The best marker needs to be DARK and reasonably opaque - and easy to remove. Black white board markers are best, black wax crayons, chinagraph pencils and indelible markers running a close second.
(see my next Instructable on resurecting white boarrd markers)
It works like this:
The rim is rubbed with a dish washing abrasive pad and some kind of solvent such as kerosine, turpentine, acetone, dish washing soapy water etc... making it more or less oil free and clean.
An ink ring is applied to the side of the rim, by placing the marker on the side of the rim, and rotating the wheel slowly.
Then the wheel is roatated really fast, some kind of friction material - usually wood, is slowly brought towards the rim, until the high spots JUST start to rub against the wood, and rub the ink off.
Bingo! There are all your high spots where the ink is rubbed off, and the low spots are where the ink still remains.
The beauty of this system lies in it's absolute simplicity, and the combination of 4 feed back systems.
You can VISUALLY see the high and low spots RECORDED, where they occur, on the rim.
You can FEEL the high and low spots, as the dowel runs over them.
You can see the GAP between the dowel and the rim.
You can hear the rubbing of the dowel on the rims high spots.
And as you dial the wheel in - by very fine adjustments of the spoke tension - tightening some spokes, and loosening others - in 1/8th, 1/4 to 1/3rd turn increments - you can dial the wheel in absolutely true - to easily within about 0.2mm or 0.3mm - because this is incredibly tactile, and you can SEE and FEEL and HEAR the dowel and the WAY it rubs on the rim.
When the rim is out of true, the dowel rubs against the rim, with a "silence" where it runs above the low area, and a "ssssttttt" where it rubs on the high spot. So as the wheel spins it makes a "silence" - "ssssttttt" - "silence" - "ssssttttt" -"silence" - "ssssttttt" -"silence" - "ssssttttt".
And when the rim is running perfectly true, the noise of the dragging dowel is "Ssssssssssssssssssssssssssssssssssssss" with no real variation in tone or breaks in the tone.
And you can FEEL it - the tactile feed back. And you can SEE how the rim runs closer / far away / closer / far away - from the dowel or if it runs parallel.
This is so fiendlishly simple and brilliant to use.
Step 1. Push the marker pen against the rim and rotate the wheel slowly.
One pen width and one revolution seems enough.
Step 1: Rubbing Your Rim
Something about the size of a big pencil....
Soft wood works better though. Edge on works best.
Spin your rim up fast, taking great care NOT to feed yourself into the wheel or to have things jam and come back and poke your eye out and feed the wood into the rim SLOWLY, and it will hit the high spots, and rub the ink off.
Step 2: Truing the Rim
One of the techniques for picking the tight and loose spokes is to tap them with a little piece of wooden dowel, as the wheel spins slowly..
I prefer dowel, at gives a nicer note. The tight tight spokes will sound like "ping" note, and the loose spokes will give a dead or flat note.
Sometimes the really best moves are only 1/4 to 1/3rd of a turn of the spoke nipple.
In reality, the truing stand, comes from the days and the need to actually build your own wheel, and it make working on the wheel at a comfortable height, with no other obstacles in place, like the wheel mounts / chain stays.
A proper truing stand, is a fixed, rigid way to build a wheel, and grind off the excess spoke lenghts, check the run out or dishing, and all sorts of things.
It really is good to have or make one.
But for periodic maintenance, pulling the wheel out of the bike and adjusting the warped or slightly wobbly rim, it's easier to leave the wheel IN the bike and do it like this.
Since few people build their own wheels, it also negates he need to take the wheel out and buy or make a truing stand, or to take the bike to a bike shop and to pay them to do it for you.... and pay good money to do something that is no harder than picking your own nose.
Given how easy it is, and how long it takes to take the bike to the bike shop, and leave it there, and then come back and then go back there and then bring it back, it's rather foolish in my opinion, to pay for this and to spend all that time and running around on something that only requires a GOOD QUALITY spoke wrench, a comfy seat, a chinagraph pencil and 5 or 10 minutes of your time.
The first time will take a while, but once you get the hang of it, it's as easy as pie....
Using this method means that for small knocks to the spokes that result in the wheel being warped, or just general wear and tear, you can now easily adjust and retrue your rim, on the bike.
Perhaps the great art is actually learned by doing, that of seeing just how much variation in the true running of the rim, small adjustments make.
Sometimes an area can be pulled in by tightening or loosening a number of spokes in an eleptical fashion, but say 1/4 turn, 1/3 turn, 1/2 turn, 2/3 turn, 2/3 turn, 1/2 turn, 1/3 turn, 1/4 turn....
Or maybe loosening or tightening only 1 or 2 spokes by 1/4 or 1/2 a turn etc... loosen 2 of them slightly on one side and tighten 3 slightly on the other....
I seems to be really rare that you need to actully need to tighten any spokes up by several complete revolutions of the spoke nipple.
Go carefully, make small adjustments, and take observations, or notes...
Practice makes perfect.
Soon enough, it becomes an intuitive proccess.
And use GOOD QUALITY bike tools - they make an easy job, easier.
And check the TONE or NOTE of your spokes, with a light tap of them as you slowly rotate the wheel.
The NOTE (musical) ought to be fairly consistent, it little higher is OK but a flat note from a loose spoke is NOT accceptable.
In a fundamental sense, a bicycle is merely HANGING by fine wire rods, from the rim, to the hub / axle.
And the spokes ideally, ought to be in equal tension and in balance.
The dishing or offselt in rear wheels, means that a small variation in tension and tone exists between one side of the wheel and the other...
When a spoke is too tight, it is carrying too much load, and when it is loose or broken the other spokes beside it, carry it's load.
Being a big bloke, until I got some THICK ROOTED spokes my back wheel spokes used to break fairly regularly.
Now that problem is solved. But I used to replace the rear wheel spokes, up until about 2 or 3 of them had broken in the roots, from fatigue and excessive stress, but it was at this point that I figured by this time, the rest of the remaining spokes were not that far behind....
By the time the fourth one went, I figured that the whole wheel needed to be relaced with NEW spokes.....
But there are THICK rooted staineless steel spokes.... for bigger people and tandems etc...
So here you have a great way to retrue your rims, on the bike, to a very high degree of accuracy, in a really splendid and visually and sensually tactile way.
Step 3: Things That You Can and Can't Fix, by Truing the Rim.
Some rims, are just plain too thin, too cheap, and the alloy is too soft - and they need to be retrued every two weeks....
The answer to that is to take the rim / wheel back and get it swapped for a decent one.
And sometimes that terrible back wheel wobble, isn't really the rim being out of true, it may be due to riding on that bike with the irritating slow leak and you can't find the puncture repair kit... and so you tolerate the slow leak... as it only needs pumping up every 3 or 4 days..
And your in a rush, the wheel is a bit too flat, and so you say "I will pump it up when I get home....".
And that wobble in the rear wheel only gets worse.....
"Doh!" - major bulge / carcass failure.....
Oh well my rim is now true. Pity about the tyre though.