What Are These Adjustment Screws On Wheel Mountings (Hangers??) For?

[youngoldbloke]

The screws make wheel replacement faster, but that, in principle, could also be done by accurately locating the closed end of the dropout.

The screws are screws because they can fine-adjust the axle location backwards and forwards. This is necessary to accommodate different gearing (as well as mechanical wear). Changing the number of teeth on the rear sprocket or chainring alters the required chain length, and because chain lengths can only be selected in fairly coarse, 1/2 inch increments, adjustment in the rear-axle-to-bottom-bracket separation is needed in order to maintain chain tension/avoid chain droop.

The first sentence is correct, thats all. How can these screws maintain tension when the chain pull is forward, away from them? They do not stop the wheel moving forward. Chaintugs prevent the wheel being pulled forward, these have NO such function. They simply allow the initial ideal positioning of the rear wheel axle.

 

[youngoldbloke]

BTW Snailracer I'm talking about ALL bikes with forward facing dropouts with adjuster screws, not just my own. We fitted fixed wheels to frames with these, just as people do today, but you really have to make sure the nuts are tight, because the tendency is for the wheel to be pulled forward - out of the dropout. That is why rearward facing ends are used on fixed frames.

 

[snailracer]

Well, I'll dispute it. Many frames, generally cheaper ones, were built like this for derailleur use. See Sheldon's site, look at the Hanger vs Frame Mount illustrations.
The fact that they could be used for fixed, even though they were far from ideal for this, does not mean that they were intended for this purpose.
Just let it go, for Pete's sake.

Also Sheldon:

"Dropout
A type of forkend that allows the rear wheel to be removed without derailing the chain first.
Track and BMX bicycles do not have rear dropouts; they use fork ends that open to the rear.
A current fad has led to the revival of this inferior forkend style for single speed bikes.

Rear dropouts come in two styles:

• Horizontal dropouts have a longish slot for the rear axle to fit into, which runs more-or-less horizontally along the dropout. They permit the wheel to be placed in various positions front to rear. Horizontal dropouts are necessary for bicycles which don't have derailers, because the axle must be moveable to adjust the chain tension.
  With horizontal dropouts, it is possible to mis-align the wheel in the frame if it is installed carelessly. The axle nuts or quick-release must be tightened quite securely, or the chain tension may pull the axle askew...

...A few single-speed or internal-hub gear bikes use vertical dropouts with an eccentric bottom bracket to permit chain tension adjustment."
http://www.sheldonbrown.com/gloss_dr-z.html
http://www.sheldonbrown.com/gloss_dr-z.html
(under Dropout)

So, not only does Sheldon confirm that horizontal rear dropouts are indeed used on non-derailleur bikes, he also considers them more suitable for that purpose than rear-facing track-ends.

 

[snailracer]

The first sentence is correct, thats all. How can these screws maintain tension when the chain pull is forward, away from them? They do not stop the wheel moving forward. Chaintugs prevent the wheel being pulled forward, these have NO such function. They simply allow the initial ideal positioning of the rear wheel axle.

We are not disagreeing here. The chain tension is set by the location of the axle, the screws only help accurate axle location so they indirectly set the chain tension. The screws exert no forces at any time.

 

[youngoldbloke]

We are not disagreeing here. The chain tension is set by the location of the axle, the screws only help accurate axle location so they indirectly set the chain tension. The screws exert no forces at any time.

OK, we're back to square one. They are adjustment screws, found on forged dropouts fitted to higher spec steel frames intended for use with derailleur gear systems. They allow optimum positioning of the rear wheel axle. Nothing to do with fixed or single speed. BTW I've never seen them on dropouts without the deraiilleur hanger. Anyone?

 

[snailracer]

OK, we're back to square one. They are adjustment screws, found on forged dropouts fitted to higher spec steel frames intended for use with derailleur gear systems. They allow optimum positioning of the rear wheel axle. Nothing to do with fixed or single speed. BTW I've never seen them on dropouts without the deraiilleur hanger. Anyone?

A derailleur hardly needs to be optimally positioned, note there is no equivalent adjustment on a modern derailleur bike with vertical dropouts.

Adjustment screws aren't a necessity, they are just a convenience feature present on fancier frames, so I don't know why there is such a hangup about them. Even a SS Raleigh shopper bike has forward-facing horizontal dropouts, yet apparently, to some, that is impossible, it can't possibly be right and must be an aberration.

 

[ayceejay]

BTW what you all are calling adjustment screws had a spring in them, what was its function, I wonder?

 

[Poacher]

BTW what you all are calling adjustment screws had a spring in them, what was its function, I wonder?

Not sure, but possibly to apply pressure on the screws to prevent them from unscrewing and thereby changing position?

 

[youngoldbloke]

A derailleur hardly needs to be optimally positioned, note there is no equivalent adjustment on a modern derailleur bike with vertical dropouts.

Adjustment screws aren't a necessity, they are just a convenience feature present on fancier frames, so I don't know why there is such a hangup about them. Even a SS Raleigh shopper bike has forward-facing horizontal dropouts, yet apparently, to some, that is impossible, it can't possibly be right and must be an aberration.

It was not about 'optimal positioning of the derailleur' it was about being able to remove the rear wheel and replace it quickly and easily in a correct, centred position. Though it is true that there was an optimal position for the rear wheel in relation to the derailleur, which is why you didn't simply shove the wheel as far back into the dropouts as possible. The vertical dfropout on a modern bike places the mech in the correct position relative to the wheel, so adjustment screws are not needed. The cheap pressed forward facing dropout was and still is the norm on many bikes.

 

[youngoldbloke]

Not sure, but possibly to apply pressure on the screws to prevent them from unscrewing and thereby changing position?

Absolutely correct.

 

[ayceejay]

Not sure, but possibly to apply pressure on the screws to prevent them from unscrewing and thereby changing position?

That sounds feasible. I was wondering if it provided any damping (shock absorption) or at least was intended to. When the wheel goes in is it pulled back so the the spring is totally compressed or is there meant to be some, what's the word - spring in it?
I was writing this as y/o/b was posting

 

[Poacher]

A derailleur hardly needs to be optimally positioned, note there is no equivalent adjustment on a modern derailleur bike with vertical dropouts.

Adjustment screws aren't a necessity, they are just a convenience feature present on fancier frames, so I don't know why there is such a hangup about them. Even a SS Raleigh shopper bike has forward-facing horizontal dropouts, yet apparently, to some, that is impossible, it can't possibly be right and must be an aberration.

As far as I am aware, nobody has said that using forward facing dropouts for fixies is impossible - I've ridden fixie on such frames in the dim and distant past, and even had a double sided hub with fixie one side and a 5 speed block on t'other. What you seem incapable of grasping, however, is that these frames, whether fitted with adjusters or not, were not designed specifically for fixie/SS use, even though many of them are now offered on ebay with this description. I'd hazard a guess that well over 95% of such frames were only ever used with derailleurs. Many (most?) have a brazed on pip on the downtube in exactly the right place to stop band-on gear levers from slipping. Many more have brazed on bosses in exactly the right place for braze-on fitting downtube gear levers. What purpose do these serve on a frame designed, according to you, for fixie/SS use?


Edit: A further clue: these frames are nearly always 130mm or 126mm i.e to fit multi speed hubs, while fixie/SS hubs are usually 120mm OLN - I'm aware that some hubs are now offered in 130mm OLN, but that's just so they can be used in frames which weren't designed to be fixie!!!

 

[Poacher]

That sounds feasible. I was wondering if it provided any damping (shock absorption) or at least was intended to. When the wheel goes in is it pulled back so the the spring is totally compressed or is there meant to be some, what's the word - spring in it?
I was writing this as y/o/b was posting

The spring can't be compressed by pulling the wheel back, or at least not to any useful extent, as the dropout itself is threaded to accept the adjuster screw.

 

[Citius]

Incidentally, I believe the dropout as shown in the OP was a feature of frames built during a certain period using Columbus tubing.

The dropouts are agnostic to the tubing being used. The dropouts on my frame are identical to that. Made by Columbus, but attached to Reynolds tubing.

 

[raleighnut]

Ditto the 2 frames I've got with those dropouts, one is 531 (a Worksop Raleigh) the other a 653 tubeset