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ispy
03-11-2008, 03:27 PM
This falls into the category of "definitely-newbie-question" so I beg everyone's indulgence. I suspect the answer must be too obvious since I've found almost no mention of it on the interweb (except, of course, Sheldon Brown).

Currently/slowly building up a '68 Schwinn Paramount as my (first fixed-gear) commuter. I've been diligently making my way through the fixed-gear threads and I'm confused as to what the main rationale would be behind choosing, say, 44/17 vs. 46/18 vs. 49/19 since they produce roughly the same gearing ratio (+/- 2.55) and roughly the same gear inches. I understand that, given the ratio being the same, the combo with larger ring/cog should cause less wear/tear on the drivetrain. And of course a larger ring can produce a lot more speed if mated with a small-enough cog. But if the same gear inch can be produced by multiple ring/cog combos, how does one decide to go which way?

Thanks.

Grant McLean
03-11-2008, 03:30 PM
If you like to skid, the odd combinations will spread the number of bald spots
around the tire.

otherwise, gear inches is gear inches... doesn't matter how you get there.

-g

markie
03-11-2008, 03:43 PM
Go bigger ring then cog changes have a smaller % effect.

Personally for road use I just use the 39T inner ring form a regular road crankset.

bumperjohn
03-11-2008, 03:53 PM
I use a 48-18 set up on my fixie, used to run a 16 rear cog. It can be real tough on my commute home which is up some serious hills but I like the gear ratio just fine.

John

Ti Designs
03-11-2008, 03:59 PM
If you like to skid, the odd combinations will spread the number of bald spots around the tire.

He may be on to something! I run a 42x18 and I have one large bald spot. This has nothing to do with tires...

goonster
03-11-2008, 04:01 PM
Good points so far, and I'll add that bigger sprockets are more mechanically efficient.

Very frequently the choice is driven by what is available when doing a conversion, e.g. 42t ring from a road crank or 48t ring from a track crank, and then folks go from there.

ZONIE
03-11-2008, 04:07 PM
Check out the link below for direct access to the downloads. Or just go to their website. It is kinda dedicated to the cause.

www.fixedgearfever.com

http://www.fixedgearfever.com/modules.php?name=Downloads

Boundgear
03-11-2008, 04:10 PM
I ride 45/17 during winter (69 inches) and bump up the front ring during the summer. 17 gives you the most skid spots (prime numbers are what you are looking for) and though I don't skid like a kid, I did find that 45/15 was stupid as I got a bald spot as large as the one on top of my head. I personally think that 17 makes the front ring easy to keep the gear inches between 65-90 than say 13 or 19 do.

I'd love a '68 paramount....

Fixed
03-11-2008, 04:10 PM
bro keep it cheap i run with a 50 x17 one my road bike and a 40 X 14 on my mt bike both are fixed keep it real cheers :beer:

regularguy412
03-11-2008, 04:57 PM
I run a 42/16 on my fixie. It's just about perfect for the rolling/flat terrain around here.

You can go here and get all your gearing options checked out:

http://software.bareknucklebrigade.com/rabbit.applet.html

You have to have Java enabled on your computer to run it, but that's a free download. The second tab on the applet gives skid patches for given gear combos.

Enjoy!

Mike in AR:beer:

mosca
03-11-2008, 05:15 PM
The different gear combos will result in slightly different effective chainstay lengths, if you're sensitive about such things. Probably not a big deal for an older Paramount, they have nice long slotted dropouts, iirc.

97CSI
03-11-2008, 05:59 PM
Currently/slowly building up a '68 Schwinn Paramount as my (first fixed-gear) commuter.ispy - please keep us up-to-date on your progress. I'm just starting to gather the info/parts to convert my '87 Paramount to a single-speed. Will be most interested in your build/progress.

RudAwkning
03-11-2008, 06:10 PM
ispy - please keep us up-to-date on your progress. I'm just starting to gather the info/parts to convert my '87 Paramount to a single-speed. Will be most interested in your build/progress.

Definitely don't run a cog that is divisible into your chainring. You'll end up with a fatigued drivetrain and threadbare tires sooner than you'd like.

I'm running a 50/19 combo. about 71ish gear inches. Good enough to get me up anything up to a 6% average grade before discomfort settles in.

rustychisel
03-11-2008, 07:43 PM
Definitely don't run a cog that is divisible into your chainring. You'll end up with a fatigued drivetrain and threadbare tires sooner than you'd like.


Oh pluuuuuuease...

most people work out what gear they want (say 70inch) then eyeball the bits they've got lying around... uh, a 42T chainring... well, that'd mean a 16 sprocket, which DuraAce just happen to make in 3/32, so if I buy that and a 3/32 chain I'm good to go.

Later on they get to spend money replacing bits and tweaking (fettling in the UK, mostly). It ain't rocket science and you don't need hoooey about increased wear in the drivetrain and tighter radii inefficiencies from smaller chainrings. The differences are negligible, the weight savings by going smaller are miniscule, the wear rates unmeasurable.

What matters can be the proportion of change in ratios and the wear pattern on a tyre if you're the sort of muppet who likes to skid.

barry1021
03-11-2008, 07:54 PM
He may be on to something! I run a 42x18 and I have one large bald spot. This has nothing to do with tires...

RoFL!!! :p

b21

ispy
03-11-2008, 08:11 PM
Thanks for all the wisdom. I certainly didn't know any of this.

Grant: By "odd combo" do you mean odd/even or odd/odd combos?

RudAwkning: How does the "don't run a cog that is divisible into your chainring" work? I used to think I was mathematically above-average but lately this hasn't be the case...

Fixed: I'm sorry bro but I sprang for Phil Wood hubs.

97CSi: At first I wanted to be lean and cheap about it (didn't we all?) but then a long-suppressed desire for high-flange Phil's took hold. I guess I like the perversity of mixing really nice parts with really humble/normal parts; yes the Paramount is cool, 100% chromed (I love chromed forks), but its craftsmanship is pretty crude imo and the chrome, although it's 99% intact, isn't dulled in various places, but that's fine with me. For cranks I was going to adapt an old road crank I had lying around but I liked the idea of a real single-speed/fixed-gear chainring so I'm now looking at a Sugino (I know it's Japanese and the Paramounts were all Campy, but the proper Campy Pista cranks are so overpriced these days and I'm already in deep trouble with the bank account manager as it is), haven't bit the bullet on this yet b/c of my conscience. For a headset I'd like a nice Campy 1" threaded affair with engraved name but that'll require hunting. I do have an old Mafac Racer which will be cleaned up and bolted onto the front fork! Oh, and rims: probably Mavic MA3's (now called "Open Sport"... groan) with 27mm Rivendell Ruffy-Tuffy's. So as you can see, still a mutt.

(If anyone has a nice crank or headset for sale please PM me).

Thanks again for all the advice.






If you like to skid, the odd combinations will spread the number of bald spots
around the tire.

otherwise, gear inches is gear inches... doesn't matter how you get there.

-g

Boundgear
03-11-2008, 08:33 PM
Skid spots 101

Reduce the gear ratio to the smallest equivalent whole number ratio.
The denominator of the resulting fraction is the number of skid patches you will have on your rear tire.

Examples:
45/15 simplifies to 3/1 so there would only be 1 skid patch.
42/15 simplifies to 14/5, so there would be 5 skid patches.
43/15 can't be further simplified, so there would be 15 skid patches.

test: 47-17=?

For the math chaeeelenged- your prime numbers=
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67

Good luck finding a 67 chain ring or a 3 cog though.

If you have the chance and or money to choose your gear, 17 and 19 sized cogs work best. Again, at least to my opinion, I prefer 17 because you can get a wide range of gear inches out of it and still keep yo ty(i)res.

ispy
03-11-2008, 09:01 PM
Grant: By "odd combo" do you mean odd/even or odd/odd combos?

RudAwkning: How does the "don't run a cog that is divisible into your chainring" work? I used to think I was mathematically above-average but lately this hasn't be the case...




OK I went out for some fresh air and now I get it... thanks!

bironi
03-11-2008, 09:03 PM
"if you're the sort of muppet who likes to skid"

Yes, I am occasionally, :beer: but I like your attitude. :beer: :beer:

TimD
03-11-2008, 09:37 PM
About the same as 42x16, but the monster ring scares the hell out of the rest of the peloton. :banana:

BUTCH RIDES
03-11-2008, 09:45 PM
Oh pluuuuuuease...

most people work out what gear they want (say 70inch) then eyeball the bits they've got lying around... uh, a 42T chainring... well, that'd mean a 16 sprocket, which DuraAce just happen to make in 3/32, so if I buy that and a 3/32 chain I'm good to go.

Later on they get to spend money replacing bits and tweaking (fettling in the UK, mostly). It ain't rocket science and you don't need hoooey about increased wear in the drivetrain and tighter radii inefficiencies from smaller chainrings. The differences are negligible, the weight savings by going smaller are miniscule, the wear rates unmeasurable.

What matters can be the proportion of change in ratios and the wear pattern on a tyre if you're the sort of muppet who likes to skid.
cool

DRZRM
03-11-2008, 09:45 PM
Smaller ring/cog combo are lighter (only a bit) and supposedly wear faster (only a bit), they also clear logs better on the trails, but this is probably not a concern on that frame.

See "Big or Small" on Sheldon Brown (RIP) link below:

http://www.sheldonbrown.com/fixed.html

And check out the "Extending Bicycle Chain and Sprocket Life" page for why even/even ring cog combinations make sense (though I don't really keep track when I pull my wheel, I like to know someone might be).

http://www.sheldonbrown.com/chain-life.html

RudAwkning
03-11-2008, 10:35 PM
Oh pluuuuuuease...

most people work out what gear they want (say 70inch) then eyeball the bits they've got lying around... uh, a 42T chainring... well, that'd mean a 16 sprocket, which DuraAce just happen to make in 3/32, so if I buy that and a 3/32 chain I'm good to go.

Later on they get to spend money replacing bits and tweaking (fettling in the UK, mostly). It ain't rocket science and you don't need hoooey about increased wear in the drivetrain and tighter radii inefficiencies from smaller chainrings. The differences are negligible, the weight savings by going smaller are miniscule, the wear rates unmeasurable.

What matters can be the proportion of change in ratios and the wear pattern on a tyre if you're the sort of muppet who likes to skid.

I speak from experience (and no, I'm not a "muppet who likes to skid"). What do you speak from other than "your arse"?

And "pluuuuuuease" is not a word.

rustychisel
03-11-2008, 10:39 PM
"if you're the sort of muppet who likes to skid"

Yes, I am occasionally, :beer: but I like your attitude. :beer: :beer:

Yeah sorry, I get a bit opinionated sometimes, and I really don't like perceived wisdom as fact, so I'll raise you another pint :beer: and maybe another one for luck :beer:

An' ya know what: it strikes me not too many people on this forum are into wearing their parts right out before they go out and spend some on the new shiny ones... right? Sure not me.

WadePatton
03-12-2008, 12:38 AM
42x15 came on it (converted bike) and works great for the gentle rollers around here.

as mentioned--when in doubt, put a monster ring on to tweak the rest of the boys. :bike:

rustychisel
03-12-2008, 01:04 AM
What do you speak from other than "your arse"?

You're right, my arse speaks volumes (though not a language you'd understand). Have a beer too! :beer: After all, as you've so perceptively noted, I have nothing better to do than post on websites in pontification of questions about which I know nothing.

Now are we :cool: ?

RudAwkning
03-12-2008, 10:44 AM
You're right, my arse speaks volumes (though not a language you'd understand). Have a beer too! :beer: After all, as you've so perceptively noted, I have nothing better to do than post on websites in pontification of questions about which I know nothing.

Now are we :cool: ?

We cool. And for the record, I'm fluent in "arse". :beer: