Author Topic: Front Derailleur for Half-Step plus Granny  (Read 1334 times)

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Offline GopherBroak

Front Derailleur for Half-Step plus Granny
« on: August 28, 2013, 06:08:33 pm »
I've been using a ~1984 Nishiki Riviera GT for loaded touring for some years. I like its simplicity and ruggedness. It fits me very well, but it could use just a wee little tweak in the drivetrain configuration.

Currently, I am running 50/40/28 chainwheels (2 of them Sugino Cycloid) with a 5 spd 14-16-20-24-28 freewheel. I hardly ever use the 50 tooth chainwheel and often find that I cannot find a comfortable gear ratio from those now available for long slogs.

So I would like to install a 38/34/26 chainwheel configuration, but I will not be able to lower the Shimano FD any further because the bottom of the cage is currently just a half cm above the chainstay and the rear derailleur cable that rides on it.

QUESTION 1: I have friction shifters front and rear. The bottom of the FD cage will be below the chain when its engaged with the smaller 26 teeth inner chainwheel. But I wonder what other sorts of shifting problems, if any, can I expect if I just swap out the chainwheels and leave the FD where it is?

QUESTION 2: If I need to replace the FD, which of the many models available would work best for this chainwheel configuration?

Thanks in advance,

GopherBroak

Offline RussSeaton

Re: Front Derailleur for Half-Step plus Granny
« Reply #1 on: August 28, 2013, 09:34:10 pm »
Your new chainrings are only 12 teeth between inner and outer.  So any regular double front derailleur will easily shift this combination.  Just use a normal double front derailleur.  A road racing type front derailleur.  Go with a road model, not a mountain bike model.  Although both would probably work fine.  But you should stick with a double front derailleur, not a triple mountain bike style.  Any Shimano or SRAM double front derailleur will work fine with your friction shifting lever.  Just put it on the bike as low as possible and if its a bit high over the outer chainring, no problem.  You will still be able to shift just fine.  I'd also suggest putting on a 24 tooth inner chainring, go as low as possible.

Offline dkoloko

Re: Front Derailleur for Half-Step plus Granny
« Reply #2 on: August 29, 2013, 10:40:54 am »
The simplest way to get half step and the one I'd recommend is to change 40T to 45, and that's all. You will be using the 50 with half step. Whether you lower the 28T chainring to 24 depends on low gearing you need and how it works out for half step. Each shift on front should be half of each shift on the rear.

Offline GopherBroak

Re: Front Derailleur for Half-Step plus Granny
« Reply #3 on: August 30, 2013, 03:05:57 pm »
Thanks for the insights, RussSeaton!  I hesitated to go down to 24 tooth because of the chainstay clearance problem with my current derailleur.  The minor axis on my elliptical Sugino Cycloid  28 tooth granny is about the same diameter as a circular 26 tooth, so I figured my current derailleur could handle it.  When I get a different derailleur, I'll look at the issue again. 

Do you suggest using a steel chainring for a granny gear that low?  Or for any of the others?  I believe that the cycloid 28 and 40 tooth chainwheels currently installed are both steel.  They've lasted a long time.

Thanks for the post, dkoloko!  My current problem is that I've found after several long tours that I seldom have any use for chainwheel/cog tooth ratios greater than about 2.5/1.  That's why I want to go to the lower half step setup, so as to open up more ratios between 2.0 and 2.5 than the single jump I have now.


Offline RussSeaton

Re: Front Derailleur for Half-Step plus Granny
« Reply #4 on: August 30, 2013, 07:16:20 pm »
With a 1984 bike, I'm thinking you have a 5 or 6 or 7 speed freewheel on it.  That will work well for half-step gearing.  Your rear spacing is probably 120mm or 126mm.  Not current 130mm road or 135mm mountain bike spacing.  So changing to a 8-9-10 speed cassette rear wheel may not be too easy.  You could still force a 130mm road wheel into your dropouts and it would work.  You could change to 9 or 10 speed cassette.  Going to 9 or 10 speed would make half-step unnecessary.  With 9 or 10 cogs, you have close enough gears to shift with one chainring all day long on all terrain.  But changing to 9 or 10 speed would require a fair number of new parts to replace.  Something you might not want to do.

Go with aluminum chainrings.  With the shifting assist tabs on them if you can.  Cost more to get chainrings with the shift assist tabs.  But maybe worth it for shifting to a bigger ring.  You will never use the inner chainring enough to ever wear out an aluminum ring.  Steel lasts longer, yes.  But aluminum rings last almost forever too.  Wearing out chainrings is not a problem peope should worry about.

Offline GopherBroak

Re: Front Derailleur for Half-Step plus Granny
« Reply #5 on: August 31, 2013, 05:32:01 pm »
My bike came with a 5 speed 14-28 Suntour freewheel.  Back in the day, I could have had that freewheel customized to get the desired effect, but that is no longer possible. 

Rear dropout spacing is 120 (actually ~122) mm.  Wheels are 27".  Last summer, I spent 5 months touring Europe and Canada and carried a roll-up 27 inch tire because they are so hard to come by.  I considered changing to 700C wheels, but the cantilever brakes have no adjustment for wheel height, so I would have to replace them. 

As you can see, one thing leads to another and I am content just to improve the drive train a bit.   The bike is tough and reliable, and fairly easy for me to maintain and service, and I've kinda bonded with it.  Those are things that I might lose with a newer bike.

Honestly, I am not convinced that 9 or 10 speeds is either necessary or practical for touring.  Chains are narrower, and therefore weaker, and not so easily found.  Wheels are deeply dished and also weaker.  I met folks touring with that kind of setup who were using just a few of the 27 gears they had available because the others were out of their comfort ranges, and carrying all the weight that those extra gears require.

My objective is to have as many gear ratios in my comfort range as possible, in a setup that is easy to repair and maintain.

Thanks for the advice on chainwheels, RussSeaton.  I'm more confident now that I can get this bike into the kind of configuration that will suit my cycling style.