Bicycles and Aerodynamics

by Rainer Pivit

published in Radfahren 2/1990, pp. 40 - 44

Translated by Damon Rinard and John Allen from the original article in German at:

(Numbers in parentheses refer to the pertinent bibliography)

Other articles by Rainer Pivit published in "Radfahren" magazine:

Aerodynamics has become very important in bicycle racing. Aerodynamics had already placed its imprint on technology in track racing at the 1984 Olympics in Los Angeles, but aerodynamic improvements first showed a transformative effect on the road in the last stage of the 1989 Tour de France. Lemond clearly had better aerodynamics than Fignon. But can everyday bicyclists also benefit from better aerodynamics?

It has long been recognized that air resistance consumes almost the entire power output of the cyclist at higher speeds. Already around 1895, disc wheels were available to reduce air resistance. There were even front wheels then with four aerodynamically-shaped spokes (23). Wheels of this type, of composite materials rather than of sheet metal, now are the norm on extreme triathlon bicycles.

Restrictive Regulations

The idea that a different rider position would result in a more favorable frontal area, and so a lower air resistance, also dates to before the turn of the century. Mochet's recumbent bicycle set several new hour records. From 1913 on, records were set on aerodynamically faired racing bicycles (5, 6). The governing body of bicycle racing, Union Cycliste Internationale (UCI), did not recognize these records as regular, and through changes in regulations,tried to prevent possible technical advantages for individual racers: racing should be a contest between athletes, not technological improvements. The most important incentive for aerodynamic improvements therefore fell away, until later.

A professor who was tired of explaining to his students why water boils and why perpetual motion is a faulty concept can be thanked for the revival of the topic of aerodynamics in bicycling. Chester R. Kyle planned a bicycle project in 1973 to determine what might be improved. Measurements were taken to settle a bet as to whether tubular or wired-on tires are better. The results showed that the bicyclist's real physical enemy is air resistance.

These results led quickly to improvements in the conventional bicycle (coverings of thin sheeting for the frame and wheels), and an aerodynamic fairing for a conventional racing bicycle which reduced its air resistance by 80%.

In 1975, Kyle and Jack Lambie organized the first race between streamlined "human-powered vehicles" (HPVs). Four of the 14 participants went faster than any previous bicycle, except for those which had been drafting motorized vehicles. A year later, the International Human Powered Vehicle Association (IHPVA) was founded to organize races unencumbered by the restricted UCI rules, and to support technical progress in HPVs (16).

Kyle's Olympic Project

Starting in 1982, Kyle and others developed equipment for the US Olympic bicycle racing team. To be sure, there had already been aerodynamic components, for example the Czechoslovakian team's aerodynamic helmets, but now for the first time, the complete bicycle-and-rider system was aerodynamically optimized.

The UCI rules require a conventional riding position and prohibit any aerodynamic accessory. Aerodynamic design of necessary components is, however, not prohibited. This means, for example, that covering a spoked wheel with plastic sheeting is prohibited, as this has no load-bearing function -- it serves only an aerodynamic purpose. The covering is permitted, on the other hand, if the wheel has so few spokes that it is not sufficiently stable for use in racing, and the additional load-bearing function of sheeting (of composite material) is necessary. Later, rules were added which somewhat further restricted this policy: for example, the main frame of the bicycle must consist of three tubes, which may not be of any arbitrary width. Wheels must (still now) have at least 16 spokes, or a full disc.

The bicycles developed in the US Olympic project with Kyle, which became known as "Funny Bikes", were very successful at the Olympics. The reconfiguration was so thorough that only very few components, for example the tires, remained unchanged. For the 1988 Olympics in Seoul, however, other countries' teams had caught up, so that the US racers could no longer profit as strongly from the technical advantages of their Funny Bikes.

Triathletes Improve Handlebars and Wheels

Some of the ideas from the US Olympic program were commercialized, and so ordinary bicycle racers also can now benefit from better aerodynamics. The new ideas were taken up most intensively in the triathlon community. Equipment requirements were not as rigid as in conventional road racing, and some additional technical improvements also improved the chance of winning.

The most obvious improvement was with triathlon bars (Scott handlebars), which result in an aerodynamically more advantageous position, also less fatiguing in long races. Wheels of composite materials and 3 to 5 thick aerodynamically shaped spokes (Tri-spoke) came along more recently. Bicycles with such a front wheel are ridable in sidewinds, unlike bicycles with a front disc wheel.

To summarize, three levels of aerodynamic development can be identified: first, racing bicycles conforming to the restrictive UCI regulations, next triathlon bicycles with greater toleration of technical advantages, but with a conventional rider position and without aerodynamic fairings, and third, HPVs with no design restrictions.

Improvements Are Usually Targeted Toward Racing

For an everyday cyclist, the direction which technology is taking with HPVs is certainly the most interesting. Why should a cyclist riding is street traffic be subject to the rules of racing clubs, in addition to the traffic law? The everyday cyclist would like to get from point A to B as comfortably and quickly as possible, and so is very open to technical advantages. A contest of athletic performance of everyday cyclists in street traffic with regulations establishing a level technological playing field makes no sense at all. It is therefore very unfortunate that the industry (and also the media) are mostly interested in racing-related innovations..

If one does not consider the regulations which limit the application of technology, efficient designs are possible. The speed record for bicycles over a distance of 200 m with flying start is a good 105 km/h (May 1986 at 2400 m altitude). The world hour record is at present 73 km/h (September 1989). Both records are held by the "Gold Rush", built by Gardner Martin, with Fred Markham ("Fast Freddy") as rider. The Gold Rush has very good aerodynamics: an effective frontal area of 0.046 m2 is reported - a twelfth that of a conventional racing bicycle; also, the vehicle weighs only 14.5 kg (19). Certainly, vehicles such as the Gold Rush are not suitable for everyday use, but other vehicles quite suited to everyday use have lower drag than racing machines which meet the regulations of the sport federations.

Aero Shopping List for an Ordinary Racing Cyclist

How can an ordinary racing cyclist improve aerodynamics? The aerodynamic drag of a conventional racing cycle without the rider is about a third that of the bicycle and rider together (12). Thus it is already clear that it doesn't make sense to ride an aerodynamically optimized racing bicycle wearing aerodynamically unfavorable clothes (e.g., normal everyday clothing).

The aero shopping list assembled by Kyle (13), shows possibilities for reducing aerodynamic drag. The costs are rough estimates; the proportional reduction of aero drag are relative to a conventional racing cycle and a rider with the usual racing clothing (cycling shorts, jersey, cotton socks, gloves with knit backs) and without a helmet; the time gained is with respect to a 40 km time trial at approximately 37 km/h - elapsed time 1 h 5 min. At higher speeds, the time gained is reduced because of the shorter riding time.

Aero Shopping List



Time saved
over 40 km

Costs per % of
Aerodynamic Advantage






Remove water bottle and cage





Tape over shoe laces





Pump under top tube instead of in front of seat tube





Shave the legs





Remove the small chainring





Fill the front tire gap at the rim





Benotto Aero bottle with cage





Smooth nylon socks





Pearl Izumi Lycra shoe covers





Aero helmet. ANSI approved Bell Stratos.





Aero front wheel: Araya aero rim,
28 Hoshi bladed spokes,
Dura Ace hub,
Avocet 190 g tire





One-piece skinsuit, short sleeves and legs





Aero rear wheel: as above, but 32 spokes





Aero brakes and levers, Dia Compe AGC 300





Gloves with Lycra backs





Disk wheel in front





Clipless pedals





Disk wheel in back





Cinelli aero bar





Edco Competition aero crankset





Shimano Sante aero derailleur





A moderately priced upgrade in the aerodynamics of a bike and rider with two aero spoke wheels, aero brakes, aero bottle, ANSI-approved aero helmet, one-piece skinsuit, aero shoe covers, gloves with Lycra backs, silicone filling the gap between tires and rims, shaved legs and pump under the top tube costs about 1100 DM. In a 40-km time trial, the rider so equipped is 3 min 6 seconds faster than a conventionally equipped colleague producing the same power, because his aero drag is reduced by bout 21%. The speed of the aero cyclist is 4.8% higher than that of his colleague. (The most recent Tour de France was won with a lead of only 0.0025%).

A cyclist who wants to invest more cash (900 DM) in the chance of victory and installs an aero crankset, an aerodynamic derailleur, aero bars and clipless pedals can undercut his conventional colleague's aero drag value by around 23% and thus gain a lead of 3 min 30 seconds with the same power output.

Clothing and Helmet

In (15), Kyle points out that compared to the usual combination (long-sleeved wool road jersey, Lycra racing shorts) aero drag can be reduced by 7.5% with a one-piece long-sleeved Lycra skinsuit; the same suit with a rubberized coating gives an advantage of 8.4%. Aero helmets as they are used for racing, which do not however meet the ANSI safety requirements, reduce the aero drag by approximately 2% compared to a bald head or a rubber cap over the hair. The Bell Stratos, an ANSI approved helmet, increases the aero drag by approximately 1.3 % over a bald head. Short hair worsens it around 4.6%, long hair around 8.6%. The leather hairnet helmets which racers still often use - although completely insufficient according to ANSI - increase the aero drag by 6.3%. The common ANSI-approved Bell V1 Pro helmet increases drag by around 9.8% compared to a bald head. So far, no measurements have been published concerning the effect of beards.

Disk Wheels are the Most Advantageous

New wheels offer the largest aerodynamic advantage for the bicycle itself. Disk wheels are the most advantageous. Problematic, however, are the high price and the serious steering difficulties in a crosswind with a front disk wheel. However, an aero steel-spoked wheel's air resistance clearly can be lowered. The wheel should be spoked radially with as few spokes as possible.

Bladed spokes have 85% of the air resistance of normal round spokes (13). Narrow 18 mm tires likewise reduce air resistance. The rear wheel runs in a region where the air flow is already influenced by other components. Thus the effect of an aerodynamically better rear wheel is not as pronounced as with the front wheel. A disk in the rear wheel is not justifiable with a limited budget; a rear wheel with aero rim and bladed spokes is justifiable.

A single wheel, turning as it does on the bicycle, has an effective frontal area cwA of 0.05 m2 according to measurements by LeHanneur (10). Roval racing wheels, however, (developed in 1977: deep rim, bladed spokes with hidden nipples, 24 spokes for each wheel) have a cwA of approximately 0.03 m2.

From measurements by Kyle (17), a good, spinning disk wheel (AeroSport flat disk 26"; Kyle works with the AeroSport firm) has an aero drag 35% of an appropriate conventional 27" wheel (normal rim, 36 round spokes). However, Kyle determined that another disk had a value of 54% that of the conventional wheel. There are thus significant differences between disks. But also, a 24" wheel with aero rim and 18 aero spokes had only 40% of the aero drag of the conventional wheel.

Comparative measurements between normal wheels, the combination with disk in the back and spoke wheel in front, as well as disk both in front and in back were executed by the editors of "Bike Tech" on a time trial bike (with a measuring procedure whose accuracy is not yet known) (22). Replacing a conventional rear wheel with a Campagnolo Ghibili disk resulted in a reduction of aero drag by around 2.8%; replacing the 26" front wheel with an identical disk reduced the aero drag by 7.1% compared to the conventional configuration.

Aerodynamic Frames

Finally we come to the frame. Investigations by Kyle (12) show that aero drag for a track bike and rider is reduced by around 5% with an aero frame like the ones developed for the 1984 Olympics, in comparison with a conventional track bike. It is particularly interesting that with a light sidewind around 10° the track bike with aero frame cuts aero drag around 12%, and with a 20° sidewind the bike with an aero frame has around 11% better drag than the conventional track bike.

In (17) Kyle presents investigations of commercially-available frames. Compared with a Gios steel road frame, an aluminum Cannondale frame with rider achieved a reduction in aero drag of around 1.6%; a Trek aluminum frame was appropriately even with the Gios, a Kestrel 4000 composite frame brought a reduction of 4.7% and a very sophisticated aero bike by Gleb - this time with 32 aero spokes instead of the 36 round spokes with the other bicycles - obtained an advantage of 7%. The track machines for the 4000 m individual pursuit riders of the US team in the 1984 Olympics achieved an aero drag reduction of about 16% compared to the Gios road bike.

Tour de France in the Wind Tunnel

In wind tunnel studies, Steve Hed (18) tried a simulation of Fignon and LeMond in the last stage of the '89 Tour de France. LeMond rode with a plunging handlebar (bull horn bars) with Scott clip on aero bar, achieving the same very favorable aerodynamic position as with a normal Scott handlebar. Also, he wore a Giro aero helmet.

Fignon, however, rode without a helmet - with a pony tail - and with only the plunging handlebar. Hed's measurements show a 22% advantage in aero drag for LeMond compared to Fignon. If Fignon had ridden with his team's aero helmet, then the difference would still have amounted to 17%. The difference between Fignon and LeMond was not really quite so large, however, since Fignon used a front disk wheel, and LeMond used one with 32 spokes. Hed did not use the different wheels in the wind tunnel. In any case, measurements show clear advantages for the Scott aero bar, particularly with a position where the elbows are brought close together.

Now, after all the racing cyclist stuff, where is the bicycle as a means of transport? Aerodynamics is nowadays primarily a topic for the racing cyclist. Here each aerodynamic advantage - no matter how small - contributes to the victory, so long as the additional weight is not counted as excessive. However, additional criteria apply to the everyday rider. For example, the racer pays attention to certain clothing conventions. Racing shorts are fashionable, but the racer's one-piece Lycra skinsuit is (still?) not.

The Everyday Rider Could Make Use of HPV Developments

Fenders increase aero drag by approximately 5% (11), but nevertheless I would not like to leave them off. Am I to ride on vacation with a sag wagon because the panniers and water bottle would increase the aero drag by approximately 12% or 2%? No, no, that won't do. The aero developments in racing do almost nothing for the everyday rider.

Nevertheless, perhaps wheels made from plastic with a few aerodynamic spokes can, over time, become accepted for normal bicycle use. Apart from the better aerodynamics - comparable with disk wheels - this would have the positive side effect that the problem of broken (steel) spokes with wheels that are almost always badly built would go away. The technologically lowest-ranking factories which build wheels clearly do not have production quality under control, and would be replaced by factories using high-tech plastic technology.

Compared with extensive research on racing bicycles, there are relatively few measurements of ordinary bicycles. In (8) the influence of (weather-related) clothing was determined. A rider with summer sport clothing (running shorts and sleeveless T-shirt - fresh from the gym) on a Dutch style upright bike served as the reference .

In contrast to this, aero drag increased by 19% for a long-sleeved shirt and long pants. Adding a zipped-up wind-shell jacket increased drag to 24% more than with sport clothing. For winter, a German Federal Armed Forces Parka and gloves resulted in 40% higher aero drag. With a rain cape and rain trousers, the cyclist became a wind collector: 69% worse aero drag than the summer sport clothes. Hopefully it does not rain very often!

Nevertheless, some developments with HPVs suggest that aerodynamics and rain protection can be compatible. In the long term, it can be hoped that the everyday rider will benefit from HPV development efforts; however, racing cycle development is to a large extent irrelevant for the everyday rider.

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© by Rainer Pivit, 03/2000

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