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Old 03-26-07, 02:47 PM   #1
robo
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What is a versatile gearing range for a 3x9 drivetrain?

I'm asking just because i'm not sure where to start here.. I'm building up my first road-ish bike, and need to choose a cassette.

On the front, i have a 26-36-46 triple crank. I plan to use the bike as an 'all around' road bike. Mostly general road riding, not racing, perhaps some longer trips, and dirt road riding as well. I'm 27 and relatively fit.

I was looking at a 12-25 cassette, and plugged the numbers into Sheldon's gear calculator. Problem is, i don't know how to interpret the results, although my guess was that the mountain crank mated with the roadie cassette might give a good compromise gearing..

Attached is a screenshot of what i got. Does this gearing sound acceptable for my purposes?


For those averse to clicking, it ranges from 27.0 to 99.7 gear inches..


thanks!

-robin
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File Type: gif gear-ratio.gif (25.6 KB, 18 views)
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Old 03-26-07, 02:54 PM   #2
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What is the lowest gear you think you need? Go 1 gear lower and calculate up for there.
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Old 03-26-07, 03:12 PM   #3
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If possible compare the gearing and terrain you are considering with gearing and terrain you have ridden in the past. A 12-25 cassette with your particular triple will give you very low gearing as compared to typical road bikes. But, in my opinion, typical road bikes have gearing too high for most riders. You could consider an 11-23 cassette for flatter terrain or high speed descents. What is best for you will depend mostly on the type of terrain you will be riding and your physical conditioning. And it never hurts to have more than one cassette.
You should also consider the cadence range you plan to ride. A cadence of 85 - 100 is best for most riders.

Al

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Old 03-26-07, 03:15 PM   #4
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I think you'll be more than fine with that combination....perhaps 23 for the low end. When I was 27 I used to ride a 42-52 upfront, and 13-21 in the rear, and never had too much difficulty getting up hills. I suspect with the triple up front, 23 would be more than adequate. But if you want to play it safer, try the 25, then after riding it some, you'll know...

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Old 03-26-07, 03:18 PM   #5
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You're my age and I'm relatively fit, too
I'm guessing you plan to use 700c wheels, not 650b as the predictor spits out? Although it's not a huge diff either way.

My main nice ride, a rebuilt Centurion (see my sig) has 48/36/24 chainrings and a 12-25 cassette. It's certainly a wide enough range for nearly anything I'd encounter in regular road riding, unless I were carrying gear or a pack on my bike along with myself.
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Old 03-26-07, 03:25 PM   #6
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In my opinion, anything over 100 gear inches is a waste for me, as a casual rider, so you are fine on the high end, right at 100 gear inches...

Unless you plan on cruising at over 30 mph, the high end is fine... If you want to go faster on a descent, get up to speed, and get into an aero position... If you insist on powering down minor hills at 40+ mph, then you will need higher gearing, but otherwise, the high end is fine.

And I would say that 27 gear inches should be good for most climbs, so that seems like a reasonable cassette for that crank.
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Old 03-26-07, 04:29 PM   #7
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Cool - thanks. The bike will indeed have 650b wheels, BTW.

One more twist is that i'm planning to put it on an older Ultegra 8-speed rear cassette, which while it fits 9-speed cassettes, won't take an 11-t rear. So 12t is my smallest option at the back.

So i think i'll go with this cassette, and if i find that i need something higher or lower, i can either get a bigger large chainring, or a smaller granny ring.


Does that sound like a reasonable plan?


Thanks


-robin
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Old 03-26-07, 04:31 PM   #8
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The top end seems a bit low for a road bike, but unless you want to pedal past 30 mph you should be fine. The low end should be nice for any climb down to about 4 mph (slower than that, you start to fall over anyway!) The close spacing for your chainrings will allow you to fine tune your gears and use less front shifting.

edit: oh if you have 650c wheels, the gearing will be even lower. What size tires will you be using on them?
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Old 03-26-07, 05:35 PM   #9
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Quote:
Originally Posted by forensicchemist
I think you'll be more than fine with that combination....perhaps 23 for the low end. When I was 27 I used to ride a 42-52 upfront, and 13-21 in the rear, and never had too much difficulty getting up hills. I suspect with the triple up front, 23 would be more than adequate. But if you want to play it safer, try the 25, then after riding it some, you'll know...

mark
you must have been very strong or don't have real hills where you live. those are andy hampsten or marco pantani gears.

i live in silicon valley and we have plenty of steep long climbs plus i am a big guy. in my prime (late 30s) i climbed everything in a 38 x 26 and by roadie standards that was pretty wide range on an 8 sp drivetrain.

that said the OP's gearing is waaay lower than i'd ever want on a road bike unless it were a tourer.

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Old 03-26-07, 06:14 PM   #10
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When you say the gearing is way too low, is that related to the cassette, or the chainrings? Because AFAIK the cassette can't get that much higher (an 11t cog is out)..

If i replaced the 46t big ring with a 48t, i'd get a maximum of 104 gear inches at the high end...
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Old 03-26-07, 06:33 PM   #11
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The chainrings. Most triples on road bikes have something like 53, 42, 30. So yours will be closer, which just means you will not be able to pedal after you reach about 27-30 mph, but most leisure riders would be fine coasting at those speeds anyway. I would personally use something more like the standard road setup, but aside from fast downhills, you should have a gear for anything else with your current plan.
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Old 03-26-07, 06:42 PM   #12
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Cool.. i'll see how it goes. Again, this is my first road bike so i'm not quite sure what to expect. Years of mountain biking, and i never once thought about gearing, despite going through some different chainring sizes etc. The low end was always low enough, and the high end was high enough, and there seemed to be enough gears in between!
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Old 03-26-07, 07:00 PM   #13
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Your 650 wheels make your gearing even lower than a typical road bike but still, I'd rather be too low than too high.

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