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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?


We are reinventing wheel here. Aero formulas from Sheldon Brown and racing bike chart
Our enemies 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.

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    I don't know of any, and some decent searching has returned nothing useful. Probably because each part doesn't have a specific wind resistance. Instead, the whole collection of parts (ie the whole bike+rider) works as one object in the wind. – Criggie Aug 9 '19 at 7:53
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    I'm fairly sure the problem with this question is that an individual component's contribution to the aerodynamics is affected by every other component. – HAEM Aug 9 '19 at 11:48
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    The biggest aerodynamic suck is the rider. – Daniel R Hicks Aug 9 '19 at 17:16
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    @DavidRicherby the reason this question has a lot of downvotes because the original poster has a history of asking questions that are poorly phrased or can't be answered easily. Tom, StackExchange doesn't have haters, but it is very strongly moderated. You've got advice on asking clearer, more answerable questions before, but you've ignored it. If you feel like there are too many haters here, try Reddit, e.g. /r/bicycles, but I don't think your reception there is likely to be that much better. – Weiwen Ng Aug 10 '19 at 10:50
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    @Tom Sorry but there are many, many questions from first-time users that don't get downvoted. I still think this is an OK-but-not-great question but you should take the hint from the large number of downvotes and closures you get across all your questions. It's because of the way you post, not because we hate new users. – David Richerby Aug 10 '19 at 10:57
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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: enter image description here

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.

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    @Tom if you don't care about exact numbers with this question there is no need to ask it. The differences to the overall aerodynamics are too tiny to get anything but random noise when not measuring with the utmost care. And don't even think about changing a tyre. The difference in rolling resistance will spoil all measurements. tl:dr if you are not meticulous, don't bother with marginal gains. – gschenk Aug 11 '19 at 7:48
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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


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: Wider can and does often have lower resistance ?! 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.

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  • Generic tables like this are useless. There is such a large variance between components they can cross boundaries between several categories. – Andy P Aug 12 '19 at 8:32
  • you are missing the point. There is so much variation between different models of tyre you can't derive any meaningful data from a 'base tyre type'. High quality touring can actually have less resistance than a low quality narrow 'racing' tyre. bicyclerollingresistance.com – Andy P Aug 12 '19 at 10:32
  • Wider can and does often have lower resistance. For example a 40c Schwalbe Marathon Almotion @ 45psi is measured to have less resistance than a 25C Schwalbe Lugano @ 120psi. Whilst there may be trends between tyre widths and genres, the variability in quality is too much to be able to draw any conclusions if a change would help or not – Andy P Aug 12 '19 at 11:22
  • 622x35c WTB ALLTERRAINasaurus has much higher rolling resistance @515kPa (max.) than Schwalbe you are writting about which have worst resistance result in tests. Wider, but approximately 1 minute/km slower on 20km daily flat, asphalt commute. – Tom Aug 19 '19 at 17:55

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