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I wouldn't trust a bike mechanic that uses WD-40 as a chain lubricant. The only possible scenario I can think of is if they live in an extremely dry place with minimal chance of rust. I live in the UK, if you use WD-40 as a lubricant your chain will be rusty by the end of the week. Use an oil lube (e.g. I use Finish Line Wet).

Edit: And it's not "going all religious", it's because I do 6,000km on my bike every year. I know through my own mistakes that WD-40 is not a good chain lube.

I know an (e)bike rental operation that uses wd40 almost exclusively as chain "lube". Their current ebikes have something like 4-5k on the odo, powertrains still the original ones. But they clean/apply the wd40 to the chain between every rental, I guess that makes a difference. So my guess is that if you use wd40 often enough, it is fine.

Are you sure it's WD40 and not WD40-branded chain lube? I use that on my motorbike, and it's nothing to do with the WD40 spray - just the same parent company.

WD-40 IS good for cleaning chains and other parts of the drivetrain but not great as a lube. My guess is the convenience of a quick spray and turn of the pedals, then back out to rent outweighs what a bike mechanic would do for their own ride.

WD-40 does not have sufficient film strength. Constantly renewing it won't fix that.

It likely works for that e-bike rental operation because there's almost zero load on the chain; tourists renting e-bikes are soft-pedaling and letting the hub motors do all the work.

My guess is that WD-40 is being used just to keep the chains clean so tourists don't complain about greasy marks on their legs...or because they see the sparkling chain and think the bikes are "well maintained." Being so light, it would also be easy to wipe off various parts of the bike, again helping it look "well maintained."

Center motor, so if anything, the load is higher on the chain than normal bikes.

I am not sure how much more than 5k you can realistically expect for a lifetime for an ebike drivetrain regardless how you maintain it. You need to clean the bike anyway between the customers. If a quick wipe with wd40 gives you 5k, I am not sure if the extra miles on the drivetrain justify the extra work and extra cost of a fancier maintenance.

A belt would solve those problems or a chain guard.

I do use it on shift cables and derailleur mechanisms. Mostly because I haven't figured out anything that is a better solution.

Just to clarify: I agree that it's not a very good chain lube in general (and I don't use it myself anymore after having tested it), but I'm also not going to distrust people applying it as such because depending on the situation it is actually usable. Also see sibling comment.

> Because of the penetrating/cleaning/anti-rust properties combined it has the tendency to give a super clean chain with not a lot of dirt in it (unlike any other pure lubricant since those just attract and accumulate dirt). And just enough lubricating properties to get some mileage out of it (don't remember, 200km or so), as long as it doesn't rain.

This is basically the theory behind Rock'n'Roll's lubes [1] (and perhaps other dry lubes, i don't know):

> Rock'N'Roll chain lubes are formulated to clean and lube at the same time when applied. EXTREME, ABSOLUTE DRY and GOLD go deep down into the links, trapping dirt and floating it to the surface where you can wipe it off. Rock'N'Roll chain lubes create a protective membrane that keeps new dirt out and the lube inside, where it's needed.

So you douse the chain with it, run it round to work it in, then wipe off as much as you can - the stuff you wipe off carries away loads of filth, and the bit that stays behind dries to leave a wax/teflon layer on the working surfaces of the links. Or something. Whatever it does, it seems to work pretty well!

[1] https://rocklube.eu/en/12-chain-lubes

> It's the typcial 'one-stop for everything' problem: it's not bad a

It absolutely is bad. It's mineral oil with a few random additives thrown in. https://www.wired.com/2009/04/st-whatsinside-6/

Popular Mechanics tested WD-40 in five popular uses and found it to be the worst choice in every case. https://www.popularmechanics.com/cars/how-to/a6064/wd-40-vs-...

> Wrt lubricating properties: there's numerous threads of cyclists going all religious over this.

The cycling community overwhelmingly has been telling generations of newbie cyclists to stop hosing down their chains with wd40 and use a proper oil. There are a few people who swear by it, but they're people who have never tried anything else, or not actually looked at their chain wear.

> Because of the penetrating/cleaning/anti-rust properties combined it has the tendency to give a super clean chain with not a lot of dirt in it

WD-40 does not have any special penetrating abilities. Further, the gaps in a bike chain between the various parts are not so small that one needs a penetrating lubricant.

What is important is wear, not how clean the chain looks. Wear happens on the pins, inside rollers, and the holes on the chain plates. The chain lengthening means wear on the sprockets, which are significantly more expensive than the chain. A 10-speed chain is maybe $50 at most for a pretty nice one, and chainrings plus cassette can be significantly more than that.

The proper chain lube to use depends on the intended conditions, but any lubricant needs to have sufficient film strength - ie keep metal from directly contacting metal.

WD-40 has virtually zero film strength. There are a thousand lubricants out there that are better.

> (unlike any other pure lubricant since those just attract and accumulate dirt).

I'm not sure what "pure lubricant" means, but there are plenty of dry lubricants suitable for chain use. They are designed for dry conditions, especially dusty ones.

Riding in wet conditions usually means you're using a fairly thick chain lubricant.

Periodically measure the chain with a ruler to check for chain stretch and replace before wear gets too high that it starts destroying your cogs.

Editing to add:

If you want to use a wet lubricant for chains, bar and chain oil (ie chainsaw oil) will work just fine.

If you want a dry lubricant for chains, use something like Finish Line PTFE. Dupont themselves also sell a PTFE spray, as do several other companies.

If you want a crazy penetrating lubricant, McLube's Sailkoat is pretty crazy stuff, but a large spray can is $20+.

If you want rust prevention/protection, LPS-3.

If you need a penetrant or rust breaker for bolts, you can try the following: Mouse Milk ($$$), Kroil. Mouse Milk is weird stuff, I believe mostly d-limolene (so don't use it near waterways!) but apparently popular for lubricating very high temperature stuff (turbo wastegates, for example) because it does not leave ash/residue behind.

It absolutely is bad. It's mineral oil with a few random additives thrown in

Please quote properly: I said it's not bad at what it does and 'not bad' does not mean good. Also: if the metric of what's inside is what we'd be using, most of the other products you mention would also be pretty bad :)

For the rest, same as my other reply: I'm sorry if I gave the impression that I somehow agree it's in general a good idea to use WD-40 as chain lube. I still do not, and I don't use it myself as such because the other dedicated options are better. But thanks for listing a bunch of them.