Gearing

14 messages
10/05/2005 at 13:39
Hello,

Can someone explain to a retard what gear ratios are and on what basis one should decide to change them.

Am replacing cassette, and wondering whether I need to change my current arrangement. Apparently I have a thing called a 12-25 on the back. I think 12 is the number of teeth on the smallest cog, and 25 the number on the largest. Is this right?

And, if I like to ride with high cadence (85-95), like to stay seated on hills, but am doing Austria and some other events with short steepish hills, is 12-25 ok or should I think of something else?

I know the thing is nine-speed but that's it!

Ta

xMLKx
10/05/2005 at 13:42
I've changed to 12-27 for Switz but the hills there can easily be done on 25 (even 23) but I'm crap on hills and like to spin.

Depends upon how you find hills....

I do notice the jump now in the missing gears in my cassette especially as I only have 8 to play with.
cougie    pirate
10/05/2005 at 13:46
Okey dokey.

Yup - that's correct.

Not done Austria, but IronRose, Candy and Mon all have - they should be able to give you that info. I think a 25 is OK - BUT - what size chain rings do you have on the front ?

52/39 or something ?
cougie    pirate
10/05/2005 at 13:47
TC - you still on Cassette - I've switched to MP3 - way of the future ! ;-)
10/05/2005 at 15:58
a 12-25 will be fine for Austria, with a 39/53 on the front. you might drop below 85 cadence on Rupertiberg for a couple of minutes, but you won't have to stand up. just make sure you ride the course beforehand so you change to the small chain ring in good time. my chain fell off on the steep bit and i had to get some women to give me an illegal launch start so i could get going again.
10/05/2005 at 16:46
cheers - i'm always in the small ring anyway.
Illegal push up the hill most welcome i think!
cougie    pirate
10/05/2005 at 16:47
Likely story Candy. You dropped the chain deliberately near a bunch of friendly frauleins for some cheap thrills.
10/05/2005 at 16:48
you'll need to get into the big ring to milk those long descents for all they are worth though!
10/05/2005 at 16:59
long descents I shall stop pedalling, close my eyes and let the Power of Greyskull guide me home.
Or maybe i grab the nearest frauleine and stick her in my shopping basket to add extra weight.
10/05/2005 at 17:14
I shall be peddling like feck on the downhills to make up for the slow uphills..........
10/05/2005 at 18:23
there is apparently a big difference between switz and austria - switz apparently has short, steep, bendy, dangerous ones, whereas all but 2 in Austria are long and gradual. you really need to put the pressure on on those. big ring, smallest gear, stay aero, and pump those pedals. it allows you to gain more on the descents than you lose on the climbs. i passed loads of people who were coasting too much.
10/05/2005 at 20:59
need to push down Austrian hills as CO says, coasting for a rest at the top for 15 secs or so is fine tho ;-)
10/05/2005 at 22:23
nicholas rose, what a slacker. you realise that 3 laps times 15 seconds slacking was the difference between 10:29:xx and 10:30:xx, young man.
Suffolk Punch    pirate
11/05/2005 at 18:42
I'm planning on flying down those descents as my cycling fitness is way off allowing me to "ride" the climbs as I'd like to. I'm sure my Corima Aeros will help....

As for gear ratios, they're easy. If you here cycling speak such as "yeah, like, I was on the rivet spinning out 53x12, like". It means he was going pretty fast, or lying. That refers to the 53 toothed chainring on the front and the 12 toothed spocket on the rear. The gear changes the distance the bike travels with each pedal revolution. The further the bike travels with each revolution, the harder the gear is to turn.

You can work out an approximate distance tarvelled by the bike for every revolution with the following equation:

(Chainring teeth\Wheel diameter (inches))\rear sprocket teeth

I use an approximation of 27", so a 700C wheel will result in slightly less distance travlled.

Eg. 53*27\12 for 53 * 12 gearing:

119.2" travelled each pedal rev

However, mechanics play a funny game here. For example, it may be easier to turn a higher gear using the small chainring than a lower gear using the larger chainring. You'll find there is a certain amount of 'crossover'. Also, you may well find yourself adopting a different pedalling style when using the large chainring.

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