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What Is This Gearing Optimized For?

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What Is This Gearing Optimized For?

Old 04-15-14, 08:30 PM
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zazenzach
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What Is This Gearing Optimized For?

I honestly know next to nothing when it comes to gearing. i threw together this 12 speed with 38-53 crank and a 13-30 freewheel. picture shows gear inches etc.

Am I right in assuming this is for touring? ive put some miles on it and it feels a bit uneven.
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Old 04-15-14, 08:41 PM
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I don't know what it's for but those are some big jumps in gear inches. Touring sounds about right I suppose.
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Old 04-15-14, 08:44 PM
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That jump between 4 & 5 is absurd IMO.
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Old 04-15-14, 08:52 PM
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Well, I wouldn't dream of running that combo. Too many duplicates or near duplicates. and absolute chasms between 77, 93, and 108 gear inches.
What you need are fairly closely spaced steps in your preferred cruising range (mine is approximately 70-90 gear inches), not more than 10% steps between your upper cruising range and your top gear, and whatever steps you can tolerate between your bottom cruising range and your bottom gear (which typically can be fairly wide).
Distinct gears should be considered precious, and any duplicates or near-duplicates a waste of this precious resource. A valid exception to this dictum is the classic single-step setup, but that is a bit of an anachronism these days with wide range crossover gearing and indexed shifting. I still have one bike set up this way, and it is great for zoning on long rides, but there is a price paid in bottom to top gear range.
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Last edited by old's'cool; 04-16-14 at 03:57 PM. Reason: vocabulary
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Old 04-15-14, 08:56 PM
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Originally Posted by old's'cool View Post
Well, I wouldn't dream of running that combo. Too many duplicates or near duplicates. and absolute caverns between 77, 93, and 108 gear inches.
What you need are fairly closely spaced steps in your preferred cruising range (mine is approximately 70-90 gear inches), not more than 10% steps between your upper cruising range and your top gear, and whatever steps you can tolerate between your bottom cruising range and your bottom gear (which typically can be fairly wide).
Distinct gears should be considered precious, and any duplicates or near-duplicates a waste of this precious resource. A valid exception to this dictum is the classic single-step setup, but that is a bit of an anachronism these days with wide range crossover gearing and indexed shifting. I still have one bike set up this way, and it is great for zoning on long rides, but there is a price paid in bottom to top gear range.
Originally Posted by Bill Kapaun View Post
That jump between 4 & 5 is absurd IMO.
should i be changing out the crank rings? to more of a compact range or something??? what are your suggestions?

id like to keep the freewheel if possible as it is dura-ace and matches my wheelset.
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Old 04-15-14, 09:10 PM
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Originally Posted by Bill Kapaun View Post
That jump between 4 & 5 is absurd IMO.
Exactly what I was thinking.
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Old 04-15-14, 10:51 PM
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This is a Dura Ace freewheel? What kind of roadie needs a 30t low gear?

I think the biggest problem here is the gap between the 2nd and 3rd cogs, this freewheel really needed a 17 more than it needs a 30. If your heart is set on keeping the freewheel, I would use either a triple with large chainrings (52-42-30), whcih would give you a nice high gear and an absurd low gear that will let you ride even when it would be faster to walk, OR a 52-42 double, which would produce a tolerable range of gear ratios considering you're saddled with an extremely low bailout gear.

Last edited by lasauge; 04-16-14 at 09:50 AM.
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Old 04-16-14, 04:25 AM
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That's a cool graph. What program do you use to calculate gear inches?
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Old 04-16-14, 05:05 AM
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Why not approach this differently? First, you're in charge of your own build, so don't let some component part (a DA freewheel) dictate to you whether or not you'll use it. Decide in advance what you want the gearing to accomplish and how you want those GI spreads to be arranged for your purpose. Then select accordingly.

Why not go 7-speed on the rear? That'll let you fill in. What are the top range and bottom end that you need for your riding style and most likely riding spots? Draw out the chart that you want, and use the calculator "what if" capability to choose what you'll use.

Say that you keep that strange DA freewheel (I wouldn't..., but would sell it to pay for the new freewheel), then you'll have to look at a smaller outer chainring to bring those black higher gears back downward, and to move the overlap points lower, giving yourself more options. Maybe only 5-6% decrease would do it, just looking at the chart. So that would be a 50T. Plug that in and see how the profile looks.

If you really need the 38x30T low end, then maybe a 13-30T 7-speed and a 38x50 ringset might work. Try it out with the calculator and see...

Anyway, you're in charge, you decide...
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Old 04-16-14, 05:18 AM
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On further review, the ruling on the field stands. That's a strange set of cogs. Either (preferably) the 19 ought to be 18 or the 15 ought to be 16. At least that way it would start with more consistent spacing. Then a 52T big ring would give it a more useful crossover. Perhaps the crank can't go below 38.
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Old 04-16-14, 12:11 PM
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The low gear is a bit high for touring in hilly terrain. But it might be fine for flat to gently rolling - I've toured with a 40" low gear in gently rolling terrain.

Gearing very similar to this is what I use on my 6-speeder when I travel to the mountains - 39-53 crank with 13-15-18-22-26-30 freewheel.

If you don't need the 34" low gear, you could change to a 45 inner ring and it will give you a gear between the 53/15 and 53/19

Last edited by Gonzo Bob; 04-16-14 at 12:14 PM.
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Old 04-16-14, 04:27 PM
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I can't come up with any combo that I would personally use keeping either the freewheel or the chainringset as-is. I would be changing both, to some extent, to get something useful to me.
The only combo I'd remotely consider, keeping the 48-53 chainrings, would be a 13-17 corncob for the smallest 5 sprockets, and you pick your bailout largest sprocket; for me and the riding I do that would be in the 20-24 range. But I'm not a fan of cross-over gearing; I only use it on bikes that I'm kept with non-triple cranksets for nostalgic reasons. The rest of my fleet is set up with a triple, half-step or single-step plus granny combo.
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Old 04-16-14, 07:20 PM
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Originally Posted by Chuckk View Post
I bet that DA RD doesn't have a THIRTY TWO tooth capacity!

Optimized for nothing, either somebody just threw parts together or decided that they wanted giant bail-out gearing.
I think I've seen those big last steps on old French bikes.
How's the shifting?
you'd lose the bet then . I'm running a deore xt rd-m739 sgs with exactly a 32 tooth capacity. shifting is very crisp.

as my original post stated it was basically thrown together with parts on hand. i bought a frakenbike and then switched out some parts. didn't want to sink any money into the build but looks like i'll have to with the funky gearing.



Originally Posted by Phil_gretz View Post
Why not approach this differently? First, you're in charge of your own build, so don't let some component part (a DA freewheel) dictate to you whether or not you'll use it. Decide in advance what you want the gearing to accomplish and how you want those GI spreads to be arranged for your purpose. Then select accordingly.

Originally Posted by old's'cool View Post
I can't come up with any combo that I would personally use keeping either the freewheel or the chainringset as-is. I would be changing both, to some extent, to get something useful to me.
i think you're both right. I think I'm going to ditch the freewheel and crankset and stick with a more traditional touring gearing. i'd been thinking of upgrading everything to 8 speed tricolor anyway.

no wonder i got the dura ace freewheel for so cheap, it's pretty much unusable. i wonder what on earth its purpose is for.
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Old 04-16-14, 07:42 PM
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If you want to keep the freewheel have you considered swapping out cogs? Not sure what's available for that particular freewheel but I've re-cogged a couple over the past couple of years to get the gearing i wanted (then got the IGH bug and only obsess over one sprocket).
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Old 04-16-14, 07:53 PM
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Originally Posted by markk900 View Post
If you want to keep the freewheel have you considered swapping out cogs? Not sure what's available for that particular freewheel but I've re-cogged a couple over the past couple of years to get the gearing i wanted (then got the IGH bug and only obsess over one sprocket).
are you confusing a cassette with a freewheel? ive never heard doing that with a freewheel....anyways dissassembling a freewheel and putting back all those ball bearings sounds like the 7th level of hell to me.
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Old 04-16-14, 08:19 PM
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Originally Posted by zazenzach View Post
are you confusing a cassette with a freewheel? ive never heard doing that with a freewheel....anyways dissassembling a freewheel and putting back all those ball bearings sounds like the 7th level of hell to me.
No big deal really, to change out the cogs. As long as you can get the smaller cogs unscrewed that is. Disassembling and overhauling the body is optional, but also no big deal. There are a few threads in the archives on this.
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Old 04-17-14, 12:14 AM
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Originally Posted by zazenzach View Post
are you confusing a cassette with a freewheel? ive never heard doing that with a freewheel....anyways dissassembling a freewheel and putting back all those ball bearings sounds like the 7th level of hell to me.
You can take cogs off a freewheel body much like you can take a cassette off of a freehub. For the Dura-Ace 6-speed freewheel, you just unthread the smallest cog - thread the freewheel onto a wheel and use two chain whips - it may take a lot of force. You can get loose Shimano freewheel cogs at Loose Screws Bicycle Small Parts ALL items are 20% off the listed prices.<br>Tiered discounts are applied in the shopping cart. (they are currently having an inventory liquidation sale until April 25) but selection is extremely limited. I have cogs for my Dura-Ace 6-speed freewheel to run 13-18, 13-21, 13-23, 13-26, and 13-30. Some have come from loosescrews and others from donor freewheels I got on ebay for $1.
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