How to clean rim brake track efficiently?

What are the most efficient and effective ways to clean brake tracks on rims?

The only case where you want to clean brake tracks is if you have just built the wheel and are worried about the oil/grease used to lubricate nipples and spoke threads contaminating the brake track, and if you have oiled your chain carelessly and got some chain oil on the brake tracks.

In such cases, you need to clean the brake tracks with a degreaser.

It is generally understood that rim brakes work better and pads last longer on clean brake tracks.

Is it?

My understanding contradicts this. My understanding is that in dirty / wet conditions, the dirt embeds into the brake pad, and no matter how well you clean the brake tracks, the dirt embedded into the brake pad still grinds your rims away.

In contrast, the brake pads do a tremendously good job of cleaning the brake tracks from dirt. In fact, brake tracks on a dirty bicycle are one of the few places that are clean. Similar to a dry chain (dirty) having rollers that are clean unlike the rest of the chain.

To prevent this grinding compound embedding into the brake pads, select a good brake pad compound. In particular, Kool Stop salmon colored pads resist dirt embedding. The salmon color comes from the color of iron oxide (rust), which the pad compound has. No black brake pad is as good as the Kool Stop salmon pads.

Dirt on brake tracks tends to tenaciously sit in groves.

No, the dirt sits in the brake pad.

It depends on the contamination.

If mud has dried on there, water and a clean brush or rag are sufficient - no oily rags though, and no soap. I have enough rags (old t-shirts and bedding) that after wiping braking surfaces I might use them on less important parts of the bike but then throw them away. This is also what I'd do to the rims if cleaning the whole bike.

If you have or suspect oil contamination, perhaps from chain oil, first I'd use a clean dry rag to remove any obvious stuff, then a clean rag with a few drops of meths (denatured alcohol). Disc brake cleaner works well (spray based on isopropyl alcohol) but it's more expensive than meths and I see no reason to get it on the tyres.

Paper towel is fine too, of course, but it always seems to snag on something. And there's definitely no need to take the wheel off, though being able to spin it makes the task easier

Fold a paper towel a couple of times and stick it between pad and rim. Squeeze the brake lever and rotate the tire.

Depending on the contaminant you may want to wet the towel, douse it lightly with a solvent, or (to get solvents off) use alcohol.

When I need to get it actually clean, and the whole area is really dirty with caked-on grime or dirt, what I use is a brush like this (pictured is from a Finish Line set):

Using warm water, I get the rim/tire area wet, then put a generous amount of dish soap directly on the brush and get it wet too. Then I go around scrubbing at it. When complete, rinse with more water. This is a good way of getting what you can off quickly and easily from a filthy wheel. You can do it on or off the bike, either outside with a hose or a inside with a utility sink faucet.

Usually after doing this I would finish the brake track in particular at least with one pass with alcohol (70+ percent isopropyl, ethanol, or ethanol/methanol type denatured) on a clean rag, because knowing that you're leaving it residue-free is good form.

If you specifically want to get the brake track returned to as pristine as you can reasonably get it, there's a tool for that. Mavic and SwissStop make them and (in my experience) they are most commonly known as a rim eraser.

This is a small rubber block with an ultra fine embedded abrasive that you work against the rim. I usually do it after cleaning, but that's not strictly necessary. (I've used the Mavic one a lot; the SwissStop is new to me upon googling just now.) It can usually make them pretty darn smooth and nearly new-looking. It's the only method I know of that strips away the black crud that frequently mars heavily used rims. In terms of results, they're superior to everything else I've tried, but they are a fair amount of work. I've long wished they would have designed it to be stuck on the end of a power tool somehow. When done, do a final wiping pass with a clean, dry rag.

If it's lightly to moderately dirty, and not heavily caked up, I usually just use a microfiber rag and one of the various pink cleaning sprays from Finish Line, Muc-Off, etc. Then I usually finish with alcohol on the brake track, using a clean section of rag. This is fast and good enough when you don't want to spend a ton of time.

I tend to just wipe around the rim with a clean or cleanish rag, or perhaps a paper towel. Depends what's in my hand at the time.

There are three types of dirt I've noticed:

1. the dry crusty powdery silt that sticks to the rim. Black or grey.
2. black fines that stick to the brake pad, and the brake arms.
3. larger detritus that embeds into the brake pad

The first two wipe off mostly okay, provided you can get access. The third tends to be metallic and needs to be removed from the brake pad with a pick or sharp probe. Otherwise these cause rim erosion.

I don't get carried away with cleaning, on the basis its going to start getting dirty again tomorrow/the next ride.