[CR]Aero fenders, Singer geometry, crosswinds

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Date: Thu, 19 Jun 2003 07:25:03 -0700
To: classicrendezvous@bikelist.org
From: "Jan Heine" <heine@mindspring.com>
Subject: [CR]Aero fenders, Singer geometry, crosswinds

AERO FENDERS:

I am amazed by statements that claim aerodynamics don't matter for cehicles that go slower than 120 mph (rough paraphrase here). Does that mean that Eddy Merckx hour record was awfully slow, and that Obree, Rominger, Boardman et al. just were plain stronger? And that Boardman's current record, on a "classic" bike, shows that he is/was getting old (he barely beat Eddy's)?

Of course, not all fenders can claim to provide an aerodynamic advantage, just like they don't even all keep you dry. A fender that ends right on top of the front wheel (at 90 degrees), sticks up 3" and is angled upward probably channels air onto the tire, rather than away.

However, looking at the best photo of a relatively recent racing motorbike that I could find (thanks Raoul for the info on racing motorbikes that introduced at least some data into the discussion), http://www.allenmuseum.com/tz250g.htm the fenders on French bikes don't look that different (in front of the tire). What appears to matter is how far the fender extends forward from the fork crown, and how closely it hugs the tire. Here are some measurements - the distance the fenders extend forward from the fork crown:

- 1948 Herse tandem 650B with Lefol hammered: 29 cm - mid-1950s Singer 700C with smooth fenders: 30 cm - Esge: 19-21 cm, depending on whether clip is mounted in front or behind fork crown - Jan's Rivendell: 37.5 cm (rear fender cut down to use on front)

On the Rivendell, the fender extends forward roughly twice as far as Esges do. (However, the instability in cross-winds, apparent even without fenders, probably is exacerbated by this). The Rivendell's fenders also are only 2 cm above the tire, and the gap on each side is no more than 8 mm. And the fenders have a much more rounded profile than Esges, so they come further down the sides (photo of the bike still at http://www.mindspring.com/~heine/bikesite/bikesite/rivrando.html)

Obviously, any potential benefit is too small to notice among the many other factors that affect bicycle speed, and we don't have measurements. It may be similar to the difference in drag between a 28-spoke and a 40-spoke wheel - not noticeable (at least by myself, let's not start another thread!), but quite measurable. However, when trying to set a best time over a long-distance course (average speed about 18 mph), I want every potential advantage possible, because a gain of 5 minutes over 275 miles can make all the difference. Maybe it is only psychological, but one should not underestimate the placebo effect!

Of course, on the French bikes, the fenders extend forward not for aero advantage, but to keep rider and handlebar bag clear of spray exiting the front of the fender.

SINGER GEOMETRY

The geometry for one Alex Singer randonneur bike (700C, 1962) can be found at the Vintage Bicycle Quarterly web site at http://www.mindspring.com/~heine/bikesite/bikesite/singer.html However, note that it is difficult accurately to measure things like fork offset...

Lastly, Singers being expensive... Considering the amount of time that is spent on building one, I think any U.S. frame builder would charge as much or more for a bike with hand-made lugs (hand-filed, fillet-brazed to smoothen the radius), custom fillet-brazed stem and racks, integrated fenders and lights, and NOS components. For a while, they were a bargain, but over the last year, the Dollar has lost 30% of its value... (Of course, while Singers may be value for money, they still cost a lot.)

Jan Heine, Seattle, who didn't think that inserting the two words "aerodynamic advantage" into a general overview of fenders would spiral out of control. I inserted the words because it bothers me that most people think one should remove fenders if one wants to go fast...