Gearing Question(s)

[Dave7]

My terminology may not be correct but hear goes
My bike has 20 gears. Shimano 105s. Comapct front. 11-28 at the back.
I mainly ride on the smallest chainring (front) as I tend to cruise 12-18 mph. I notice that when changing the rear up/down there is just one change (somewhere near the middle) when the difference seems noticeably greater than any other changes....it is the same feeling whether changing up or down.
I would have thought the sprocket/cogs have evenly spaced, progressively larger/smaller number of teeth but the maths dont seem to work out in my head.
So..............
IS THERE really one change that is bigger/smaller than the others or is it my imagination ?

 

[raleighnut]

Yep, @Nigelnaturist is your guy for explaining/hating this jump.

 

[si_c]

Assuming you have the 10 speed 105 setup, the 11-28t cassette has the following tooth counts 11-12-13-14-15-17-19-21-24-28, the bigger differences are at the big end, in the middle there are only 1 or 2 tooth differences between the cogs. For the 11 speed 11-12-13-14-15-17-19-21-23-25-28. This is of course assuming you have the shimano rear cassette. If you have a non-shimano cassette, it is entirely possible there is a larger jump in the middle somewhere, although I think there tends to be a greater difference at the larger end of the cassette between the low gears.

 

[bpsmith]

If I make the assumption that you ride at a cadence of 80 and have the Shimano 10 speed 11-28 cassette listed above then, on 34 at the front, your 12-18 mph range means you are using the sprockets between 11 and 17. The 16 tooth sprocket is quite possibly the one that you are noticing the difference on.

You would have to change to an 11-23 or a 12-25 to get that 16 tooth sprocket.

 

[Dogtrousers]

Here's a picture. The Y axis is gear inches. The left hand stack of points is the ratios in the little ring. The right hand stack is the big ring. You can see the big jump from 15-17 in the middle. Assuming you have 11-12-13-14-15-17-19-21-24-28, 34/50

 

[Dave7]

[QUOTE 3800232, member: 9609"]how many teeth do you have on each sprocket ? starting from the smallest ideally they should increase by a similar percentage all the way up to the biggest.
my are as follows - I would imagine a roadie in the flatlands would find these differences too big, but for a plodder like me in hill countryside they are good for me.

32 - 14.3% easier than the 28 tooth
28 - 16.7%
24 - 14.3%
21 - 16.7%
18 - 12.5%
16 - 14.3%
14[/QUOTE]
All I can tell you is that it's 11-28. I have been on the Giant website but the Full spec' page** doesn't give those details.
**http://www.giant-bicycles.com/en-gb...t.defy.advanced.2/14975/66538/#specifications

 

[Dave7]

Assuming you have the 10 speed 105 setup, the 11-28t cassette has the following tooth counts 11-12-13-14-15-17-19-21-24-28, the bigger differences are at the big end, in the middle there are only 1 or 2 tooth differences between the cogs. For the 11 speed 11-12-13-14-15-17-19-21-23-25-28. This is of course assuming you have the shimano rear cassette**. If you have a non-shimano cassette, it is entirely possible there is a larger jump in the middle somewhere, although I think there tends to be a greater difference at the larger end of the cassette between the low gears.

That is very interesting..........thanks.
Where do you get that information ?? I am about to change to 11-32 for a bit of help on the hills so would like to see the format for that.
** It is all Shimano (10 speed 105s)

 

[Dave7]

Here's a picture. The Y axis is gear inches. The left hand stack of points is the ratios in the little ring. The right hand stack is the big ring. You can see the big jump from 15-17 in the middle. Assuming you have 11-12-13-14-15-17-19-21-24-28, 34/50

I must be honest and say..........that has somewhat lost me (Y axis & gear inches etc.). You are talking to a 68 year old that left school with absolutely no qualifications
I can see the "big jump" from 15 to 17 and that coincides with what I feel is happening.
Thanks you for that.

 

[Dogtrousers]

I must be honest and say..........that has somewhat lost me (Y axis & gear inches etc.). You are talking to a 68 year old that left school with absolutely no qualifications
I can see the "big jump" from 15 to 17 and that coincides with what I feel is happening.
Thanks you for that.

Well, that's basically what I was trying to show, so I'm happy

 

[si_c]

That is very interesting..........thanks.
Where do you get that information ?? I am about to change to 11-32 for a bit of help on the hills so would like to see the format for that.
** It is all Shimano (10 speed 105s)

I pulled it from the shimano website:

http://cycle.shimano-eu.com/publish...d/105_5700/product.-code-CS-5700.-type-..html

 

[kiriyama]

I noticed this when I changed from an 11-25 to an 11-28. Worth the inconvenience for that extra gear when you live somewhere hilly!

Might be smoother shifting to have an 11-23/25 on the back and a triple chain ring on the front (triples have an extra even smaller chainring) but I can't be bothered to do the maths and I'm too cool to have a triple