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Do you know how much of a difference it is to ride with specific gear ratio (example 48/16) with 28" wheels and 26" wheels?

David Richerby
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Ari
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    All of the relevant formulas are linear, so with 26" wheels instead of 28" wheels your speed/effort is 26/28 as much as for the 28" wheels. You don't even need to know pi. :) – Nobody Nov 06 '18 at 21:51

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Yes. You can do the math on this: (chainring ÷ sprocket) × wheel size. With a wheel that has an outer diameter at the tire of 26", you'd get 78 gear inches. With a 28" wheel, it would be 84 gear inches, or about 7% higher.

On a multi-gear setup, I've found that a 7% step is just about the smallest step that's really noticeable.

Adam Rice
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    Going via gear-inches is actually just a long way around to noticing that 28 is 8% bigger than 26. (8% because you rounded 7.69% the wrong way.) – David Richerby Nov 07 '18 at 17:40
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A larger wheel (including the tire) just gives a higher effective gear ratio.vBicycle gear ratios are often specified in gear inches, which takes the diameter of the driving wheel into account.

Gear inches = diameter drive wheel (in inches) × size front sprocket / size rear sprocket

[Source: https://www.sheldonbrown.com/gain.html]. Use of inches is traditional, you could of course use metric units.

Obviously, you can calculate the sprocket ratios which give comparable gear inch values for each wheel size.

Also, you can directly calculate the difference in effective gearing by simply dividing one wheel diameter by another. Assuming wheel with tires have an actual diameter of 28" and 26", a 28" wheel gives 28/26 = 1.07 i.e. 7% higher gear ratio over a 26" wheel.

Choosing 26 and 28" wheel diameters for comparison is a little strange. A 559mm rim MTB wheel with a 2" tire would be about 26" in diameter. A 622mm MTB wheel with a 2.25" tire would be about 29".

Assuming you would use similar tire sizes on each size wheel, you can simply divide rim diameters. 622mm / 559mm = 1.11, i.e. the larger wheel gives about a 11% higher effective gear ratio.

Argenti Apparatus
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    Not sure if this is region-specific, but in German discussions I’m often see the term „Entfaltung“ (“development”) used. It describes how far you move with each turn of the cranks, which is somewhat more meaningful than “gear inches” which use wheel diameter. Development = wheel circumference × front sprocket/rear sprocket. Of course for a complete picture you also have to take crankarm length into consideration. – Michael Nov 06 '18 at 19:17
  • @Michael, I'm not sure how meaningful how far I travel for one crank revolution is to me. Wheel diameter is easier to find than circumference (i.e it saves multiplying by π). – Argenti Apparatus Nov 06 '18 at 19:28
  • @Michael: Crankarm length plays only a part in leverage not in development. It doesn't intervene in the calculation. It's big ring/sprocket multiplied by wheel circumference. Where would you include the crankarm in the calculation? – Carel Nov 06 '18 at 20:18
  • 28" is used to mean a fairly thin 700c by some manufacturers (like Schwalbe). So a 28x1.125 (700x28) would be around 622+56=678 diameter while a 26x2.4 would 559+122=681, i.e. for plausible tyre sizes the 26" wheel could come up the same diameter as the 28", or even bigger. – Chris H Nov 06 '18 at 22:00
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    @ChrisH Gotcha. Although 26" implies an MTB wheel, 28" implies a road wheel; with appropriately different tire sizes. – Argenti Apparatus Nov 06 '18 at 22:06
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    Development (based on circumference) is the way this concept is usually expressed in Europe. There's not much to choose between that and gear-inches, just what you're accustomed to.

    Sheldon Brown did propose "gain ratio" as a way to incorporate crankarm length.

     – Adam Rice Nov 07 '18 at 00:21
  • @Carel: A longer crank arm requires less force with the same gear ratio, just like smaller tires. – Michael Nov 07 '18 at 11:35
  • @Michael: but has no incidence on covered distance. Because it changes the diameter of the 'foot circle' and along with that the work of muscles and joints it has quite an incidence on biodynamics. Another reason for shorter cranks: the bottom bracket can be lowered for aerodynamic advantage. Without a lowered BB, shorter cranks allow a deeper leaning angle in turns with turning cranks without the risk of pedal strike, the reason of their use in criterium races. – Carel Nov 08 '18 at 15:56
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    @Carel: Of course it doesn’t change how much distance you cover per crank arm revolution, but it changes how much distance you cover per millimeter of foot movement. I’m also not advocating to change crank arm length to fix gearing, I simply stated that it has some effect on how much force you need. – Michael Nov 08 '18 at 18:30
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A 26" wheel ridden at 26 km/h will give you exactly the same cadence as
a 28" wheel ridden at 28 km/h.

So, a gear that's optimal for riding 26 km/h on a 26" wheel will be optimal for 28 km/h on a 28" wheel. And vice versa. It's really as simple as that.

cmaster - reinstate monica
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