Are the adjustment screws for the rear drop outs necessary? ......do you use them? .....and if you do how should they be adjusted? .....the rear hub has to be approx. in the "middle" or more to the "front"? .....normally it is only used to take up slack in the chain for e.g. single speed bikes? ....or?

Yes, I use them. No, they're not necessary.
They help to align the wheel when you're putting it in, and they nicely fill the holes in the dropouts.

The axle should not sit right at the back or the front of the dropout. Somewhere in the middle is where the relative positions of the cogs and upper derailleur pulley are ideal.

Dropout adjusters are intended to fine tune and facilitate rear wheel installation. You use the adjusters to roughly establish the fore/aft position of the wheel then dial one in or out so that the rim is centred between the chain stays. The next time you reinstall the wheel you just pull it back so that it seats against the stops and it should be in the exact same position.

While you can do it without adjusters, they certainly speed up the process. This is especially important in race situations where the ability to quicky and precisely align the rear wheel while changing a flat, is critical.

The fore/aft position allows one to optimize the shifting performance. Moving the wheel in the dropouts affects the chain gap, which is the distance along the chain from the point it contacts the freewheel to the point it contacts the jockey (top) derailleur pulley. Modern derailleurs, chains and freewheels tend to perform better with short chain gaps while older derailleurs, chain and freewheels perform better with longer chain gaps.

The fore/aft postion can also used to fine tune the wheelbase. A longer wheelbase offer a more comfortable ride and better straight line tracking, while shorter wheelbases makes the handling quicker and stiffens up the rear triangle. At least that how it works in theory. Many cyclists cannot tell the difference.

Moving the rear wheel back all the way will also sometimes allow you to gain a couple extra teeth of maximum cog size, for a lower gear.

The long, horizontal dropout was invented during the days of single speeds, to allow the accommodation different sizes of rear cogs without removing or adding chain links. Once multiple cog freewheels and derailleurs came along this was no longer necessary, except in rare cases like the Campagnolo Cambio Corsa. Manufacturers retained the long dropouts but added the adjuster screws. With the arrival of indexed shifting, manufacturers started incorporating vertical dropouts which prevent fore/aft adjustment of wheel position. This prevents owners from inadvertanetly altering the chain gap, which is critical in the optimum performance of indexed shifting systems.

It's impossible to say exactly where in the dropouts you should situate the rear wheel without knowing your bicycle and preferences. Start in the middle and experiment to find what suits you best.

Thank you for the answers. I think I have a good feeling for how to adjust the rear wheel. I have a set of adjustment screws which I will install then my frame comes back from painting.

While it's convenient, and easy, to not use the axle adjusters, in no way should you consider the rear wheel perfectly aligned if they're not present. I've got several high end frames, and with the axle adjusters missing, and the wheels slid all the way back, they're far from perfectly centered, and in one case, not even close.

OK, so you use the adjusters to fine tune the wheel so it sits exact in centre. So frames are not that accurate. Do you also get "vintage" adjuster screws or just buy a new set? ....it seems to be standard M3 screws and nuts?

I've only ever seen the one threading.
It's unlikely that you'd get disqualified from l'Eroica for using new ones.

I did without the adjustment screws for a long time, no big deal. But several months ago I picked up some new screws at the hardware store and used them to dial in a nice position as T-Mar explained. Now rear wheel installation is so easy that I feel like an idiot for waiting so long.

M3x.5

Another encylopedic post from T-mar... Thanks!

i didn't like my old '83 nishiki international that had a little screw/clip'washer thing only on one side, forcing me to manually align the other side for the wheel to be centered. it's much easier to have an adjuster screw in each side. looks kind of elegant too.

They're also another quick visual indicator as to a frame's quality, although there are many perfectly good frames without them.

Doesn't the b-tension screw allow one to adjusst the chain gap regardless of where the wheel is positioned in the dropout?

It does, but many of the C&V derailleurs do not have a B-tension screws. It didn't become standard until the advent of indexed shifting. Also, it provides relatively fine adjustments. Dependng on the dropout, derailleur, chain and freewheel combination, you may have to make coarse adjustments with the wheel position in order to get into the applicable range of the B-tension screw. For instance, if you took an old frame with long Campagnolo droputs and tried to set it up with a modern derailleur, 8-10 speed HG cogs and the matching chain, you could easily have too long a chain gap for optimal shifting performance, if you located the wheel at the back of the dropouts.

What's a "B tension screw" ?

My guess is that it is the adjustment screw that are very close to axel where you attach the derailleurs to the frame.....?

I was just joking. None of my bikes are new enough to have B screws on their derailleurs.

Ok.....but what does the "B" stands for?

Yes, it's the screw that varies the spring tension in the derailleur's top pivot. It adjusts the amount of deraileur rotation about the top pivot, allowing adjustment of chain gap and large cog clearance.

I strong suspect, based on the emoticon, that rootboy's comment was made in jest. He's been around long enough to know what a B-tension screw is, though he may have no experience with one. It's quite possible that all his bicycle's pre-date this feature. A lot of these C&V guys get stuck in their ways and just aren't capable of understanding any of the newer technology.

Derailleurs are classified a single or dual/double pivot types. In a single pivot derailleur the cage rotates about the lower pivot. There is no rotation about the top/mounting bolt, with the body position being fixed. On a dual pivot derailleur the 2nd pivot is called the B-pivot based on the alphabetical sequence. Similarily the spring associated with it is called the B-spring and the adjustment screw associated with it is called the B-screw.

con-sarned new fangled technology, anyway...

No B screws in this household. Unless you count me.

T-Mar, I realize you wrote this about 5 years ago, but wanted to say that this is a really useful post. Thx.