Re: [CR]Fenders and cross-winds

Example: Production Builders:Tonard
Date: Wed, 18 Jun 2003 17:42:38 -0400
From: "Mara & Steven Maasland" <>
Subject: Re: [CR]Fenders and cross-winds

Jan wrote:
> As far as fenders slowing me down - I doubt it. I think any effect
> is
> too small to notice. But my times on a given course with racing
> bikes
> and with randonneur bikes don't seem to vary much. Nor are people
> on
> state-of-the-art racing bikes able to drop the randonneur bikes on
> longer rides.

The most basic aerodynamic studies will clearly demonstrate that the wider frontal aspect of a traditional front or rear fender will have a negative effect on Cx (drag coefficient related to resistance to forward advancement.) Frontal area of a bike is however but a minor component of the Cx of a bike with cyclist aboard. The biggest influences on Cx are the frontal area of the rider and the turbulence created by both the bike and rider. There is nothing about fenders that will bring about any diminishments in the air turbulence whatsoever. Most definitely not those created by the worst culprits on the bike, namely the wheel and rider. The increase in Cx will indeed be minimal, but your original claim was that fenders improved aerodynamics, hence a reduction in Cx. This is obviously not true. All the discussion about your personal ride times and comparing randonneur bikes to state-of-the- art racing bikes is purely a canard because you are not factoring in all of the other variables that exist in the equation.
> However, as I said, the evidence is based on hearsay. Anybody got
> access to a wind tunnel? I can provide a bike with what I think
> may
> be aerodynamic fenders (photo at
> Then we could also determine whether the handlebar bag also
> reduces
> the wind resistance, acting as a fairing (illegal for UCI races!).

The handlebar bag can indeed be fashioned to reduce air turbulence, as well as reduce frontal area incidence in the Cx. The same could also possibly hold true for panniers.
> As far as the increase in frontal area that Grant Mc Lean
> mentioned -
> that is negligible for the front, if the fender fits well, and
> none
> for the rear. (The seat tube is fatter than the fender.) And a
> more
> aerodynamic shape often has a bit more frontal area (like a
> teardrop
> that beats a smaller cube in aerodynamics.)

You forget that the Cx coefficient is a fluid and not a simple two- dimensional measurement as your comment would contend. The seat tube can indeed be wider than a fender (however my experience is that this is almost never the case), but the seat tube does not create a void in which an advancing narrower part can then fit. Wider frontal area is always negative. The space occupied by the seat tube will almost immediately be filled with the creation of turbulence. The shape solely affects the amount of turbulence. The Cx of a small object will always be inferior to that of a larger object with the identical shape. The sole way for a befendered bike to be more aerodynamic than a non- befendered bike is to use the fenders to reduce the turbulence. To date, to the best of my knowledge, this has never been achieved.
> P.S.: Isn't this fender topic slightly OT, and more suited to some
> bicycle tech or randonneuring newsgroup.

Yes, perhaps it is. Why then did you bring it up?

Steven Maasland Moorestown, (where people sue the school board to become sole valedictorian)NJ