Ratio question

lizzylad84

Is 34/25 the same as 39/27(8)?

Seaswimmer

lizzylad84 wrote: »

Is 34/25 the same as 39/27(8)?

1.36 v 1.44 (27) and 1.39 (28)

so not quite..

Al Wright

If you take the wheel circumference into account,
Distance travelled per crank rev = Wheel Circ. x chainwheel teeth /sprocket teeth.

As an example: 700C wheel with a 28mm tyre has a circumference of about 2.2m

Therefore distance travelled;
34/25 arrangement; 2.2 x 34/25 = almost 3 metres
39/27 arrangement; 2.2 x 39/27 = almost 3.18 metres

There is a link on CTC website to a spreadsheet that includes calculations for all combinations
http://www.ctc.org.uk/cyclists-library/components/transmission-gears

Unknown Soldier

I have and 11-32 on the rear with a 50/34 crankset.

Am I wrong in thinking that adding a crank set of 52/36 will make my rear 32 a 30?

The extra two front teeth detracting from the rear?

crosstownk

Unknown Soldier wrote: »

I have and 11-32 on the rear with a 50/34 crankset.

Am I wrong in thinking that adding a crank set of 52/36 will make my rear 32 a 30?

The extra two front teeth detracting from the rear?

34x32 will give a ratio of 1.0625:1

36x32 will give a ratio of 1.125:1

To answer your question, 34x30 will result in 1.1333r:1 - so basically the answer is yes - not exactly but damn close.

bren_mc

Unknown Soldier wrote: »

I have and 11-32 on the rear with a 50/34 crankset.

Am I wrong in thinking that adding a crank set of 52/36 will make my rear 32 a 30?

The extra two front teeth detracting from the rear?

The calculation is not quite what you have but the end result is quite similar. 36 / 32 would be the equivalent of having 34 / 30.22

worked out as follows:

36/32 = 1.125

34/1.125 = 30.222

Unknown Soldier

Cheers for the replies and info.

I'm off to become a "Goat" with added speed.

It will be the death of me