Re: [問題] 花鼓的問題

[licker (sPECIALIZED)]

※ 引述《licker (sPECIALIZED)》之銘言：
: 摘錄zipp對他們ceramic bearing花鼓的說法(Dec 9,2003):
:   How much benefit is possible from adopting this new technology? According to
: reports from real world testing done by ZIPP sponsored Team CSC an average
: reduction in wattage of  three to four percent under our standard bearing
: systems, already the tightest standard within the industry can be expected. For
: an average trained cyclist developing 250 watts, that's a savings of
: approximately 10 watts. At any level of competition, that is significant......
: ........................................................................
: ..Anecdotally, one our ZIPP representatives recently became a world record
: holder on the track. After numerous attempts and misses at the record by a few
: hundredths of a second, he broke the record after switching to the ceramic
: bearings. He has since lowered that record again using the same set up, but in
: several tries without the ceramic bearings has been unable to ever match his
: original record breaking attempt. Of course this was not a scientific test, but
: try to tell him the bearings don't make a difference!
: 我是不知道這裡說的使用ceramic bearing花鼓的輪組最便宜是什麼價位
: 但兩個輪子加起來我猜應該不只一兩萬
: 結論: 我建議不用換
阿 才發現有人覺得zipp那段話是虎爛:(出處:velonews網站)

  On the recent subject of bearing friction, I think it's worth taking claims
of increased performance with a grain of salt. The amount of power dissipated
in even a standard steel ball bearing hub is quite small. I've always believed
this but decided to calculate it for kicks. In case you're interested, the
calculation is below.

Typical coefficient of friction for a ball bearing is about mu=1.5e-3

(for example, http://www.ntnamerica.com/Engineering/PDFs/2200/frictemp.pdf)
Power dissipated in one bearing is

P1 = mu * (m/2) * g * V_bearing where m is mass of rider+bike V_bearing is
linear speed the bearing rotates at.
P_bearingloss = 2*P1 total power lost in two wheels
V_bearing = V_bike * d/D d = bearing race diameter = wheel diameter
P_bearingloss = mu * mg * d/D * V_bike
P_bearingloss = C_bearingloss * mg * V_bike where C_bearingloss = mu * d/D, can
 be compared to C_rolling resistance of tires
For a bearing race diameter of 20 mm and wheel diameter of 668 mm (700x23) C_
bearingloss = 4.5e-5
for comparison, C_rolling resistance is supposed to be 4e-3 for smooth pavement
 (e.g. from www.analyticcycling.com), or 100x higher.
(我也看不懂這是啥)

  For a rider+bike of 75 kg traveling at 10 m/s, I get that the power dissipated
in wheel bearings is 0.33 watts. I suspect this verges on negligible. A major t
echnological breakthrough that cut bearing friction in half would only gain 0.1
6 watts. It might be significant in hourrecords or even the pursuit world recor
d. At my low level of competition, I think the sleep gained in not worrying abo
ut it has a greater performance benefit.


而且  誠如upsha所言 也有人這麼說:(出處:仍是velonews網站)
  Given a typical 250 watt output, the rough breakdown would be:

80 percent, 200 watts is aerodynamic friction
15 percent, 37 watts is tire rolling resistance
5 percent, 12 watts is mechanical losses of which
75 percent, 9 watts is drivetrain(bottom bracket, chain, derailleur)
25 percent, 3 watts is wheel hubs/bearings.

  You can adjust the percentages somewhat to your personal preferences but the
end result will always be a wheel bearing total loss much less than Mr. Vance's
vastly overstated claims of 10 watts reduction. Even an estimate of a 1 watt
reduction, from 3 to 2 watts, is possibly too large, since most hub losses are
due to the seals.
  Put a tiny drop of Teflon based lube on the inside surfaces of your hub
seals, save more watts, and hundreds of dollars.

所以  我更是建議不用換了

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推 Uxorious:percent跟watt的大小好像對不太起來？
推 licker:如果注意of which的話  應該對的差不多
推 Uxorious:哈哈哈看到了XDD
→ Uxorious:對不起看的很不仔細......
推 licker:其實我也是你說了才發現