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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 05-08-07, 12:59 AM   #1
vee_dub
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51/20 v 42/16 Gearing ??

Hey,

Ok the question is....
51/20 make up of 67 gear inches and 42/16 make up of 69 gear inches..they have similar gear inches.

I am a newbie. I locate in Sydney I could not find a 42T chainring but I could find a 20T Philwood cog. I am just wondering the pros and cons using big chainring and big cog relatively to small CR and small cogs to achieve similar gear inches? Despite the weight factor.



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Old 05-08-07, 01:34 AM   #2
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Big chainring/cog combos have been said to wear slower, as the wear is spread out over more teeth.

there are a ton of threads about this same topic, the search button is yer friend.
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Old 05-08-07, 03:42 AM   #3
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That's not a bad ratio for sydney hills, unless you live on Carrington Road Bronte. Western suburbs can even happily go 53-16 most places. Eastern suburbs/northern beaches: that will make you strong.

if you want more chainrings, i have been happy with the BlackSpire stuff from Canadia. all sizes BCD combos in 8/9 speed, no ramps: good for fixed on 3/32 chains. Make sure your chain fits the Phil cog!

No practical difference at all, just a tad heavier and you have slightly less space around your BB for climbing kerbs etc. (Oh, you're going fixed... that's noice. keep a front brake on the bike at least till you don't feel you need it anymore)
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Old 05-08-07, 03:45 AM   #4
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Thanks for all the help...
Yep...i have 1/8 Chaing with superb pro cranks and 51 chainring and 16t cog.

Running 51/16 at the moment my chain sits in the moddle of the track dropout if i got 51/20 would i need to extend the chain or get a new chain?
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Old 05-08-07, 04:19 AM   #5
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if you don't have an extra link for your chain your gonna need a new one.

new chains are nice and can be had cheaply.
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Old 05-08-07, 04:22 AM   #6
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Yep I dont have extra link because I got the bike secondhand, the seller promised me will give me few cogs and lockrings..but end up he bailed out.
Tried to msg him .. he wouldnt reply.

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Old 05-08-07, 06:50 AM   #7
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Quote:
Originally Posted by pirate
Big chainring/cog combos have been said to wear slower, as the wear is spread out over more teeth.

there are a ton of threads about this same topic, the search button is yer friend.
I always wondered if the fact that each rotation involves less angle for each chain link to turn helps chain stretch too.
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Old 05-08-07, 08:13 AM   #8
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Big rings are more efficient.
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Old 05-08-07, 08:17 AM   #9
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in my experience, finding big enough cogs to use a big ring and keep a reasonable gain ratio is the hardest part. If you've already got a 20t, then there isn't a good reason not to try out a 51 or 53 ring. Another advantage of bigger drivetrain that hasn't been mentioned is that adjustments are finer— adding or losing a tooth has a smaller effect (percent change) since there are more teeth involved.
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Old 05-08-07, 08:53 AM   #10
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Okies dokies..thanks guys...
Well I am currently running 51T chainring and 16T cog as i said.
I want to run lower gear inch..so I guess I will get a 19 or 20T cogs..

And would larger cogs easier to skid with rather than 51/16 I am having hard time to skid on pavement but able to skid on wet and on grass..

Cheer,
Dub.

Last edited by vee_dub; 05-08-07 at 09:01 AM.
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Old 05-08-07, 10:16 AM   #11
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Quote:
Originally Posted by chase.
Another advantage of bigger drivetrain that hasn't been mentioned is that adjustments are fineró adding or losing a tooth has a smaller effect (percent change) since there are more teeth involved.
isn't that in reverse?

if I have 48-18 I get 70.1 g.i.; 48-14 I get 90.1 g.i.. A difference of 20 gear inches.
if I have 52-18 I get 75.9 g.i.; 52-14 I get 97.6 g.i.. A difference of 21.7 gear inches.

I've always thought the smaller drives power up fast, but yes, the larger feel more efficient at speed.
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Old 05-08-07, 10:29 AM   #12
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51/19 and 42/16 Have same gear ratio...therefore they should be the same right? Like effort to pedal and effort to skid???
I am really bad at mechanic and physic, hoping someone can enlighten me.

Dub.
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Old 05-08-07, 10:43 AM   #13
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Quote:
Originally Posted by yairi
Big rings are more efficient.
WTF? Efficient how?
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Old 05-08-07, 12:27 PM   #14
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Less drivetrain loss.
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Old 05-08-07, 01:55 PM   #15
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Quote:
Originally Posted by me thinkst
isn't that in reverse?

if I have 48-18 I get 70.1 g.i.; 48-14 I get 90.1 g.i.. A difference of 20 gear inches.
if I have 52-18 I get 75.9 g.i.; 52-14 I get 97.6 g.i.. A difference of 21.7 gear inches.

I've always thought the smaller drives power up fast, but yes, the larger feel more efficient at speed.
I meant that a one-tooth difference from 51 to 52 is a smaller delta than 42 to 43, so if you're trying to dial in your cadence or overall gear inch measurement, it would be easier to get it right.
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Old 05-08-07, 02:01 PM   #16
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Quote:
Originally Posted by vee_dub
51/19 and 42/16 Have same gear ratio...therefore they should be the same right? Like effort to pedal and effort to skid???
I am really bad at mechanic and physic, hoping someone can enlighten me.

Dub.
It will feel like the almost the gear at speed, difference of 1.6". I think the 42 will skid easier, as well as accelerate faster.
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Old 05-08-07, 02:05 PM   #17
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Quote:
Originally Posted by chase.
I meant that a one-tooth difference from 51 to 52 is a smaller delta than 42 to 43, so if you're trying to dial in your cadence or overall gear inch measurement, it would be easier to get it right.
gotcha...
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Old 05-08-07, 02:47 PM   #18
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51/20.

Forget weight, its all about asthetics, and your drivetrain will last longer. as there is less stress on the the bigger wheels.

Ride safe in razzle dazzle town.
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Old 05-08-07, 03:00 PM   #19
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absolutely, the 51-20 will look better. 42t chainring will look like mountain bike gears.
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Old 05-08-07, 03:02 PM   #20
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A 42t is more aerodynamic. Duh!
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Old 05-08-07, 05:30 PM   #21
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Quote:
Originally Posted by me thinkst
It will feel like the almost the gear at speed, difference of 1.6". I think the 42 will skid easier, as well as accelerate faster.
Mmmh yer its 1.6" difference but the acceleration and skidability (my own stupid words) varies that much?????
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