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Can someone explain something to me about gearing

Old 06-30-11, 09:30 AM
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JAJ0404
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Can someone explain something to me about gearing

After many years of riding a bike, I'm now trying to understand the mechanicals behind the bike. I've been tinkering with my gearing but have run into something I just don't understand. If you go to a calculator like Sheldon Brown's for gear inches, just about any common combination of chainrings/cassettes gives you what I'm going to call overlap from the large ring to the small. What I mean is, for example, if you put in 53X39, with a cassette of 12-25 (700x23/172.5), your large ring will show gear inches from 116.1 to 55.7. The small ring will start at 85.4 and go to 41.0. It looks like there is overlap as you go from 10th at 55.7 to 9th at 85.4. Am I really not smoothly decending from 18 to 1? Or is there something else I'm missing here? Either an answer or a link to somewhere that would explain this would be greatly appreciated!
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Old 06-30-11, 09:51 AM
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You are exactly right. Multi-chainring (front gear) derailleur equipped bikes have tonnes of overlap between the gears. If you wanted to go from easiest to hardest gears in the smallest possible steps then you would have to find a complicated series fo shifts and memorize it. Luckily, there is no requirement to always go to the closest gear in the smallest step possible. You are free to switch in larger jumps, or just shift from one gear to another in whatever order you wish to keep you feet moving at a speed you find comfortable. The only general reccomendations are: try to keep the pedals turning at a fairly brisk pace (~90 rpm or higher), and avoid cross chaining (don't use large chainring/largest cog or smallest chainring/smallest cog) as these gears put the chain and derailleurs at severe angles and can cause accelerated wear or damage to the drivetrain. And even these are just reccomendations. You go ahead and ride however you like.

The only bikes that do not have overlap are single speeds, bikes with internally geared hubs (IGHs) and bikes with multiple rear cogs and only one chainring up front.
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Old 06-30-11, 09:51 AM
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If i understand right.... U mean that some gear ratios are repeated??? yes. Some combinations are almost the same but the feel of the gears are different. For example (just putting numbers in my head ok? i might be off because im not looking at any tables right now ok?) 52x19 is around the same than 42x16 but they feel completely different.

Now with a triple geared bike is even worse because there u have stuff repeated like like 3 times with some gears, u get the same development using 2 or 3 different combinations of gears, non efficient if you ask me, but for people that really can't climb at all it works. Now u know why compact cranksets are sold

How the gear will feel is given by the cog, as smaller the cog less torque has, as bigger the cog more torque it has. So even thought u have 2 gears that are almost the same they will feel different.

Have no idea what u mean with decending from 18 to 1 ??
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Old 06-30-11, 10:01 AM
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1. You shouldn't be using the 53:25 combo, or the 53:23 for that matter.
2. Referring to bicycle gearing as 1st, 2nd,.....18th makes little sense.
3. With bicycle gearing, "overlap" commonly means repetitive gears, i.e., duplication, not an overlap of range.
4. Mortal humans have a rather narrow power band. It's practical to utilize all gearing, shifting chainrings as necessary
5. Avoid cross-chaining, but use all other available ratios to maintain your desired cadence.
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Old 06-30-11, 10:14 AM
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Or get an IGH and the gearing is all sequencial.

But the overlap in gear inches is better now a days than 30 years ago. Standard double chainrings were 52-42, no the standard is 53-39 or for a compact double 50-34, this is for road cranksets. I think some of the reason for the overlap is not wanting too much jump in the front chainrings for smoother shifting.

Last edited by cyclist2000; 06-30-11 at 10:19 AM.
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Old 06-30-11, 10:15 AM
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Thanks for the answers. Is there any mechanical reason why they couldn't eliminate this by going to a smaller inner ring, like a 53X25, where there are no repeated gears? Is that too big of a jump to ensure a good chain transition or something?

(Have no idea what u mean with decending from 18 to 1 ?? - I meant going from 18th gear down through the gears to 1st gear)
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Old 06-30-11, 11:05 AM
  #7  
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Originally Posted by JAJ0404 View Post
Thanks for the answers. Is there any mechanical reason why they couldn't eliminate this by going to a smaller inner ring, like a 53X25, where there are no repeated gears? Is that too big of a jump to ensure a good chain transition or something?
1) That big of spread between the front gears would be a mechanical problem, leading to dropped chains, etc.
2) You want the overlap so you can avoid cross shifting or frequent chainring shifts.

The 18-1 comment doesn't make sense because you don't give each gear combination a sequential number in cycling. In reality, a bike with 2 front and 9 rear only has 14 useable combinations. There's a reason many cyclists resent early road bikes ever being called a "10 speed"
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Old 06-30-11, 11:18 AM
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I think the assumption of gearing most folks understand is one of "linearity." It's easy to understand, and on flat ground, with small variations in elevation or wind and fitness, linear gearing is straightforward and works. But the debate you're bringing up is the one being determined today, whether that linearity continues, even to lower gear ratios for ever steeper hill climbing.

And for some folks, they'd prefer a straight block rear and compact, but high differential front (e.g. 50 x 34), to minimize the overlap. But the flip side are folks that might only want a triple up front with close ratio double big rings (50 x 44) plus a bailout (e.g. 24) granny gear, and the rear is a narrow ratio 12 - 19 except for the last cog, which is a 34. The reasoning here is that most of the time, on flat or slightly sloped ground, they can move at a good clip, and for short sections, 90% of the time, honking out of the saddle to overcome a small hill and rest coming down the back side works great. But on the long (greater than 1/2 mile slogs up a steeper slope, especially with panniers and stuff), you need a granny gear to sustain that kind of pull indefinitely or the body starts to reject that kind of exertion in all sorts of nasty ways. So depending on fitness level, age, etc. you might see some red-faced folks pushing bikes up hills panting because the gearing isn't low enough and they've run out of aerobic capacity to sustain the level of exertion to overcome the hill at a speed where they can maintain balance and control and pedal comfortably and sustainably.

For me, it depends on the ride. And probably for lots of enthusiasts, we have more than 1 bike. One with a triple for steeper terrains, and one with a double and more narrow range rear cluster for road. Some of us have just a single-speed commuter too and bikes for all sorts of other occasions. There's no reason for not trying to setup a bike with wider range front gearing although, the issue might be finding a dual ring FD that has a cage low enough for a 25 small ring. Then you're limited to available triple FDs that have cages intended, for what you already suspected, as triple cranks with smaller hops between rings. But I have a touring bike right now with a triple 50x44x24, so a big jump between inner and middle rings isn't really a shifting issue.

If you have the gumption to try it, I'd like to hear about the experiences. I used to relish the challenge of enduring cycling on the edge of my fitness limit. I'd ride all over the place in a double with the lowest being a 42F x 23R or 42F x 21R and honk up hills. But as I got older, heavier, lazier, suffered more injuries, etc., a granny gear is now desirable and necessary. So I'm looking at a bike with mostly linear gearing, but with a really low granny/bailout gear.
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Old 06-30-11, 11:35 AM
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Originally Posted by ultraman6970 View Post
If i understand right.... U mean that some gear ratios are repeated??? yes. Some combinations are almost the same but the feel of the gears are different. For example (just putting numbers in my head ok? i might be off because im not looking at any tables right now ok?) 52x19 is around the same than 42x16 but they feel completely different.

Now with a triple geared bike is even worse because there u have stuff repeated like like 3 times with some gears, u get the same development using 2 or 3 different combinations of gears, non efficient if you ask me, but for people that really can't climb at all it works. Now u know why compact cranksets are sold

How the gear will feel is given by the cog, as smaller the cog less torque has, as bigger the cog more torque it has. So even thought u have 2 gears that are almost the same they will feel different.

Have no idea what u mean with decending from 18 to 1 ??

On my bike (mountain bike) the chainrings at the front are 44-32-22 and the sprockets at the back are 11-13-15-17-20-23-26-30-34

So based on the chainring I'm using the gearing, calculated as the ratio between the front and rear cogs, is (to three decimal places):


44:- 1.294 1.467 1.692 1.913 2.200 2.588 2.933 3.385 4.000
32:- 0.941 1.067 1.231 1.391 1.600 1.882 2.133 2.462 2.909
22:- 0.647 0.733 0.846 0.957 1.100 1.294 1.467 1.692 2.000

As you can see there are lots of similar gears. Referring to gear combinations as chainring/sprocket where small numbers indicate large cogs we can see that, for example, 1/5 is very similar to 2/7 which is similar to 3/9. 1/1 is similar to 2/3 and identical to 3/6. 1/2 is identical to 3/7, and 1/3 is identical to 3/8.

Which gear to choose would depend on what type of flexibility you want. If in any given situation you're comfortable with a gearing of about 1.6-1.7 but expect to want to go lower rather than higher then 2/5 makes more sense than 1/3. From 1/3 the only way you can go down is to 1/2 (which gets into chain-crossing territory) or to 2/3 which represents quite a substantial drop in gearing. From 2/5 you can drop to 2/4 which isn't such a drop, but you can still drop to 3/5 if you need a big drop.

If you're looking for gearing around 2 but expect to want to change up then 3/9 makes little sense because you've got nowhere to go and you've got chain-crossing issues. 2/7 makes more sense, but 1/5 probably makes more sense still because it gives you more scope to change up if you need it.

Last edited by contango; 06-30-11 at 11:39 AM.
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Old 06-30-11, 11:37 AM
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Originally Posted by gyozadude View Post
I'd ride all over the place in a double with the lowest being a 42F x 23R or 42F x 21R and honk up hills. But as I got older, heavier, lazier, suffered more injuries, etc., a granny gear is now desirable and necessary. So I'm looking at a bike with mostly linear gearing, but with a really low granny/bailout gear.
That's exactly what started all of this for me. I just rode. If I couldn't get up a hill, it was because I wasn't in good enough shape, or my equipment was outdated and it was time to upgrade to a new bike. Once I crossed over to buying a $2500 bike (I know, peanuts for some of you) I decided I couldn't just upgrade to a new bike, and I realized I'm never going to be in the kind of shape I used to be. Right now, I'm running out of gears about 95% of the way up big hills. So I started looking for a way to get another gear or two. I finally decided to change cassettes from my 12-25 to a 13-30. I don't plan on being in that low gear much, but it will be nice to have when I need it. That brought me to the question of overlap, it looked like a lot of waste, but I understand it a little better now. I also see why labeling gears 1-18 doesn't make sense, for just that same reason.

Thanks everyone for the information - - I learned something today, can't say that every day.
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Old 06-30-11, 11:51 AM
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Originally Posted by ultraman6970 View Post
52x19 is around the same than 42x16 but they feel completely different.
These aren't equivalent. Just looking strictly at ratios:

52 / 19 = 2.74
42 / 16 = 2.63

So, yes they'll feel different. If they really were the same ratio, they'd feel the same. 42/16 is closer to 52/20 (2.60)
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Old 06-30-11, 12:30 PM
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Overlap is a good thing. Without it you'll do a lot more shifting on the front.
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Old 06-30-11, 12:58 PM
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Originally Posted by BluesDawg View Post
Overlap is a good thing. Without it you'll do a lot more shifting on the front.
And, at least with my motor, the small difference between near-identical ratios sometimes represents a welcome difference between almost and exactly right gearing for a given situation.

It seems that many rookie riders and even some with experience assume the small ring is just where you find your low gears, medium just for medium and large just for high.
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Old 06-30-11, 03:57 PM
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Originally Posted by Ex Pres View Post
I'm running a 52/34 front by 12/22 7s rear on one bike and still have a couple of gears that overlap. But it's real close to sequential; and close ratio.
Overlap is also good because it reduces the need to cross-chain. You might be able to have close to 14 unique gears, but some (especially the low-end of the 52) will cause considerable cross-chaining.
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Old 06-30-11, 04:50 PM
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On my tourer I am running a half-step with a grandpa gear. The front is spaced at 10% with a 44-40 and a 20t grandpa ring. The back is spaced at 20% with an 11-13-16-19-23-28-34. To get a 10% change sometimes will require a double shift. With this set up I have 18 separate usable ratios. You won't get that on an 8, 9, 10, or 11 speed cogset.
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Old 06-30-11, 07:38 PM
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I said that i was just putting numbers from my head because i was NOT LOOKING AT THE TABLES AND THAT I WAS PROBABLY OFF!!!.... dammit!

These people

Originally Posted by JiveTurkey View Post
These aren't equivalent. Just looking strictly at ratios:

52 / 19 = 2.74
42 / 16 = 2.63

So, yes they'll feel different. If they really were the same ratio, they'd feel the same. 42/16 is closer to 52/20 (2.60)
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Old 06-30-11, 08:28 PM
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Contango i would advice you to just test the different gears, many will feel the same or based in your table they should feel the same because are close but in reality arent the same either. As for when use one or the other depends on you, my particular case i was pretty strong as a tracker but in the road i never went under 53x15 in a peloton (well if you put less than that the group let you behind), and I won a few things with 53x16 more than nothing because it was uphill, i was fast and because after 90 miles there is nothing else there. So many of the questions u have it depends, and the only way to know is just experiment with the gears and find the ones u like, be careful with the cross chain as somebody mentioned before.

Personally i hate odd cogs and chainrings because is hard for me to pace with them. Other people dislike cassettes that are jumping around (me) from a 17 to a 19 then a 24 for example. I would be happy with a 14-15-16-17-18-19-20-21-22-23, all my life i had hard times with freewheels and cassettes that have gears that are skipped, well that was long time ago, now whatever is just fine im not racing no more.

Cheers.
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Old 06-30-11, 09:03 PM
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Originally Posted by ultraman6970 View Post
I said that i was just putting numbers from my head because i was NOT LOOKING AT THE TABLES AND THAT I WAS PROBABLY OFF!!!.... dammit!

These people
It's called a calculator.
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Old 06-30-11, 09:04 PM
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Originally Posted by DCB0 View Post
You are exactly right. Multi-chainring (front gear) derailleur equipped bikes have tonnes of overlap between the gears.
Usually. Compact cranks and tight cogsets don't especially when you've yet to upgrade to 10 or 11 cogs in back and that's not a good thing - you really want the repeated gears for faster smoother shifting and less chain noise.

I currently ride 50-34x13-14-15-16-17-18-19-21-23. Disregarding the fully cross-chained 50x23 and 34x13 combinations (which are noisier and can lead to chain rub issues on the derailleur or big ring depending on equipment and setup) there's only one overlapping gear ratio provided by 50x21 and 34x14.

At a sustainable hard pace that means the small ring is only good for about 19 MPH and big ring down to 17. Going slower reasonable limits are about 18 and 15 MPH respectively. The net effect is that the wrong terrain, wind, fatigue, and rest day combinations there's a lot of shifting between rings which means the next gear is on the other ring five cogs away (ex - 34x15 is one notch easier than 50x21). That's more of a hassle and slower than one click on the rear shifter by itself.

It also means that in a lot of situations there's a lot more chain noise than with more overlap, as with 50-40-30x13-14-15-16-17-18-19-21 which provides the same overall range but would let me ride 40x16 or 40x17 in the middle of the cassette instead of the extreme combinations necessary with the wide range front and one end of the cassette.

If you wanted to go from easiest to hardest gears in the smallest possible steps then you would have to find a complicated series fo shifts and memorize it. Luckily, there is no requirement to always go to the closest gear in the smallest step possible.
Disregarding half-step setups people generally use the rings to select ranges, like on a 4x4 with a two speed transfer case. Steep climbs always call for the smallest ring; steep descents and big tail winds on flat ground always use the big ring. In between you might choose a ring to get tighter spacing (ex - with 53-39 x 12-13-14-15-17-19-21-23 you might ride 39x14 instead of 53x19 because the next higher and lower gears are closer), to minimize the shifting (you might go over a highway overpass using 53x21 instead of the 39x15 or 39x16 you'd use for a sustained grade of the same steepness because you'll be back at a fast pace in thirty seconds), or just get a better and quieter chainline (with 50-40-30x13-14-15-16-17-18-19-21-23 I'd take 40x17 in the middle of the cassette over 50x21)
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Old 06-30-11, 09:13 PM
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Originally Posted by ultraman6970 View Post
Personally i hate odd cogs and chainrings because is hard for me to pace with them. Other people dislike cassettes that are jumping around (me) from a 17 to a 19 then a 24 for example. I would be happy with a 14-15-16-17-18-19-20-21-22-23, all my life i had hard times with freewheels and cassettes that have gears that are skipped, well that was long time ago, now whatever is just fine im not racing no more.
Campagnolo makes 14-15-16-17-18-19-20-21-22-23 10 speed corncobs (the Veloce one can import for $45 has been discontinued, but you can still get the Centaur flavor).

Miche makes Shimano and Campagnolo splined 8/9/10 speed loose cogs with 11-16T first position sprockets and one tooth increments up to 29 teeth. I think Marchisio does the same thing. Cassettes mixed together from them should shift as well as things did before we got ramps and odd tooth profiles.

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Old 06-30-11, 09:52 PM
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Here's a graphic showing the three gear inch ranges.. I stole the numbers from contango's post above.. but it shows the overlap by the rear sprockets for each of the three front sprockets..

Attached Images
File Type: gif
gears.GIF (81.3 KB, 8 views)

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Old 06-30-11, 09:52 PM
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https://www.jbarrm.com/cycal/cycal.html
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Old 06-30-11, 10:07 PM
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Originally Posted by DCB0 View Post
The only bikes that do not have overlap are single speeds, bikes with internally geared hubs (IGHs) and bikes with multiple rear cogs and only one chainring up front.
that can be summed up as: any bikes with only one chainring in the front

also i think "half step" geared bikes dont have overlap
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Old 06-30-11, 11:00 PM
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Originally Posted by frantik View Post
also i think "half step" geared bikes dont have overlap
By definition they do. May not have any perfectly-duplicate gears, but definite overlap.
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Old 07-01-11, 02:13 AM
  #25  
frantik
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i thought the point of half step gearing was to eliminate overlap?
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