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Gear Ratios

by Jetmans Dad
Wed, Oct 24, 2018 11:02
12

Hi there, 

I am currently riding a triple with fairly standard 50/39/30 chainset and 11-28 cassette on the back. Is there an easy way of putting my 24 gears into their ratio order in order to see in black and white where the duplications are. 

It is more for interest than anything else, but I am also looking at a new bike and tempted to go 2x11 instead of a triple next time, and would also like to make a comparison with the potential options for the new beast. 

I assume it is not quite as simple as just adding the total number of teeth together?

David

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12 comments

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SilverBugle | 6 years ago
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Sora FC3503 and 105 FC5703 chainsets are still on sale and both have a 74 BCD inner.  I know you can fit a 26 inner to both because I replaced the 30 on the Sora on my Roubaix with a basic Stronglight alloy 26 (and you can find a good selection of those at Spa Cycles).  I have just replaced the 3503 with a 5703 chainset and switched the 26 over.  That is running quite happily with the rest of the 9 speed Sora groupset, including chain and I haven't touched the front mech.  Next stage , which is going to be tedious because of the internal cable routing, is to replace the Sora shifters for the 105 equivalents and the 11-32 9 speed casette to a 12-28 10 speed.  That will give me nice small gaps between the gears.  I won't miss the 11, but I might miss 26/32.lowest gear.  I would be interested to know if BehindTheBikeSheds has actually fitted a 24 to this type of set up without adjusting the front mech or is just theorising.  When it is all done I will have the gear ratios that suit me rather than what Mr Shimano thinks I need and will have saved 250g along the way.

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BehindTheBikesheds | 6 years ago
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If you're simply after a lower gear, pop a 26 or 24 on the inner, you're likely to not need to change the front derailleur at all. Be wary of going 2x11 to cover the same low/high as you will have bigger jumps between the ratios, 30/28 needs 34/32, if like me you have a 24 inner then you'd need 34x40 to replicate the ratio, this is even worse and produces massive jumps, it's a real bane when trying to keep a steady cadence whether increasing or decreasing speed and adjusting for incline/declination.

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rdmp2 replied to BehindTheBikesheds | 6 years ago
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Assuming (possibly incorrectly) that the op is looking for same high/low combinations then 2x11 will offer smaller increments between gears than 3x8, not bigger (except when front shifting obvs)

 

BehindTheBikesheds wrote:

If you're simply after a lower gear, pop a 26 or 24 on the inner, you're likely to not need to change the front derailleur at all. Be wary of going 2x11 to cover the same low/high as you will have bigger jumps between the ratios, 30/28 needs 34/32, if like me you have a 24 inner then you'd need 34x40 to replicate the ratio, this is even worse and produces massive jumps, it's a real bane when trying to keep a steady cadence whether increasing or decreasing speed and adjusting for incline/declination.

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BehindTheBikesheds replied to rdmp2 | 6 years ago
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rdmp2 wrote:

Assuming (possibly incorrectly) that the op is looking for same high/low combinations then 2x11 will offer smaller increments between gears than 3x8, not bigger (except when front shifting obvs)

 

BehindTheBikesheds wrote:

If you're simply after a lower gear, pop a 26 or 24 on the inner, you're likely to not need to change the front derailleur at all. Be wary of going 2x11 to cover the same low/high as you will have bigger jumps between the ratios, 30/28 needs 34/32, if like me you have a 24 inner then you'd need 34x40 to replicate the ratio, this is even worse and produces massive jumps, it's a real bane when trying to keep a steady cadence whether increasing or decreasing speed and adjusting for incline/declination.

I was thinking of 9 or 10 speed not 8 so my bad, however upon looking if you check out the middle gears actually the 11 speed with an 11-40 does have a wider gap between them.

With a 32mm tyre:

11-40 +34 gives 29.1" - 42.9" over 4 sprockets

11-28 +24 gives 30.3" - 42.4" over 4 sprockets

The important 17/19/21+39 gives 60.8/54.4/49.3

The 21/24/27 + 50 on the double gives you 63.1/55.3/49.1

Still horses for courses and far cheaper to whack a 24 sprocket on a triple than going to the massive expense to getting the wider range on a double.

 

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fukawitribe replied to BehindTheBikesheds | 6 years ago
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BehindTheBikesheds wrote:

Still horses for courses and far cheaper to whack a 24 sprocket on a triple than going to the massive expense to getting the wider range on a double.

The OP was considering a new bike - if that wasn't for the gearing alone then the difference in cost between those two might be moot. It also doesn't sound like they're trying to significantly extend the bottom range, just compare the options of double to triple.

 

Edit : I would love to put a smaller ring on the inner of my 50-39-30 but can't go any lower due to Shimano's odd mounting decision for the FC-4603 meaning it has a 92mm BCD granny rather than a 74mm... hurrumph.

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Jetmans Dad replied to fukawitribe | 6 years ago
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fukawitribe wrote:

BehindTheBikesheds wrote:

Still horses for courses and far cheaper to whack a 24 sprocket on a triple than going to the massive expense to getting the wider range on a double.

The OP was considering a new bike - if that wasn't for the gearing alone then the difference in cost between those two might be moot. It also doesn't sound like they're trying to significantly extend the bottom range, just compare the options of double to triple.

Yeah, it was really so I can see how the ratios of the 2x11 compare to the 3x8 and see what the options look like. I live in a fairly flat area of the country so even the range I have at the moment is probably more than I really need on a day to day basis. 

Informative debate, though. Thank you. 

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Jetmans Dad | 6 years ago
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Wow, fantastic responses ... exactly what I was after. 

Thank you, 

D

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rdmp2 | 6 years ago
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Use this link. Put your existing setup in and use "compare" button to put new option side by side. If you are looking for same spread as existing setup 50/34 11-32 is bang on.

http://ritzelrechner.de/

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armb replied to rdmp2 | 6 years ago
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rdmp2 wrote:

Use this link. Put your existing setup in and use "compare" button to put new option side by side. If you are looking for same spread as existing setup 50/34 11-32 is bang on.

http://ritzelrechner.de/

You can link directly to specific comparisons, for example that's

http://ritzelrechner.de/?GR=DERS&KB=34,50&RZ=11,12,13,14,16,18,20,22,25,...

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fukawitribe | 6 years ago
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http://www.gear-calculator.com/

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StraelGuy | 6 years ago
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Easy to do in Excel. Create a small spreadsheet with your chainrings as 3 rows and your sprockets as the columns and then a basic formula in each cell and you'll be able to see all your ratios.

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Rod Marton | 6 years ago
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For each gear combination, divide the number of teeth on the chainring by the number of teeth on the cassette cog and multiply by 27. This gives the gear in terms of 'gear inches', which is the usual way of comparing ratios in this country. For example, your top gear is (50/11)*27 = 123 inches.

I know it's a strange measurement, but it dates back to the days of penny farthings when the only way to have a different gear was to have a different sized wheel.

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