It's the bike
It's the Bike!

By Warren Beauchamp
3/14/03

As Lance Armstrong noted on his book, in the world of UCI and USCF legal diamond frame bikes, it's not about the bikes, it's about the riders. While diamond frame bike manufacturers would all like you to believe that their bike give the rider an edge over their competitors model, in reality it is the riders superbly trained physique and innate genetic abilities that are almost solely responsible for the bike's speeds, and the races won.

In the world of Human Powered Vehicles, where the shape of the vehicle is not nearly so rigid, a riders physical condition certainly plays a large role in his ultimate speed as well as his race winning ability, but the bike itself can also play a large role. It is a well known fact that the aerodynamic advantage gained by riding a recumbent in the low racer position, or in a streamliner at the extreme end, can provide a mediocre rider with enough of an edge to beat upright riders of superior physical abilities. 

The speed gain that a recumbent bike can provide is a function of the seat recline, bottom bracket height, seat height, and the total vehicle weight. Most bikes built in the USA are designed with comfort in mind and have relatively upright seats, bottom brackets lower than the seat, high seats, and weights above 30 pounds. While these bikes can be fast with a strong rider, the main advantage they have over the standard road bike is in comfort. A few USA manufacturers and many European manufacturers make bikes with seats that recline beyond 35 degrees, and with bottom brackets above the height of the seat. These bikes are in almost every case faster than road bikes with comparable athletes. Tests of recumbent bikes by road bike riders almost never show a speed gain while riding the recumbent bikes because recumbent bikes utilize a different set of muscles than upright bikes. It normally takes at least a couple of months of training in the recumbent position to acclimate the muscles to the new position. 

The fastest bike for you may well be based on the terrain in which you ride. If you are riding in flat or rolling areas, the low racer platform is generally recognized as being the fastest platform, but in areas with long ascents, and long descents, a high racer type bike will probably be faster. The low racer is the most aerodynamically efficient platform, but due to the frame complexity it can be heavy. Generally high racers can be designed with extremely simple, lightweight frames. In addition, the convoluted chain line of the low racer is slightly less efficient than the simple and straight chain line of the high racer the high racer, which causes a slight speed reduction during those very low speed/high power hill climbs. On flat or rolling courses, all bets are off though, the design compromises inherent in the low racer platform allow the rider to cruise in the most aerodynamic position, low to the ground. The proximity of the seat to the ground is especially important because wind speeds drop significantly as they approach the ground. Any wind except tailwinds are detrimental to biking speeds and tailwinds never make up for speed lost in head winds.

It has been observed that many recumbent racers who previously had finished in the middle of the pack on a higher, more upright recumbent often come back the following year with a low racer and then finish in the lead pack. 

The question of whether an extremely light low racer is faster than a high racer of comparable weight on mountainous routes has yet to be answered, but I suspect that they are at least as fast. The next few years should be very interesting in this respect as a number of manufacturers are beginning to build lightweight low racers. 

Whatever platform is fastest for you will be even faster with aerodynamic aids. At the bottom end of that spectrum are wheel disks. Wheel disks will provide a small aerodynamic advantage. More so for low racers with big back wheels than for other platforms, as the disks acts act as a splitter plate, simulating a tail fairing. While finding wheel disks in recumbent sizes may be difficult, they are available if you look hard. You may also consider building them.

The next step in the quest for aerodynamics depends on what you are riding. If you have a bike with an extremely upright seat, like a Tour Easy or other long wheelbase bike, a front fairing will give you the most benefit. As the seat reclines more, such as in most SWB designs, the benefit of a front fairing decreases. This is due to a combination of the frontal area of the rider becoming reduced as the seat leans back, and the fact that the rider becomes farther away from the fairing as the seat leans back. For those bikes with a reclined seat angle, a tail fairing will make more of a difference. There are many production tail fairings available, all from Europe. As with any recumbent accessory, you can also build your own. When building (or buying) a tail fairing, remember, bigger is better. Tail fairings can be constructed of anything from inexpensive and lightweight Coroplast (Coroflute), to exotic carbon fiber composite. The main design guidelines for the most efficient tail fairing are that it should be slightly wider and taller than your torso's frontal area, it should be about 3 times as long as it is wide (Use 12 degree rule), and that it should be as rounded off as possible. A good tail fairing can add 2 MPH or more at speeds over 20MPH. 

To go even faster, combinations of front and rear fairings, front fairings with body socks, and full fairings are in order. The combination of a front and rear fairing is an improvement over just one of those, but not as much as you would think. It's not until you tie the front and rear fairings together that the big benefits begin. This can be accomplished by simply stretching spandex between the front and rear fairings, but rigid sides to your fairing work better as they will not sag or act like as much of a sail. The more of the bike you can close off, the faster you will go, so if you are going to go through the trouble of adding the sides, you should close off as much of the top and bottom as possible. While doing this, remember to keep the fairing as rounded as possible. This is important from the side view as well as the frontal view, as a round sided fairing will handle much better in the wind than a fairing with flat sides. 

If you are planning on using your fairing on the road, be sure to design leave your head out in the open, so you have a 360 degree view. It's already harder to see around yourself on a recumbent than on an upright bike, which is why recumbent riders always use mirrors. Leaving the head exposed doesn't slow you down that much at practical fairing speeds, and you will probably want an even larger opening than just for your head to make it easier to get in and out and to provide some ventilation. While racing, you can plan on always being in motion to keep the air moving through the fairing, but on the road you may have to stop for extended periods of time, or crank slowly up a hill in a stagnant pool of air. You will want good ventilation to keep you cool in these conditions. 

Streamliners are the ultimate in human powered speed, but even these have differing levels of performance. Some fully enclosed streamliners are designed for road races, and are shorter, more rounded, and often suspended. Others are designed for circuit racing on velodromes and car tracks. These are more aerodynamic, can have front suspension, and need to be able to lean at least 45 degrees in turns without scraping their bodywork. Lastly are the speedbikes, which are designed for all out straight line speed. The bikes are completely sealed, usually have no suspension, are geared for speeds in excess of 70 MPH, and have bodies with the most laminar shape that the designer can envision and build. Some of these bikes do not even have windshields, the riders navigate completely by remote video camera and LCD monitor. 

As I have noted above, anybody with the time, imagination, or money can buy or build a vehicle which will allow them to go considerably faster than they would be able to go on an upright bike. A rider who is fast to begin with will be blazingly fast on a streamlined recumbent. Recumbent racers with tail fairings in Europe are regularly averaging speeds in excess of 30 MPH in 1 hour races. As of 2002 the all out speed record for human power was set at 81 MPH. Streamlined circuit racers are pushing the traction limits of bike tires by averaging 40MPH on small velodromes designed for much slower upright track bikes. 

So really, its about the bike...

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Copyright 2003 Warren Beauchamp. All rights reserved.