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Old 10-08-07, 07:20 PM   #1
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Calculation of gear inches

What's the convention on this calculation of gear inches in the track field?

I note that a lot of people are quoting their gearing based on the 27" wheel, even though pretty much everyone rides on 700c. The difference may not be large, but it would appear that a good section of the track community are still living in the past, and out of reality with the equipments they use.

So what's the deal with this? Is the 27" wheel reference so deeply entrenched in track cycling? Or is there a move to face up with the reality?
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Old 10-08-07, 08:26 PM   #2
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The individual gear inches (say, 84 - 86 - 82) don't really mean anything significant. It's just an easy way of comparing one gear size relative to another. It matters not that the old 27" wheel size is still used as part of the equation.

There's probably a better way of measuring gearing such as Rollout or Gain Ratios but we are really more interested in relativity than actual gear ratios. Gear Inches are so engrained in cycling that all the old geezers (like me) understand them and young whipper snappers learn them.
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Old 10-08-07, 08:28 PM   #3
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There are so few absolutes in this world left to cling to, don't take away 50x15 = 90"
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Old 10-08-07, 08:39 PM   #4
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There are so few absolutes in this world left to cling to, don't take away 50x15 = 90"
Wasn't it Henry Rollins (Black Flag) that said "Friends may come and go but 500lbs will always be 500lbs."?

I guess you could modify that.
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Old 10-08-07, 09:00 PM   #5
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The individual gear inches (say, 84 - 86 - 82) don't really mean anything significant. It's just an easy way of comparing one gear size relative to another. It matters not that the old 27" wheel size is still used as part of the equation.

There's probably a better way of measuring gearing such as Rollout or Gain Ratios but we are really more interested in relativity than actual gear ratios. Gear Inches are so engrained in cycling that all the old geezers (like me) understand them and young whipper snappers learn them.
Yes, I appreciated the fact that this is all for comparative purposes. However, I am just amazed that there are so many who likes to stay with the old way, making accurate comparisons b/n track and other types of bikes difficult (yes, I appreciate the difference is only less than 3%).
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Old 10-08-07, 09:26 PM   #6
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Yes, I appreciated the fact that this is all for comparative purposes. However, I am just amazed that there are so many who likes to stay with the old way, making accurate comparisons b/n track and other types of bikes difficult (yes, I appreciate the difference is only less than 3%).
Why change if the present method (gear inches) is just for comparing gear ratios? What's not to understand about a 90" gear being bigger than an 88? We know that going from a 50/16 to a 50/15 will take us from 84" to 90" but if that jump is too big we need to go with 48/15 which will give us 86" or 52/16 for an 88. Most current trackies can pull that stuff out of their head.

Any other method will end up giving us what we already have - a gear comparison. What real benefit will change bring? I really don't want to compare gear sizes on my track bike vs a Moulton. If I ever do I'll get out my calculator.

Edit - I'll assume you're all switched over to the metric system from the silly, meaningless, ancient Imperial system. If so you will know relatively how tall I am at 1.7526 metres. That means nothing to most of us but my 5' 9" does.

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Old 10-08-07, 09:48 PM   #7
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Why change if the present method (gear inches) is just for comparing gear ratios? What's not to understand about a 90" gear being bigger than an 88? We know that going from a 50/16 to a 50/15 will take us from 84" to 90" but if that jump is too big we need to go with 48/15 which will give us 86" or 52/16 for an 88. Most current trackies can pull that stuff out of their head.

Any other method will end up giving us what we already have - a gear comparison. What real benefit will change bring? I really don't want to compare gear sizes on my track bike vs a Moulton. If I ever do I'll get out my calculator.
Why let reality and facts get in the way of convenience? Is that how trackies think?
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Old 10-08-07, 10:03 PM   #8
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Why let reality and facts get in the way of convenience? Is that how trackies think?
No, and why do you need to compair w road gears? Just know that 1 tooth in front= 2 and 1 tooth in back=6. How many decimal places do we need to take this to in order to make it reality?
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Old 10-08-07, 11:01 PM   #9
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No, and why do you need to compair w road gears? Just know that 1 tooth in front= 2 and 1 tooth in back=6. How many decimal places do we need to take this to in order to make it reality?
If that's the case, then why not just state the straight ratio b/n the number of front and rear teeth? Why bother adding the variable of wheel size in the equation? Given the preference is a constant of 27, why not use 10 or 20? It's even easier to calculate. Seems to me that people are trading their personal convenience for the primary reason on why gearing was defined that way.
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Old 10-08-07, 11:05 PM   #10
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There's probably a better way of measuring gearing such as Rollout or Gain Ratios but we are really more interested in relativity than actual gear ratios.
Junior gearing is still measured by rollout. Probably because 700c is a different rollout than 650c.
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Old 10-09-07, 02:39 AM   #11
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Dude, if you want to calculate gears so they are exact, go ahead, you'll be in your own little world doing your own thing. Like Mike said, it's for comparing relative sizes of gears. Yes we know that if you have a gear spread on a 700c and a 27 inch wheel, they are going to be different. The ratios are the same and that's all anyone cares about. Why reinvent a system that already works just fine and everyone gets.

Sure you can just state the ratios tooth x tooth. All you're doing is eliminating the "rollout" from the actual equation. People are still going to reference gears by rollout, so what's the point of dropping all the rollout numbers by 3%?

why not use a rifle to kill a fly instead of a fly swatter? they both work, one's already the accepted norm, but i bet the rifle would be a hell of a lot more accurate and lethal

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Old 10-09-07, 03:02 AM   #12
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I actually find the fly swatter to be a more effective tool than the rifle... when I'm killing flies.
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Old 10-09-07, 04:47 AM   #13
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Dude, if you want to calculate gears so they are exact, go ahead, you'll be in your own little world doing your own thing. Like Mike said, it's for comparing relative sizes of gears. Yes we know that if you have a gear spread on a 700c and a 27 inch wheel, they are going to be different. The ratios are the same and that's all anyone cares about. Why reinvent a system that already works just fine and everyone gets.
Okay so if my roommate wants to compare gearing with me, she should multiply her gear ratio by 27", even though her track bike has 24" wheels because, like Mike said, it's for comparing relative sizes of gears.

You see my point? Gear inches do more than just compare gear ratios, they compare wheel/tire sizes as well. It's slightly more abstract than development/roll-out but not much - multiply your gear inches by pi and you get your development/roll-out.

The difference between 700C wheels with skinny tires (20-23C) and 27" wheels is pretty small so for simple comparisons it's fine, but at that point, why bother multiplying by 27 in the first place? Just compare the gear ratios (i.e. - 3 is a smaller gearing than 3.2).
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Old 10-09-07, 05:56 AM   #14
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Sogood, so what's your suggestion of how we should state our gear sizes? And how do you propose to get the whole of the English speaking cycling world to change to your method?

I don't understand the "hands" measurement in horse circles. "15 hands" means nothing to me but I'm sure 5' would, compared to a 5' 5" horse. But if I got into horses I'll bet the "hands" measurement would make sense in time.

Yes I'm sure 48 div by 16 (which equals 3) would make sense in time and just as much sense as 48 div by 16 x 27 (which equals 81) but Gear Inches has been around for a little while (like a hundred years) and almost everyone who's really into cycling understands it.

Sorry if you don't agree with the majority of the English speaking cycling world. We're happy with the present system but then I'm happy with Imperial measurement even though I live in Canada and some stuff is measured in Metric. Try going to the lumberyard and asking for a ten foot 2x4 in metric. Hell a 2x4 doesn't even measure 2x4 but we ALL know how relative that is to a 2x6 that doesn't measure 2x6 either.
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Old 10-09-07, 09:07 AM   #15
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If that's the case, then why not just state the straight ratio b/n the number of front and rear teeth? Why bother adding the variable of wheel size in the equation? Given the preference is a constant of 27, why not use 10 or 20? It's even easier to calculate. Seems to me that people are trading their personal convenience for the primary reason on why gearing was defined that way.
"Jargon is terminology that relates to a specific activity, profession or group. Much like slang it develops as a kind of shorthand, to express ideas that are frequently discussed between members of a group."

If my coach or team mate asks me what im riding and I reply 88; He knows what that means, knows the strategic implications that has on how I should ride, ect. A lot of unspoken communication in that simple exchange.

As an engineer I agree with your accuracy argument, as a racer I dont really feel like changing the world on this one.
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Old 10-09-07, 10:03 AM   #16
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"Jargon is terminology that relates to a specific activity, profession or group. Much like slang it develops as a kind of shorthand, to express ideas that are frequently discussed between members of a group."

If my coach or team mate asks me what im riding and I reply 88; He knows what that means, knows the strategic implications that has on how I should ride, ect. A lot of unspoken communication in that simple exchange.

As an engineer I agree with your accuracy argument, as a racer I dont really feel like changing the world on this one.
Best answer yet. Thanks.
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Old 10-09-07, 02:38 PM   #17
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As an engineer I agree with your accuracy argument, as a racer I dont really feel like changing the world on this one.
The only time it would make a difference is that you could be specific about the difference between race tires and training tires. Still it's usually not more then a 1/2" so just saying a "little bit" is probably adequate.
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Old 10-09-07, 05:24 PM   #18
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Sogood, so what's your suggestion of how we should state our gear sizes? And how do you propose to get the whole of the English speaking cycling world to change to your method?
I don't propose my own system but just surprised that people are clinging to a spec (27") that has long disappeared. If years ago the Brits had the 700c wheels, the person who came up with that gearing calculation would have used the 700c spec to fully realise the purpose of the gearing calculation (relationship of three variables). I think that guy would be turning in his grave given what people are doing to his mathematical invention.

As much as 3% is a tiny difference b/n the 27" and 700c spec. But in these days of high tech sports science where winning and losing is separated my mere 1/100th of a second, how can people be so blasť with this number? Do the top tier sports scientists also ignore the 27" vs 700c spec in their calculations for the world cup or Olympics?
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Old 10-09-07, 05:29 PM   #19
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As an engineer I agree with your accuracy argument, as a racer I dont really feel like changing the world on this one.
Thank you. So it is an attitude issue with track riders knowingly staying inaccurate. At the same time, I wonder how many track riders actually know that they are quoting inaccurate numbers?
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Old 10-09-07, 06:12 PM   #20
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Sogood, so what's your suggestion of how we should state our gear sizes? And how do you propose to get the whole of the English speaking cycling world to change to your method?

I don't understand the "hands" measurement in horse circles. "15 hands" means nothing to me but I'm sure 5' would, compared to a 5' 5" horse. But if I got into horses I'll bet the "hands" measurement would make sense in time.

Yes I'm sure 48 div by 16 (which equals 3) would make sense in time and just as much sense as 48 div by 16 x 27 (which equals 81) but Gear Inches has been around for a little while (like a hundred years) and almost everyone who's really into cycling understands it.

Sorry if you don't agree with the majority of the English speaking cycling world. We're happy with the present system but then I'm happy with Imperial measurement even though I live in Canada and some stuff is measured in Metric. Try going to the lumberyard and asking for a ten foot 2x4 in metric. Hell a 2x4 doesn't even measure 2x4 but we ALL know how relative that is to a 2x6 that doesn't measure 2x6 either.
Mike, you seem to be completely missing the point as to why people use gear inches over gear ratios. Gear inches (and development meters) take into account your wheel/tire size which allows you to compare how "hard" or "easy" a gear/wheel combo is to another. If a mountain biker, a roadie, a BMXer and a guy on a folding bike wanted to compare their gearing, using gear inches (or development meters) would be a far superior method to just gear ratios, because riding a 48x16 with 20" tires is a lot easier than riding a 48x16 with 700x23C tires.

Sogood isn't suggesting we stop using gear inches but that people use the correct tire measurement when doing the calculations. 27" maybe be "close enough" when comparing 700C tires but it's not accurate and makes comparisons with other wheel sizes difficult.

So for the record, a 700C wheel is 622mm in diameter, or 24.5". Add on a 23C tire (which is 23mm thick, adding a total of 46mm to the diameter of the wheel) and you get a diameter of 668mm or 26.3".

My track gearing is 48x15 so that would give me the following gear inches:
27" tire: 86.4"
700x23C tire: 84.2"
700x20C tire: 83.4"

So if I'm using a 20C tire and do the calculates with 27", I'm off by 3 gear inches, which is significant.
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Old 10-09-07, 08:01 PM   #21
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Thank you. So it is an attitude issue with track riders knowingly staying inaccurate. At the same time, I wonder how many track riders actually know that they are quoting inaccurate numbers?
Without a doubt, its jargon more than purely technical info. When I say im riding a 90 or 92 that's an expression that my intention is to push a high pace as much as to define a specific and accurate gear ratio.

If im gonna be really accurate dont I need to also factor in Tire Pressure, rider weight, weight distribution? Really doesn't seem worth all the work so I can say im riding a 91.2879 or whatever.
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Old 10-09-07, 08:27 PM   #22
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Do the top tier sports scientists also ignore the 27" vs 700c spec in their calculations for the world cup or Olympics?
Probably (at least the elite coaches I know do)-- they pick the right gear for the situation, but they call it the same thing as everybody else. That is, if they'll even tell you...
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Old 10-09-07, 09:41 PM   #23
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The calculation is chainring teeth divided by cog teeth, multiplied by a constant. Whatever you want to make the constant, it still is a reliable ratio to use for comparison of gearing. It happens to work into a number that is big enough so you aren't working out into two decimal places plus it's something everyone has worked with for years. If you want to go around saying your gear ratio is 2.328, fine. Even on the track where people are changing gears repeatedly in an evening, and a couple inches worth of gear is meaningful, people just use the traditional measure. Frankly, there aren't many road wheels that aren't 700C any more and nobody's going to get pedantic about the measurement. You have to multiply the gear (in inches) by pi anyway to get rollout, which means you could argue that no one's expressed it right since time began anyway. Time to move on. Next thread?
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Old 10-10-07, 12:13 AM   #24
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The calculation is chainring teeth divided by cog teeth, multiplied by a constant. Whatever you want to make the constant, it still is a reliable ratio to use for comparison of gearing. It happens to work into a number that is big enough so you aren't working out into two decimal places plus it's something everyone has worked with for years. If you want to go around saying your gear ratio is 2.328, fine. Even on the track where people are changing gears repeatedly in an evening, and a couple inches worth of gear is meaningful, people just use the traditional measure. Frankly, there aren't many road wheels that aren't 700C any more and nobody's going to get pedantic about the measurement. You have to multiply the gear (in inches) by pi anyway to get rollout, which means you could argue that no one's expressed it right since time began anyway. Time to move on. Next thread?
Historically gear inches were used when people were still riding penny-farthings. The number of gear inches was simply the diameter of the big wheel. This was useful when comparing two penny-farthings and gave just as much information as roll-out (though again, slightly more abstract). When the safety bicycle was invented they then had to multiply the wheel diameter by the gear ratio, which is what is used today.

Multiplying by 27" isn't about multiplying by a constant (if that were the case, everyone would use 10 or 100). It's about expressing a number that is accurate independent of the size of the chainring, cog and tire. It's not about how many decimals you need to express, it's about having a figure that can be compared across multiple bike setups.

Even if you are using 700C road wheels, different tire sizes are going to give you a different number of gear inches. A bike geared at 51x15 with a 20C tire will have a gearing of 88.6". Throw a 30C tire on and it's now 91.3". This isn't being pedantic either - I use 23C tires on my commuter bike but when it snows I put 32C tires on, which increases my gearing by 2.1".

Take a look at any gear inch calculator. It will ask you for your wheel size and your tire size. This is because it does it correctly. You can bet that on the professional level they are using the correct method.

I'm sorry if you've been doing it wrong your entire life but that's no reason to spread misinformation.

Now it is time to move on. Next thread.

EDIT: Basically what I'm trying to say is that while multiplying your gear ratio by 27" might be a decent approximation for a 700C wheel it is not the proper method for calculating gear inches. It's an approximation and it doesn't work for other wheel/tire sizes.

The correct way is by multiplying by the diameter of the wheel. Multiplying by 27" is like multiplying by 3 instead of pi to determine the roll out. A decent approximation, but when you try to claim that multiplying by 3 is the appropriate method you just sound foolish.

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Old 10-10-07, 06:21 AM   #25
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Take a look at any gear inch calculator. It will ask you for your wheel size and your tire size. This is because it does it correctly. You can bet that on the professional level they are using the correct method.
I wouldn't be so sure. Everyone I know uses the method that they've known since their first coach told them to put an 81 on.

You seem to misunderstand what gear inches are used for at the track. Gear inches are used so that you can relate what gear you're in to someone else in an easily remembered number. Since everyone has a 19-23mm tires you're off by a half inch at most which as far as talking to others isn't really meaningful. However since EVERYONE understands gear inches to be based on a 27" wheel saying anything else is going to convey incorrect information. The other use is for you to know what various gears feel like to you. It's far more important that you remember what the number is than it be an actual calculation of gear inches. And that means that one set of numbers is better than a different one for every mm of tire size so why not just use 27".


for example:
Everyone get in an 81 for this warmup.
Guy on motor:what gear are you in
You(breathlessly):84.
hmmm last time I was here I was spinning out in an 88.6 but fine at home. Now I'm spinning out in an 88.6 at home I should gear up even more here.

As I said the only advantage would be to have an exact relation between race tires and training tires rather then the normal "it's a little bit lower."
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