gear ratios

shiznit76
shiznit76 Posts: 640
edited September 2017 in Road beginners
Hi, if I were riding a compact chainset with 34 on front and 28 on back, what would equivalent gearing at back be be with a 36 chainring on front? This is probably an absolutely shockingly basic question, but I am new to thsi

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  • Alex99
    Alex99 Posts: 1,407
    shiznit76 wrote:
    Hi, if I were riding a compact chainset with 34 on front and 28 on back, what would equivalent gearing at back be be with a 36 chainring on front? This is probably an absolutely shockingly basic question, but I am new to thsi

    It is shockingly basic. But the answer is 29.65.
  • andcp
    andcp Posts: 644
    Have a play with this: http://www.gear-calculator.com/#KB=34,5 ... =2099&SL=2
    "It must be true, it's on the internet" - Winston Churchill
  • trivial_poursuivant
    trivial_poursuivant Posts: 1,136
    Download bike gear calculator for your phone, you can see all the possible gear combinations and their speed/cadence variations
  • shiznit76
    shiznit76 Posts: 640
    Alex99 wrote:
    shiznit76 wrote:
    Hi, if I were riding a compact chainset with 34 on front and 28 on back, what would equivalent gearing at back be be with a 36 chainring on front? This is probably an absolutely shockingly basic question, but I am new to thsi



    It is shockingly basic. But the answer is 29.65.


    is there a simple equation to work this out?
  • Alex99
    Alex99 Posts: 1,407
    shiznit76 wrote:
    Alex99 wrote:
    shiznit76 wrote:
    Hi, if I were riding a compact chainset with 34 on front and 28 on back, what would equivalent gearing at back be be with a 36 chainring on front? This is probably an absolutely shockingly basic question, but I am new to thsi



    It is shockingly basic. But the answer is 29.65.


    is there a simple equation to work this out?

    Equation 1): ratio = chainring teeth / sprocket teeth

    Rearranges to Equation 2): sprocket teeth = chainring teeth / ratio

    Using Equation 1: The ratio with 34 28 is 34/28 = 1.214 (meaning the rear wheel turns 1.214 times every time the crank goes around).

    Then using Equation 2 and the ratio we just calculated:
    36 / 1.214 = 29.65 (round to 30). Or if you have a 39t chain ring, 39/1.214 = 32.11 (round to 32).
  • imposter2.0
    imposter2.0 Posts: 12,028
    Take a camera with you, so you can film the shop assistant's face when you ask for a cassette with a big sprocket with 29.65 teeth...
  • paul2718
    paul2718 Posts: 471
    28/34=S/36, so S = (36 * 28)/34 = 29.65

    (Both sides of the equation are equal, but we don't know the top part of the right, the equivalent sprocket. If we multiply both sides by 36 they remain equal, but now it turns into S=.... and the answer falls out.)

    So back in the real world 36x30 is the same as 34x28.

    Paul
  • shiznit76
    shiznit76 Posts: 640
    edited September 2017
    cheers
  • webboo
    webboo Posts: 6,087
    When you find out actually you haven't got the right gear ratio and end up walking up that hill, you might wish you hadn't had your sense of humour surgically removed.
  • shiznit76
    shiznit76 Posts: 640
    cheers
  • webboo
    webboo Posts: 6,087
    Someone does the maths for you which explains the sprocket sizes, the someone else makes a joke and you can't raise a :) :roll:
  • shiznit76
    shiznit76 Posts: 640
    Webboo wrote:
    Someone does the maths for you which explains the sprocket sizes, the someone else makes a joke and you can't raise a :) :roll:
    :D:D:D , sorry
  • davidof
    davidof Posts: 3,103
    shiznit76 wrote:
    Imposter wrote:
    Take a camera with you, so you can film the shop assistant's face when you ask for a cassette with a big sprocket with 29.65 teeth...
    This is supposed to be for beginners so why dig me out for asking a beginners question? This is what is wrong with so many "experinced" cyclists, to far up their own backside that newbies feel like idiots.

    because it is not a beginners cycling question but a beginners algebra question. So if you are under, say 12, then fair enough, otherwise you should have learned all this in school.
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  • kesa
    kesa Posts: 35
    For me i entered all my cog sizes and then chainring sizes into excel and simply worked out the ratios of each individual combination. Then i simply change one cell value as needed.
  • shiznit76
    shiznit76 Posts: 640
    Kesa wrote:
    For me i entered all my cog sizes and then chainring sizes into excel and simply worked out the ratios of each individual combination. Then i simply change one cell value as needed.


    Cheers, that's more like sensible answer looking for
  • shiznit76
    shiznit76 Posts: 640
    davidof wrote:
    shiznit76 wrote:
    Imposter wrote:
    Take a camera with you, so you can film the shop assistant's face when you ask for a cassette with a big sprocket with 29.65 teeth...
    This is supposed to be for beginners so why dig me out for asking a beginners question? This is what is wrong with so many "experinced" cyclists, to far up their own backside that newbies feel like idiots.

    because it is not a beginners cycling question but a beginners algebra question. So if you are under, say 12, then fair enough, otherwise you should have learned all this in school.


    Another keyboard warrior, thanks for advice, keep up the good work
  • fat daddy
    fat daddy Posts: 2,605
    Imposter wrote:
    Take a camera with you, so you can film the shop assistant's face when you ask for a cassette with a big sprocket with 29.65 teeth...

    I know this is in jest .... but I have a sprocket with approximately 29.65 teeth on it .... I don't use it any more for obvious reasons .. but they do exist :D
  • shiznit76
    shiznit76 Posts: 640
    fat daddy wrote:
    Imposter wrote:
    Take a camera with you, so you can film the shop assistant's face when you ask for a cassette with a big sprocket with 29.65 teeth...

    I know this is in jest .... but I have a sprocket with approximately 29.65 teeth on it .... I don't use it any more for obvious reasons .. but they do exist :D

    Get it on eBay!

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