Double -> triple bodge question

[mattc]

(This is an idea to make a bike more usable using parts from the (clean) bin as far as possible, as an experiment before I decide how the bike will be used long-term).

I have a old-ish shimano DOUBLE x10 STi setup, with a regular road derailleur. If I fitted a triple chainset (with the recommended BB), would the shifter probably give me:

- just the middle ring or
- middle+Small or
- middle+Big ??

Or the above but with the modifier "badly", or "barely".
Or some result I hadn't considered.

(Assume that I adjust the limit screws to stop it going where I don't want it to. Limit screws I understand, BB lengths less so!)

There are various other bodges I can do (which will require me to buy at least 1 new part), but let's keep things simple for now ....

[Brucey]

it'll give you two chainrings, provided the appropriate FD is used.  Trim clicks may or may not be terribly useful.

FWIW if you route the FD control via a shimano RH ergo boss (the one with the stepped Quick-action cable adjuster) you might be able to use this (and the last trim click) to select the inner ring in an emergency, whilst using the other two chainrings the rest of the time.



edit; looking at it now, the stroke probably isn't long enough, not without modification, anyway...

BTW some road FDs won't reach far enough to get to the outside ring of a triple, but this varies with chainline as well as FD type.

cheers

[Cudzoziemiec]

Based on the behaviour of a double FD with those super-compacts which are in fact triples with their outers removed, it'll give you inner and middle. You might have to remove the outer to avoid the mech cage clashing with the teeth.

But I dare say it could be set up to give other results.

[Adam]

Depending upon the model of shifter, if it has a trim mode, like a ½ step, then even though it's only a double, with careful adjustment you can use it to give access to all 3 chainrings.  I've done this on an old Specialized Sequoia. 

[rafletcher]

Depending upon the model of shifter, if it has a trim mode, like a ½ step, then even though it's only a double, with careful adjustment you can use it to give access to all 3 chainrings.  I've done this on an old Specialized Sequoia.

The issue with this will be the possibility of very poor shifting to the inner ring, as the mech won't have the longer cage tail that triple mechs have.

[Adam]

Depending upon the model of shifter, if it has a trim mode, like a ½ step, then even though it's only a double, with careful adjustment you can use it to give access to all 3 chainrings.  I've done this on an old Specialized Sequoia.

The issue with this will be the possibility of very poor shifting to the inner ring, as the mech won't have the longer cage tail that triple mechs have.

I don't remember changing the rear mech but it might not have been too small to start with.  I'd got it set up, so that when you went from 5th to 4th on the back, then there was enough slack so on the left hand shifter, you could then drop it onto the granny.

[jsabine]

Depending upon the model of shifter, if it has a trim mode, like a ½ step, then even though it's only a double, with careful adjustment you can use it to give access to all 3 chainrings.  I've done this on an old Specialized Sequoia.

The issue with this will be the possibility of very poor shifting to the inner ring, as the mech won't have the longer cage tail that triple mechs have.

Triple fronts often don't actually have a longer cage - the difference tends to be the shape and depth of the inner plate.

Certainly I've got a bike - admittedly 8sp, and the one that lives at my mother-in-law's, so it doesn't get ridden very often - that uses a double Mirage front to change quite happily over a triple chainset.

[mattc]

Tips much appreciated folks. Stage 1 of the bodge complete, confirming most comments here:

Covers small+middle ring OK without any great fettling skill. I had to remove the big ring as the derailleur was snagging on it - confirms how the 'deeper' triple cages work as they do!

(I don't have a suitable front shift lever to easily bodge on currently -without cannibalising other valued machines! -  so I can't test that setup yet. If anyone can suggest how to put a DT shifter on a 40mm aluminium down-tube, that might get me to that step - in the meantime I can ride the bike quite a lot with the 2 rings I have, so that's a result    )

[LittleWheelsandBig]

You need an Erickson Gizzmo but they've been out of production for many years. Somebody has tried to copy it though.
https://www.thingiverse.com/thing:1988515

[Brucey]

Erickson gizmo works in the same way as this shifter



which is an SA one, about a hundred years old. Nothing new under the sun and all that!

regarding alternative shifters there are various (mostly quite expensive) brackets here

https://www.sjscycles.co.uk/gear-spares-other/

which allow you to mount a shifter on the bars. A bar-end shifter would work too.  If you can get a bracket to mount on the bars somewhere (I have mounted something suitable at the handlebar clamp BTW) you can mount a thumbshifter or w.h.y. .

If you can get some vintage suntour thumbshifters like this



they use a simple band to mount, which means that a new band can easily be made, of the correct length to allow these shifters to be fitted to a handlebar or stem.


There are lots of ways of getting a workable shifter!

cheers

[Paul Rainbow]

You need an Erickson Gizzmo but they've been out of production for many years. Somebody has tried to copy it though.
https://www.thingiverse.com/thing:1988515

One on ebay now... https://www.ebay.com/itm/Erickson-STI-Gizzmo-for-Triple-NOS-Erickson-Design-Shimano-7400-6400-brifter-shi/223449608110?hash=item3406a26fae:g:HDMAAOSwEIhZg5zh&frcectupt=true

Looks interesting, never seen one before!