Mount derailleur on horizontal dropouts?
 

I’m looking at buying a frame to convert to my indoor trainer bike. Browsing local offerings I found a cool old bike that fits me and looks cool with a fresh coat of powder. I like shiny things.

Is there an adapter, claw, or whatever to do this? I’ll be running 11sp rear. This looks like 70’s to me, I was wearing diapers then.

It’s 126mm and it’ll stretch. It fits. I have a spare fork. It’s all I need for some video game action. Can I make this beast shift?

https://cimg7.ibsrv.net/gimg/bikefor...c87fb46cb.jpeg

Most low end derailleurs come with claws attached fir this kind of frame. They should be good enough for trainer use.

OTOH, if you already have a derailleur, or want something nicer search "derailleur mounting claw" and you'll find exactly what you need for a few bucks.

Can he find a low end derailleur with claw that will span 11 cogs? That's a lot of reach. Edit: a claw will mean that derailleur needs to reach in addition the the thickness s of the hanger to shift to the biggest cog.

A way to do this would be to get a second claw. Cut both to make a top that extends 1/2" below the dropout and a bottom that stops just below the dropout. Clamp them together to form a single hanger that now hangs where an integral hanger would be. Drill the overlap for 2 bolts. Not simple. The inside would need to be clean, so perhaps countersunk for the bolt heads. The attachment has to be rock solid. Failure here will be very expensive. Locktite red + lock washers.

Here is Shimano's frame spec recommendation for SIS. Note that the angle measurements is from axle to BB line. Also note the position of the axle in front of the RD mount position.
This is older info so pre-11 speed. Don't know if it matters.

https://cimg4.ibsrv.net/gimg/bikefor...ba56a744b1.jpg

Is this doo-hickey a "claw?" Never heard it called that. You need one of these, anyway.

https://cimg5.ibsrv.net/gimg/bikefor...f48525e133.jpg

Yes, it's a claw, as in claw mount derailleur.

And many have the built in offset (like the one pictured) so the RD is in the same place it would be with a built in hanger.

The OP has plenty of options, and if this is to be only used on a trainer, he doesn't need to spend much.

Which trainer do you have? If on the offchance it’s a kickr core (but not for some reason right now the full fat kickr), you can use Zwift’s virtual shifting on that now and don’t need a derailleur.

I presume you don't have thru axles? That would complicate it. I ran bikes with 'claws' like that for years; can't see any reason it wouldn't work with 11-speed.

Cool, it’s possible.

Now I’m having the dilemma of “why”. I have a perfectly suited road bike that almost never gets used due to the gravel and MTB nature of most of the rides here. It just seems a little too nice for trainer duty.

I can mail you a claw, like the one pictured in my comment.
Only it lacks the fixing bolt & nut. It would work fine, as long as you clamp in the wheel.
Feel to PM me with your address.

I tend to follow this logic. But for a trainer bike, I’d get one I didn’t need to fiddle with. Not worth the effort to go nowhere on it.

John

You may run into issue with the hanger nut to the cassette lock ring when using the claw with modern equipment

It used to be just a derailleur hanger, but then aluminium frames and a hundred different sorts of derailleur hanger emerged, and it was helpful to differentiate this from those.

We called derailleurs with that part, like the Shimano Eagle, "claw mount" going back to the late sixties.

So. "Claw" is basically a retronym coming into play when the part is sold without the POS derailleur attached.

Yes, I use a derailleur with that integral with it (riveted on), for my folder with no conventional rear derailleur mount. Mine also has the punch mark at the slot radius, which puts a significant protrusion on the back side, to line up in horizontal dropouts to help keep from rotating. However, my bike has vertical dropouts so mounting with that would have caused the hanger to be laterally crooked, so I first ground that off on the backside to flush, spot of paint, then mounted on the bike under the axle nut, oriented by eye. The bolt and nut are also suppose to fit into a horizontal dropout, had to discard for mine, so when the wheel is off, the derailleur is just hanging in mid-air, not ideal, but it works. I tried using the bolt hole to one of the threaded rack eyelets, but it resulted in the claw being under only half the axle nut, I didn't like that asymmetrical loading, so removed the bolt and put the claw back fully under the axle nut.