|
|
Bike Calculator
The calculators that cyclists have used for 10 years are now located here, and improved! Plus new calculators. Some results from the Calculators...Have you ever wondered how much faster you would go if you spent $5 on a pair of titanium water bottle cage screws? How much faster you would go if you lost ten pounds? Whether you should go anaerobic up that short hill? If that almost imperceptible headwind could be responsible for your slow speed (and not last night's chili)? Let's answer some simple questions. First, why are even small headwinds so unpleasant? The following graph shows the effect on a rider putting out 150 watts for two positions, on the hoods (lower) and using an aerobar (upper):
This graph comes from one of the "Speed" calculators. A headwind of 5 mph reduces speed by nearly 3 mph. This is the equivalent of a 0.73% grade. You would have to increase power from 150 to 215 watts to compensate (see one of the "Power" calculators). And don't we all try, slaves to our cyclocomputers? Here is the effect of grade on speed, for the same two positions (hoods and aerobar), at 150 watts:
How does weight influence these curves? If you lost 10 lbs (about 5%), you would be able to go about 5% faster on the steepest hills and 0.4% faster on the level; you'd go about 2% slower on the downhills. Over a simulated 20-mile closed-circuit ride with a variety of grades, a 10-lb difference produced a 33 second difference. (You can do this sort of calculation with one of the "Six Segment" calculators.) This may or may not seem significant in the context of a time trial. On the other hand, there were two hills on this simulated route where the heavier rider falls back 14 seconds. That is, about 200 feet back and well-dropped. A two-lb difference that you can buy at a bike shop for $500 amounts to only 7 seconds on this circuit, but again, a two-lb penalty can mean cresting a hill 50 feet behind your better-sponsored buddies. Here is a chart that gives speed versus power for the same two positions again:
The advantage of the aero position seems overstated (it is more accepted that it is worth one or two mph). But for many, the aerobar position is not entirely comfortable, and they cannot peddle as hard. (Losing ten pounds might provide an added bonus here.) If you can do 17.2 mph when riding on the brake hoods on a road bike with thin high pressure tires, you can only expect to go 14.4 mph on a fat tire mountain bike. This results from the increase in rolling resistance from 0.004 to 0.012. (Trivia: it is the low pressure of fat tires that increases rolling resistance.) What do the pro's put out? In the final stage of the 1989 Tour de France, Greg Lemond averaged 34 mph with a 5 mph tailwind. According to the sort of calculations you can do here, he was putting out 513 watts. |
Go to:
|
del.icio.us