40/24 double mod on Bombadil

[Jared Volpe]

So I want to do a 40/24 double mod with a Sugino double FD.  

Any suggestions out there? Stainless? Aluminium? More than 24t on the granny? Lessons learned? Chainrings you are happy with?  I've been talking offline with Keven (original inspiration?), lister Jeremy (who is going to help me out once i dial in the parts/setup) and lister Zach who made the mod himself... but I wanted to open it up to the group.  

Thanks!

Jared

[Jim Mather]

I've done that on a couple of bikes, including a Bombadil, and find it
very useful gearing. A 24 with a 32 in back will get a loaded Bomba up
most hills. I've used the steel 24 ring that Riv sells. It's been
fine. What are you switching from?

jim m
wc ca

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[René Sterental]

Riv's version is 26/40. Don't know why they didn't go to 24, but my guess is it has to do the step up and the front derailer efficiency, if that's what that's called. 

I'd be interested to see if and how well it works for you. I have the 32/40 currently on the Betty and love it. It's not that I do much climbing on the Betty now, and the 40 feels fantastic with the 12/34 9 speed cassette. I just got the 26/40 which I may put on the Hunqapillar once it's reprinted with the 12/36 cassette, but  until I lose significant weight, I'd seriously consider swapping the  26 for a 24 if it works well 

René  

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[ted]

24/40 worked fine on my bombadill. Same size gap as the common 34/50
compact.

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[Garth]

With my Bombadil a 24t ring is as large as I could go with needing a longer BB using a 110mm Tange.  And yes .... SS is the only way to go for the small rings. 

[ted]

I always thought it was odd that small rings were al and big cogs were
steel. Seems like if you don't want al cogs for >25 teeth you would
want steel rings for the small (say <36) rings. Same # of teeth means
same load, same wear, very similar weight.

On the bb front, converting a triple to a double using the middle and
small rings should mean you need a longer bb to keep the spec chain
line. Not that I bothered about that, but ...

[William]

Re: chainline.  

You normally try to center the middle ring on the cogset when you run a triple.  so with a 9 speed cassette, you'd line up the middle chainring with cog #5

If your 24/40/chainguard setup is going to be ridden as a 1x9 plus granny (as most people do), then leaving your BB alone is actually precisely the right thing to do.  Center that 40 on the #5 cog and all nine are available to you.  The only no-no gears are the 2 or 3 small cogs when you are in the small chainring, gears that nobody needs anyway.  This is one of the cases where doing it the easy way and doing it the right way might be the same thing!  :-)

[ted]

Color me slow or weak or whatever, but when I ride my bombadill in the
open spaces its more like the small ring is the default and the 40 is
just for downhill. That said I still think the chain line is perfectly
acceptable without a longer bb.

[Mike]

I keep threatening to set one of my bikes up with this sorta wide-range double. I still have the Sugino crank from my Quickbeam with 40/32 rings. From what I hear you can use a regular road double derailer. It makes a lot of sense for commuting, rambling and even touring. 

As for rings... Surly makes nice stainless steel rings. I use one on my singlespeed commuter. Although the rings don't have ramps or pins, I still think they'd be fine for this kind of use. I guess you could combine Surly rings, a Wipperman chain and a nice cassette for a heavy duty long lasting drivetrain.

mike

[Jared Volpe]

Thanks for your input everyone!  This was totally helpful.  Got the bike back on the road today and it is awesome.  Went with the chainring guard, a 40t and a 24t all from Riv.

On Monday, January 21, 2013 7:15:38 PM UTC-8, Jared Volpe wrote:

[Andy Smitty Schmidt]

I've run the 40/26 in the past. Short answer is that it's great configuration. Enjoy it. 

A few more data points... FWIW...

I run a 36/24 (steel/steel) on my Big Dummy... 26t is fine on my Homer but the 24t comes in handy when the load gets big. 2t makes a difference.

For reasons too long and not important enough to explain here... about 6 months ago I switched from 40/26 on my AHH to 42/38/26. I'm not sure if the 42/38 is technically a half-step, but it seems to give me a smaller jump than a rear shift... fun to toy with. 

--Smitty

On Monday, January 21, 2013 7:15:38 PM UTC-8, Jared Volpe wrote:

[JL]

I really liked how the gearing worked out when I set up a 110/74 double on my CB-O townie bike.  I set it up similar to the riv quickbeam cranksets with the blank chainring in the outer position.  Go for it! I bet that crank setup is going to be really nice on your Bomba

JL

[PATRICK MOORE]

I call this sort of gearing "subcomact" and like the switch to 38/24 on the Fargo (from a 46/36/24 triple). I lose some of the intermediate gears but have the same range and, more important in this case is that when moving from smooth, flat surfaces to sandy, hilly surfaces I don't need to switch between outer and middle. I simply swapped a 38 for the 36 and a bash guard for the 46.

I switched from a 7 sp (for Big Apples, 16-18-20-22-26-30-34 or suchlike) to 8 speed (ditto: 13-15-16-17-19-22-26-34). It would be even better with 9 speeds and a 22-25-29-34 progression (Big Apples), but not so much better -- for my purposes -- to be worth the hassle of seeking out the needed spacers and cogs. I gear slightly higher and somewhat closer for the Kojak wheels: 12-13-14-15-16-18-21-26.

I moved the spindle to the left by a couple of mm so that the chain tracks pretty straight between the 17 and 19 t cogs (65 and 58" gears; on the Kojaks: 15 and 16 t, 69 and 65").

Patrick "ain't it fun obsessing about gearing?" Moore

On Sat, Feb 9, 2013 at 8:50 PM, JL <subf...@gmail.com> wrote:

I really liked how the gearing worked out when I set up a 110/74 double on my CB-O townie bike.  I set it up similar to the riv quickbeam cranksets with the blank chainring in the outer position.  Go for it! I bet that crank setup is going to be really nice on your Bomba

JL

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[PATRICK MOORE]

Whoops! I mean to say that I moved it to the RIGHT a couple of mm.

[PATRICK MOORE]

You mean "shorter", right? -- and that only if you use the outer and middle positions. If you simply remove the outer, there is no need for a new bb at all since normally a middle ring is centered on the cassette already. (In my case, I had a triple biased toward the left to allow me to use the outer (46) with all (7) cogs; when I ditched the 46, I moved it back to the normal "triple" position with the middle -- now outer -- once again centered on the cassette.

On Mon, Jan 21, 2013 at 9:51 PM, ted <ted....@comcast.net> wrote:

On the bb front, converting a triple to a double using the middle and
small rings should mean you need a longer bb to keep the spec chain
line. Not that I bothered about that, but ...

On Jan 21, 8:29 pm, Garth <garth...@gmail.com> wrote:
> With my Bombadil a 24t ring is as large as I could go with needing a longer
> BB using a 110mm Tange.  And yes .... SS is the only way to go for the
> small rings.

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[PATRICK MOORE]

Not if you are using a 34 or 36 in back. (Well, I've used a short cage, 8-sp era Ultegra with a 14-32 7 speed, but the rd wasn't happy with the 32).

On Wed, Jan 23, 2013 at 7:29 AM, Mike <mjaw...@gmail.com> wrote:

From what I hear you can use a regular road double derailer. It makes a lot of sense for commuting, rambling and even touring. 

--

[ted]

This is where medium cage derailers are great.

On Feb 10, 7:26 am, PATRICK MOORE <bertin...@gmail.com> wrote:
> Not if you are using a 34 or 36 in back. (Well, I've used a short cage,
> 8-sp era Ultegra with a 14-32 7 speed, but the rd wasn't happy with the 32).
>

[PATRICK MOORE]

Will they accomodate 34 or even 36 to cogs? I've never used one.

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[William]

I've used the shorter cage XT with a 12-36 cassette and a double chainring.  The M751 GS is the model. 

[charlie]

 I know quite a few people are going nuts over uber wide cassettes and two rings so maybe they are on to something. Either way steel rings are a good investment. I purchased Surly stainless rings (44&34) and they work fine on my triple with a steel 24 tooth.

On Monday, January 21, 2013 7:15:38 PM UTC-8, Jared Volpe wrote:

So I want to do a 40/24 double mod with a Sugino double FD.  

rly 

[René Sterental]

I just got my Hunqapillar back from the painter last week, and today my LBS installed the headset, BB and crankset. I decided to install the stock Riv 26/40, although may go down to 24 in the future.

The thing is, the Phil BB had to be shifted to the right all the way, with the left side flush with the BB shell/frame in order for the 40 ring to clear the chain stay. In fact, there is about 1mm between the sharp teeth of the chainring and the chain stay. Do I need to up to a larger BB spindle? I think I have a 111, so next size up is 113.

What do you guys think? Do I need more clearance between the ring and the chain stay? Actually, the 26 is also very close to the chain stay. I used to have a 24/36/46 before.

Thanks,

René

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[William]

Yes, I do think you want a slightly longer BB when you switch from a triple to a supercompact double. 

[Andy Smitty Schmidt]

yes... longer BB sounds like the ticket.

my 2 cents.

--Smitty

On Thursday, March 7, 2013 7:45:38 PM UTC-8, René wrote: