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Around where I live the common wisdom is that on a road, gravel or similar bike, a carbon fork will cushion some of the vibration more than a metal fork.

On some web discussion forums I see that opinion reiterated. I don't have any personal experience of it yet.

If indeed it is the case, given that composites can be incredibly rigid, how is this damping implemented? Is this a property of the composite that it can be formed in such a way that rigidity is in certain directions only? Finally, does anyone have any pointers to evidence of this fork property? Is this urban legend or is there truth to it?

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    Carbon can be tuned in ways that metals can't really. But a steel fork feels quite different to an aluminium one anyway, so not all metals are the same – Chris H Jun 20 '18 at 7:54
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    Whilst I haven't particularly noticed the damping of my carbon-forked bike over my steel one, I can definitely attest that my carbon seatpost removes / damps way more "road-buzz" compared to the previous aluminium one that it replaced. – Diado Jun 20 '18 at 8:54
  • @Diado. Interesting. I wonder if this is to do with harmonics. – Sentinel Jun 20 '18 at 12:56
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    I too have read and heard a lot about how CF dampens road bumps, making for a more comfortable ride. This article and this one compare steel/aum/carbon from a scientific standpoint, but they do not quantify the vibration dampening of steel/aluminum/carbon. I'd be interested to see if anyone had any data on that characteristic of carbon fiber. – Sam Jun 20 '18 at 18:06
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Having only my experience as source, it isn't a myth. Carbon forks tend to "copy" the road better, translating into a more soft riding experience for your arms. It makes the behaviour of the bike a little more "nervous" though.

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From personal experience I tend to agree. However, I think it’s not really because the carbon acts as a suspension/cushion but be because a carbon fork is usually lighter. Fork and front wheel are essentially an “unsprung mass” (assuming that your slightly relaxed arms act as suspension). The heavier they are (compared to the rider) the more they’ll tend to bounce over rough ground.

I’d love to see somebody mount an accelerometer to their handlebars and measure acceleration (vibrations) for forks and front wheels with different weights and materials.

  • I wonder if the accelerometers in mobile phones are accurate enough to measure vibration. In fact I wonder if there is an app..... – Sentinel Jun 24 '18 at 13:03
  • Actually a heavier bike would be accelerated less by surface irregularities. – Argenti Apparatus Jun 28 '18 at 17:26
  • @ArgentiApparatus: Only if it’s heavy enough to deform the road instead of bouncing ;) – Michael Jul 1 '18 at 15:03
  • @Michael F=ma more mass less acceleration. Tire deforms more – Argenti Apparatus Jul 1 '18 at 16:16
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I've ridden both steel forks and carbon forks. Carbon fiber will damp vibrations much, much more than aluminum forks, which used to exist but are AFAIK very rare - they only existed as a lighter alternative to steel forks. When carbon came on the scene, they went away.

I've searched for evidence, but I can't quite seem to find much that specifically addresses vibration damping in steel vs carbon forks.

There is some discussion of steel vs carbon rigid forks on the Singletrack forum here, and more on Bikeforums, but neither thread appears to be conclusive. Ibis bikes have a good primer on materials properties for carbon, steel, titanium, and aluminum, and the carbon page gets at what @Chris H said - carbon can be tuned in a lot of ways. It can be made rigid in one direction but more compliant in another. That said, there are a wide range of steel tubes that vary in diameter and wall thickness that can also tune the ride.

I will say that I don't think that this conventional wisdom is necessarily true. Bikes are complex objects, and there are a lot of aspects apart from fork material that damp vibrations - e.g. your tire size and pressure, your stem, your bar tape, your gloves, the rest of the frame. I have a road and a CX bike with steel forks, and I love them, but I also raced a season on a carbon Giant TCR in about 2005, and it was a good ride. The frame and fork did damp vibrations considerably. You are probably better off test riding whatever bike it is you're interested in. Carbon fiber is much stronger than it maybe used to be, and it is unquestionably lighter than a steel fork, so I wouldn't hesitate to get a carbon fork if you like the overall bike.

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