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Custom half-step freewheel

Old 03-22-21, 09:46 PM
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mountaindave 
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Custom half-step freewheel

Prepare for an extreme bike nerd-out:

Thanks to @smontanaro, the Bay, and Sutherland's handbook, I was able to combine two freewheels into one. (Actually it took three, but it should have only taken two). I combined four sprockets from a Shimano 5s FW (MF-Z012 14-32) and the first two from a 6s (600 MF-6208 13-21). I obviously used the 6s body.

I now have what I believe to be the only indexable, 6-speed half-step specific freewheel: 13-14-17-21-26-32. I am using Shimano SL-BS50 bar ends with the little plastic clippy thing that converts it from
7s to 6s. I have a 50-45-32 up front. I know the 13t sprocket doesn't follow the half-step pattern properly, but it's like an overdrive that gives me just that little extra high end for when there's a 10 mph tailwind or slight downhill.



If you are as amazed as me and a totally obsessive about your gear ratios, please read on.

The project didn't go quite as smoothly as I had hoped (I know, shocker with almost 40 year old freewheels). I broke one of my homemade chain whips trying to get the 5s apart. I ended up using a hammer and punch which destroyed the locking sprocket, but I didn't care because I didn't need it. I was bummed to discover that the 17t sprocket had broken teeth (no wonder it was so cheap on eBay), but I figured I didn't need it - wrong.

I misread the freewheel charts in Sutherland's and actually needed it. The 17t sprocket from the 6s FW was the wrong size for its position on the FW body. Parts bin to the rescue!! I dug out an old Shimano 14-28 5s FW and it donated its properly sized 17t sprocket.

I cleaned, reassembled, reinstalled, and now have my first custom freewheel! I know some of you are probably thinking, well, duh, that used to be the only thing we could do before the mid 80's, but I was 10 back then. And it's kind of like my daughter learning to drive a manual car: it's not a skill everyone chooses to acquire. Nearly every cassette I own has been customized, but they are considerably easier to deal with than FWs - like driving an automatic car.

It's on my '81 Trek 410 BTW, a supremely comfortable ride.
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Old 03-22-21, 09:56 PM
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I have dreamed of doing what you did but haven't gone down that road yet. I do have a few old Suntour Perfect and similar freewheels and I even took one apart the other day to try to get the body off the hub (unsucessfully ).
Could you show the tools you used to do this?
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Old 03-22-21, 10:05 PM
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Here's my setup:

I use the screws to hold the FW in place. (This was staged so I didn't screw them all the way in.) The 2x4 is clamped to something stable like my basement steps. I needed a cheater bar for the third FW.

It's not unlike disassembling a Uniglide cassette but mixing and matching the FW sprockets is more complicated.
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Old 03-23-21, 03:04 AM
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Nice work, I like half step gearing. To dance the chain, you really need to know what you are doing while riding.
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Old 03-23-21, 05:54 AM
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My main rigís half-step drivetrain is friction only (with the same gearing minus the 13t sprocket) using the best friction levers known to man. Iíve learned to do the half-step dance the old fashioned way. But indexing is nice.
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Old 03-23-21, 06:41 AM
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It looks real good...nice "gear freaking".
I just threw in nominal values for the tire size and crank length for the gear chart.

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Old 03-23-21, 06:55 AM
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I have always loved either half-step or 1.5-step gearing. On my mountain bike I have 1.5-step-plus-granny, which serves me well. In that case, the 1-tooth drop between the two smallest freehub cogs fills in the top-end gap that one does not have with half-step:
48-40-28 (or 24) / 12-13-15-17-19-21-24-28 I built the 8-speed cassette out of parts of two others, by drilling out the stupid rivets that hold the four largest cogs together.

For years I have run 50-42 / 14-16-18-20-23-26 on the Bianchi most of the time, but I can quickly change to a 50-47 / 14-16-18-20-23-26 half-step configuration for mostly-flat rides.

My Peugeot beater has 45-42 / 13-15-17-20-23-26, using a stock Shimano "ultra"/narrow width freewheel. Plenty of gear range for general purpose transportation.
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Old 03-23-21, 06:56 AM
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Originally Posted by mountaindave View Post
Here's my setup:

I use the screws to hold the FW in place. (This was staged so I didn't screw them all the way in.) The 2x4 is clamped to something stable like my basement steps. I needed a cheater bar for the third FW.

It's not unlike disassembling a Uniglide cassette but mixing and matching the FW sprockets is more complicated.
Cool setup. I actually have one of the old SunTour freewheel vises, plus a pair of chain whips, to satisfy my gear-phreaking passion.
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Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069
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Old 03-23-21, 07:21 AM
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Those gear selections came out quite well!
Just looking at the cogs from the 14 to the 32, the ideal step size from one cog to the next would be 23% (as calculated by the fourth root of 32/14).
The step from the 14 to the 17 is 21.4%, which is slightly low, but the rest are remarkably close.... the step from the 21 to the 26 is 23.8%, the largest deviation from the ideal 23%.
Well done!

The step from the 45 to the 50 is 11.1%, which is also amazingly close to the ideal 10.9% (as calculated by the square root of the ideal 1.23 step between the freewheel cogs).

I've stumbled upon a 13-30 seven speed cassette that provides nearly ideal steps from cog to cog, but in general, it is fairly hard to achieve. Of course, on my 7 speed cassette, the steps are small enough that uneven step sizes wouldn't be so bad, but with your "5 speed plus overdrive", the steps are bigger and getting them spaced evenly is more important.

Congrats!

Steve in Peoria
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Old 03-23-21, 10:17 AM
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This is how much I geek out:


I use gain ratios rather than gear inches because it takes into account all factors, including crank arm length. I could get one more step down in the low-end with a 28t chain ring, but I don't plan on touring with this setup so 32 will suffice. It just gets me up the steep hills without too much suffering.

Sprockets on the left, chainrings on the top, gain ratios in bold are non-repeating, upper left is the number of unique gears (note that it's one more than the currently possible 13-speed 1x).

The percentages in between the biggest two chainrings represent the gain for a double shift. The percentages on the right represent the amount of deviation from the nominal chainring shift of 11.1%. Then I total the absolute value of deviation at the bottom: 2.6% - the lowest I have ever been able to calculate in any half-step setup I have examined... and I've examined a lot... I believe it is as close to perfect as can be achieved given the fact that fractional tooth counts are not possible.

Also note that I didn't include he 13t sprocket because it's not part of the half-step equation.
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Old 03-23-21, 10:18 AM
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Originally Posted by steelbikeguy View Post
Those gear selections came out quite well!
I've stumbled upon a 13-30 seven speed cassette that provides nearly ideal steps from cog to cog, but in general, it is fairly hard to achieve.
Thanks, and Enquiring minds want to know!
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Old 03-23-21, 12:02 PM
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Originally Posted by mountaindave View Post
Thanks, and Enquiring minds want to know!
The 13-30 seven speed is: 13-15-17-20-23-26-30
The steps range from 13% to 17.6%. Certainly not perfect, but reasonable when dealing with smaller changes in cog size.
The ideal for the 13-30 range would be15%, so it's fairly close.

I'm still using a small stash of these HG50 cassettes that I bought a long time ago. Not sure if these are still available or not... so many cassettes are being limited to those starting with 11T cogs.

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Old 03-23-21, 12:35 PM
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At least I'm not the only one that spends way too much time looking at gear charts.
If going cassette, I like the sram pg730. Works well with smaller chainrings.

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Old 03-23-21, 05:39 PM
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Several of my bikes have half-step gearing. I use Suntour Perfects because they're cheap, abundant, last forever, and are easy to work on. (Also, I have a ton of bodies and loose cogs and spacers on hand.) I tend to use a 46-42-28 in front, and a 14-17-21-26-32 in back--basically the same freewheel as the OP, but with no 13-tooth cog. With the smaller chainrings I use, I don't have that much of a high gear, but it's high enough for me.

My touring bike has a 46-42-28 with a 14-17-21-26-32-38 freewheel. I don't use the 28-38 combo often, but it has come in handy at times on some desperate dirt roads here in Vermont.
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Old 03-23-21, 08:35 PM
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Originally Posted by droppedandlost View Post
At least I'm not the only one that spends way too much time looking at gear charts.
If going cassette, I like the sram pg730. Works well with smaller chainrings.

That site is awesome for visualizing gearing choices, Iíve spent some time there. But Iíve looked so long at my spreadsheet that Iím like those guys in the matrix looking at the code: ďAll I see is blonde, brunette, redhead.Ē

I have used Shimano and Sunrace cassettes. The nice thing about 7/8s is that they generally donít use spiders for any of the sprockets.
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Old 03-24-21, 07:44 PM
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I have a half step plus granny formula I've been using for the past several years, but due to the growing scarcity of vintage freewheels and sprockets, if I shared it, I would have to kill you.
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Old 03-24-21, 07:50 PM
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Originally Posted by old's'cool View Post
I have a half step plus granny formula I've been using for the past several years, but due to the growing scarcity of vintage freewheels and sprockets, if I shared it, I would have to kill you.
No worries. If you're nerdy enough to identify with my thread, I completely understand.
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