gear ratios
shiznit76
Posts: 640
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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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 29.65.0 
Have a play with this: http://www.gearcalculator.com/#KB=34,5 ... =2099&SL=2"It must be true, it's on the internet"  Winston Churchill0

Download bike gear calculator for your phone, you can see all the possible gear combinations and their speed/cadence variations0

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?0 
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).0 
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...0

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.
Paul0 
cheers0

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.0

cheers0

Someone does the maths for you which explains the sprocket sizes, the someone else makes a joke and you can't raise a :roll:0

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...
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.BASI Nordic Ski Instructor
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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.0

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...
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 work0 
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 exist0 
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
Get it on eBay!0