# Found the Magic Gear... now want to change it



## OldZaskar (Jul 1, 2009)

We know finding the magic gear on a SS conversion is tough - and lucky. I pulled this off and have been mostly happy. But, I guess my fitness has increased? I want a bit more gear.

I'm running a 52/18. Is it possible to figure this out - "backwards" as opposed to using eehouse.org's site? If a 52/18 nets the magic gear, is there a way to calculate if a 52/16 will? I'm thinking that there's like one link for X teeth you move up??? Okay, not really remember that old rule huh.


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## axlenut (Sep 28, 2010)

Hi, dropping from a 18 to a 16 on the rear should require exactly one link longer on the chain as each link covers two teeth. 

However, I never knew how the magic gear works - what happens when the chain wears and gets slack?

Also, if you are using 700x23 tires you have a 76 inch gear now. The change would give you 85.5 That seems like a lot of gear to me

I run 71 gear inches and the only time I spin out is on very fast group rides. The rest of the time it is spot on for me.

Later, Axlenut


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## OldZaskar (Jul 1, 2009)

Thanks axlenut. ^ that's ^ what I was looking for. I'm going to try the 52/16 (85.5 gear inches) and see how it feels. It's a big jump - about 12%. 

On my weekday club rides, there are two sections - basically flat, slightly downhill - where the line (8-12) of us will get up to 30-32 mph. The average for the 26 mile ride is in the 22-23 mph. At 120 rpm, the 52/18 is at 27 mph... the 18 nets me 31 mph. That keeps me in the mix on those faster sections.

Of course there's the issue of those hills...


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## JCavilia (Sep 12, 2005)

no, no, no. You should listen to axlenut when he says he doesn't know how the magic gear works. First, dropping to a smaller cog would mean a shorter chain, not longer. Second, the one-link difference would describe the chain length if you were simply wrapping the chain all the way around a cog, but that's not what's happening. The chain only goes halfway around the cog, and the axle only moves half as far as the change in chain length (because there are two runs of chain front to back).

Sheldon says this:


> Adding or subtracting a link in the chain will move the axle 1/2". Changing either sprocket size by one tooth is the equivalent of moving the axle 1/8" (4 mm).


I infer that changing the cog by two teeth should be equivalent to moving the axle 1/4". And if removing a link would move the axle 1/2", then a half-link should move it 1/4'. If that's correct, then changing the 18 to a 16 and substituting a half-link for one existing link should put you back where you want.

I think.


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## JCavilia (Sep 12, 2005)

If I understand how to read the results from the calculator at eehouse, I think this confirms what I suggested above. Comparing 52x18 with 52x16 and a chain a half-link shorter, it shows a stay length that differs by less than a millimeter (those are centimeters in the table). That's pretty close.
--------------------------------------------------------------------------------

Ring_Cog__ _Stay_____ Chain____G. Inches 
52___16____ 43.201_____51.5_____85.0 
52___18_____43.268 ____52.0_____75.6 

http://eehouse.org/fixin/formfmu.php?maxRing=52&minRing=52&maxCog=18&minCog=16&stayLen=43&wheelDiam=26.16&isMetric=1&display=table&useHalfLink=1&stretch=0.00&axleAdjust=vert&sortKey=Stay_length


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## OldZaskar (Jul 1, 2009)

JCavilia - thank you!

As it happens, I ordered 3 half-links earlier this week for another build - well, one for the build and two just to have. Looks like I'll be down to one spare ;-)

Thanks again!


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## JCavilia (Sep 12, 2005)

OldZaskar said:


> JCavilia - thank you!
> 
> As it happens, I ordered 3 half-links earlier this week for another build - well, one for the build and two just to have. Looks like I'll be down to one spare ;-)
> 
> Thanks again!


Good luck, and let us know how it works out. This is all hypothetical for me, as all my fixies are built on old frames with horizontal dropouts.

And be careful grinding that monster gear up the hills. Don't want any knee damage


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## markaitch (Nov 3, 2010)

both axlenut & JCavilia have given excellent info here but i have a question for you, OldZaskar...

why are you so adamantly opposed to using a tensioner?

you can change your rings & fws around almost as much as you could possibly want with a tensioner & not be limited like you are experiencing in your quest for magic gears. 

also...i am a person who rides admittedly insanely big gear inches (right now 52/17) but it is completely flat here. lately, however, it seems that no matter what direction i ride, i am always facing into a headwind & lemme tellya even a slight breeze is not fun to fight when riding directly into it on big gearing. its even got me considering backing my ratio off a bit. so i can tell you in no uncertain terms...if you have more than slight slopes where you ride or unless you have monster legs, forget that 52/16 idea.

have fun & good luck...


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## OldZaskar (Jul 1, 2009)

markaitch... The main reason for not using a tensioner is aesthetic. I just LOVE the look of a single speed or fixie with a "pure" chain line. I do like the reduced noise that comes from not using the tensioner - yeah, I know... that's a stretch. 

On the gearing... I've been riding with 52/18 or a year or more around Atlanta (very hilly area) and it's pretty close to perfect. Perfect would be a bit more gear. Maybe the 16 is going to be too much. Maybe a 17 would be just right. I'll report back once I do the swap. 

Thanks guys.


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## OldZaskar (Jul 1, 2009)

Amazingly, the math matched reality - the calcs (per JCavilia) suggested that dropping from an 18 to a 16 would require the use of a half link... I just swapped the cogs and refitted the chain with the half link. It worked. I took a spin around the neighborhood and it rode great. I was tempted to ride with my club tomorrow but I'm almost 4 weeks into the (successful) recovery of a hamstring injury. Grinding out that ratio is going to half to wait a bit. But I think it's going to be dead on! 

And Jay - that .5mm worked in my favor. With the 18, the chain always felt just a tiny bit loose. Not anymore - it's perfect. 

Thanks for the help.


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## axlenut (Sep 28, 2010)

Hi, thanks for the update. I was curious how it would work out. Looks like we both learned something. I was wrong in thinking it would take a full link, glad you got it sorted out and let us know how it does on the group rides.

Later, Axlenut


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## f3rg (May 11, 2008)

I ran 53/16 on 25c tires for a few months, and it worked really well, but once the heavy winds of springtime hit, it became taxing on my knees. 52/16 on 23c sounds like a much better deal, but be prepared for rough climbs on windy days.

Honestly, 52/17 may be a better idea for a few weeks/months until you get your legs built up to it, and then proceed with the 16T.


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## OldZaskar (Jul 1, 2009)

Finally rode the 52/16 - after two unsuccessful hamstring recoveries. I rode 26 miles over rolling/hilly roads with my club yesterday... it was perfect, e.g. had to grunt the climbs, but could finally hang on the flats and slight downhills. I can maintain 32mph at a comfortable cadence. LOVING this bike again!


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## markaitch (Nov 3, 2010)

OldZaskar said:


> Finally rode the 52/16 - after two unsuccessful hamstring recoveries. I rode 26 miles over rolling/hilly roads with my club yesterday... it was perfect, e.g. had to grunt the climbs, but could finally hang on the flats and slight downhills. I can maintain 32mph at a comfortable cadence. LOVING this bike again!


earlier in this thread i mentioned that after extensive personal experience with big gear inches, it is my belief that one needs monster legs to be able to ride 52/16 especially in an area with any hills. 

are you aware that 32mph on that gearing works out to about 126 rpm? you maintain that cadence over 26 rolling/hilly miles & consider it to be comfortable, on over 85 gi?

you really do have legs of steel :eek6:


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## OldZaskar (Jul 1, 2009)

markaitch said:


> earlier in this thread i mentioned that after extensive personal experience with big gear inches, it is my belief that one needs monster legs to be able to ride 52/16 especially in an area with any hills.
> 
> are you aware that 32mph on that gearing works out to about 126 rpm? you maintain that cadence over 26 rolling/hilly miles & consider it to be comfortable, on over 85 gi?
> 
> you really do have legs of steel :eek6:


I had to cancel 5 appointments with pro teams this weekend - Guinness wanted to do an interview and photo shoot. Well, if I could do 32 mph over hilly terrain on a SS for 26 miles...

Sorry, I may not have been clear. There is a section of the 26 mile loop that gets over 30 mph - a mostly flat, slightly downhill 2-3 mile stretch. With the 52/18, I'd spin out or at least it was very difficult to maintain the speed - in a pace line. The 52/16 lets me do that section at a reasonable - high, but doable cadence. We average in the 21-23 mph range for the 26 miles... not 32 ;-)

This is the ride profile...
(elevation gain for the loop is 1,400')


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## holyshmokes (Aug 2, 2012)

I went from a 19 to a 17 recently. Couldn't be happier


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## OldZaskar (Jul 1, 2009)

holyshmokes said:


> I went from a 19 to a 17 recently. Couldn't be happier


Right there with ya. I'm enjoying this bike again. 

When I first built the bike a few years ago, my club wasn't as fast as it is today. So, I could ride the single speed any of the "scheduled" days and get a little bit more out of the ride - as compared to my geared bike. But, the group got fast. The 22mph avg. for our 26 mile loop fell... I couldn't do that (Tuesday; hang or drop) ride on the single speed anymore. Then 23 mph avg fell... Even Thursday's ride (no drop) ride was too strenuous on the single speed - just couldn't keep up on the fast sections. But now - with 85(ish) gear inches - I can ride the bike on all but the fastest ride. Well, not the weekend rides... 60+ miles at 20+ mph... I need gears for that!


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