Double step gearing



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Doug Goncz

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Here's an interesting gear combination for you gearheads:

24 / 35 / 52 x 11 / 15 / 16 / 19 / 23 / 28 / 34

This actually works out to an eleven speed.

I find the steps particularly even, though large. And the double step means there is a lot of
duplication. You gear down two in back and up one in front, no matter where you are, to find a
duplicate. I think that requires a lot of planning and terrain awareness from the rider, but little
looking down at the indactors, if equipped, or wondering what's next. Less confusion and more
awareness.

In fact, if you take the log of the ratios and scale from 1 to 21, you find the only gears provided
are odd numbers. All of them. Eleven neatly spaced gears with duplicates. I rule out big/big and
small/small and their two adjacent positions due to chainline and chain length problems.

I'm currently running 24/38/52 and am having trouble. I've ordered an R440 FD to try this with. If
it doesn't work I'll go 42 middle front for a single/triple step setup.

I don't know how it's going to shift. It's got a whopping second/large front step. Really huge. The
R440 is for cogs up to 53.

I've got a Mathcad spreadsheet showing the logarithms if you'd like, or you can go to
sheldonbrown.com, who are supplying the parts, and use their gear computer, or another of
your choice.

I like the idea of looking ahead and saying _in advance_ which range I need to be in. We'll just
have to see if I am capable of this. I plan on setting up a beeper to warn me when I get adjacent
big/big or small/small so I can reverse the commanded shift and get back to a range.

They say we are far from half-step / granny now and are more like low/med/high "range" gearing.
Well, this takes that to the extreme. It's like 48% from 24 to 35, and then 49% from 35 to 52. Very
even there. And the rear is like 18-20-21-20-21-18% or something like that. Even.

Now if I could just get that FLIR system up to read the terrain and make all the shifts for me. Ah
well, after I get the Dewars installed, maybe.

But will it shift? And if it won't, and I can't buy a derailer, how do I build a derailer or
derailer cage that will shift it?

I have a milling machine and small lathe.

Do you know how hard it is to find a 110/35 cog? Jeez, that's a hen's tooth.

My senior project at ODU: Google Groups, then "dgoncz" and some of: ultracapacitor bicycle
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In article <[email protected]>, [email protected] says...

...

> But will it shift? And if it won't, and I can't buy a derailer, how do I build a derailer or
> derailer cage that will shift it?

Is your concern with the front? Because you should have no problem with the rear if you use a wide-
range der like a Deore.

....

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

REAL programmers write self-modifying code.
 
Doug Goncz <[email protected]> wrote:
>Here's an interesting gear combination for you gearheads:
>24 / 35 / 52 x 11 / 15 / 16 / 19 / 23 / 28 / 34 I don't know how it's going to shift. It's got a
> whopping second/large front step. Really huge. The R440 is for cogs up to 53.

I use a 52/34 double with a normal Tiagra front derailleur (intended for use with triples, so
effectively I have your setup with the granny missing) without any trouble; of course, this is
without indexed front shifting. I think with friction front shifting almost any derailleur will do
provided the cage can physically accomodate the chain in all postions.
--
David Damerell <[email protected]> flcl?
 
David Damerell wrote:

> I use a 52/34 double with a normal Tiagra front derailleur (intended for use with triples...of
> course, this is without indexed front shifting. I think with friction front shifting almost any
> derailleur will do provided the cage can physically accomodate the chain in all postions.

That's true for doubles, and, in fact, even front indexing isn't fussy at all with doubles. Anything
that can shift three can also shift two.

For triples, it's a different story. Even with friction, an even-spaced triple setup needs a
"triple" type front derailer to make a reliable shift from the granny to the middle. (Old-fashioned
half-step setups, where the two outer chainrings are nearly the same size, work fine with "double"
type front derailers.)

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