gears

[makbike]

Sandy:

I found it quite helpful to calculate my gear inches. Once I had them calculated I made a small gear chart and taped it to my top tube. I can quickly refer to it when looking for the gear to match my terrain, wind, etc.

Here is the formula for calculating gear inches:

Gear Inches = Rear Wheel Diameter x # of teeth on front chainring
# of teeth on rear cog

Here is what the range of gear inches is best used for:

20" steep hills with loaded bike
30" steep hills
40" somewhat steep hills
50" Moderate uphills
60" easy riding on flat ground or slight uphills
70" brisk riding on level ground
80" hard riding on level ground or slight downhills
90" sprinting on level ground or moderate downhills
100" somewhat steep downhills

on my bike the combination of small ring on the front chainring and small on cog on the rear gives me 100" - a very tough and big gear to push but it does come in handy for the long downhills. On the other hand the combination of frong chainring and large cog on the back gives me a 38" gear a very small gear and very easy so I use it on those tough climbs.

I hope this helps!

[BleeckerSt_Girl]

Sandy, here are some articles that talk about gear shifting:
http://sheldonbrown.com/gears.html
http://www.bicyclesouth.com/shifting.htm
http://bicycleuniverse.info/eqp/gears.html

[anakiwa]

Looking at it really simply-

Think about how many teeth you're moving in the front versus how many teeth you're moving in the back (to make the wheel turn).

In the front the small ring is the easier ring (low gear). With one turn of the pedals you aren't moving that many teeth and will have to turn the pedals several time to move as many teeth as you would in the big ring. (But it will be easier to turn the pedals since you aren't accomplishing as much.)

In the back the big ring is the easier ring (low gear). As you're pedaling, the number of teeth you turn in the front will cause the same number of teeth to move in the back. If you're in the easier (larger) gear in the back, you'll have to pedal more times (move more teeth) to turn the wheel a whole revolution.

Hope that helps.

[sandy45]

i just want to see if i have this right....in the back...larger ring = low gear which you spin your peddles more to move your bike. and smaller ring = high gear which you dont have to spin that much to move the bike farther.

it is mainly the back that i am worried about. i dont move my front too mcuh for the terrain i am on.

Thanks for all your help!! if i explained it right then i finally understand!

[anakiwa]

You have it right.

I don't know what sort of terrain you're cycling on, but generally you want to shift both the front and the back.

The front is for major changes- if you think about it you're jumping from 30 to 39 or 39 to 52 (assuming you have a standard triple)- this is going to make a big difference. If you ride in rolling terrain you'll need to be able to shift the front regularly.

The back is for fine-tuning. If you have a 12-25 (one standard road bike cassette) you generally won't be moving by more than 2 teeth at a time. This will make it easier or harder, but you'll have to move a lot of gears to make a big difference.

If you look at the way the bike is set up, you'll notice that the front and back are aligned so the easy gears are on the same side (inside- close to the bike) and the hard gears are on the same side (outside- farther from the bike). In general, you don't want the chain to have to cross-over too much (refered to as cross-chaining). So if you're going up a steep hill you should be in the small ring in the front and one of the bigger rings in the back. If you're on a gradual downhill you want to be in the bigger ring in the front and one of the smaller rings in the back. If you're somewhere in between you'll want to be in the middle ring in front and one of the middle gears in the back.

Good luck!