How much resistance comes from each part of a bicycle? [closed]

Question

How does one decide which part of a bicycle is the best candidate to upgrade or tune if the goal is higher speed for the same energy? For example, should one upgrade wheels, or tyres, or change to lighter parts, or to reduce aerodynamic drag with fairings?

Is there any way to compare the influence of each part? How much power can you save, and is it significant enough that you can recognize the difference? For example, do aero improvements make sense if speeds are very low and, if not, how can you determine the speed above which it does make sense?

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We are reinventing wheel here. [Aero formulas from Sheldon Brown][1] and racing bike chart

Few similar links answering this question:

• resistance types
  
• aerodynamics part 1
  
• aero (exploratorium.edu)
  
• human body front area depending on pose in case it will be possible to ride in horizontal position drag must be way smaller as front area will be at least 5x smaller.

Interesting answers https://gearandgrit.com/the-science-of-cycling-aerodynamics/

How Fast Could You Go?

Lightning F-40

Aerodynamics of human-powered vehicles (PDF or HTML)

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This page can help a lot: http://diginfo.ru/en/cycling_en/how-spent-cycling-power-during-moving-a-bike/

Answer 1

Answer: This question cannot be answered in a simple tabular format because the resistance of every part depends on every other part.

IE, a wheel and tyre and spokes will have an effective "cross section" which is the hole it has to punch through the air.

That area is mitigated by the shape's curves. From wikipedia:

So for simple shapes in isolation, the drag coefficient is known, and you can measure the cross sectional area in square metres.

Your problem is that a bicycle is not a sphere or anything simple - its a complex series of parts and they're hitting the air at different delays. So when the air hits your downtube, its already been distrupted by the front wheel, forks, and headtube, as well as being in close proximity to your shin which is a periodic displacement of air.

To approach what you're asking - you'll need either to buy time in a wind tunnel, or fit a power meter on your bike and measure your times.

Doing this with scientific rigour means

• doing each run at least 3 times
• riding to a set power that you personally can maintain for the whole distance - no more and no less.
• riding a distance of at least 30 minutes
• having a route with no chance of stopping at traffic lights or similar
• in an environment with consistent winds/temperatures/humidity across all your trials
• and having a way of measuring your time as accurately as possible between a well defined start and stop point.

Then swap the one part you're testing for the other part, and repeat the three runs.

The difference in time will show you how much power you've saved/lost with the one variance. If you want to test 5 types of pedals, that's 15 runs.

A circular route will help too, if you can find one that works for all the above requirements.

Ideally your rider would not know which parts are being tested on each run, so they can not be swayed to push harder or softer subconsciously.

One might reasonably assume that Manufacturers would release this kind of data, especially for their high-end items. And they do with statements like "saves 17 seconds in a 40 km time trial, over last year's model." Which is relatively useless as a comparison.

tl:dr - there's too much interdependence to make a simple table that is also accurate.

Answer 2

Edit - tables using same values as example below - 180cm/80kg rider, 15kg bike, hands on the tops bike

- narrow racing tyre:
Aproximate power formula P = (0.875492969 * v) + (v³ / 150.37973)
for > 20km/h max error 3.5% / avg error 1.046% (rolling + air)

Share (%)

Speed (km/h)         11     15     20     25
Rolling resistance 49,82  35,42  23,91  16,91%
Air resistance     50,01  64,42  75,94  82,97%

Power needed (W)

Speed (km/h)        11     15     20      25
Rolling resistance 9,63  13,13  17,51   21,89 W
Air resistance     9,67  23,89  55,62  107,43 W
Total power       19,33  37,09  73,23  129,48 W

- robust wide touring tire (%)

Speed (km/h)         11     15     20     25
Rolling resistance 60,15  45,44  32,30  23,59%
Air resistance     39,85  54,56  67,70  76,41%

Speed (km/h)         11     15     20      25
Rolling resistance 14,59  19,90  26,53   33,17 W
Air resistance      9,67  23,89  55,62  107,43 W
Total power        24,26  43,79  82,15  140,60 W

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In Michael's link rolling resistance formula is computed this way:

CrEff = LoadV[Bike#] * CCrV[Bike#] * CrV + (1.0 - LoadV[Bike#]) * CrH
(Rolling drag coefficients: Cr front (w/o wheeldiameter correction): CrV Cr rear: CrH)

Frg = 9.81 * weight * (CrEff * cos(Slope) + sin(Slope))

P = Cm[bike#] * V * (... + Frg)

Power loss of tyres, flat: P = Cm[bike#] * V * 9.81 * weight * CrEff

Example 80kg rider, 15kg bike, narrow racing tyre (Cm = 1,025 - hands on the tops):
P = v * 0,8756446875 (W; km/h)
(24,32% of 72W share @20km/h)

or

P = v * 1,326734375 for robust wide touring tires (thread)
(29,48% of 90W share @20km/h)

Power ratio between narrow and worst resistance tyres in example from that form is 25% (72/90W).

Tyre description                       Cr
narrow racing tire (high pressure)     0.0033
medium-wide high pressure slick        0.0031
wide high pressure slick               0.0029
robust wide touring tire (thread)      0.0050
Rinkowsky radial ply tire (wide slick) 0.0016
offroad tire 1.75"                     0.0046

Bike# + description                                       LoadV CCrV
0  Roadster                                               0.33  1
1  MTB                                                    0.45  1
2  Tandem                                                 0.5   1
3  hands on the tops (top of handlebar)                   0.4   1
4  hands on the drops (bottom of handlebar)               0.45  1
5  Triathlon Bicycle                                      0.47  1
6  Superman Position                                      0.48  1
7  Tandem with racing bars                                0.32  1.25
8  LongWheelBase under seat steering, commuting equipped  0.55  1.25
9  ShortWheelBase under seat steering, commuting equipped 0.55  1.25
10 Lowracer above seat steering Kreuzotter race           0.63  1.25
11 Streamlining tailbox Kreuzotter race                   0.63  1.25
12 Streamlined Lowracer White Hawk                        0.55  1.25
13 Streamlined Trike Quest                                0.72  1.5
14 Handbike 3 wheel                                       0.5   1.5

Do not like public lies - here is one example: LaFerrari (400km/h top speed) could be overtaken by Peel P50 (45km/h), but do not take it seriously - one went out of petrol or was parking probably ;-) Anyway one can pay 3x more for top wider to beat worst narrow (by resistance) if he feel physics or material limits are misleading.