What should I look for when buying chain lube / lubricant?

Stop using WD-40. It's not a lube but a degreaser.

The most important thing to consider when buying a chain lube is your riding conditions. There are dry and wet chain lubes. Choose accordingly.

Any tips for reducing chain wear?

Make sure the chain is relativelly clean and dry before relubing. Relubing a chain full which is of dust and soil will make them act like grinding material which will wear your chain down.

Go to a bike store and buy purpose-made chain oil. It will generally come in 2-3 grades from "dry" to "wet". "Dry" you'd use in dry, dusty conditions. "Wet" you'd (obviously) use in conditions where it's frequently wet. You can read the blurb on each bottle to see what sounds best for you.

At the very least, wipe the chain with a rag before oiling. Ideally, use some sort of "chain washer" (ask at the bike store) to clean the chain before oiling.

WD-40 is the wrong stuff since it pretty much evaporates off. Motor oil is also not ideal. 3-in-1 oil is also not ideal since it gums up. Using a purpose bicycle chain lube will improve longevity. The particular choice of lube is a bit of a religious choice, but they are marketed with specific conditions quoted. You can find one at your bike shop on which riding conditions you do, and then use it.

This link to Sheldon Brown is a good read on chain maintenance and when to replace your chain. For cleaning your chain, you can use something like the Park Tool CG-2.2 - its essentially a case, which you put in something like citrus degreaser and close it over your chain. then you spin the chain, and it brushes the chain and washes it in the degreaser.

I use industrial chain lube spray from the hardware store, because it is several times cheaper than dedicated bike lubes and flows well into the chain links.

Is WD-40 suitable for bicycle chains?

No. WD-40 is more solvent than lubricant. It means "water displacement". For that it might work. For bicycle chains it is not much better than any other volatile solvent such as water (yes, if you have ridden in rain you have noticed a wet chain doesn't squeak so water is lubricating it -- when the rain stops, the squeaking starts).

Would alternatives provide better chain longevity?

Yes. Use a thixotropic motorcycle chain lubricant in a spray can.

The spray can is agitated before application. The thixotropy of the lubricant makes it thin after agitation. Thus, when sprayed, the thin lubricant penetrates to the innards of the chain easily. When left to settle, it becomes thick, staying inside the chain. When you start to ride, the thixotropy makes it thin again, not resisting motion as much. When left to settle, it becomes thick again, staying inside the chain and preventing drops of lubricant on the floor.

Also remember to only lubricate a chain that squeaks and remove all external dirt you can easily remove from the chain. Don't lubricate a dirty chain! Don't also lubricate a chain that already has oil. If the chain has (clean) oil inside, it has also (dirty) oil outside. Cleaning an oily chain is practically impossible without first removing the oil by a solvent. Oiling an already oily and thus dirty chain carries the dirt inside the chain, destroying the chain in no time.

So, I repeat: only oil a chain that squeaks! Do not do any "preventive maintenance", or early oiling.

When shopping around for lubricant, what are the most important things to look for?

Thixotropy. Unfortunately, most marketers do not mention this property in the label of the product. However, if it is marketed as a motorcycle lubricant and is in a spray can, and if it is a wet lubricant as opposed to a dry lubricant, it very well could be thixotropic. You can test the thixotropy of a lubricant by agitating a spray can and spraying it to a transparent container. Then move the lubricant in the container by tilting. The lubricant should flow easily. Then leave the lubricant in the container to settle. Tilt the container after it has settled for a day. It should be very thick (but of course if you tilt it actively many times, it becomes gradually thin again due to thixotropy).

What do you use and why?

A thixotropic motorcycle chain lubricant, due to its thixotropy properties that mean it easily penetrates a chain after shaking the spray can, and when left to settle, it stays inside the chain. When starting to ride, it becomes thin again not resisting forwards motion of the bike, and when parking the bike, it becomes thick again, not dropping on the floor.

Avoid the so-called dry lubricants. They require constant reapplication even if riding in completely dry conditions. My wet chain lubricant lasts for hundreds of kilometers if not thousand.

I love the idea of waxes, but they wear off of the load bearing surfaces rapidly, and are hard to re-apply as frequently as I would like to keep my chain sufficiently protected. I have used Triflow on my chains for years. It does a great job of slowing wear. It accumulates gunk fast but works fine as a chain lube. It sticks to my chains and keeps them quiet and moving smoothly between cleanings. It doesn't wash off in wet conditions. I've tried gazillions of different lubes over the years, but I always come back to Triflow.

That Being said, try a lube you've never used before on a freshly cleaned chain and take note of how it performs and how well you feel it works. Maybe Triflow isnt the lube for you, but experimentation is always a good thing.

Your points:

• Is WD-40 suitable for bicycle chains?

  Yes. It may not be as good as dedicated products in this or some other aspect but it is tested by many and it DOES work.

• Would alternatives provide better chain longevity?

  Probably. Dedicated products will likely work better in the conditions they were designed for. Dry lubes in dry conditions, wet lubes in wet conditions. There are many products available, some will be better, some will be worse.

• When shopping around for lubricant, what are the most important things to look for?

  Dry vs. wet lubes. This is by FAR the most important distinction.

• What do you use and why?

  Polls are off topic. I will not mention dedicated products but I mostly use certain ceramic-based dry lubes. Dust is by far my biggest enemy in these very dry years and I need my chain to attract as little dust as possible. At the current time I temporarily switched to the cheapest mineral oil they had since my favourite product wasn't available. It also lubes well, maybe even better, but the chain is significantly more ugly and attracts grime more.

Your specific question about WD-40:

This is hugely unpopular at this site and will surely be downvoted into oblivion, but many people report success when using WD-40, the classical one, as the only chain lube and a degreaser at the same time. The most public of them likely being Simon Richardson, a former professional racer (also a cyclocross racer) and now a presenter of GCN - the Global Cycling Network. For example, but not only, here

Also, while WD does really stand for "water displacement" it is actually a lubricant at the same time. The vendor's page says:

Myth: WD-40® Multi-Use Product is not really a lubricant.

Fact: While the “W-D” in WD-40® stands for Water Displacement, WD-40® Multi-Use Product is a unique, special blend of lubricants. The product’s formulation also contains anti-corrosion agents and ingredients for penetration, water displacement and soil removal.

I used to use it too, but now I mostly use other lubes, ceramic ones or other dry ones. My last encounter with a wet one (green Finish Line) was very unpleasant because although it was somewhat wet outside, it did not straight-out rain and it left my chain in a horrible mess, noisy in an unusual way, and was very hard to get off even using a chain washing tool. Think twice before using when it is not straight-out raining. Perhaps a small bottle of a thin oil with you in case of a rainshower would be better. Even re-lubing mid-ride might be better (for long rides, especially multi-day ones).

I will attempt to summarize what one should look for in a lubricant without making specific product recommendations.

In the past, lubricants have been classified as wet and dry. Wet lubes are like oils. Dry lubes are thought to mostly dry off after application. I believe that conventional wisdom may say that dry lubes are best if you're riding mainly in dry conditions, as they attract less grime. Wet lubes are often used in wet conditions. Some dry lubricants contain wax, which is a hydrocarbon that's solid at room temperature - in contrast, wet lubes are hydrocarbons that are liquid at room temperature. In addition, our chains come shipped in a cosmoline-like grease; this grease is very lubricious, and some riders regard it as a superior lube. However, I'm not sure that we can get our hands on it, and I don't think many people put grease in general on their chain.

Chains wear from friction between the pins and the rollers. Lubricants need to penetrate inside between the pins and the rollers, i.e. inside the chain. As we ride, dirt gets kicked onto the chain. Some of it works its way into the rollers. Here, it forms a grinding paste with the lube. While I'm not an engineer, I would expect that lubricants probably have two correlated but separate characteristics: their effect on drivetrain friction, and their effect on chain durability. A lubricant that has high lubricity would reducing the friction of the pins and rollers sliding against each other. I'd expect this to reduce drivetrain wear by itself. There's a paragraph in the Cyclingtips article where Smith says:

If contamination was removed from the equation, say, like in a track environment, or a very clean road ride, increased friction does not always correlate to wear ... For example, compare a newer-technology dry lubricant, such as (CeramicSpeed) UFO Drip, Molten Speed Wax, or (CeramicSpeed) UFO Chains versus a thick sticky grease. The dry lubricants, from an efficiency standpoint, will be much faster than the greased chain. However, the greased chain might show less wear over time.

However, because grease, like the stuff our chains come shipped in, is very sticky, it will attract a lot of dirt. Thus, grease is likely to lead to poor longevity in actual riding conditions. (NB: Smith has contended elsewhere that the grease also produces very high drivetrain friction, mainly due to viscous drag and stiction, albeit these properties by themselves shouldn't cause chain wear.)

I'm attempting to summarize a couple of Velonews tests of chain lubricant. The first test was in the print magazine, dated I believe 2015, and is here. The second may also have been print-only, but Squirt (NB: they make a lube, so commercial interest) reproduced it here. The third is a Cyclingtips article. All involve data from Jason Smith, formerly an independent chain friction researcher; he, his workshop, and his intellectual property were bought by Ceramicspeed, but he was independent at the time of both Velonews articles. The last involves work by Smith and Adam Kerin; the latter is an independent researcher who studies drivetrain wear. Smith is and was set up to measure both drivetrain friction and durability; Kerin is set up to measure durability only.

First, consider what conditions you ride in. I bet that most of us mainly ride in dry conditions. Some may ride through the occasional shower, and probably a few more head out when the roads are a bit wet. I don't expect that many of us consistently ride in the rain.

Lubricant Recommendations

The short version: avoid all aerosol lubes. Avoid White Lightning Epic Ride. Avoid other dry lubes where you can see there is a low ratio of lubricating substances to carrier fluid.

Spray lubricants, including WD-40's original formula, are not thoroughly discussed in the first Velonews article, but the CT article says why they are bad: they're mainly carrier and very little lubricant. In addition, aerosol WD-40 is generally thought to be a mix of solvents and lubricant.

I would also be cautious with selecting a dry lubricant. The image below is my personal bottle of White Lightning Clean Ride, which is a dry lube (NB: and which I use on my cleats, not my chain!!). I let the bottle settle untouched, and the white stuff at the bottom is the wax and other lubricating agents. The clear carrier fluid may be heptane; in any case, White Lightning does describe the lube as flammable. Kerin and Smith both argue that many traditional dry lubes are bad, precisely because of the low ratio of carrier to lubricant (see the Cyclingtips article).

If you ride very frequently in wet conditions, the Cyclingtips and first Velonews article say that heavier oil-based lubes could work. However, they seem to imply that these are not the best all-conditions lubes for dry riding. In terms of traditional drip lubes, the CT article points to Nix Frix Shun and Rock-n-Roll Gold as good contenders, but note that this is based on Kerin's testing of only ten different lubes (i.e. he may not have selected other good wet lubes). PTFE as an additive should be helpful in reducing drivetrain friction, and thus reducing wear somewhat.

Some drip wax lubes, which would traditionally be considered dry lubes, have excellent performance in the dry and should perform acceptably in normal amounts of rain. However, many of them do require you to completely remove the existing oil-based lubricants from the chain, which is an involved process. If you are not able to investigate how to do this, I would stay away from this class of lubes entirely. The same goes for immersion waxing, be that in paraffin or in paraffin with additives (e.g. Molten Speed Wax, which adds PTFE and molybdenum disulfide). I previously wrote an answer that attempted to explain why molten wax may outperform other lubricants.

Drip wax lubes include Squirt, Smoove, Ceramicspeed's UFO drip (which is extremely expensive and thus most riders should avoid), Tru Tension Tungsten, and Silca's super secret chain lube (both not reviewed at the time of the CT article). I list these lubes not to recommend any particular one. Rather, readers should avoid these lubes unless willing to put in the work. If applied to a greasy chain, these lubes won't adhere.

Maintenance

If nothing else, wipe your chain with a clean rag after every ride. This reduces the amount of dirt that enters the chain's rollers. I believe that degreasing frequently isn't necessary. However, lubricating fairly frequently is necessary. Pick an interval you can remember and sustain. Weekly would probably be fine for many riders (daily is likely too often). If your chain is squeaking, you have metal rubbing against metal, and you're wearing things down. I speak from personal experience here!

You should occasionally clean your chain more thoroughly. An on-bike chain cleaner filled with some solvent (which you can dilute) is good, because it brushes inside the chain. I personally don't rate putting degreaser on a rag and wiping the chain as highly as this option. In my experience, it's best to run the chain cleaner multiple times with fresh solvent each time. Each run will remove some dirt from inside the chain, the bristles will pick some of the dirt back up and move it into the chain.

If you are more determined, you can get a reusable quick link (e.g. YBN, Connex, some models of KMC), and you can occasionally remove your chain from the bike, put it in a bottle with solvent, and shake it. See the paragraph above about refreshing the solvent, only this time it's more important because you're otherwise shaking the chain in dirty solvent.

Frankly, if you are more meticulous about cleaning your chain, it may not matter so much what lubricant you use, provided you don't use one of the ones I suggested to avoid.