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Understanding Gearing

Old 07-22-08, 10:47 AM
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Carys
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Understanding Gearing

Anyone know of a good on-line article that will help me understand gearing a bit better? I need to understand a bit better what the REAL differences are between the gearing on the bikes I'm looking at. Most are 48/38/28 with 11-32 8 speed, but a few are slightly different...and I'm not sure what that means for the riding I do and if one is more suitable than the other.

Thanks so much!
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Old 07-22-08, 10:49 AM
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http://www.sheldonbrown.com/gears.html
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Old 07-22-08, 10:51 AM
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Theres a lot of overlap in gearing.
The way I think of it is:
Select your front gear for the type of terrain
Select your rear gear for the difficulty of terrain
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Old 07-22-08, 10:57 AM
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Hmm, how does one figure out what their Optimal Cadence is? I don't have a cadence meter at this time, but I am curious.

It seems most people talk about ranges between 70 and 110 Cadence, which is Rotations per minute if I understand it correctly.

Seems most people specifically talk about ranges in the mid 90's.

How do they determine what their Optimal Cadence is? Is there a calculation? Do you require a Meter to monitor your heart rate and find a healthy heart rate at certain RPMs?
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Old 07-22-08, 11:02 AM
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When I was first starting, I really couldn't compare the bikes either. I mean, I could do the math, and compare; but really, it was meaningless w/o anything to compare to. After putting some miles onto an old road bike, I started to find out some things by personal experience:

-the deep gears (low gear inches) can have large steps (big changes) and it doesn't bother me much. When I am downshifting on hills, I don't need the gears all that close together.
-deep gears on my road bike is anything below about 50 gear inches.
-I need deep gears for my hills! I love my triple and its granny gear (the 30T) on my current bike.
-The lowest gear on my old road bike was 36 gear inches, and I felt that I wanted deeper gears than that, for reserve. My new bike goes down to 32 (but a lighter bike with better wheels means I rarely need to go below 36 anyhow).
-I found that I often cruise in the 70 gear inches. But that's in this area that I want lots of gear choices, as when I'm trying to maintain some high speed, I like to be able to dial in the precise gear. Hence, I like the 12-25 with a triple, for my road bike.
-I like the 42 middle ring to that 12-25. I find that I spend most of my time in that chainring. It covers the range of gear inches for moderately rolling ground and my power output / speed. If I had a 39 or a 45, I would not be as happy.
-If I climb it in the granny gear, I can use the big ring (52T) to go down it. But otherwise I rarely use above 90 gear inches. I typically am not even hitting 20mph on flats.
-MTB's, on the other hand, use even lower gearing. I think off-road I tended to use around 26-30 gear inches much of the time, when crawling over rocks and whatnot.
-Similarly, as I tow my kids in the kiddie trailer, I'm finding 30 gear inches to be the gear I'm commonly in.
-So, on the MTB I like wide gear ratios, and a triple also -- although, the big ring is even less used. The cassette on the MTB beater I have is 11-28, I think I'd like an even wider range than that.
-On the MTB, when I need to downshift, I need to downshift. Like an amount equal to two gearshifts on the road bike. Hence, wider gear spacing works perfect there.

That came out longer than I thought!
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Old 07-22-08, 11:04 AM
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Originally Posted by cg1985 View Post
Hmm, how does one figure out what their Optimal Cadence is? I don't have a cadence meter at this time, but I am curious.

It seems most people talk about ranges between 70 and 110 Cadence, which is Rotations per minute if I understand it correctly.

Seems most people specifically talk about ranges in the mid 90's.

How do they determine what their Optimal Cadence is? Is there a calculation? Do you require a Meter to monitor your heart rate and find a healthy heart rate at certain RPMs?
You can get spedometers (often just called "computers") for your bike that also have cadence readout. But you can find out, based upon your current gearing, what speed you must be doing in each gear in order to be doing a cadence of 90 rpm. [Yes, cadence = rpm.]

http://www.sheldonbrown.com/gears/

As for "optimal", that will depend upon the rider. Most people like 90; some prefer 80, others much higher. It will depend upon your fitness and mood.
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Old 07-22-08, 11:11 AM
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Originally Posted by supton View Post
You can get spedometers (often just called "computers") for your bike that also have cadence readout. But you can find out, based upon your current gearing, what speed you must be doing in each gear in order to be doing a cadence of 90 rpm. [Yes, cadence = rpm.]

http://www.sheldonbrown.com/gears/

As for "optimal", that will depend upon the rider. Most people like 90; some prefer 80, others much higher. It will depend upon your fitness and mood.
Ah, so you look at what speed it takes to comfortable at a high cadence? and As you grow in fitness, you'll find yourself spinning faster at said speed, or I suppose you'll have a higher speed at the same cadence?
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Old 07-22-08, 11:44 AM
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Well, what I did was this: on my bike, I found out what gears it had, then found out what 90 rpm in each gear should result in for speed. Well, I found out for a few gears, the ones I used most -- I didn't memorize all 12 gears! Then, over the course of the next few rides, I would look ever so often, see what speed I was pushing and in which gear. I found that I naturally tended to do 90rpm, at least when the going was not too tough.

As for getting more fit, I'm not sure. I haven't bothered to measure lately. I do know that I'm more comfortable now than I was before. But it's not like I'm turning 120 rpm all the time. If anything, it's that I have the option of spinning at 100, 110 rpm on some hills, whereas before I was stuck going at a slower speed.
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Old 07-22-08, 08:18 PM
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Originally Posted by cg1985 View Post
Hmm, how does one figure out what their Optimal Cadence is? I don't have a cadence meter at this time, but I am curious.
My best cruising-quickly cadence is almost identical to my jogging cadence. This, for example, is about 82 RPM:

http://www.youtube.com/watch?v=CHtVBN--AoU

As far as all the maths involved, the only time I've ever really paid any attention was when I was deciding whether to switch to a compact crank. I was using Sheldon's gear ratio calculator to see how much overlap there would be between the two chainrings, which determines how much I'd need to shift the rear to match whatever cadence I'm pedaling at the time.

I haven't visited that page in months, though.
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Old 07-23-08, 10:26 AM
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Originally Posted by Hobartlemagne View Post
Theres a lot of overlap in gearing.
The way I think of it is:
Select your front gear for the type of terrain
Select your rear gear for the difficulty of terrain
Very good!! Let your body pick the effort after you pick the range. VERY good indeed!
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Old 07-23-08, 11:05 AM
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cadence depends alot of your body type, too. I am not super-fit, but my normal cruise cadence is around 110-115.
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Old 07-23-08, 11:17 AM
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Originally Posted by Carys View Post
48/38/28 with 11-32 8 speed
That's a typical, street, DO-ALL gearing. Meaning suitable for the occasional rider and can go up some pretty steep hills.

3-Chainrings are for street/mountain/offroad, the little-st chainring is called, the "nanny" gear. Get it?

A road bike built for speed would have 52/42 with 11-26. More high gears u see.
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Old 07-23-08, 12:40 PM
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For a loaded bike, while the range of gears is important, the gaps between the gears are important also. While a racing man will want his ratios close together so as to keep his cadence smooth, the tourer will want gaps between ratios in that he will expect to lose some momentum between one gear and the next due to the load he carries. The gaps in the tourers case would be wider at the bottom of his range than at the top.
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Old 07-23-08, 01:26 PM
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Pedaling large gears at low rpm will wear your knees out quickly. It will take some weeks to learn to spin the pedals at a faster cadence but in the long run it will be easier on you. 48 is a good size for your largest chainwheel (front gear). You can get up above 20mph with a 48 (front) 11 (back) gear combination on level ground. The only reason you might need a larger gear is if you have a strong tailwind and you really need to go faster. If you are going downhill and you can't spin fast enough it's time to stop pedalling, tuck your legs in and your chin down, and you'll go faster than if you were pedaling.
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Old 07-23-08, 04:37 PM
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Originally Posted by jsmithepa View Post
That's a typical, street, DO-ALL gearing. Meaning suitable for the occasional rider and can go up some pretty steep hills.

3-Chainrings are for street/mountain/offroad, the little-st chainring is called, the "nanny" gear. Get it?

A road bike built for speed would have 52/42 with 11-26. More high gears u see.
"Granny", not "nanny", I believe...'cause it's so easy to pedal, a little old lady like your grandmother could manage.

And a mountain bike might have 44/32/22 and 11-32, or there-abouts. The granny gear is like walking...you go about the same distance per crank revolution as you would in two steps of walking.
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Old 07-30-08, 11:38 AM
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Geez - you guys wanna do math or ride? Sorry but you lost me. Whatever you buy if you pedal too fast you will burn out, and if you pedal too hard (slow) you will burn out. If you have super long legs you can probably pedal harder than most people, if you are on the smaller end of height then you might something that pedals easier. I can't imagine that a middle of the road bike wouldn't be just fine. Of course you math wizards are probably the people blowing my doors off, huh? :-)
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