can anyone possibly say why some bikes are made with rear dropouts that have differing lengths? It makes centering the wheel a bit more of an effort and a firm clamp of the skewer even more of an imperative.

Not sure, but the thin tab inside the DS dropout would allow for proper positioning of the wheel when a derailleur is used but also allow for easy modification if someone wanted to convert it to FG/SS or internal gear operation. It does require a bit extra fiddling to get the wheel lined up, but the skewer has to be tight enough to prevent slipping in any event.

In theory, you wouldn't need slotted dropouts on road bikes, and in fact they ultimately wear away in favor of vertical dropouts.

But the level or manufacturing precision that makes vertical dropouts possible wasn't that common BTID, so the slotted design created a greater margin of error. The design is also a carryover from pre-derailleur frame design, where a slot was needed to set the chain tension, and the wheel was centered accordingly.

The built in stop on one side, is there to optimize the wheel position for the derailleur, yet leaves the ability to center the wheel as was done in the past. This is functionally the same as with a claw mounted derailleur, and an alternative to the micro-adjust screws used on costlier bikes.

The fact is that absent the micro-adjusters, and some aftermarket stops, SOP was to locate and center the wheel each time it was installed, which isn't a burden except for racers for whom time is critical.

It makes sense if you think about it. The right dropout anchors the axle with respect to the derailleur while the left one allows sufficient fore-and-aft adjustment to center the wheel between the stays. So, hold the axle back against the stop with your right hand and center the wheel and manipulate the quick release with the left.

It's really all you need.

Probably cheaper for them than the dropouts with adjustment screws. But better than identical dropouts with no adjustment screws (IMO). As long as the drive side is all the way back all you only have to worry about the position of the non drive side to center the rim/tire between the stays and brakes. The limit on the drive side probably also assures that the derailleur cage will be in what the maker considered optimum position with the gears.

Pretty much what the others said, just more windy.

They started half-filling the drive-side dropout when indexed shifting came on the scene (mid to late 80's). Indexed shifting works best when you always have the axle in a certain position with respect to the jockey wheel of the RD. Eventually, they just went to vertical dropouts as that completely removed any question of having the axle too far forward or back (or crooked.)

just the same as what I do with dropouts with the screw stops

Also stronger. The holes for the adjuster bolts are a common failure point for dropouts. This often happens when a poorly adjusted rear derailleur lands in the spokes and bends the dropout past the point of failure.

Ditto. Or, alternatively: index shifting required more precise axle location than "normal" horizontal dropouts offered, but manufacturers were gun-shy about the tolerances required to implement vertical dropouts. The half-filled horizontal dropout made for good index shifting while still offering some wiggle room on chainstay length.

Within a couple years, frame manufacturers had tightened up tolerances enough that vertical dropouts were practical and common.

Yes, (+1) part of indexing functioning, well, benefits from the wheel consistently being in the same place..


[Rohloff OEM 1 dropout, there is a longer left, the torque reaction stop follows the axle into that dropout, using that extra length to push against..]






.....

would anyone recommend against grinding away this metal in the dropout for an increase wheel base? I have a bike whose front derailleur cable comes uncommonly close to the rear tire ..

If it's not touching it, I would not worry about it.

If it is rubbing, then find a FD that can lend more space or go with a smaller wheel.

I'd certainly recommend against it. The change in angle would be too minor to help, and you may experience poorer shifting.

Note in # 8 that the right dropout broke , that will be stronger because of that bonus material..

there are old clamp on widgets that you can seek out to go in the other side.. people have posted 'what is this' before and pictured those.