Axle position in dropout (and derailleur hanger)
 

I have an '81 Peugeot that I've recently acquired and started to play with. It came to me with 28mm Panaracer Pasela tires, which actually measured about 25mm on the rims. I prefer wider tires, so I mounted up some 35mm tires, which measure about 34mm. I can fit these on the bike, but only if I slide the axle all the way to the rear of the dropout. One normally can't do this with a claw derailleur hanger, because the mounting bolt takes up about 1/2". But by removing that bolt, and just squeezing the claw with the skewer, it works, and provides just enough frame clearance, as depicted below:

https://cimg6.ibsrv.net/gimg/bikefor...df47c2edd6.jpg

https://cimg5.ibsrv.net/gimg/bikefor...7de1affa40.jpg

It's pretty awkward to fit the wheel this way with the chain installed, but removing the chain from the bike relieves all the tension from the derailleur and it's actually not too difficult using that method. However, I'd like a more permanent solution.

I've looked on the internet for little derailleur hanger "tabs" one might weld or braze on to the bottom of the dropout, but came up empty on that. I guess if you're building something from scratch, you'll use a dropout with an integral hanger (or a replaceable one). I could just have a claw adapter tack-welded to the frame, and clean up the paint afterward. (I wouldn't have this hanger, pictured, welded because it's part of the derailleur itself, but I'd find a claw adapter for that, and then use a traditional bolt-on derailleur.)

I'm also thinking that I could drill and tap an M6 hole in the rear of the dropout, right through the claw's mounting hole, and just thread an M6 screw into that, which would mount the derailleur fast to the frame. Does anyone see any issue with that? I believe there is plenty of material there in the frame. I could certainly slide the hanger forward just a tad to ensure there's enough meat for the hole.

I appreciate any thoughts or suggestions on this.

In your current configuration (pictured)...by not using that mounting bolt I think you may in danger of the claw slipping/pivoting back-and-forth on the axle without the second securing point. Seems like to prevent that you'd have to overtighten the QR to what might be too tight. That said...I don't think drilling/tapping a hole for that bolt would be a problem here. Still...with that size tire it's an awfully close clearance. Just my opinion, I'd rethink tire width.

Is that a 27" wheel? If so, another option would be to go with 700c wheels. They're a bit smaller, and might give you a bit more clearance. Of course then you have an issue with the brake calipers reaching the braking surface.

Also...is it just me, or in the side view pic does the very rear end of the chainstay look bent?

Dan

Not sure why removing the chain from the bike helps but an easier way to release the chain tension is just shift the front to the small ring and slip the chain off to the BB shell.

I disagree. The QR needs to be tight enough to keep chain tension from pulling the wheel forward, and there should be very little rotational force on the derailleur claw. This set-up will undoubtedly be a nuisance when removing or installing the wheel, but otherwise should work fine.
@hokiefyd Derailleur 'claw' adapters are available at bike shops for less than $10. Having one welded on - probably aligned so the back of the claw's slot is lined up with the back of the dropout would be fine. Keep in mind that welding can weaken the material being welded, and dropouts are a fairly common point of failure on bike frames, but in my opinion (FWIW) is that it would likely be fine.

I would actually get two claws, or some other item to weld to the non drive side to make that dropout thicker as well. Stamped dropouts like that are often so thin that you need to shorten the lengths of the axle stubs so the QR can tighten properly. If this is not an issue with your bike than ignore this advice.

Thanks, all!

The claw cannot rotate in this configuration -- the skewer is tight enough to hold the axle from moving forward under pedal force, which means I can't rotate the claw -- not even trying to by hand. @AnkleWork, I probably mis-spoke when I said the chain tension makes it awkward. I think it's actually the derailleur cage spring -- it wants to spring the cage all the way rearward and, with the chain installed, that means the unmounted derailleur wants to flip rearward and sort of upside down. You may be right that moving the chain down to the BB shell (and have it in the small sprocket on the rear) would be enough. With a quick link, it's easy to remove, too.

I do think the photo under-represents the tire clearance. There's about 2-3mm on either side of the tire, centered between the stays. It's "tight", but I'm comfortable with that. These tires are Bontrager Select Inverts, from an older Trek hybrid. They're marked both 37-622 and 700x35, and measure about 33mm on the rim (inflated to 50 psi). I might could squeeze a true 35mm tire in there, but I'll run these until I have a reason not to. They're smooth, comfortable, and they fit (at least with my derailleur configuration mod!).

I may just drill and tap a small hole and try that first. It's not like I'll have to really torque that bolt down -- it'll require just enough torque to keep the derailleur positioned when the wheel and skewer aren't in place. If I get to this this weekend, I'll take a few pictures and let you all know how it worked.

Dan, no, these are 622mm wheels (700c). Brake reach with these is actually very short, shorter than I expected (about 50mm). I'd like to swap center-pull brakes on this bike, but I'd have to get super short reach ones to make that work I think. You are right that the rear of the chain stay is bent slightly downward. It's like that on both sides, though it's a bit more pronounced on the drive side. I don't know if that's intentional, just due to cheap/mass production, or some other factor. This is a fairly low-end Peugeot (with the Carbolite 103 tubing), so it's definitely not something that would have been custom tuned and fitted during frame building.

In most of the derailleur adapters of your type, there is the obvious bolt, but also the claw has the slot deformed, or two nipples are pressed into the adapter to keep it registered in the slot. That extra detent limits your clearance if its in the dropout axle slot. But that registration is only important when you don't have an axle fastened in there with a quick release. You are shooting for maximum clearance in the rearward direction.

You could try the idea you had regarding moving the adapter back, and drilling and tapping a hole in the dropout. Keep in mind: this does weaken the dropout. You take responsibility for any disaster/injury/loss of life or property. If you decide to try this, I'd balance clearance with trying to get the hole in the center of the fat part of the dropout (if you have to drill near the edge, you could be compromising the dropout strength more than you want). You would want to file down whatever detent you have in the adapter so that the adapter mounts flat against the face of the dropout. You could have a welder fill the old hole, then file the bead down, if you are really a stickler.

If you really want to make this permanent and more modern, you could have a claw welded in, or a completely new dropout welded in. (pic).

Last, I

If you want to geek out, check out Derailleur Hangers Demystified - Red Clover Components

https://cimg7.ibsrv.net/gimg/bikefor...4cf93980ec.jpg
https://cimg4.ibsrv.net/gimg/bikefor...32ba08f1a3.jpg

BTW, if you do change the dropout, you may have to change the derailleur. Some of the older derailleurs don't have the range of motion required when a built-in derailleur mount is used.

Thanks! Yes, as it is, I have that "indexing bulge" on the back of the hanger sitting in the very back of the dropout slot. You're right in that I could slide it another 1/4" rearward if I filed that bulge off, but I like the idea of leaving it there. Plus, on this '81 frame, I can't really go further rearward and still have that rear mounting hole stay on the dropout. In fact, I may need to move it forward just slightly to get that little hole centered on the "meat" of the dropout material. I'll take pictures of what I do.

(If I do anything...I appreciate the comments about weakening an already thin dropout. I'd assumed that the dropouts were particularly strong parts of the frame, but maybe that's not true. Maybe I should think about how often I'd really take the rear wheel out, and decide if any risks to modifying the dropout are worth it.)

radical idea:

convert to singlespeed and lose the derailer entirely

a better bike with a better frame with non-gaspipe tubing and forged dropouts with a derailer hanger integrated would be inexpensive

not to say don't ride this but i wouldn't put much money hopes or dreams into it

Or an internally geared hub. But for a low-budget solution, the OP's solution ought to work ok, albeit with awkward rear wheel removal and perhaps somewhat degraded shifting performance.

I rode the bike some today, and it seems to be working fine. I really like the larger volume tires that this enables. It's currently friction-shifted, and that seems to be working fine. I don't guess I'm going to try to modify the dropout. I don't expect to ever have to remove the wheel (this is not a long-distance bike for me, and flats are pretty unlikely), so I don't think the extra fiddling there will have any impact on my enjoyment of the bike. I figure there's no reason to over-think this.

I appreciate the comments and suggestions.

Maybe just drill a little detent with a set screw where threaded hole is...maybe point the screw end a bit for bite...

I would do as you suggest. Bump the wheel forward, drill, tap, insert a bolt, and enjoy the ride.

Width of the tire isn’t the only factor in ride quality. A high quality 32mm tire might fit and not require messing with the drivetrain or welding the frame.

This is true. The bike came with 28mm Paselas, and I was expecting good things based on reviews I've read of those, but I wasn't very happy with their ride. The wheels have a bit of a hop to them (more than I can true out of them) and the pressures I have to keep in those 28mm tires (which really measure about 25mm) meant that I felt EVERYTHING, the road grain, the wheel hop, etc.

I very well might find some really nice 32s (that actually measure 32mm!). The 35mm Bontragers (34mm actual) have a very nice ride quality and also tolerate lower pressures, low enough that I don't really feel the hop in the rims anymore. They also have a raised center tread (not unlike something like a Continental Tour Ride) which gives them a very smooth and comfortable ride. So I'll run these for now.

This bike is N+5 for me, so it's not a have-to-fix-it-now-or-else bike. I like these older Peugeots and this one is in a color I like, so I popped on it. Lots of fun for 40 bucks.