Gearing Question

[Longshot]

OK, help me out here please.

I have a triple with 8 gears on the back and, in order to understand the differences between the various gearing combinations, I ran the numbers on Excel to get the ratios of each combinations.

For ease, I labelled the biggest at the front "A", middle "B", etc and, on the back I labelled the lowest gear "1", through to the highest gear "8".

Obviously, my top gear is A8.

Interestingly, A7 and B8 are almost identical ratio. However, on the road, A7 feels quite a bit harder to work than B8. Is there a reason for this that I'm not understanding?

 

[SpokeyDokey]

OK, help me out here please.

I have a triple with 8 gears on the back and, in order to understand the differences between the various gearing combinations, I ran the numbers on Excel to get the ratios of each combinations.

For ease, I labelled the biggest at the front "A", middle "B", etc and, on the back I labelled the lowest gear "1", through to the highest gear "8".

Obviously, my top gear is A8.

Interestingly, A7 and B8 are almost identical ratio. However, on the road, A7 feels quite a bit harder to work than B8. Is there a reason for this that I'm not understanding?

Only that small differences make a big difference.

Use this:

http://www.bikecalc.com/gear_ratios

 

[snailracer]

....
Interestingly, A7 and B8 are almost identical ratio. However, on the road, A7 feels quite a bit harder to work than B8. Is there a reason for this that I'm not understanding?

Both those gears are quite high, which implies high speed. At high speeds, air resistance is the dominant factor. The power required to overcome air resistance is proportional to speed cubed, so a small increase in speed requires a large increase in power. For example, a 10% increase in speed requires roughly a 33% increase in power. So small differences in ratio, at high speeds, results in a large differences in power i.e. rider effort. Of course, all this assumes that A7 is faster than B8, otherwise I'm talking b0ll0cks.

 

[ColinJ]

It seems unlikely that the step between rings at the front is almost identical to the step between sprockets at the back. How many teeth are there on the rings and sprockets in question?

 

[Longshot]

Both those gears are quite high, which implies high speed. At high speeds, air resistance is the dominant factor. The power required to overcome air resistance is proportional to speed cubed, so a small increase in speed requires a large increase in power. For example, a 10% increase in speed requires roughly a 33% increase in power. So small differences in ratio, at high speeds, results in a large differences in power i.e. rider effort. Of course, all this assumes that A7 is faster than B8, otherwise I'm talking b0ll0cks.

Sorry, A7 is marginally slower than B8 according to the numbers.

 

[Longshot]

It seems unlikely that the step between rings at the front is almost identical to the step between sprockets at the back. How many teeth are there on the rings and sprockets in question?

This is the set up - 48/38/28 front and 11/32 rear. The final column shows the ratio

(A) 48 (8) 11 R 4.36
(B) 38 (8) 11 R 3.45
(A) 48 (7) 14 R 3.43
(A) 48 (6) 17 R 2.82
(B) 38 (7) 14 R 2.71
(C) 28 (8) 11 R 2.55
(A) 48 (5) 20 R 2.40
(B) 38 (6) 17 R 2.24
(A) 48 (4) 23 R 2.09
(C) 28 (7) 14 R 2.00
(B) 38 (5) 20 R 1.90
(A) 48 (3) 26 R 1.85
(A) 48 (2) 29 R 1.66
(B) 38 (4) 23 R 1.65
(C) 28 (6) 17 R 1.65
(A) 48 (1) 32 R 1.50
(B) 38 (3) 26 R 1.46
(C) 28 (5) 20 R 1.40
(B) 38 (2) 29 R 1.31
(C) 28 (4) 23 R 1.22
(B) 38 (1) 32 R 1.19
(C) 28 (3) 26 R 1.08
(C) 28 (2) 29 R 0.97
(C) 28 (1) 32 R 0.88

 

[ColinJ]

Ah - huge steps between the sprockets!

I can't explain the apparent difference you are experiencing, because the ratios are almost identical.

What I can say though, is that I wouldn't fancy those big steps between gears at the back. I bet you very rarely need to use a 48/11 gear. My highest gear is a 52/14 and that is fine to well over 30 mph which I can only do for a very short distance or downhill. Do you ever really use the 48/11 or the 28/32?

Something like a 13-26 (13.14.15.17.19.21.23.26) would be a lot nicer to use if you didn't need the extreme gears that your current setup offers.

 

[Longshot]

Ah - huge steps between the sprockets!

I can't explain the apparent difference you are experiencing, because the ratios are almost identical.

What I can say though, is that I wouldn't fancy those big steps between gears at the back. I bet you very rarely need to use a 48/11 gear. My highest gear is a 52/14 and that is fine to well over 30 mph which I can only do for a very short distance or downhill. Do you ever really use the 48/11 or the 28/32?

Something like a 13-26 (13.14.15.17.19.21.23.26) would be a lot nicer to use if you didn't need the extreme gears that your current setup offers.

Thanks. I do use the 48/11 but only on downhills. I errm do actually use the 28/32 - being a fat sod, I do need it uphill!

 

[ColinJ]

Thanks. I do use the 48/11 but only on downhills. I errm do actually use the 28/32 - being a fat sod, I do need it uphill!

No shame in that - my bottom gear is a 26/28! (I only geared my bike down to that when I was at my fattest and I intend to go back to higher gearing as soon as my current health & fitness problems allow me to.)

Give it a year or two and I bet a more compact cassette will become a realistic option for you. You could then replace the 28 ring with a 26 to give you a low gear of 26/26 which would be about 14% harder than the one you have now.

 

[Longshot]

Give it a year or two and I bet a more compact cassette will become a realistic option for you. You could then replace the 28 ring with a 26 to give you a low gear of 26/26 which would be about 14% harder than the one you have now.

Indeed. I'm looking at N+1 options already but won't pull the trigger until I know I've improved enough to make the hills with a compact set up.

 

[Nigelnaturist]

No shame in that - my bottom gear is a 26/28! (I only geared my bike down to that when I was at my fattest and I intend to go back to higher gearing as soon as my current health & fitness problems allow me to.)

Give it a year or two and I bet a more compact cassette will become a realistic option for you. You could then replace the 28 ring with a 26 to give you a low gear of 26/26 which would be about 14% harder than the one you have now.

This, I started last year and geared my bike with a 48x34 and 26x13 on a 7 sp, though I did change that fairly quickly to 48x28 and 48x24, so I ended up with a 48/38/26 front and 11-13-15-17-19-21-24 rear which worked really well for me, as I got fitter I changed the front back back to the original 52/40/30 and currently run a 13-15-17-19-21-23 -26, though i very rarely use the 30th ring these days unless going up a long hill (of which there are not to many around here, so steep short ones though).

The gears are what I had on the left yours on the right, I have come across it said for a given ratio it's better to be on the larger ring on the front, something to do with less actual moving parts at any given moment ( I think it's because as the chain is in contact with the front chain ring less is moving, not to sure of the full terminology)
You might do better changing the 28 front ring and 11-13-15-17-19-21-24-28