Originally Posted by
Walter S
Wikipedia says IGH is about 2% less efficient than derailleur gearing. What does that really mean to your riding experience and speed? I guess that for the same effort, you transfer 2% less force to the wheels. But since effort has a nonlinear relationship to speed, as your effort increases from low to medium to high, the actual reduction in speed relative to derailleur gearing is progressively less.
So the actual reduction in speed is less and less as effort increases. Is my thinking correct about this?
The Wikipedia article was biased and had an agenda. It appears the forum members accepted Chester Kyle’s 2% loss in friction as gospel without noticing the study was flawed.
First, the study failed to mention the loss of energy due to the coaster brake fixed to many internal hubs. They conveniently left this out because friction losses would probably bring efficiency losses past 5% or more! I even sold my brand new (Bianchi Milano) because the 7 speed roller brake scrubbed off so much speed leaving me exhausted. I replaced that bike with a 20 year old Univega hybrid with an 8 speed cassette because it was far more efficient.
The Wikipedia article even lists the coaster brake as an advantage! How can it be advantage if it slows the bike down? The Sram Spectro 3 (coaster brake edition) was notorious for making the rear wheel come to a complete stop in 30 seconds or less after spinning it by hand.
Second, the study was done in room temperature and not in cold weather. Anyone who uses internal hubs knows you’re going to experience friction losses when the temperature drops below 30F degrees. Once the oil or grease start to freeze, friction losses are much higher than 2%.
Third, the Wikipedia article states hub gears can be used for mountain biking. There is only one internal hub that can be used for mountain biking. All others have been destroyed on the trails.
Fourth, the study did not mention the energy that must be used to rotate the heavy internal hub from a full stop. Since his mechanical contraption was only able to determine friction losses within the hub, it could not measure the human element in this equation.. Yet for some reason, everyone who rides a hub gear bike (7 or more gears) complains about the weight in the rear wheel?
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One other point should be made. While propelling, a part of the rider's energy is consumed by the clutch's designed-in friction. Even though the wheel might be able to spin an entire minute with the bike upside down and hand cranked, the propelling state consumes energy overcoming the clutch's intended friction. It's not much, and it's tiny with respect to wind resistance (and maybe even tire resistance), but it's there. If there's one design flaw in a coaster brake, this is it.
Overhauling a Coaster Brake Bike