Bicycle gears.

[styley]

On a 21 speed pedal bike there are 3 cogs at the pedals and 7 cogs on the rear wheel. How do you tell which gear is which in terms of the cogs, as in 1 to 21. Also does it get progressively harder to pedal as the gears go up from 1 to 21 or does the numbers matter in that way. I've confused myself here.

[mibn2cweus]

The pedal gears give you three separate ranges. The gear ratios provided by each sprocket tend to overlap. To shift progressively from the lowest (slowest) to the highest (fastest) gear ratio requires changing both front and rear sprockets for each gear ratio. Fortunately shifting progressively through each gear ratio to arrive at the one that works best is unnecessary (and rarely if ever practical).

If you must know which gear ratio (�speed�) is which you will probably just have to count the teeth in each gear and divide to find the gear ratio of each combination.

bicycle_gearing

[sarnieken]

Or, in answer to your question,

1-7 is Small front cog, big back. to Small front, small back.
8-14 is middle front and then the rears from big to small again.
15 - 21 is the big front and the rears from big to small.

Hardest gear is big front and small rear.

yes, the numbers matter and it does get harder the higher gear you go. Lower gears are ideally designed to 'get you going' or are for terrain. The idea behind the gearing is to allow you to maintain a god level of speed with the most efficient, less tiring peddling.

When you get used to the gears you tend to only use a small number of them as you find the gears that suit you.

Hope this helps,
K

[Teddio]

To avoid chain and sprocket wear don't use gear combinations which bend the chain such as 1 (big sprocket on front) with 7 (smallest sprocket on rear)

[Loosehead]

There are 21 chain positions but there will not be 21 gears. To work out a gear take the teeth on the front, multiply by the size of the wheel in inches and divide by the number if teeth on the back. do that for all combinations and you'll find that in reality there are much less that 21 ratios.

[mibn2cweus]

Using this gear ratio calculator you will see that the range of ratios provided by the pedal gears overlap so that ratio progression is not as straightforward as 1-7, 8-14, 15-21.

As loosehead pointed out some gear combinations provide a virtually identicle gear ratio. Also many changes to the next ratio require shifting of both front and rear sprockets.

[Toureman]

Good answers but I think the question asker will now be more confused than ever !

[mibn2cweus]

Teddio, You're advice to avoid using opposing sprocket gears because of the extreme angle of alignment this puts on the chain in relation to the gears has merit however the largest gear in one set provides the best alignment with the smallest gear in the other and vice versa. These arrangements also provide the highest and lowest gear ratio combinations making the use of the most extreme chain angles unnecessary since a similar gear ratio is usually available using gears that share a better alignment. To maintain the best alignment the smallest gear in one set should be used with the largest gears in the other set when the smallest or largest gear ratios are desired.

Toureman, And we thought learning to ride a one speed bike was challenging!

[mibn2cweus]

Incidently:

Don't forget to look up ahead occasionally when inspecting gear configurations to see if the car in front of you has come to a stop! . . . I learned that the hard way.

[Toureman]

It's interesting driving a truck with a splitter in the rear axle, gives you 16/18 gears, same as the bike some gears are obtained by using both gearboxes at the same time as you use both sets of cogs on the bike.

[Teddio]

Doh! sorry Mib, I meant to say avoid combining the smallest front sprocket with the smallest rear sprocket. Incidentally, elliptical front sprockets increase cycling efficiency.

[styley]

What sarnieken said there about the gears, is that correct. I feel that through that theory, gear 7 would be harder to pedal than gear 8. i.e small front, small back would be harder to pedal than middle front, big back.

[oldrenders]

Bring back Sturmey Archer 3 speed hubs, I say!