쉐도잉 연습: How Tire Rolling Resistance Affects Cycling Speed ? - 영상으로 영어 말하기 배우기

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What is rolling resistance and why should you think about it on the bike?
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Rolling resistance is, quite simply, the energy that is lost as a tyre rolls along a surface.
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The energy is mostly lost because of the constant deformation of that tyre against the surface.
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Now, whilst paying attention to rolling resistance is important, it's not actually the biggest resistance factor when it comes to cycling fast.
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Air resistance rises in a squared ratio with increased speed.
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At a speed of 20 kilometers an hour on a level ground, air resistance has already become the main resistance force.
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And the faster you go, the more air resistance increases exponentially.
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So before even thinking about rolling resistance, get aero.
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Acceleration energy is also expended, for instance, the weight of the wheels is of great importance when this mass has to be brought up to rotation.
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Then when riding uphill, the main resistance force to be overcome is the gradient resistance.
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This is basically the additional resistance added by fighting gravity.
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And in addition to these, there are other friction resistances in the chain, the bottom bracket, and other rotating parts.
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Now, in a well-serviced bicycle, these represent a very minor part of the total resistance.
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So, should you just ignore rolling resistance then?
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Well, no. Because improving your rolling resistance may be the cheapest
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and easiest upgrade you can make to your bike to go faster.
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You can improve all the others by getting aero, by getting a good bike fit and spending the time getting used to it, by getting aerodynamic and light frame,
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by getting some aerodynamic race wheels, and even by upgrading the bearings to maybe ceramic bearings.
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But you can get big gains simply by upgrading your tires and improving your rolling resistance.
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And of course, pumping those tires to the right pressure.
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It's pretty simple.
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A tire with a higher rolling resistance will require more power
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to attain the same speed than a tire with a lower rolling resistance, will require less power.
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So what factors affect the tyres rolling resistance?
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Tyre pressure.
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On a completely smooth surface the following applies.
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The higher the inflation pressure the less the tyre deforms and thus the lower the rolling resistance.
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However on an imperfect surface which we are always riding on lower inflation pressures cause the opposite, lower rolling resistance.
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Imperfections in the road on a very hard tyre will cause bouncing and skipping and increased resistance, not to mention the toll that takes on the rider in terms of fatigue.
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Whereas a tyre with low inflation pressure can adapt better to the rugged surface.
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It sinks into the ground less and absorbs imperfections rather than pushing against them and bouncing off them.
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And so with a softer tyre the whole rotational mass is held back much less on the uneven surface.
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Tire width.
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At the same tyre pressure on a smooth surface a wider tyre will have lower rolling resistance than a narrower tyre.
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This is essentially because a wider tyre with the same pressure actually has an effect of higher pressure
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because a wider tyre with a higher air volume will have a higher casing tension.
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Basically the wider tyre will be harder because it needs more air to fill it and the contact patch, the bit of the tire touching the road, will be smaller and wider, decreasing the rolling resistance.
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But again this only holds true on a smooth surface.
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On an imperfect surface with the pressure corrected for the width to get the tire to the right hardness, the contact patch on the road for a wider tire will be shorter and wider than a narrow tire,
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decreasing the rolling resistance.
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Importantly the wider the tyre will have more versatility and the range of pressures you can actually use, allowing you to more easily correct for the roughness of the surface.
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Tyre construction.
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Obviously the tyre construction has an effect on rolling resistance.
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By using less material, less material can and will be deformed.
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And the more flexible the material is, such as the rubber compound, the less energy is lost through deformation.
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Generally, smoother treads have a lower rolling resistance than rougher treads
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and that is why almost all road
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and triathlon racing tires have very smooth tread patterns
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if any tread pattern at all interestingly actually in racing tires for the road the tread pattern
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that is there is actually not there for grip
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or water dispersion it's mostly there for aerodynamics
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because the tread pattern actually trips the laminar flow as
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that of that air that's hitting the tire to improve the aerodynamics So,
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should you consult a website like BicycleRollingResistance.com where they list all the tested rolling resistance of all tyres
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and simply choose the one from the top of the list?
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Well, yes and no. Yes, the tires on the top of that list will be the fastest.
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However, they're always compromises.
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Some of them may sacrifice durability for that extra speed and be more prone to punctures.
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Some of them may have a different compound that sacrifices comfort
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and grip and road feel and some may simply not work well with your wheel and bike setup.
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It's also worth pointing out that the difference between the top of
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that list of racing tires and the middle of
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that list of racing tires is about a two to three watt saving
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which is an almost imperceptible difference for most mere mortals.
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They will however have a significant difference in those racing tires over your standard training tires.
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So the answer is that the best tire for you depends on many factors
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but it is worth considering investing the $100 to $200 in a good pair of racing tyres.
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It may just be the cheapest watts you buy this season.
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One more thing before we go, you may be asking which is faster rolling resistance-wise, tubeless or clincher?
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Well, the speed of a tyre actually depends on its construction and not whether it's set up clincher or tubeless.
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So, a slow tubeless tyre will actually be slower than a fast clincher tyre.
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However, generally speaking, setup does have better rolling resistance than a tube setup.
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However, if you put a latex tube in a clincher, the rolling resistance is actually the same as tubeless.
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I hope you've enjoyed this video.
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Happy riding!

이 레슨의 어휘와 말하기 포인트

이 영상에는 섀도잉할 문장 75개와 단어 1065개가 있습니다. 말하는 구간의 길이는 5:59입니다. 화자는 분당 약 178단어로, 일상 대화에 가까운 자연스러운 속도로 말합니다. 영어에서 가장 많이 쓰이는 3,000단어에 속하는 단어가 76%뿐이라 어휘가 어려운 편입니다.

이 영상의 핵심 어휘

영상에 나오는 익혀 둘 만한 단어 15개를 발음, 뜻과 함께 정리했습니다.

단어발음뜻
tyre 명사/taɪə(ɹ)/타이어
tire 동사/ˈtaɪ̯ɚ/피곤하다
inflation 명사/ɪnˈfleɪ.ʃən/인플레이션, 인플레
narrow 형용사/ˈnæɹəʊ/좁은, 좁다
tube 명사/tuːb/튜브
sacrifice 명사/ˈsæk.ɹɪ.faɪs/희생
bearing 명사/ˈbɛɹɪŋ/베어링
depend 동사/dɪˈpɛnd/의존하다, ...에 달려 있다
compound 명사/ˈkɑmpaʊnd/화합물
width 명사/ˈwɪtθ/폭
watt 명사/wɑt/와트
ignore 동사/ɪɡˈnɔː/무시하다
ratio 명사/ˈɹeɪ.ʃoʊ/비, 비율
pump 명사/pʌmp/펌프
overcome 동사/ˌəʊ.vəˈkʌm/극복하다, 이겨내다

영상에 나오는 구동사

단어뜻
point out 동사가리키다

주의할 발음

  • “th” 소리: smooth /smuːð/, width /ˈwɪtθ/, triathlon /tɹaɪˈæθˌlɑn/
  • “sh”와 “zh” 소리: inflation /ɪnˈfleɪ.ʃən/, essentially /ɪˈsɛnʃəli/, ratio /ˈɹeɪ.ʃoʊ/, tension /ˈtɛnʃən/, rotation /ɹoʊˈteɪʃən/
  • 긴 단어 — 강세 위치에 주의: essentially /ɪˈsɛnʃəli/, importantly /ɪmˈpɔɹ.tənt.li/, acceleration /əkˌsɛl.əˈɹeɪ.ʃən/, aerodynamic /ˌɛəɹəʊdaɪˈnæmɪk/, deformation /ˌdɛfəˈmeɪʃən/

이 영상으로 연습하는 방법

  1. 먼저 말하지 않고 영상을 끝까지 듣고 모르는 단어를 적어 둡니다.
  2. 0.75배속으로 한 문장씩 섀도잉을 시작하고, 익숙해지면 보통 속도로 돌아갑니다.
  3. 자신의 목소리를 녹음해 원본과 비교하고, tyre, tire, inflation 같은 단어에 특히 주의합니다.

이 영상의 문법

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수동태 be + 과거분사 — 누가 하는지보다 무슨 일이 일어나는지에 초점is lost · is also expended · be overcome
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