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Old 04-21-05, 04:10 AM   #1
billsmaine
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OCR 2 shifting

Hi All!, I am just getting back into biking after close to a 20 year absence and am really enjoying it. I bought a Giant OCR 2 bike and have been slowly getting used to the differences in technology the years have brought. The gears are paired with the brakes and work with a sidways motion. A black lever is used to shift up and the brake handle is pushed sideways to shift down. I am finding the gears but am having trouble organizing a picture in my mind of the gear layout. Eventually I get to the gear I want but there is no organized pattern emerging. Can anyone explain for me the gear sequencing on this bike? I could really use the help! Thanks. Bill
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Old 04-21-05, 04:45 AM   #2
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Hi Bill, here is a link to a bicycle gear/shifting chart.

http://www.panix.com/~jbarrm/cycal/cycal.30f.html

There are so many possibilities on chain ring/cassette patterns that you need to put your chain rings and each cog on your cassette into this chart to really tell where the shift points should be.
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Old 04-21-05, 05:33 AM   #3
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The Giant OCR3 has a 30/42/52 front triple chainring setup (I'm going to assume a 170mm crank) and a SRAM PG-950 12-26 cassette with a gear breakdown of 12-13-14-15-17-19-21-23-26. Based on that data and assuming a nominal 27" wheel diameter, I plugged everything into the gear calculator at this website and got the following shifting pattern.

Code:
Gear-Inch Chart
         (9)   (8)   (7)   (6)   (5)   (4)   (3)   (2)   (1)
    |    12    13    14    15    17    19    21    23    26
----+------------------------------------------------------
 52 | 114.3 105.5  98.0  91.4  80.7  72.2  65.3  59.6  52.8
 42 |  92.3  85.2  79.1  73.9  65.2  58.3  52.8  48.2  42.6
 30 |  65.9  60.9  56.5  52.8  46.5  41.6  37.7  34.4  30.4

Semi-Log Graph
  2                 3           4         5      6      7     8    9   1   1   2  3
 ----------------------------------------------------------------------------------
I                   1   2     3   4    5    6  7  8  9                             
M                                  1  2     3   4    5    6  7  8   9              
O                                           1  2     3   4    5    6  7   8  9     

Sheldon Brown's Gain Ratio Chart
    |    12    13    14    15    17    19    21    23    26
----+------------------------------------------------------
 52 |  8.54  7.88  7.32  6.83  6.03  5.39  4.88  4.46  3.94
 42 |  6.90  6.37  5.91  5.52  4.87  4.36  3.94  3.60  3.18
 30 |  4.93  4.55  4.22  3.94  3.48  3.11  2.82  2.57  2.27

Rollout Table in Inches
    |     12     13     14     15     17     19     21     23     26
----+---------------------------------------------------------------
 52 |  359.1  331.5  307.8  287.3  253.5  226.8  205.2  187.4  165.7
 42 |  290.0  267.7  248.6  232.0  204.7  183.2  165.7  151.3  133.9
 30 |  207.2  191.2  177.6  165.7  146.2  130.8  118.4  108.1   95.6
The semi-log chart is probably what you're looking for. This chart shows gear position as overlayed onto a development table. Across the top are gear-inches. The letters on the side denote (I)nner, (M)iddle and (O)utter chainrings and the numbers in each row indicate cog position with 1=26T and 9=12T.
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Old 04-21-05, 09:06 AM   #4
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Here's what I do (disregard the charts at first... they are there for mathematicians and confusion)

Find a front chain ring (left shifter) that provides you with a comfortable range of gearing (likely the small one or the middle one)
Keep it there . In other words, for now, ignore the left-hand brake-gear change lever (think of it as a front-brake lever... and remember: when you are flying down hill, engage the right or BACK brake lever first or you will end up cartwheeling on your bike!)

Now, use the gray shift lever on the right to move into easier gears (up hills or coming to stops); use the smaller/black shift lever to move into harder to pedal gears (down hills or on flats or with a tail wind)
LArge-gray lever on right: EASY gears
SMall black lever on right: harder gears

I have only two chainrings in front. I rarely transition to the larger chainring... only if I am on a long flat or down hill and want to 'tweak' (increase) my candence (pedal rotation speed) a bit. I will shift into the easiest gear in back and then shift up to a the larger cog in front (the difference is dramatic!) As my conditioning gets better, I may hesitate shifting up or down to allow my legs to work a wee bit harder... but mostly I use the gears to keep my rhythm smooth and seamless... by feel

That's my approach. I'm not counting teeth or analyzing ratios or such. I am listening to my legs and cardio rate, and adjusting for my comfort and speed. I adjust the gearing based on my needs not on some perceived mathematical scheme. All that rot is interesting later, over a beer with the biker geeks... while I am on the bike, I use a more intuitive approach.
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Old 04-21-05, 09:16 AM   #5
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And as you start up a hill, Sigurdd50, with someone coming up fast you have to shift one ring and six cogs because you didn't plan in advance and he goes by like you are standing still. Every ring/cog combination provides some points that are best for shifting between rings. It's nice to know what those points are. I guess you youngsters can overcome such lapses, but us older guys have to hold on to every advantage we find.
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Old 04-21-05, 09:34 AM   #6
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Quote:
And as you start up a hill, Sigurdd50, with someone coming up fast you have to shift one ring and six cogs because you didn't plan in advance and he goes by like you are standing still. Every ring/cog combination provides some points that are best for shifting between rings. It's nice to know what those points are. I guess you youngsters can overcome such lapses, but us older guys have to hold on to every advantage we find.
okay, since the initial poster did not indicate that he/she was or wasn't an advanced rider (I'm guessing they are a competent rider) or engaged in racing... I assumed that the rider was referring to basic riding and not racing, so worrying about (one's pride) when you are passed by some young hot shot is not a huge issue.
And to clarify, I'll say that I am not riding to race, just riding to ride for fun, and to get in shape for some casual summer touring, although I put on some speed when I need to (and at 50, with 35 years of riding, I can keep up), and I ride in smaller groups presently... not so much in club rides. If some rider blows by me, so be it. For me it ain't a race.

But if you re-read my first note, you may note that I'm not doing much shifting off the front rings... just up and down the back cog... as I hit the hill, to maintain cadence, i've already downshifted to maintain rhythm... this the key for me. Maintaining fluency in my cadence. If I hit my last easiest gear and I have 1-200 yards of hill left, I'll get up off the saddle and go
(to be honest, dare I admit this... but I run out of gears, and there is a lot of hill left, I"ll get off and walk and enjoy the scenery... perhaps this is the kind of post the belongs over inthe 'Touring' forum *laughs*)
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Old 04-21-05, 09:43 AM   #7
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I know people in the days of downtube shifters that had a shifting pattern taped to their stem since it was difficult to shift both the front and rear quickly and efficiently. I come close to running out of gears before I run out of hill as well, but knowing the best point to shift between rings makes it a little easier and often that translates to a little more enjoyment. You don't have to be a racer, but just someone that sort of keeps this info in the back of his mind to make even the hardest hills a little friendlier.
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Old 04-21-05, 10:31 AM   #8
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Thanks for the info.
I will find a comfortable position following your suggestions and go for it. You've help me quite a bit!
Thanks again, Bill
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Old 04-21-05, 11:14 AM   #9
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I know people in the days of downtube shifters that had a shifting pattern taped to their stem since it was difficult to shift both the front and rear quickly and efficiently
I agree here
especially in the day of downtube, fiction shifters (my Dawes still has the old Simplex friction shifters, but they control an older Suntour or Shimano 5-speed changer); that's an adventure going from one front gear to the next! I never count on being able to shift the big gears on the fly, and I wouldn't recommend it to anyone else -- even inthe age of STI.

On the other hand... moving up and down the rear gear cluster is a BREEEEEEZE with a Shimano 105 etc (I mean, it was 25+ years between buying new bikes and this new shifting system makes riding a blast!)

I relegate playing with the front gearing to when I am on a good long down hill or flat and want to get some extra OOOMPH. When I see a hill coming, I move back to the small gear (for you triple folks, the 'granny' gear) well before I start to climb.

The key is: get comfortable with any system, get out, and have some fun!
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Old 04-21-05, 01:25 PM   #10
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I think knowing your transition points is also important and this is what the semi-log chart depicts. It helps you shift in a way that preserves a better chainline thus allowing you to better avoid situations in which you may throw a chain.
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Old 04-21-05, 05:33 PM   #11
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Quote:
Originally Posted by khuon
Code:
Semi-Log Graph
  2                 3           4         5      6      7     8    9   1   1   2  3
 ----------------------------------------------------------------------------------
I                   1   2     3   4    5    6  7  8  9                             
M                                  1  2     3   4    5    6  7  8   9              
O                                           1  2     3   4    5    6  7   8  9     

Sheldon Brown's Gain Ratio Chart
    |    12    13    14    15    17    19    21    23    26
----+------------------------------------------------------
 52 |  8.54  7.88  7.32  6.83  6.03  5.39  4.88  4.46  3.94
 42 |  6.90  6.37  5.91  5.52  4.87  4.36  3.94  3.60  3.18
 30 |  4.93  4.55  4.22  3.94  3.48  3.11  2.82  2.57  2.27
The semi-log chart is probably what you're looking for. This chart shows gear position as overlayed onto a development table. Across the top are gear-inches. The letters on the side denote (I)nner, (M)iddle and (O)utter chainrings and the numbers in each row indicate cog position with 1=26T and 9=12T.
The gear-inch chart is OK to compare gear ratios on a single bicycle, but aside from the fact that it is not dimensionless and, worse yet, is measured in inches, the gain ratio is the only fair way to compare gear-ratios among different bicycles. And I can't for the life of me figure out why the plot is semi-logarithmic. It only covers a factor of about 4 along the x-axis and the forward movement of the bicycle in relation to the rotations of the crank, i.e., the gear-inches, couldn't be more linear. Am I missing something here?
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Old 04-21-05, 05:46 PM   #12
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Quote:
Originally Posted by jimshapiro
The gear-inch chart is OK to compare gear ratios on a single bicycle
Which is exactly what the original poster wanted.


Quote:
Originally Posted by jimshapiro
And I can't for the life of me figure out why the plot is semi-logarithmic. It only covers a factor of about 4 along the x-axis and the forward movement of the bicycle in relation to the rotations of the crank, i.e., the gear-inches, couldn't be more linear. Am I missing something here?
It's semi-log in order to normalise the viewing so that one can determine appropriate overlap and shift points. the original poster is not interested in the actual numbers nor how they compare to other gear setups on other bicycles. The original poster was interested in figuring out the pattern of gearing progression on the Giant OCR2 and how it relates to which gear combination.
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Old 04-22-05, 08:16 AM   #13
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Quote:
Originally Posted by khuon
It's semi-log in order to normalise the viewing so that one can determine appropriate overlap and shift points. the original poster is not interested in the actual numbers nor how they compare to other gear setups on other bicycles. The original poster was interested in figuring out the pattern of gearing progression on the Giant OCR2 and how it relates to which gear combination.
How does a sem-logarithmic graph "normalize the viewing"? The purpose of such plots is to linearize exponential relationships, generally for curve-fitting purposes, but everything here is linear. The overlap and shift points, whereever they are, will be on both linear and semi-logarithmic plots, just in different places. Does it have something to do with the angle of the chain between extreme positions of the chainrings and cogs?
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Old 04-22-05, 08:46 AM   #14
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Quote:
Originally Posted by jimshapiro
How does a sem-logarithmic graph "normalize the viewing"? The purpose of such plots is to linearize exponential relationships, generally for curve-fitting purposes, but everything here is linear. The overlap and shift points, whereever they are, will be on both linear and semi-logarithmic plots, just in different places. Does it have something to do with the angle of the chain between extreme positions of the chainrings and cogs?
What I should have said was "normalise for webpage viewing". My guess is that the author wanted this ascii plot to fit within the boundaries of the webpage. I agree that it's all linear. And in hindsite, he probably should have just plotted it on a linear plot. It also looks like his plotting code may be slightly flawed because it generates some incorrect positioning. Here's the linear plot. Notice some of the cog positioning relationships have changed around the 60 to 65 gear-inch range.

Code:
Linear Graph                                                                         
  2          3          4          5          6          7          8          9          10         11         12         13
 ----------------------------------------------------------------------------------------------------------------------------
I            1    2  3    4  5        6   7   8     9        
M                          1     2    3     4      5         6     7     8       9  
O                                     1       2     3      4         5          6       7       8        9
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Old 04-22-05, 10:00 AM   #15
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Quote:
Originally Posted by khuon
It also looks like his plotting code may be slightly flawed because it generates some incorrect positioning. Here's the linear plot. Notice some of the cog positioning relationships have changed around the 60 to 65 gear-inch range.

Code:
Linear Graph                                                                         
  2          3          4          5          6          7          8          9          10         11         12         13
 ----------------------------------------------------------------------------------------------------------------------------
I            1    2  3    4  5        6   7   8     9        
M                          1     2    3     4      5         6     7     8       9  
O                                     1       2     3      4         5          6       7       8        9
I agree. I checked a few of his numbers and they were correct, but the plot is suspect. For example M-4 is 58.3 and O-2 is 59.6, putting the latter to the right of the former, on either plot, but those two points are in the reversed (wrong) order on the log plot. I'll write a little program to do the same calculations and plot. Stay tuned.
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Old 04-22-05, 10:09 AM   #16
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Quote:
Originally Posted by jimshapiro
I'll write a little program to do the same calculations and plot. Stay tuned.
Well, as you rightly point out in a previous post, the better numbers to use would be gain-ratios so maybe you should plot those instead. I had a Tcl script which calculated and plotted rollout.
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Old 05-12-05, 03:22 PM   #17
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Quote:
Originally Posted by jimshapiro
It only covers a factor of about 4 along the x-axis and the forward movement of the bicycle in relation to the rotations of the crank, i.e., the gear-inches, couldn't be more linear. Am I missing something here?
Don't mean to argue, but "gear inches" are not the forward travel of the bike. You'd have to factor by pi to get that. A 100 inch gear will actually send you 314.16 inches down the road for each full rotation of the chain ring.
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Old 05-12-05, 03:37 PM   #18
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Hi Bill,
I see you are from Maine? The shop you got it from would be glad to show you anything you need to know. If it was Allspeed, I have done business with them on and off since the 80's. They would help, heck it's easy enough that i could show you.

Being a lazy sod I mostly leave it on the middle chainring up front. I just work up and down the rear gears. When I hit a real hill, I jump down to the wimp gear. When I go down the hill, it's up to the big ring. (Mostly I coast downhill, I am in pretty bad shape).

I think everybody does it a little differently. You will get some chain rub, a little nudge on the left will bring the front derailleur into line. It's actually pretty easy, and once you get used to it, you'll wonder how you ever lived without it.
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Old 11-22-15, 06:35 PM   #19
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You ... Sir, thank you. Much Appreciated.
Cheers,
Peter

Quote:
Originally Posted by Sigurdd50 View Post
Here's what I do (disregard the charts at first... they are there for mathematicians and confusion)

Find a front chain ring (left shifter) that provides you with a comfortable range of gearing (likely the small one or the middle one)
Keep it there . In other words, for now, ignore the left-hand brake-gear change lever (think of it as a front-brake lever... and remember: when you are flying down hill, engage the right or BACK brake lever first or you will end up cartwheeling on your bike!)

Now, use the gray shift lever on the right to move into easier gears (up hills or coming to stops); use the smaller/black shift lever to move into harder to pedal gears (down hills or on flats or with a tail wind)
LArge-gray lever on right: EASY gears
SMall black lever on right: harder gears

I have only two chainrings in front. I rarely transition to the larger chainring... only if I am on a long flat or down hill and want to 'tweak' (increase) my candence (pedal rotation speed) a bit. I will shift into the easiest gear in back and then shift up to a the larger cog in front (the difference is dramatic!) As my conditioning gets better, I may hesitate shifting up or down to allow my legs to work a wee bit harder... but mostly I use the gears to keep my rhythm smooth and seamless... by feel

That's my approach. I'm not counting teeth or analyzing ratios or such. I am listening to my legs and cardio rate, and adjusting for my comfort and speed. I adjust the gearing based on my needs not on some perceived mathematical scheme. All that rot is interesting later, over a beer with the biker geeks... while I am on the bike, I use a more intuitive approach.
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