Hi,
Those are some very good points - worth discussing. Let me start with a sort of a digression or a disclaimer (depending on how you look at it):
I wrote the
chain lubricant and bearing greases articles primarily to satisfy my own curiosity - and published them in case that my knowledge and experience can help others. They allowed me to consult experts in the field (mechanical engineers and chemists), get information, books/reading material recommendations, and get corrected for any mistakes. The articles also got many comments with praises and constructive criticism.
The bottom line is that for chain and bearing lubrication, especially with bicycles, dirt is the main problem (with lubricant depletion coming in close second, but that is often either exagerrated or caused by dirt intrusion primarily). So it is a lot more important to clean and lubricate the chain regularly, than it is to use some high-end lubricant (though I did not like
the results I got with chain waxing).
Now, I'll concentrate on the discussion points:
1) Pressures on the bearing surfaces of a bike chain are EXTREMELY high. The issue is not large force, it's the small contact area.
The contact between the pin and the roller is ideally a line. Let's be generous and say it's 0.5 mm wide. Chain inner width (10 speed) is 2.18 mm. Again we'll be generous and say all of that is used.
Take a 200 lb. rider, standing on one pedal. Multiply the the crank length/pin circle (175/110) and we get 318 lbs. tension on the chain. In a sprint this would be much higher.
Take that "force" and divide it by the contact area and we get 188,329 PSI.
Ideally that force is spread among a number of teeth. In practice a single tooth will take the majority of the load. But even if we divide it by half the number of teeth on a 12 tooth sproket we still have 31,388 PSI.
For comparison the typical pressure on a big end bearing in a passenger car's engine is about 6,000 PSI.
A cyclist can exert about 1000 Watts of power for a relatively short burst. Most riding for average cyclists is done with less than 200 W power (the strong athletes can sustain 400 W for a few hours).
An average motorcycle has about 50,000 W of power and can easily run on half that power for a very long time.
The rear chainring of my 100 HP (69,000 W) Yamaha is under 6 mm thick.
A 12-speed sprocket is about 1.5 mm thick.
So we have a 4 times thicker chainring, loaded with over 10 times more torque and power.
If we compare roller width, we have just over 2 mm for the 12-speed bike chains (11/128" ~ 2.18 mm),
versus 8 mm for my Yamaha FZS600.
Again, about 4 times wider, with over 10 times more power and torque transferred.
Factory recommends SAE 30W to SAE 50W motor oil for chain lubrication.
My conclusion is that if a motorcycle chain can run for about 15,000 km with that oil, that oil is probably good enough to lubricate bicycle chain too in terms of lubricant film's strenght.
2) You mention that gear oil can be corrosive to aluminum due to the Extreme Pressure additives. I can not find any reference to aluminum but do find cautions concerning yellow metals. Regardless, the issue is compounds created from the EP additives which can form if they are used as motor oils within an internal combustion engine where they're exposed to high temperatures, water, and combustion byproducts. None of these are issues on a bicycle chain.
Fair point. I agree. Though I think that any EP additives are needless for bicycle chain lubrication (even if they don't cause any direct harm, they are "taking place" of oil or some additives that could be beneficial to bicycle chains). Though, as I said, regular cleaning and re-lubrication is a 100 times more important.
3) Viscosity is actually similar to motor oils. I imagine the concern here is getting the oil into the small spaces between the rollers and pins. I find this "issue" mentioned frequently on the web but I have seen no problems with this. The 85W gear oil flows and wicks into the gaps easily.
Depending on your riding conditions and your chain cleaning methods, the results may differ. Having said that, generally, I agree - 85W is perfectly fine. I use very viscous chain-saw oil for my chains and even that is quite OK (but it does have downsides and it won't flow at -20 C, so it helps to dillute it with some diesel especially in the winter).
4) Dirt accumulation is no worse than other wet lubricants. I drip oil onto the chain, let it sit for a few hours, then wipe the external surfaces with a rag.
In my experience, the less viscous oils/lubricants tend to attract less dirt (and need more frequent re-application even in dry conditions).
5) I previously used to use high quality motor oil as a chain lube. Lots squeaking. A local bike mechanic told me that the detergents used in motor oil make it unsuitable for bike chains. I have not researched this but I have found gear oil to be greatly superior.
I've had no problems using (clean, not used, of course) engine oil. Yamaha recommended it for the motorcycle chain in the owner's/user manual. If gear oil works for you - great. I use mostly chain-saw bar oil and it gets the job done, costs next-to-nothing and can easily be sourced.
Relja
