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Aerodynamic Drag of Streamlined Handlebars

On January 5, 1995, an aerodynamic test of bicycles and components was conducted at the Texas A & M wind tunnel in College Station, Texas. The testing was organized by Mr. John Cobb of Bicycle SPorts, Shreveport Louisiana, and Mr. Steve Hed, of Hed Design, White Bear Minnesota. Data collection was performed by Texas A & M wind tunnel staff, directed by Mr. Oran Nicks. Testing of handlebars was directed by Jim Martin of Team EDS.

The leading edge of a bicycle (i.e., handlebars, head tube, fork and wheel) encounter relatively calm air, and are not influenced by interaction with the riders body. It is reasonable to believe that changes in the aerodynamic drag of leading edge components will have a similar effect on both bare bike and bike rider aerodynamic drag. Some aerodynamic bicycles have minimized aerodynamic drag due to handlebars by eliminating the standard grip altogether. While this arrangement results in low aerodynamic drag, it may make the bicycle difficult to control in turns. The use of handlebars with a streamlined aerodynamic cross section might result in low aerodynamic drag while preserving bike control. Therefore, the purpose of this investigation was to determine if handlebars with streamlined aerodynamic cross section could affect the aerodynamic drag of a bare bicycle, and if so, to determine if the same changes in drag were observed for a bike and rider. Additionally, if differences in drag were found, mathematical modeling would be used to predict the effect on finish times in competitive events.

Five handlebars configurations were tested on a Softride Power V bicycle, both as bare bike and with as a bike with rider. The handle bars tested included three configurations of Vision Tech bars with streamlined tubing; 'hook' hand grips with brake levers, 'hook' hand grips without brake levers, and streamlined grips. These Vision Tech bars were compared with two typical aero bars that are popular among triathletes and cyclists; Profile cowhorn with Profile 'Airstryke' clip-on, and Scott 'Extreme'. Each set of handlebars was adjusted to postition the elbows pads at the same height, and the riders elbows were measured and placed in the same fore-aft position for each test. Arm position was also maintained at a simialar angle for each test. A standard drop handle bar with Scott clip-on aero bar was also tested on the bare bike, but not with a rider. Rider position could not be matched with that combination.

All tests were conducted at approximately 30 mph, and the drag force results were then normalized to 30 mph by multiplying the measured drag by the square ratio of 30 mph to the actual velocity (i.e., 5.64 lb. at 29.9 mph yields a drag of 5.64 lb.*(30/29.9)2=5.68 lb. at 30 mph).

In order to access the performance implications of the current wind tunnel results, a mathmatical model was used to predict changes in cycling velocity due to reductions in aerodynamic drag. The prediction equation modeled steady state cycling on a smooth, level asphalt road, and is based on power consumption by three sources: aerodynamic drag of bike and rider, rolling resistance of tire, and aerodynamic drag of spinning the wheels. The equation is: Power = V3CdAþ/2 + WFrV + FwV3 , where: V = velocity (m/s), CdAþ/2 is the Coefficient of drag times 1/2 the air density times frontal area (to get this number, you must determine drag force in the wind tunnel: drag force = V2Cdþ/2 and then divide by V2), W = combined weight of bike and rider, Fr = rolling friction, and is about 0.0022 for Continental Olympic tire or 0.0027 for high pressure clincher tires on asphalt, and Fw is a measure of the drad to rotate the wheel, and is about 0.008 for a rear disc and aero front (about 20 watts at 30 mph).

Results

Results for the handle bar testing are summarized in Table 1 below. The Vision Tech handlebars were significantly lower in drag that the other bars tested when analyzed with a two tailed Student's t test (p<0.05). Additionally, regression analysis indicated that the bare bike drag was significantly correlated with the bike and rider drag (p<0.02). This correlation suggests that our riders's position was well matched in each configuration tested. Although the drop bar and clip-on combination was not tested with a rider, the significant correlation of bike and rider vs. bare bike drag suggests that the combination would be similar to the cow-horn and clip-on if tested with a rider.

Table 1
Handlebars Bare Bike (lbs. @ 30 mph) Bike and Rider (lbs. @ 30 mph)
Vision Tech hooks and brake levers 1.72 5.72
Vision Tech hooks no brake levers 1.66 5.75
Vision Tech steamline grips 1.65 5.63
Profile cowhorn and Airstryke clip on 1.97 5.97
Scott Extreme 2.01 5.92
Profile cowhorn and Airstryke clip on 1.99 NA

Mathematical modeling predicted that the Vision Tech handle bar with hook grips and brake levers would result in time savings of 0:43 to 1:01 for a 40 kilometer time trial, depending on the average speed of the rider (Table 2) when compared to the cow-horn and clip-on.

Table 2
Handlebars 18mph 22mph 26mph 28mph 30mph
Vision Tech hokks and brake levers 1:21:48 1:07:00 56:32 52:28 49:00
Vision Tech streamline grips 1:21:18 1:06:40 56:10 52:10 48:45
Profile cowhorn and Airstryke clip on 1:22:49 1:07:49 57:19 53:10 49:40
Scott Extreme 1:22:43 1:07:41 57:11 53:00 49:32

These 40k times were determined by first calculating the power required for the cowhorn and clip-on combination to achieve the given velocity. Then, the new velocity was calculated at the same power but with the reduced drag associated with different handlebars. For the 18, 22, 26, 28, and 30 mph velocities, the power was 94, 163, 262, 325, and 395 respectively. Additional calculations were made to determine the performance of Vision Tech handlebars with streamlined grips compared with a cowhorn and clip-on configuration in timed track cycling events; 1000 meter time trial, and 4000 meter pursuit. These predictions assume no change in performance during the first half lap, and steady speed thereafter. A rider who was capable of riding a 1:12 kilometer time trial with standard cowhorn and clip on bars would save 0.65 seconds with Vision Tech handlebars. Similarly, a rider with a 5:00 performance in the 4000 m pursuit would save 3.6 seconds.

All three Vision Tech handlebar configurations reduce drag by about 0.2-0.3 lb. compared with standard handle bars typically used by competitive triathletes and cyclists. These different times often represent significant differences in race finish placing. It is clear that use of the handlebars with streamlined aerodynamic cross section will improve performance dramatically, and may significantly affect race finishes.

It was interesting that the brake levers had almost no effect on the drag of the handlebars with 'hook' grips. However, the use of streamlined grips reduced overall drag an additional 0.1 lb., which could yield an additional time savings of 20 to 30 seconds in a 40 kilometer time trial. Although a road racing bike must be equipped with brakes and brake levers, track bikes do not have brakes. Therefore, it is recommended that bars for use exclusively on the velodrome be equipped with streamlined grips.

In conclusion, wind tunnel testing showed that handlebars with streamlined tubing offer a significant reduction in aerodynamic drag compared with bars currently used by most racers. This reduction in aerodynamic drag compared with bars currently used by most racers. This reduction in drag should result in performance differences that could substantially affect race placing for triathletes and cyclists. These improvements in performance need not come at the expense of bike handling and safety.




© 1999 Vision Tech USA, INC.