On Thu, 11 Nov 2004 18:21:17 +0000, Zog The Undeniable
<
[email protected]> wrote:
>[email protected] wrote:
>
>> On 11 Nov 2004 06:48:44 -0800, [email protected]
>> (supabonbon) wrote:
>>
>>
>>>A couple riders have brought up a discussion on chainwear recently.
>>>That made me recall a Jericho SS showing off a belt drive they called
>>>'Red October'. I've also seen them on Strida folding bikes. I'm sure
>>>it's not a new concept.
>>>Anybody out there actually riding a belt? I'm curious about pros and
>>>cons. If they're trusted on motorcycles, why not bikes? You'd think
>>>the drivetrain would last forever.
>>>/s
>>
>>
>> Dear SBB,
>>
>> One objection to a belt drive is that it won't work with the
>> derailleur system.
>>
>> If this is overcome by the use of a motorcycle-style
>> internal gear system, then the problem is that a belt drive
>> is less efficient at transmitting a bicycle's feeble power
>> than a chain drive.
>
>Most belts are also endless for maximum strength, so you'd need raised
>chainstays or a monostay design to avoid having to loop the belt round
>the frame.
>
>But belts can be pretty efficient - probably as good as a dirty chain
>[1] and quiet.
>
>[1] the inherent problem being that flexing rubbery things always
>involves a loss of energy - it's called hysteresis. But how efficient
>is your chain after 200 miles on wet roads?
Dear Zog,
Surprisingly, the efficiency of chains suffers hardly at all
due to grime or lack of lubrication--those evils affect
longevity. For efficiency, it's sprocket size and tension
that matter:
[long quote begins]
The researchers found two factors that seemed to affect the
bicycle chain drive's efficiency. Surprisingly, lubrication
was not one of them.
"The first factor was sprocket size," Spicer says. "The
larger the sprocket, the higher the efficiency we recorded."
The sprocket is the circular plate whose teeth catch the
chain links and move them along. Between the front and rear
sprockets, the chain links line up straight. But when the
links reach the sprocket, they bend slightly as they curl
around the gear. "When the sprocket is larger, the links
bend at a smaller angle," Spicer explains. "There's less
frictional work, and as a result, less energy is lost."
The second factor that affected efficiency was tension in
the chain. The higher the chain tension, Spicer says, the
higher the efficiency score. "This is actually not in the
direction you'd expect, based simply on friction," he says.
"It's not clear to us at this time why this occurs."
The Johns Hopkins engineers made another interesting
discovery when they looked at the role of lubricants. The
team purchased three popular products used to "grease" a
bicycle chain: a wax-based lubricant, a synthetic oil and a
"dry" lithium-based spray lubricant. In lab tests comparing
the three products, there was no significant difference in
energy efficiency. "Then we removed any lubricant from the
chain and ran the test again," Spicer recalls. "We were
surprised to find that the efficiency was essentially the
same as when it was lubricated."
The researcher speculates that a bicycle lubricant does not
play a critical role under clean lab conditions, using a
brand new chain. But it may contribute to energy efficiency
in the rugged outdoors. "The role of the lubricant, as far
as we can tell, is to take up space so that dirt doesn't get
into the chain," Spicer says. "The lubricant is essentially
a clean substance that fills up the spaces so that dirt
doesn't get into the critical portions of the chain where
the parts are very tightly meshed. But in lab conditions,
where there is no dirt, it makes no difference. On the road,
we believe the lubricant mostly assumes the role of keeping
out dirt, which could very well affect friction in the drive
train."
http://www.jhu.edu/news_info/news/home99/aug99/bike.html
Carl Fogel
