not realise is that compared to a few short years ago, we are now in a golden age of mountain bike technology. Anyone who rode in the '90s will tell you that the idea that a solid 95%+ of products on the market being structurally up to the task is huge progress. My first riser bar was a Club Roost Go Fast bar (maybe it was called something else, all I remember is that it had "Go Fast" etched into it). The other thing I remember is that it needed a brace across the middle to keep the two sides properly joined together. It is a mark of progress that many of our younger readers probably can't even imagine riding with a wobbly handlebar, but back then we accepted it and told ourselves it looked more moto like that... The same goes for the rest of the bike; frames and forks flexed, wheels bent, seatposts snapped. I don't think you could pay the modern World Cup racers to take to the slopes with the original 32mm-stanchioned Boxxer. You don't tend to see frames smeared black around the stays where the wheel and frame made contact under load. It was a big engineering challenge, one the industry rose to meet admirably. What this meant is that for much of mountain bike history, stiffer meant better. It was a good mantra. It worked. The problem is that today things are so good that it is no longer true. Unless you are buying inappropriate kit for your riding, you rarely have to consider whether your components will be structurally sound. It is a given that it will be stiff enough and that mantra is now out of date. The problem is that this next step in bicycle evolution isn't as clean cut. "Appropriately stiff" is a much shittier marketing line than "better." It is much harder to talk to consumers about compliance and feel, especially when you have spent the last twenty years telling them that stiffer = better. But I believe that is where we are today and those are the conversations about bikes we need to start having.
My Personal Stiffness
Don't get me wrong, I love carbon wheels. I rode shitty bikes for enough years to love the warm glow of satisfaction in having a bike that is almost all carbon and ridiculously light. Even as a bitter industry cynic, I never get tired of having great bicycles to ride, it is a privilege that I could not afford if I did anything else for a living. I love the menacing deep sections, the zip of acceleration that you only get with a couple of thousand dollars-worth of wheels. So it was only natural that when it came to build my bikes I sought out carbon wheels. For a few years I ran the Ibis 741 then 941 wheels on my bikes and the wide, fat profile and the low weight felt great.
The problem started when I changed bikes. I had been riding an Orbea Occam TR and it felt good. I didn't spend too much time thinking about it, the bike just worked and I had fun. When I replaced the Orbea with my current Scott Spark I started noticing something (I wrote quite a bit about how I set my Spark up last year). My new Spark was a noticeably stiffer frame, much more direct and pointy than the Orbea, but I was struggling for traction. On off-cambers and hardpack terrain the bike was skittish and I found it hard to hold a line. This lead me to start to think about what I could do to find more traction, I didn't want to play too much with fork setup or tire pressures and casings as I had found a setup that worked for me; I really liked the way the frame felt and the shape of it, which left me looking at the wheels.
TestingTo make the test useful I needed the closest I could find to direct equivalents - wheels where the main difference was only in the material used. This lead me to DT Swiss and their XMC1200 and XM1501 wheels. Both are designed by the same people with the same style of riding in mind, and they share the same hubs, spoke count and inner width (30mm). The XMCs do have slightly fancier spokes, but other than that they are as close to direct equivalents as exists in the market today. One thing I did realise when putting both pairs under close scrutiny was that the weight difference was much smaller than I expected - around 100g per wheel, some of which can be attributed to the lighter Aerolite spokes on the carbon wheels. I will say that on the trail the weight difference did not make a big difference for me.With both sets of wheels mounted up with my preferred combo of Schwalbe Magic Mary on the front and Rock Razor on the rear, I headed up to Viola St Gree - a little gem of a bike park in Piedmont that boasts a pair of incredible blue trails that would be a lot of fun to session on my Spark. Before riding I checked the tire pressures to make sure they were at my preferred 23/28psi setup. I then did a couple of laps on each set then switched wheels and carried this pattern over ten laps, using the afternoon laps as my timed tests. It came down to the final two hot laps (on my final lap we stopped to take photos) - the first on carbon, then a final hot lap on the aluminum. Looking back, I can see that my heart rate ran higher on the second run, but I tried to be as consistent as I could in putting down the pedal strokes and I'd put that difference down to getting caught up in a good lap.On the carbon rims I felt faster where the going was easier, I cannot deny that - there is nothing like the feel of railing a smooth berm on a good carbon rim, there is an incredibly positive feeling of drive that the aluminum could not match. Yet as I got further into the 7 minute-plus run, I was starting to feel a little beaten up, there was quite a lot of chatter being transmitted back to me and when it came to dusty, hardpack off-cambers I was struggling to get the bike to hook up.
The big difference with the aluminum rim was in the smoothness, there was an immediately noticeable difference in the ride, everything felt a little more fluid. While the feeling in the berms was good, it just wasn't that same driving sensation. On the off-camber sections where I was struggling for grip on the carbon rims I was finding it easier to hold my lines, and there was a very definite improvement in overall grip. On the long, five minute second main sector of Ottovolante (OV Sector 2) I was flying on my final run - that reduced chatter and additional grip makes a big difference when you are a few minutes into a trail, and I felt like I could ride harder for longer. The one caveat here is that on my timing I dropped four seconds to the carbon rim on that sector, however that can be explained away because a rider pulled up in front of me in the middle of the trail metres from the finish. In that instant I may not have been the courteous trail user I like to pride myself on being as I knew I was on for a good time. I felt even more stupid afterwards when the gentleman came over to me in the carpark to ask if I was ok... Still, on the timing sheet I only dropped 4 seconds, despite losing more than ten seconds to that incident. On the Ottovolante pt1 segment, I came out 19 seconds up compared to my time on the carbon rims - 4:49 vs 5:08 - even with that stop.
ConclusionsIf you're waiting for me to use the word "better" or tell you which one to buy, I'm going to disappoint you here. For me, for where and how I ride, this test has convinced me that I should stick to aluminum rims on this bike. With a stiff frame like my Spark, the reduced fatigue and improved traction of the more compliant rims work - it has eliminated that skittish feeling that started me down this road and put into sharp focus the difference in trail feedback between the two wheelsets. The problem with me reaching this conclusion is that I do not believe it can be generalised - my Orbea was great with carbon rims, maybe your frame will be too. I have a Specialized Stumpjumper Evo in aluminum coming and this has convinced me to go through a similar process for that bike as I'm curious to know if carbon wheels will complement the (in theory) more compliant frame.This test has lead me to believe that we should be looking at our bikes as systems, not collections of components, but that poses a huge challenge to both consumers and the industry. Unless you are happy to trust that bike companies know what they are doing in terms of overall system feel with their OE specs, how do you go about putting together your bike as a system? And how many of us don't love customising our bikes to make them our own? As a writer for Pinkbike I can phone DT and ask to borrow €3,000 of wheels to test a theory, but how many consumers are in a position to do that? At the moment there is no way to work out what frames and components work in what combinations to give the ideal level of compliance for a given rider, and I don't know how the industry would even start to address that. The other thing I am now certain of is that running down the road of "stiffer is better" is a dead end and the sooner that stops being an oft-repeated line, the better off we will all be.