On most of the older bikes I have worked with, the stamped or forged dropout is worn or marked where the ideal axle positions have been - BUT - What are the caveats for proper positioning? - Campy puts the axle just a above or about 2mm behind the mounting hole for the rear dérailleur - Shimano directly above - Lately I have had to bring axles farther back than normal in order to accommodate 34 tooth freewheels - I have not had any problems - Yet...

So... Are there rules???

I'm interested in hearing the responses here. To be clear to others that coming along, Zandoval, you are referring to horizontal or semi-horizontal dropouts, correct?

Yes - Here are some pics from Sheldon...

Great idea for a thread! Looks like I will learn something today.

ColonelJLloyd, very cool avatar. For some unknown reason though, when I see it I think of a 60's version of Max Headroom.(I have no idea why)

On stamped DO's, usually there is a stop at the rear of the mounting for the derailleur claw, which I position full rear.
-Thus, the left side is free to float fore or aft, as required to align the wheel.

On forged DO's there's usually an adjuster screw, which I set to mimic the above situation, and then net the opposite side adjuster screw to wherever the axle ends up.

( I would be interested to know if there is a better way.)

My Peugeot's forged Simplex DO's do not have any marks to show any ideal axle position, so I always just mount the wheel as far forward on the DO's as I can, making sure the QR's still have full engagement with the DO's. I figure, I might as well minimize the bike's wheelbase if I can. Don't know If it really has any perceptible effect to handking, but the bike seems to ride just fine, RD shifts OK too.

Chombi

Thanks. It's the blond pompadour (although, Headroom's wasn't a full pomp).

Chombi - Hey I like that - That also kind of moves the dérailleur farther behind the axle to give more room for more teeth...

Good topic, although I think we have disucussed this before! Having said that, I don't remember the outcome! There must be an impact to shifting quality. That topic alone is worth several pages!
What have you expereinced vs what do you think.

I have used this pic as a template when welding on dérailleur hangars to stamped dropouts - Are there critical considerations for axle position?

I've always scooted my wheels as close to the downtube as possible to shorten the wheelbase. With the limit screws, its easier to do.

Axle position in the dropout affects the following characteristics:

1. Handling: Moving the wheel forward shortens the wheelbase, making the bicycle more nimble. It also shortens the effective rear triangle, making it slightly stiffer and more responsive to pedal input.

2. Chain angle: Moving the wheel forward increases chain angle, increasing chain, cog and chainring wear when the chain is crossed-over, particularly when using stiff, bush style chains.

3. Gear capacity: Moving the axle farther back allows you run a slightly larger cog.

4. Chain wrap: Moving the axle back wraps more chain around the cog and decreases the probability of skipping, particularly with worn chain and/or cogs.

5. Chain Gap: This is the biggy. It directly affects derailleur performance. It’s the distance along the chain from were it contacts the cog to where it contacts the jockey pulley. Derailleurs with long chain gaps tend to be late shifting, that is they require more effort and overshifting with the lever in order to execute the shift. Derailleurs with short chain gaps shift early.

Optimum chain gap depends on the chain and cog type. Stiff chains and pointed cog teeth require long chain gaps, usually around 7cm. Most vintage bush type chains and flat top cogs requite about 5cm chain gap. Bushingless chains and flat top cogs require about 4cm chain gap.

Proper chain gap is critical, particularly for optimum performance of indexed derailleurs and is the prime reason that vertical dropouts dominate indexed bicycles. The manufacturer’s don’t want you to screw things up by changing the axle position! Proper chain gap for indexed systems is about 4cm.

The bottom line is that changing the axle position can affect various characteristics, depending on what you are trying to achieve. Optimizing one characteristic may mean compromising other(s).

You meant MM, not CM, right?
Thanks for the detailed explanation.

i do this too. i have never noticed a shifting issue on any of the bikes i have done this with.

I bought that CD recently...

There's a screw mounted stop available for the other side to get the wheel centered all the time once installed.

I must admit I've never thought about it.

My Peugeots have screw mounted stops on both sides, I mount the stops all the way back and pull the axle up against them. This puts the axle approximately in line with the seat stay. I could move the axle forward a bit, but I doubt if I or anyone else would feel a difference.

I removed the stops and pulled the axle all the way one time as an experiment. For some reason the chain skipped on the two smaller cogs. This doesn't make sense to me because the effect was to increase chain wrap, but it happened.

Agree with T-Mar's Point 5): Moving the axle forward or back in the dropout achieves with classic derailers what is now accomplished with the B-adjusting screw: optimizing chain gap for crisp shifting (and keeping the jockey pulley from rattling against the largest cog.) Interesting observation from Grand Bois about skipping with the axle all the way back.

Great T-Mar - Thanks for taking the time to put it down - I am going to print it out and put it in my notebook - You should consider sending your info to Sheldon's site - It certainly explains why I have, by sure luck, not had any problems so far...

Finding dérailleur placement is kind of like balancing the carbs on a 1960 Covair - Once you find that sweet spot - You are there...

Not sure what to make of that statement...
A. I've never heard of a 1960 Covair
B. I've heard of a 1960 Corvair, but I wasn't aware that any had multiple carbs (not that I'm any authority).

T-Mar, thanks for this clear and very informative reply.

Re B: as soon as you have two carburetors in a non-progressive arrangement, you have a balancing problem. Given the length of manifold run, I'd not be surprised if they used one carb per bank. Some of the similar VWs used twins (mid-70s Buses). With say, four carbs, it just gets more fun.

There's a screw mounted stop available for the other side to get the wheel centered all the time once installed.

Where might that be purchased or what is the correct name I am looking for?

One source is:
https://store.velo-orange.com/index.p...ent-screw.html