So a few months ago I decided to jump on the carbon-frame bandwagon and I bought a Look KG386 frame. It’s the 486’s younger brother, touted as being a bit less stiff and generally more comfortable than the 486, which is a full-bore, drop-the-clutch race machine.
I’ve been spending a fair amount of time (250-350 miles per week on average) on this and my other bike, a 2003 Specialized S-Works. The two bikes are configured very similarly, but not precisely the same. Both have carbon seat posts, with the one on the Look being higher quality. Both have full carbon forks, again the Look’s is of higher quality. Same component setup and I routinely interchange wheels between the two bikes. I’ve done > 10 road races so far this year using the two bikes in about even distribution.
Here’s my completely non-scientific, biased, non-controlled study, anecdotal opinion of carbon vs. aluminum:
I’ve always believed the S-Works frame to be fairly stiff. It’s a compact frame with semi-oversized aluminum tubing. It feels great climbing and in crits, where stiffness is a good thing. I’ve also read that these properties (aluminum, oversized tubing, and compact frames) make for a harsh ride, but having limited simultaneous comparison to other bikes makes it hard to quantify precisely what harsh means.
The Look is a traditional frame (not compact) with some similar qualities to the S-Works - namely a semi-aero shaped seat tube and oversized down tube. Granted, the only scientific similarity is in appearance, but it’s worth noting as I’m sure it affects ride quality in both bikes.
To my surprise, the ride of the Look frame feels virtually identical to the S-Works. Big bumps feels the same, medium bumps feel the same, and small bumps feels the same. I ride many of the same roads over-and-over, and I know 'em all like the back of my hand. Granted, this is completely non-scientific, but then again, science would be of dubious value if it proved a difference that you simply can’t feel.
The Look seems to absorb high vibrations slightly better, but to be honest, I have to really try to notice this. It’s something that I could probably mimic on the S-Works by letting out about 5lbs of tire pressure. Also, it would be easy to explain some of this by noting the differences in Specialized carbon fork technology (circa 2003) vs. Look fork technology (2005), and the difference in seat posts (27.2 mm diameter FSA carbon on the Specialized, and 25 mm diameter USE on the Look). The difference in fork feel is quite noticeable, with the Look being far superior (similar handling with better vibration and road-noise absorption).
The Look frame feels less-stiff than the S-Works, which is not what I expected. Now, I’m talking about two different types of stiffness - there’s stiffness when you’re sprinting, and there’s stiffness when you’re just riding along. In the former, I think stiffness is a virtue, in the latter I think it’s an undesired quality. The marketing of carbon frames generally hinges on its ability to deliver both - stiffness and comfort (vertical compliance).
I’m a thin guy (155ish lbs.) and I can only put out about 900 watts in a sprint, so I’m not exactly crushing the pedals or anything. I’m primarily a climber, with much of my climbing being on mountain roads between 7% and 13% grade, which means I’m out of the saddle fairly often with brief spells of 400-500 watts. The carbon frame feels sluggish and more flexible in both situations (same cranks and bb on both bikes).
Without spending too much time hashing out the lesser points, my opinion of these two frames (and only these two frames - this isn’t a study of aluminum vs. carbon in general), is that the benefits of the carbon frame (reduced transfer of high-frequency vibration) is, for me, far outweighed by the detriment of reduced stiffness. For me, the primary selling point of carbon was that you got both a more comfortable ride and improved stiffness, which are seemingly opposing ideals.
Honestly, wheel and tire choice is, on both bikes, the biggest determiner of ride characteristics. Both bikes feel harsh on Mavic Cosmic Carbones. Both bikes feel pretty comfortable on Velomax Circuits. Both bikes feel pretty springy and lively on American Classic Sprint 350s, et cetera. Gatorskins deaden the bike’s feel, Conti Sprint/Attack liven it, and Vittoria plushes it.
There are a million ways to explain away my non-scientific findings, and I understand that. However, there aren’t many ways to explain away my experience. Ultimately, for me it comes down to one thing: Are the differences between the two frames materially significant enough to justify a considerable difference in price? Not for me. If both frames were the same price, having the benefit of prior experience, I’d choose the S-Works. Perhaps this is as much a result of the type of riding I do as it is my disappointment at the lack of discernible superiority of the carbon frame (I really wanted to be blown-away, which is why I went all-out with the Look).
I’m not considering the differences in longevity of the two bikes. Carbon will probably outlast aluminum, but that’s of negligible value when most of us only keep a bike for a few years, which is far less than the life-span of most well-made carbon and aluminum bikes.
It’s also very difficult to compare the individual frames’ quality levels - i.e. perhaps the S-Works is the best-built aluminum frame on the market and the Look frame is the worst-build carbon frame on the market. In the case of the S-Works, I suppose it’s within the realm of possibility. In the case of the Look, it’s highly unlikely (it’s a monobloc frame used only in their top-end models). Personally, I’d consider the two frames to be of similar material and construction quality in their own regard.
Anyway, take my experience for what its worth. The qualities you look for in a frame may be different from mine, in which case the differences I’m experiencing could be more or less important.
