Bicycle gear ratios – gear inches - article comments

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To prevent article pages from being miles long, but preserve all the useful questions and answers provided over time, I've decided to copy/paste the website comments to the forum - and "move" further discussions here.

These are the comments from the article:
Bicycle gear ratios – gear inches

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If you can't find the answer to your question in this thread, please open a separate thread with your question/problem, in an appropriate forum section (this is the Drivetrain section).

Relja
 
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  1. TheGrave
    23/09/2016 at 13:07
    That’s another brilliant article!
    Question for you – does it make sense to try tuning front derailleur for cross-chaining? My chain is rubbing with a 3×8 setup on 8,9,17, etc. gears.
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      Relja
      23/09/2016 at 15:09
      Thanks. 🙂
      For specific answer, I’d need combo’s. I’ll presume (correct me if I’m wrong) that:
      a) 8 is smallest front and smallest rear sprocket.
      b) 9 is middle front and largest rear sprocket.
      c) 17 is largest front and largest rear.
      If using indexed front shifter, you can eigher make the FD cage sit a bit further out (tightening the FD cable a bit), eliminating the rub in a) position, but making it come sooner in b) and c) positions,
      OR
      make the FD cage sit closer to the frame (looseining the FD cable a bit), eliminating chain rub in positions b) and c), but making it worse in position a)
      However, such extreme cross chaining positions are never good for the chain and sprockets. A bit of chain rub will give you a subtle warning, without hampering gear changing or ride, to change to a better chain angle position. Positions a) and c) are especially not recommended, especially with a triple crankset. Slight loosening of the cable might make the b) position work without chain rub (but will still worsen the a) and c) ).
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    Musaran
    26/10/2018 at 18:51
    “Gear ratio is usually expressed in gear inches, i.e. the distance in inches covered by the rear wheel for one full turn of the pedals.”
    Nope, it was just an easy to calculate figure to compare to gearless penny farthings.
    ×π gives the actual distance, as you say a bit later.
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      Relja
      26/10/2018 at 19:15
      Correct, it’s a (n over-siplified?) explanation. To get the actual inches it would need to be multiplied by the Pi number. I’ll probably make a separate post explaining how exactly gear inch is calculated, since placing the explanation here would make an already long article even longer.
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    Relja
    08/11/2018 at 07:58
    Improved the gear inches explanation – using a link to a separate article, in order to keep this one shorter and simpler. Thanks again for all the suggestions. 🙂
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    invadev
    28/05/2019 at 20:01
    can someone help me my issues? I have folding bike 20×1.5 tires and using 53T chainring. I can keep it up with the other road bikers or I can over take them while I am in good condition. I can bike using between 11T and 13T rear sprocket and 53T chainring for the long period of time. My problem is when I bike against the wind it becomes very hard and heavy, so no choice but to use lower rear gear sprocket and the other road bikers do the same thing, now at this point the road bikers are much faster because they have the bigger wheels than the folding bike (20×1.5 tires). if I am going to use 60T chainring is there any changes that I can still able to keep it up with the road bikers? Any suggestions?
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      Relja
      28/05/2019 at 20:11
      If I understand correctly (in case it really is a serious question 🙂 ):
      Lower gears are much “slower” than desired. Boils down to that.
      One solution for that would be using a “road cassette” – one that has smaller differences in sprocket tooth count (i.e.: 11, 12, 13, 14, 15, 17, 19…), instead of a “MTB cassette” that is “less tightly” spaced (11, 13, 15, 18, 21, 25…).
      Using a larger chainring will make these differences even more pronounced. So while it might help with one particular gearing combination (or two), it will generally make gaps seem seven greater.
      Useful tool for these considerations is the Bicycle Gear Calculator.
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    invadev
    28/05/2019 at 21:14
    That tool helps me a lot. with 90 cadence and 60T makes different if I go down to 18T (20×1.5) 29km/h will be my speed which is much close to the road bike 30km/h. Just have to increase my cadence from 90-100 and change my tires to 20×1.3 thanks again
 
  1. Manuel MEITIN
    19/09/2020 at 17:29
    The perfect solution for all kinds of bikes is a continuously variable transmission instead of using step changes variations.
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      Relja
      20/09/2020 at 11:52
      The problem with that is how to make it – without having relatively high mechanical losses, and/or being too heavy.
      Things tried so far have one, or both of those downsides.
      While human body is quite capable of producing decent torque at a relatively wide range of RPMs, unlike most internal combustion engines.
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    ben
    24/08/2021 at 09:53
    I think here is a mistake: “Riding with a too [high] gear ratio, turning pedals slowly is similar to jumping from standing still – with both legs: lots of power in a short time, but quickly exhausting.”
    The “high” in the bracket should be “low”. As you said in the following that 20 gear inches is suitable for gradient, 100 gear inches is for flat paved road.
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    Rick C.
    24/08/2022 at 10:06
    Why do you not mention crank length in these calculations, as far as torque and the human body? It has been my experience that a longer crank arm, (180 mm), which, apparantly is no longer available, or, I’m assuming, even made, makes higher gear ranges more accessable, and therefore higher speeds attainable, and maintainable with less effort on the rider’s part, even while ascending a fairly steep hill. They’ve also, all but, stopped producing 9 tooth rear sprockets, which were widely available during the 1980’s and 90’s. Did people’s legs just suddenly get shorter and weaker, sometime over the past 3 decades? Or, is the reason, that most bicycle parts are now made in China, and, the Chinese riders have trouble reaching more than 175mm?
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    Ákos Semsey
    05/02/2023 at 22:27
    If you want to make custom calculations (not just about bikes), you might like DockCalc visual calculator. Here is an article about bike gears: https://dockcalc.com/WP/index.php/en/2023/02/05/bicycle-gears-and-air-drag-calculation/
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    Emily
    27/05/2023 at 21:12
    Thanks for this education!
    I need help for casual riding in a roly poly hilly City environment. I just bought a “simplified” Bianchi 7-speed with (obviously) single gear in front. I understood the sales pitch to be “easier operation, same range low to high, just fewer steps in between.” Really thought it would work for me, LOVE everything else about the bike, but I’m dying on the hills. Feels hard on my knees and breaking a sweat just to go get takeout wasn’t in the plan 🙂
    My front chainrin is 41 teeth (maybe 42); largest rear is a 32. Am I just a wimp who needs to build some strength, or is that setup just not going to work for someone faced with a 3-4% grade around every corner (East Nashville TN).
    My local shop offered to change out the rear cassette for one with a 34 as largest. So 2 teeth larger. Would that make any noticeable difference?
    Alternately I’m considering trading her in for the 24-speed version with the very small front gear, but will be heartbroken to give up this otherwise-perfect bike.
    Thanks for any thoughts!
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      BikeGremlin
      28/05/2023 at 21:10
      Hi Emily,
      Before I answer, this tool is very useful (and simple to use) to give you the info about different drivetrain combinations:
      gear-calculator.com (the link should open with a setup of 42T cranks and a 7-speed cassette)
      That is best to see by yourself, for yourself, how different drivetrain setups should perform (kudos to mister Dirk Feeken for making the tool 🙂 ).
      To answer the question: 2 teeth on the rear can make a noticeable difference. But it may not be enough.
      From my experience:
      My old road bike had 53-42 cranks, and 34 teeth at the rear (so a 42 – 34 combination) was not low enough for me on long steep climbs as I went past 40 years of age (before that, it was OK).
      So I swapped my cranks for 50-34. 34 front chainring gives me low enough gearing even with a 32T cassette. If I shift to 13T at the rear, it is fast (high) enough gearing for riding on flats (I avoid that combination to avoid cross-chaining, and use 50 – 18 instead which is close to that).
      Based on that, you might give it a try with a 34 or a 36T front chainring, at least until you build up strenght and endurance. 34T at the front paired with a 34T cassette will give you a one-to-one gear ratio, which is often low enough for most climbs on paved roads. It would definitely be easier than pushing 42 – 32, or even 42 – 34 combo.
      Relja
 
This topic is closed for further replies.

If you can't find the answer to your question in this thread, please open a separate thread with your question/problem, in an appropriate forum section (this is the Drivetrain section).

Relja
 
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