## Knowing gear ratios

Big Pete 1
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Joined: Mon Jan 04, 2016 1:45 pm

### Knowing gear ratios

It appears to me that many riders, including me, are not familiar with gear ratios.
Now and again I hear older riders talk about gear ratios to each other, like" During a sprint I can handle 93 but not 100."
I Know that these numbers are derived by gears and wheel diameter formula. But it seems confusing to know what is what when everybody uses different teeth numbers on their bike. So I have some questions:

1. If it was important to know these gear ratio numbers, and whatever they supposed to mean, why don't most riders (I know) use them?
2. So what is the point of knowing these figures if nobody else knows them (except the older guys)?
3. What is the advantage of knowing these figures?
4. If these ratios are important, how do I get to know these figures?

darkhorse75
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### Re: Knowing gear ratios

They're talking about ' Gear inches'. http://www.bikecalc.com/gear_inches It's just a universal measurement of how hard it is to push a certain chainring/sprocket combo.

RonK
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### Re: Knowing gear ratios

You cannot make valid gearing comparisions with another rider unless both are using the same chainring/sprocket/wheel diameters.

By reducing all this information to gear inches, valid comparisions can be made even if the rider uses a different combination.

Read Sheldon Brown. Sheldon explains gear measurement methods then takes the calculation a step further by including crank length.
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Big Pete 1
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### Re: Knowing gear ratios

Thank you darkhorse75 and Ronk for your response.
However, as I said, I already know where the term and formulas are.
Unfortunately I still have not got any answers to my original questions.

rodneycc
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### Re: Knowing gear ratios

Its nice to know when comparing compact/Semi compact and standard cranks. Also good when comparing small ring vs Big ring combos. I've never used the gear inches but have looked up the lower number gear ratio's (as in darkhorse's link).

I'm no maths giant though and can never remember off the top of my head what the exact numbers are per cog/chainring. Its something I look up after a ride out of interest (especially if I'm struggling to find the right gear for a particular piece of common terrain I'm riding and experimenting with).
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chriso_29er
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### Re: Knowing gear ratios

I cant imagine many people knowing the gear inchs of all their gear combos of a 20 speed plus bike off the top of their head.

The conversations you're refering to might be to do with single speed race bikes for example.
People would be more likely to know their preference in gear inchs which gives them the all round performance they need for the race itself and the sprint finish?

MichaelB
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Location: Adelaide, South Australia

### Re: Knowing gear ratios

Big Pete 1 wrote:
1. If it was important to know these gear ratio numbers, and whatever they supposed to mean, why don't most riders (I know) use them?
2. So what is the point of knowing these figures if nobody else knows them (except the older guys)?
3. What is the advantage of knowing these figures?
4. If these ratios are important, how do I get to know these figures?

Answers :

1. It isn't important. Just enjoy riding.
2. There isn't, unless the other person you are talki9ng to knows them.
3. Bugger all.
4. They aren't, but if you want them, google "gear inch calculation" and realise that the answer to #3 says it all

Only numbers I care about on the bike are time of day, and how much longer I can ride for before the Missus gets cranky.

Big Pete 1
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### Re: Knowing gear ratios

Okay rodneycc, chrisco, and Michael. Thanks for input.

baabaa
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### Re: Knowing gear ratios

Kinda nice to know if you ride single speed as you can buy differing sets of cogs/ freewheels and front chainrings and then end up with the same gear.
Pretty easy to talk in gear inches and "guess" a ratio on a multi geared bike if you do ride ss, but if you don't then it really is not that important.

rodneycc
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### Re: Knowing gear ratios

btw this might sound dumb but I still reckon gear ratios are too complicated with 2 chain rings. They should of made them more logical, for example:

chainring 1 cogs 1-11 easiest
chainring 2 cogs 1-11 hardest

(without that lower/end gears overlap if you know what I mean)

Just my 2c worth.

Edit: In the world of Di2 you could set it up to do that I guess....
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Alex Simmons/RST
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### Re: Knowing gear ratios

Fixed gear riders, in particular track riders, use them to work out what gearing is suitable for the event, track, conditions and form they have. They choose a cog and chainring to suit.

For bikes with multiple gears, it's not particularly relevant since you can simple change gear with a simple click or button press. All most people need to know is whether the smallest gear they have is small enough to ride up the slopes they expect to face.

The standard gear ratios most people quote are based on a hypothetical 27" wheel, (which no road or track bike uses nowadays), the real gearing is a bit different. But the 27" custom stuck and it's a convenient way to quickly convey the options, and the relative gear differences.

e.g. if I want a 90" gear, I know that's a 50x15 gear (since 27 * 50 / 15 = 90)

Most track riders will know by heart common gear ratios (as based on a 27" wheel).

Do a race and realise the track is fast today, so you want to move up an inch or two from your 91.8" and you have available 48-52T chainrings and 14 and 15 tooth cogs. It helps to know the relative gear options in your head so you can pick the right cog and chainring to fit to the bike.
e.g.
48/14 is 92.6"
52/15 is 93.6"
49/14 is 94.5"

Nikolai
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### Re: Knowing gear ratios

Big Pete 1 wrote:3. What is the advantage of knowing these figures?

I grew up with gear ratios and can't think of gears any other way. Not sure if knowing this has any advantage. And what advantage are we talking about anyway?

To give you an example... Let's say I hit a hill on 53x19 and I know at some point I'll have to drop the chain to the small ring, let's say it's 39. I know that 53x19 is almost the same as 39x14 so if I want a smooth shift without raising my cadence too much, I'd shift to 39x15 or 39x16 if the gradient is rising quick. I had to know this when I was racing.

Another scenario... You approach a hill and you know the right gear for it will be 53x19 but you don't want to mess around with too much shifting and decide to start on 39 from the bottom. When you know the ratio, you know the gear you want is 39x14.

am50em
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Location: Sydney

### Re: Knowing gear ratios

This calculator is good for visualizing and comparing different setups.
Unlike some of the others it includes tire sizes.
For fun the following compares my bike (Giant Revolt) with a "standard" road bike and adjusting cassettes for each to give the same range of development (or speed at given cadence).

http://www.gear-calculator.com/?GR=DERS&KB=32,48&RZ=11,12,13,14,15,17,19,21,23,25&UF=2170&TF=60&SL=2.5&UN=KMH&GR2=DERS&KB2=39,53&RZ2=12,13,14,15,17,19,21,24,27,30&UF2=2125

So an ultra compact (48,32) with 11-25 cassette (and wider tires) matches a standard 53,39 with a 12-30 cassette and gives the benefit of closer ratios.

RonK
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### Re: Knowing gear ratios

Big Pete 1 wrote:Thank you darkhorse75 and Ronk for your response.
However, as I said, I already know where the term and formulas are.
Unfortunately I still have not got any answers to my original questions.

If you can't see any point to it, then there clearly is no importance or advantage to you at all.

It's useful for me to know what gearing I want/need when I'm sourcing components for a build.

For example, for a roadie I'm comfortable with a standard 53/39 chainset and an 11-25 cassette.

For my touring bikes I don't care so much what the high gear is, but I know from experience that I want a low gear of around 18-20 gear inches by an available chain ring and sprocket combination to get me and my loaded bike over the passes.
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Big Pete 1
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### Re: Knowing gear ratios

Thank you baabaa, rodneycc, Nikolai, am50em, and Ronk.
I have a better understanding of the gear inch significance.

Duck!
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### Re: Knowing gear ratios

rodneycc wrote:btw this might sound dumb but I still reckon gear ratios are too complicated with 2 chain rings. They should have made them more logical, for example:

chainring 1 cogs 1-11 easiest
chainring 2 cogs 1-11 hardest

(without that lower/end gears overlap if you know what I mean)

Just my 2c worth.

Edit: In the world of Di2 you could set it up to do that I guess....

That would be virtually unrideable, because you'd have an impractically narrow cassette range and an impossibly wide chainring jump, and a huge amount of clatter and faffing around changing between low and high ranges.

The Synchro function on Di2 doesn't so much eliminate overlapping gears, but works around them by its strategic placement of chainring shifts in the gear sequence, but you only get around 15 individual ratios (I haven't precisely counted how many it leaves you with out of the 22 on the bike).
I had a thought, but it got run over as it crossed my mind.

piledhigher
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Location: Kew, Victoria

### Re: Knowing gear ratios

Alex Simmons/RST wrote:Fixed gear riders, in particular track riders, use them to work out what gearing is suitable for the event, track, conditions and form they have. They choose a cog and chainring to suit.

So much this, when I was riding track most had a chart of gear inches covering the rings and cogs they had, I was lazy and had a rule of thumb, 50x15 was my base, 90 inches, add a cog tooth is roughly 6 inches, add a chain ring tooth is roughly 1 inch. I've seen people change a cog ad chain ring to get a extra 1/2 inch.

Derny Driver
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### Re: Knowing gear ratios

piledhigher wrote: I've seen people change a cog and chain ring to get a extra 1/2 inch.

Oh for sure - I did a special order of 4 unusual sized chainrings and cogs for my ladies Teams Pursuit team at Nationals so that I could have them on .8 of an inch bigger than what they usually ride. Exact gearing is very important for track racing. Anyone who has done a track race on too big or small a gear will know all about it.

piledhigher
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### Re: Knowing gear ratios

Derny Driver wrote:
piledhigher wrote: I've seen people change a cog and chain ring to get a extra 1/2 inch.

Oh for sure - I did a special order of 4 unusual sized chainrings and cogs for my ladies Teams Pursuit team at Nationals so that I could have them on .8 of an inch bigger than what they usually ride. Exact gearing is very important for track racing. Anyone who has done a track race on too big or small a gear will know all about it.

But to me it gets to princess and the pea stuff, on a track bike I can managed pretty easily 20x gear inch sized steps between and 84 for club training and 104 for a motorpace at horsham with 3 cogs and 4 chainrings, faffing to get even smaller steps seems excessive.

Derny Driver
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### Re: Knowing gear ratios

piledhigher wrote:But to me it gets to princess and the pea stuff, on a track bike I can managed pretty easily 20x gear inch sized steps between and 84 for club training and 104 for a motorpace at horsham with 3 cogs and 4 chainrings, faffing to get even smaller steps seems excessive.

To ride, say a pursuit, faster - you have 2 choices, pedal faster (cadence) or increase the gear inches and pedal at the same rate as before. I have had a team lose a National TP title by 5 hundredths of a second after 12 laps. Many titles are decided by very small margins. Im not looking for marginal gains but rather optimum performance. I do extensive practise with my riders wearing full race kit, race wheels, trying different gears and different cadences to find the best gear for the event and rider.
I currently have a lady who can run 8 laps like clockwork on a 94 inch gear, she has done it many times and is always within a second of her target. We need to take 8 seconds off her pursuit time, so I have twice put her on 95 inches and she can only manage 3 laps before blowing up in spectacular fashion. My job is to problem solve what is going on - nevertheless my point is that a gear inch on a track bike, in certain cases, is quite a jump in my opinion.

am50em
Posts: 402
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Location: Sydney

### Re: Knowing gear ratios

rodneycc wrote:btw this might sound dumb but I still reckon gear ratios are too complicated with 2 chain rings. They should of made them more logical, for example:

chainring 1 cogs 1-11 easiest
chainring 2 cogs 1-11 hardest

(without that lower/end gears overlap if you know what I mean)

Like this
http://www.gear-calculator.com/?GR=DERS ... 95&SL=2.6&

rodneycc
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### Re: Knowing gear ratios

Duck! wrote:That would be virtually unrideable, because you'd have an impractically narrow cassette range and an impossibly wide chainring jump, and a huge amount of clatter and faffing around changing between low and high ranges.

The Synchro function on Di2 doesn't so much eliminate overlapping gears, but works around them by its strategic placement of chainring shifts in the gear sequence, but you only get around 15 individual ratios (I haven't precisely counted how many it leaves you with out of the 22 on the bike).

Yeah I know I'm getting into wild hypertheticals and I'm a bit conflicted as well because I actually don't like large jumps in large range cassettes but I would of thought factory techs would of looked at the design of the front derailleur and tried to accomodate like a 34/53 chainring combo and address that chainring jump to widen those ratios and smooth over the jumps? Or is that pushing the boundaries of the design.

The 1x chainring mtb system with one of those massive 11-46 cassettes are kind of interesting as well. Wonder what the jumps are like with that? Prob doesn't matter as much on the trails the chain jumps? Id like to try that one day.

Its a long way from the 30 gear triple (which I kind of really liked the ratios with the triple except for the front derailleur changes).
So there I am conflicted again!
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Alex Simmons/RST
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### Re: Knowing gear ratios

Derny Driver wrote:I currently have a lady who can run 8 laps like clockwork on a 94 inch gear, she has done it many times and is always within a second of her target. We need to take 8 seconds off her pursuit time, so I have twice put her on 95 inches and she can only manage 3 laps before blowing up in spectacular fashion. My job is to problem solve what is going on - nevertheless my point is that a gear inch on a track bike, in certain cases, is quite a jump in my opinion.

At those speeds, 1 second per lap quicker requires 15-20% more power. That's the problem. increase power that much and time to exhaustion goes from a handful of minutes to less than a minute.

am50em
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Location: Sydney

### Re: Knowing gear ratios

http://biketestreviews.com/having-the-b ... s-gearing/
A friend of mine uses a 52/36 and told me while he was out on a recent charity ride that one of the organizers had a 54/34 Di2 setup and loves it. Now that’s a 20T difference that still shifts fine!

rodneycc
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### Re: Knowing gear ratios

am50em wrote:http://biketestreviews.com/having-the-best-of-both-worlds-gearing/
A friend of mine uses a 52/36 and told me while he was out on a recent charity ride that one of the organizers had a 54/34 Di2 setup and loves it. Now that’s a 20T difference that still shifts fine!

Great Article! 34/52 yeah wouldn't mind that. Dunno about the 34/54, surely that would have some shifting issues? Funny it was older blokes doing this. I probably fit into that category, self preservation!
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