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Thread: Gear Ratio

  1. #1
    Senior Member jaxgtr's Avatar
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    Gear Ratio

    I am in need of info on how to determine what is the best Chain Rings\Cassette combo to have on my road bike. On my hybrid, I was riding a 48-38-28 triple with a 11-32 cassette, I changed the cassette to more road based 12-23 and it was working out fairly well for me. On my new bike, I have a 53-39 double with a 13-25 cassette. I find myself almost always in the large ring in about the 5th or 6th cog through out the ride. Doesn't leave a lot of options. On my Hybrid, I would ride about 65 in the middle and 35 in the large and had almost the entire cassette to play with if needed.

    Since I basically know squat about gear ratio's other the very extreme basics, I want to learn more about it. So, 1. A good resource, looked on Sheldon's site, not much on it, and 2. is a 12-23 a better option with the 53-39 on the front than the 13-25 since I am in the flat lands of the Southeast and tallest thing I will ride up is a bridge about 100 to 150 ft high. My house is 4 ft above sea level if that tells you how flat it is.

    Any help is appreciated.
    Brian | 2013 Cannondale SuperSix 5 | 2003 Trek 7300 | 2014 Trek CrossRip Comp
    Quote Originally Posted by AEO View Post
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  2. #2
    Senior Member ken cummings's Avatar
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    Way back when the first rider to drop out of a RAAM was from Florida. He had knee problems on the first major climbs. Later he said hill training for him was doing repeats over Interstate overpasses . Find the steepest slope in your area, find the cog you need to go up it, and get a cluster that goes from 11 to that cog number. Seriously, the ramp in a parking garage might be something to check out.
    This space open

  3. #3
    Senior Member jaxgtr's Avatar
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    The triple came on the hybrid which is why I was happy that this bike had a double. The granny is a waste of time and weight and I will never ever use it.
    Brian | 2013 Cannondale SuperSix 5 | 2003 Trek 7300 | 2014 Trek CrossRip Comp
    Quote Originally Posted by AEO View Post
    you should learn to embrace change, and mock it's failings every step of the way.

  4. #4
    Senior Member Bill Kapaun's Avatar
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    Not much on Sheldon's site???
    Did you look at the gear calculator?
    http://sheldonbrown.com/gears/

    Plug in you existing set up and print/save it.
    Analyze it. What ranges do you use.
    Are there any gaps you would like to fill. For example if you use 15 & 17 a lot, would a 16 be useful etc.?
    Any gears you don't use etc. What do you give up?
    Plug in the new combination.
    Compare the Gear Inches.
    Is it an improvement.
    What do you give up?

    I don't know what will work best for you. Maybe the 12-xx or even an 11-xx???

    You didn't mention the number of cogs on the back, so your mileage may....

  5. #5
    Senior Member Bill Kapaun's Avatar
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    Quote Originally Posted by ken cummings
    Way back when the first rider to drop out of a RAAM was from Florida. He had knee problems on the first major climbs. Later he said hill training for him was doing repeats over Interstate overpasses . Find the steepest slope in your area, find the cog you need to go up it, and get a cluster that goes from 11 to that cog number. Seriously, the ramp in a parking garage might be something to check out.
    I prefer to have 1 lower gear than I expect to need.

  6. #6
    Opus PATH's Avatar
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    Take alook at this. It may be of a little help.

    http://vps.arachnoid.com/bike/
    Go raibh an chóir ghaoithe i gcónaí liom!

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  7. #7
    Banned. Mr. Beanz's Avatar
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    Change the 39 chainring to a 42.

  8. #8
    Senior Member jaxgtr's Avatar
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    Quote Originally Posted by Bill Kapaun
    Not much on Sheldon's site???
    Did you look at the gear calculator?
    http://sheldonbrown.com/gears/

    Plug in you existing set up and print/save it.
    Analyze it. What ranges do you use.
    Are there any gaps you would like to fill. For example if you use 15 & 17 a lot, would a 16 be useful etc.?
    Any gears you don't use etc. What do you give up?
    Plug in the new combination.
    Compare the Gear Inches.
    Is it an improvement.
    What do you give up?

    I don't know what will work best for you. Maybe the 12-xx or even an 11-xx???

    You didn't mention the number of cogs on the back, so your mileage may....
    I saw this and yea, I can plug in all the info and get a nice print out, but I don't understand what it is telling me. I'm trying to find something that can tell me what I am looking at, what do the number mean, explain to me how to interpet the data. I have a 9 spd 13-25 setup.

    I am riding about 95% in the 53 ring and don't use 13, 23, or 25 cog for the most part, on occasion, but typically use the 15,16,17,19 and 21.
    Brian | 2013 Cannondale SuperSix 5 | 2003 Trek 7300 | 2014 Trek CrossRip Comp
    Quote Originally Posted by AEO View Post
    you should learn to embrace change, and mock it's failings every step of the way.

  9. #9
    Banned. Mr. Beanz's Avatar
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    Lets see, you don't use the 53- 23 or 25? That's great cause if you were, you'd be crossing the chain which you're not supposed to do.

    Don't use the 53-23, that's great cause that's a big gear to push. Good for a big downhill.

    You do use the 53-15,16,17,19? What's the problem?

    It's ok to use the big gear on a roadie and the middle on a hybrid. Off the top of my head, the 53/17 combo may be the same as the 38/13. So it doesn't matter if you're in a big ring or a middle ring if the gear inches match or are real close.

    Maybe both these combos equal 65 gear inches. Just guestimating. Look at the chart and compare the gear inch combos.

  10. #10
    Senior Member jaxgtr's Avatar
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    Quote Originally Posted by Mr. Beanz
    You do use the 53-15,16,17,19? What's the problem?

    It's ok to use the big gear on a roadie and the middle on a hybrid. Off the top of my head, the 53/17 combo may be the same as the 38/13. So it doesn't matter if you're in a big ring or a middle ring if the gear inches match or are real close.

    Maybe both these combos equal 65 gear inches. Just guestimating. Look at the chart and compare the gear inch combos.

    See this is the problem, earlier you mentioned change the 39 to a 42, why? What does that get me? Besides more teeth, what the difference? This is what I want to learn about. How different size cogs or rings will effect my riding or performance. Once I understand that, I can then look at all the nicely configured programs that give me lots of numbers and have a clue as to what they mean.
    Brian | 2013 Cannondale SuperSix 5 | 2003 Trek 7300 | 2014 Trek CrossRip Comp
    Quote Originally Posted by AEO View Post
    you should learn to embrace change, and mock it's failings every step of the way.

  11. #11
    Senior Member Bill Kapaun's Avatar
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    Can you live without the 25 ALL THE TIME? If you aren't POSITIVE, you probably shouldn't get rid of it.

    Will you ever need the 12. If not, a 12-23 won't do you any good since the only difference is you are swapping the 12 for the 25.

    If you expect your conditioning to improve in the future where you might use the 12 AND can live without the 25, you could make the swap then if you want.

    I like to have 1 gear lower than I expect I'll ever need.
    Last edited by Bill Kapaun; 04-12-07 at 05:03 AM.

  12. #12
    Banned. Mr. Beanz's Avatar
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    You don't have hills so you can use a 42. Which means you will be able to ride the small ring which will give you more gear combos. The 39 may be too small for you if you are not comfortable riding in it with your current set up of rear cogs.

    The 42 may give you some in between gear ratios of the 53 ring. For example, a 53/15 may give you a 75 gear inch combo. The 53/16 may give you a 78 combo. But the 42/13 may give you a 76 combo.

    Maybe you are a bit more comfy pushing the 76 combo. 75 being a bit too easy and the 78 a bit too hard. It's all about comfort on the pedals.

    Since you arent climbing, the 39 combos are too light on the flats. The 42 will give you bigger gears with the cog set up you have. Maybe your 39/16 combo might only give you a 65 gear inch combo that is way too lite for your style on the flats. SO change the 39 to the 42 tom ake the 16 cog front ring a biger gear.


    What you have to do is write down all the combos you have with your set up53/12=...53/13=...53/14=...all the way down the line. Find the gear you like. Then do the small ring the same 39/12=.... on down the line. Take note of the differences between the big gears and the small ring gears. Then do it with the 42 ring. Maybe the 42 will have gears closer to whayt you have in the big ring. If they are close, then you might want to change to the 42 just to have a close range of gears.

    Or find out what combos are on your hybrid. Then figure out if the 42 or the 39 match the gears on your road bike. Would it be closer if you had the 42? It's all about what gears you like and what gears are comfy for you.

    If you ar comfy opushing the 53/15.16.17, there is nothing wrong. If you think it's strange that you use smaller gears on yor hybrid like 48/13,14,15, there is nothing wrong.

    Hybrids are not as efficient as roadies so you would need a bigger gear. You need a lower gear on a hybrid as they are harder to push. Like a loaded touring bike, you would need the lower gears to push it up a hill. On a roadie, you could go up in a 39/25 but on the loaded touring bike, you may need a third front rig, 30/25 which would give you smaller gear combos.

    What I find thoug is that eventhough I ride the flats plenty, I am fine with the 53 or 39. I'd use about the same range as you if I were pushing the 53. But I actually prefer to use the 39/14 combo. I find it more efficient to spin my legs fast which results in les fatigue. I'm not sure why you would need to change the gears at all. On the flats, I can do 22 mph in the small ring 39/14. After that, I'd need to change to the 53 doing 24-26 mph. If you need bigger gears then you might want to work on leg speed rather than "mashing" pushing hard gears all the time which is bad for the knees.

    A 53/39 should be fine for flats.

  13. #13
    Senior Member mkadam68's Avatar
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    Back in the old days, they rode penny farthings. The gearing was fixed: one turn of the pedals made one turn of the wheel. This directly translated into linear distance (so many inches--I don't know how many). The larger the distance, the bigger the gear, the harder to turn. The inches were a direct result of how big the wheel was.

    Today, we have free-wheels: not fixed. Through some fancy-dancy algebra, we can calculate these gear inches (using Sheldon Brown's website). Then, you can compare apples to apples. (Actual inches may vary because our bodyweight compresses the tire, effectivly changing it's diameter and resulting linear distance.) And see what gearing you need.

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  14. #14
    Senior Member jaxgtr's Avatar
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    Thanks for the info, this will help. I found some info at the library and hope it will help me in my learnin'
    Brian | 2013 Cannondale SuperSix 5 | 2003 Trek 7300 | 2014 Trek CrossRip Comp
    Quote Originally Posted by AEO View Post
    you should learn to embrace change, and mock it's failings every step of the way.

  15. #15
    No one carries the DogBoy
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    jax, I'm not sure what exactly you are asking for, but basically there are a few things you can use to help you figure things out.

    1. What do gear combos mean? Gear ratios determine how many rotations of the wheel will occur with a single rotation of the cranks. The crank numbers (39/52) divided by the cluster number (12-23 or whatever) gives you this number. So, if you are in 52-15, the rear wheel will rotate 3.46 times per revolution of the crank.

    2. Based on the information in #1, figure out what cadence (number of crank rotations per minute) you like to ride (typically 80-100), and at what speed you typically travel. Use the circumference of the wheel to back into the rotation you desire. Assuming you have a 700-23c wheel, you can guestimate the circumference as 210 cm, or 82.7 in. If you typically ride 18 mph, that means 229.91 wheel rotations per minute. Divide this by your desired cadence (say 85) and you find you need a gear ratio of about 2.7. This should be about mid-cassette. If you are in your 53, that would put you in the 19 or 21 cog, and in the 39 it would be the 14 or 15 cog (but you didn't mention a 14, and I'm assuming you are running 8-sp)

    3. By my math, assuming an 85 cadence gives you the following speeds with each of your gears:
    Code:
    	39	53
    13	20.0	27.1
    15	17.3	23.5
    16	16.2	22.0
    17	15.3	20.7
    19	13.7	18.6
    21	12.4	16.8
    23	11.3	15.3
    25	10.4	14.1
    Now, maybe with this as a basis, you can explain what you are trying to do...#1: shorten the jumps between gear spacing but keep the overall spread, #2, shorten the the total width and shorten the spacing, or #3 I need more high speed gears, or #4 fewer lowspeed gears.

    Unless you are wicked fast (I'm not discounting this possibility) it seems like you have plenty of gears for typical riding. If you are racing I'd say go for an 11-21 cassette, but for the most part, I'm not sure what your goals are, so I'm having trouble assessing the best information to provide.

    EDIT: Just saw you have a 9-sp. Assuming its a 14, your new numbers are 18.5 and 25.2.
    Last edited by DogBoy; 04-13-07 at 03:47 PM.

  16. #16
    Senior Member jaxgtr's Avatar
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    Dogboy, this is exactly what I was looking for. I just needed someone to present it in a different way that I could grasp, so I have a better understanding of what the number mean and how to interpet them. I am amassing a nice collection of info and it is becoming a little more clear, less muddy as they say.

    I appreciate everyones help on this. For whatever reason, I was having a hard time grasping this, but I think the porch light has turned on.
    Brian | 2013 Cannondale SuperSix 5 | 2003 Trek 7300 | 2014 Trek CrossRip Comp
    Quote Originally Posted by AEO View Post
    you should learn to embrace change, and mock it's failings every step of the way.

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