gears...what does this mean?

Quote:

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Originally Posted by ilima

Okay.

CRANKSET FSA Vero Forged 52/42/30
This is the crankset and chainrings on the crankset. FSA (Full Speed Ahead) is a brand and Vero is the model. Forged means it's steel and heavy. It's a triple crankset with chainring sizes of 52, 42, and 30. The smaller the chainring used on the front, the easier it is to pedal and the higher your cadence will be for a set speed. 52/42/30 and 53/39/30 are common road triple combinations.

165mm (47) 170mm (50-53) 175mm (55 - 62)
This refers to the crank lengths for the different sizes of bikes in parentheses. Tall folks generally need longer cranks, shorter folks use shorter cranks.

FREEWHEEL SRAM Powerglide 950 9-speed 11-32
This refers to the cassette that's used on the back. In contrast to the chainrings, the more teeth the easier it is to pedal and the higher your cadence will be for a set speed. This is because the more teeth the fewer the revolutions of the back wheel per revolution of the cranks. This particular cassette happens to be a mountain bike cassette made by the company SRAM. Road cassettes typically only go to 27 max (SRAM to 28), while mountain cassettes go to 32 or 34.

To get easier pedaling (and to have more gears for us slowpokes up hills), you want smaller rings on the front and bigger rings on the back.

Sheldon Brown has a gear calculator that's fun to play with.
http://www.sheldonbrown.com/gears/

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OK..so 11-32 indicates that the number of teeth on each of the 9 rings is different and the smallest # is 11 and the largest 32? 11 teeth are on the smallest ring.

SO...my spinningest gear is 30/32?
and when I stay mostly on the middle ring up front...it's 42/ and 11 through 32?

and where does the RATIO part come in?

BY the way...this is the Jamis Aurora touring bike.

(thanks for all the info...!!!)

Use Sheldon Brown's calculator http://www.sheldonbrown.com/gears/.

Explanation (from the website):

Gear Inches

The simplest system in common use is the "gear inch" system. This dates back to before the invention of the chain-drive bicycle. It originally was the diameter of the drive wheel of a high-wheel bicycle. When chain-drive "safety" bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number. The examples listed above are all around 74-75 inches. The lowest gear on most mountain bikes is around 22-26 inches. The highest gear on road racing bikes is usually around 108-110 inches. Unfortunately, the handwriting is on the wall for all inch-based measurement systems.

Gain Ratio

I would like to propose a new system, which does take crank length into account. This system is independent of units, being expressed as a pure ratio.

This ratio would be calculated as follows: divide the wheel radius by the crank length; this will yield a single radius ratio applicable to all of the gears of a given bike. The individual gear ratios are calculated as with gear inches, using this radius ratio instead of the wheel size.

An Example:

A road bike with 170 mm cranks: (The usual generic diameter value for road wheels is 680 mm, so the radius would be 340 mm.)

340 mm / 170 mm = 2.0. (The radius ratio)

2.0 X 53 / 19 = 5.58

This number is a pure ratio, the units cancel out. I call this a "gain ratio" (with thanks to Osman Isvan for suggesting this term.) What it means is that for every inch, or kilometer, or furlong the pedal travels in its orbit around the bottom bracket, the bicycle will travel 5.58 inches, or kilometers, or furlongs.


Now then there's Gear Ratios, which may be important in 2 situations. The first is for fixie riders. The ratio (ring/cog) determines how many skid patches may show up on a tire. The more skid patches, the longer the tire wear. The fewer, the shorter, because you'll wear out one part really quickly.

The second situation is for those with climbing bikes (I think it's more relevant on a road or touring bike, because the approach in selecting gearing on a mtn bike etc. is different) in balancing cadence with power output. The gear ratio essentially determines how many revolutions you're going to get of the wheel per revolution of the cranks. It takes a lot less resistance to turn the cranks with a gear that will move the wheel one revolution or less than it takes to turn a 39/17, for example. Your 30/32 is smaller (easier) than a 1 ratio (30/30), so you can compare. However, you get a lot more speed per revolution of the cranks on the "harder" gear, as we all know. So, you may want to consider gear ratios in figuring out how fast you'd need to turn the cranks at a given gear to go X mph. But then, you'd probably still want to use the rpm/mph calculator for different gear setups to figure out what you want. Then, you'd plug in something like this: I can get up this hill with maybe these gears, and I think I can turn the cranks at 60rpm or 80rpm or 100rpm. If so, how fast would I be going in each of these gears? Am I ok with that, or would I rather have to put out more or less power or use different rpms in another gear to go that speed? Or do I want to fight a bigger gear to try to get more speed?

I find it's easiest to stick with the Gear Inches chart. Smaller numbers = easier.

Kali, that's also why there are bigger jumps at the larger cogs. A small jump on the small cog end with be a bigger jump in gear inches than on the large cog end. So while the shift can be hard in terms of jumping sizes of cogs, it gets less and less easy per size of cog, if that makes sense. So if you're running out of gears on that end when you're in the small ring, then you want bigger jumps to be able to feel the difference. When you're trying to fine tune a comfortable cadence on the flat with the speed you want to go, then you want the tightest gearing possible on those smaller cogs to minimize the difference in feel between each gear.