12 Speed VS 16 Speed, or Whatever

The difference between a 12 speed and a 16 speed (or whatever) bicycle is not as much the range of the cassette in the rear, but more the spacing between the cogs.

In a brief internet search you can have 6 speed rear cassettes that have a range that starts between 12 and 14 and goes to 19 to 34. So let's say a good guess is a 13-34 rear cassette on your current bike. The modern cassettes might be 11-21 or 13-23 for close gear ratios, or 11-34 for a really big ratio. So, we'll pick a 12-26 for "average."

If the cogs are something like:

**-13-**-15-**-18-**-24-*******-34
12-13-14-15-17-19-21-23-26

you are missing some top-end speed (but it's pretty hard to spin-out a 53-13) but what you're really missing is the ability to keep a constant cadence over subtley changing terrain.

sandy

Sandysandy got it right

Heres the deal
lets say you have a 12 speed bike
and a
18 speed bike

The 12 speed will have two chainrings up front
and 6 cogs in the rear

The 18 speed will like wise have two chainrings up front
on the crankset
but it will have 9 cogs in the rear
on the freewheel/cassette

The number of cogs has little to do with either the ultimate top-end speed potential or
the ease with which (theoretically) the bike will climb.
Think about that great Spinal Tap quote
"but these amps go to 11"

Bicycle gearing works this way
the bigger the chainring and the smaller the cog
the faster the bike can go, and the harder it will be to pedal
conversely
smaller chainring and bigger cog will result
in a bike that goes slow, but is easier to pedal

The standard vernacular term for measuriing the realitive size of chainrings and cogs
is teeth
Older 10-12 speed "racing" bikes typically featured a crankset with chainrings of 42 and 52 teeth
and freewheels with cogs of 13-15-16-18-21-23 teeth occasionally you found a 12 tooth small cog
touring freewheels might start with 14 and go to 27-28 (rarely but sometimes bigger)
More modern bikes often have a 38/53 chainring setup and cogs of 11-13-14-15-17-19-20-21-23
or an 12-13-14-15-17-19-21-24-27

The ultimate speed potential of a 53x12 combination is higher than that of a 52x13 (if you have the legs to turn it.)
likewise a 38x27 will make hills easier to climb than a 42x23

On the other hand, if you come across an old loaded touring bike with a pie-plate 14-32 freewheel and a 36 tooth in front, You're going to have a easy (if slow) climbing machine. Also, 53 (and larger) chainrings have been around for a long time too.
freaky-small 11 tooth cogs are, however a more recent innovation.

The taske-home message here is that look at the size of the gears, not the number of them.

clear as mud?

Edited by ride_like_u_stole_it 2004-06-24 10:39 AM

I didn't ask this question but I thank you both for supplying an answer to something I have often wondered about.  I keep on learning and that is good.  Thanks, Jim

Thanks for the lesson guys! Great info.

Sandy and Ride Like have given a great refresher of the physics of gears. There is another area of physics that may be holding you back on descents, however. Drag.

The amount of aerodynamic drag varies in proportion to the square of your speed. That means that you experience 4 times as much drag when you accelerate from 13 mph to 26 mph. As you go faster and faster, drag becomes more and more an issue. This is why recumbant bicycles haven't been allowed to race "safety" bicycles in almost 100 years. The reclined position of the rider means that, given a similar construstion technology and a equally skilled rider, a recumbant can wipe the floor with a safety bicycle 7 days a week and twice on Sunday.

It may be that those riders are passing you because they have managed to get in more aerodynamic positions. A common mistake riders make is to get low, but not think about width. If your knees and elbows are out wide, you can really hurt your speed. Practise riding low with your knees and elbows in as tight as is comfortable.

Much thanks to all that posted with advice. Amazing info, and in such detail! Thanks!

I'll be honest though...being a bike newbie, I'm going to have to do some research to fully understand all the thoughtful replies. =)