Greasing Bolts vs Not Greasing — Questions, Evidence?
 

I had been taught by some bike mechanics to grease bolts and other threads on bikes. But recently I read a thread on a Corvette forum about whether or not to grease lug nut threads. The most popular opinion was to use grease. But it emerged, with much better evidence, that you shouldn't grease — they should be left dry and clean. The better evidence came from engineers and manufacturers.

So I am wondering what Shimano, for example, has to say. Or Campy.

And are torque specs meant for greased or ungreased? (It turned out that overtorqueing is a real issue with greased lug nuts, leading to different types of weakening and failures. The torque specs are for dry threads.)

And are some but not all threads on bikes meant to be greased?

Does this apply to all bikes, all manufacturers, and all vintages?

Firstly, what was the evidence and in what way was it better?

Secondly, in many cases the decision to grease (as an anti-seize measure) depends on what metals are involved in contact. So, it is not in any way an unconditional global decision "to grease or not to grease". It depends. Anti-seizing thread on a steel alloy pedal spindle before screwing it into an aluminum alloy crank is a definite must. Meanwhile, greasing stem bolts is not necessary.

The best evidence was in the form of excerpts from the manufacturers' literature on the subject. There were also explanations and testimony from the professional engineering contingent vs the mechanic and home mechanic contingent.

There were so many opinions being slung around, sometimes with great confidence. Finally people had to eat their words when the truly solid evidence was presented.

So I'm wanting to see what companies like Shimano and Campagnolo and their engineers have to say.

I agree about anti-seize, including with titanium.

My main concern is with steel fasteners and steel threads on components. Other materials and disparate materials are also of interest though.

No offense to anyone, but I know there are many opinions. I'm looking more for references or excerpts from major manufacturers or professional engineers.

Most bicycle fasteners seem to be pretty well over-spec'ed, such that overtorqueing is not going to damage parts (except aluminum, titanium, and other weight weenie parts).

Most bike fasteners are screwed in and left until they need to be removed, often years or decades later.

When fasteners that have been left on for years are unscrewed, it takes a LOT of torque to remove them if they weren't greased during assembly. (That may be why they were over-spec'ed in the first place.)

So it's usually safe, and often beneficial, to grease steel-on-steel bolts before assembly. It's always a good idea to use anti-seize (or grease) when screwing steel into something else.

You're comparing apples to oranges. Lug nuts are a special case. You'll never see a manufacturer recommend greasing the axle studs.

My new truck has this warning under changing a tire: Never use oil or grease on bolts or nuts because the nuts might come loose. The vehicle's wheel could fall off, causing a crash.

Most other bolts should be oiled, greased or anti-seized, particularly where dissimilar metals are involved, if for no other reason but to avoid corrosion that would cause problems when disassembling a bike, or making adjustments. Even similar metals can have problems if the threads are not lubricated. I use a lot of stainless steel nuts and bolts that are prone to galling. I've assembled parts with stainless steel nuts and bolts that were only snugged up for mock-up and had the threads jam up so tight that they'd strip before they came loose for disassembly. If the bolt was a little 1/4" or 6mm, you could twist the bolt in two and not get the nut off. Most new engines have aluminum blocks, but the bolts screwed into the aluminum threads are zinc plated steel. Anti-seize is wise to insure no problems when making repairs.

For any given connection, lubricated threads apply more clamping pressure for a given amount of torque. There's nothing on a bike that's all that critical. FWIW, I'm a mechanical engineer who's been wrenching for about 50 years now. I build hot rods for a second hobby these days.

I see a few aspects that haven't been mentioned. First is the topic of "torque", or maybe over torqueing. Since this is within the control of the person holding the wrench I see less issue with lube allowing over tightening then some will claim. After all the correct torque is the minimum amount needed to secure the parts and not be over the stated max. This approach places the emphasis on the clamping pressure, which is easier to describe via the threaded fastener but ultimately it's about holding force.

Next up is the consequence of under or over torqueing. Under has two failure modes IME. One is the parts slip, like a wheel in a horizontal drop out, a seat post in the frame, cables in their anchor bolts, spoke nipples on a spoke or the bars within the stem (and other examples). Each has it's issue if happening while riding but again the person doing the work is responsible to test the security of the fasteners they work on. The other mode is after even less attention of the user, the fastener loosens so much it gets lost. But again both modes are under the control of the user, person doing the work. Proper service technique is to test before riding and also to periodically check all the fittings after use. Again lubed threads have little to do with these failure modes when the real; failure is the person and their methods (or lack of more often).

Now too high a torque is a bit different in it's failure modes. Often the failure is a cracking/breakage of the fastener or the part. Not something you want to happen while riding at the limit:) But I go back to my earlier qualifier of "proper torque", that it's the minimum needed to secure the part/fastener. When the part isn't held securely with the torque range max listed then there's something wrong with the assembly (a lack of assembly paste, incompatible parts or dimensions, wear not dealt with...) Once again this is within the responsibility of the person doing the work.

So what's my take away? Lubing will make future servicing easier and provide less chance of corrosion (galvanic or oxide) collection. How tight to make stuff is the responsibility of the person doing the work. If that person doesn't really understand what effect they are producing then they shouldn't be doing the work. (And the extension of that last statement is that as the "fudge factor" of material/weight/design has been reduced in the pursuit of "maximum performance" the skill set the person doing the work has also evolved. Home mechanics take note...) Andy

Not sure why manufacturers' recommendations are not good enough. All torque specifications assume (or state) whether and how the threads are to be lubed.

Overtorqueing lug nuts is a real issue period.

No grease may help but won't protect against poorly trained mechanics with air wrenches.

All Threaded Fasteners must be lubricated. Oil grease doesn't matter.

+1
Hubs are so lightly built that uneven or over torque easily warps the discs. (BTW, clicking a wrench on a static fastener after zapping it with a power wrench means nothing. Torque values are dynamic.)

Be specific
 

>> Write to those companies to get their replies, they have national offices <<

Overly broad, bolt size? what does it do? .. do you have a bolt that if threads are not greased will it seize ?

or are you going to just leave it there will you apply thread lock compound?

Are you willing to change hardware from the factory economic choice

to something of a higher strength steel or lighter weight alloy?





....

Personally, I grease fasteners (on bicycles) that are A. more delicate (like a cassette lock ring), B. two different metals (such as the rear derailleur with a steel bolt to an aluminum hanger), and C. areas where specific torque is important (like carbon fiber bars in an aluminum stem). Probably easier to list where I don't use grease...brake disc bolts and caliper mounting bolts (which have thread locker on them), water bottle cages, front derailleur hanger bolts, and brifte/shifter/brake lever bolts.

Things I don't grease:
- brake pad studs
- cable anchor bolts
- down tube shifter threads.

Things I grease very, very lightly:
- bottom bracket square tapers
- crank bolts
- stem clamp bolt
- seatpost bolts
- pedal dust caps.

I use anti-seize on anything I for sure want to get apart again. I use thread lock on RD pulley bolts. Never had anything which I've put together come apart which shouldn't have. I have had cassettes come loose when they were installed by bike shops.

My opinion and experience:

https://bike.bikegremlin.com/7172/anti-seize/

+1
Consider an engine, almost everything internally is lubed first during assembly. Again, apples to apples.

I lube or use at least anti-sieze all dissimilar metal parts with something, and usually a lot of other similar ones depending on if I think it will get stuck and I know from experience it may help later. If something specifically says not to, I won't and usually can deduce exactly why. Torque can be different with or without lube, no part on a bike is that critical or going to be off much one way or the other. Don't lube or put antisieze on your pedals, stem, crank bolts, bottom bracket, or whatever if you don't want.. I always do.

Coming from maintenance management in heavy industry I can tell you from the equipment manufacturers training programs for mechanics that lubricants on a bolt materially reduces the torque required to achieve bolt axial load or tension dry specification. Some lubes as high as +40% reduction. In production situations downtime to repair damaged threads or a bolt head broken off by a mechanic is very expensive.

This thread is a great example of how black/white thinking gets you further from the truth. If the answer is "it depends" then you'll have to think a little, and you don't want that.


I hope riding season returns soon for you all!

I have some anti seize high temp super thick grease that I put on my rack bolts, and from my personal experience over the years, it would appear that it helps reduce vibration caused loosening, which I have much much less of while touring, than what I recall from years ago when I didnt do this.

I equate it to that "rubbing in wax" technique, which I have never done because I was too lazy to go buy a block of wax, simply cuz I had the thick grease, and I had dirtied up all the rack bolts and therefore was too damn lazy to clean them and the bikes threads of it, as I figured it would be best if I were to try the wax thing.

ps, this automotive stuff is almost peanut butter thick.

Can anyone answer this: Why are lug nuts supposed to remain ungreased? After all, they aren't different in any fundamental way. They are threaded fasteners, quite similar to the rest. They are designed to clamp and hold and not loosen with use. In other words they perform the same function. And they need to meet the same basic requirements. So why do they recommend not greasing them? They could just adjust the torque specs accordingly....

I always grease bolts unless they tell you specifically not to. Greasing allows the bolt to tighten a bit more which helps with the spring force of the steel to secure it better, of course you won't want to do that if carbon fiber is involved due to possibility of crushing the carbon fiber. Grease actually fills in the microscopic gaps between the male and female threads which will make the bolt less likely to loosen up due to vibrations from riding. Greasing will prevent metal to metal bonding so it eliminates seizing due to oxidizing (rusting); and related to that grease will prevent moisture from seeping down threads and into the frame where it could start the rusting process of a steel frame. Since all my bikes are steel I grease all my bolts, mostly due to wanting to prevent rusting inside the frame and or seizing.

...I have always assumed that because lubricating the threads changes the torque values you need to apply, the makers decided that in most cases (including initial factory assembly) the person working on them would not take the time and trouble to lubricate them. So they give you a higher torque value (dry torque). That way, you won't have people assembling wheels and hubs with too little torque if they're dry....which is probably more dangerous than too much torque if they're lubricated.

Nobody wants to take credit for a catastrophic failure if someone driving along loses a wheel.

But I also assume the practice might lead to some galling and earlier thread failure........again an assumption on my part.

If you are deciding not to grease your bolts please please please do not bring them by the shop for us to try and remove for you. Always grease metal on metal contact or use anti-seize or a thread locking compound. Also always use a torque wrench it will help you in the end.

I'm an Engineer. A proud graduate of Georgia Tech. I've been wrenching since 1970. I grease all my threaded fasteners when I assemble or repair a bicycle, car, tractor or, boat. The main reason is so I can disassemble it and repair it again in the future. Have you ever tried to loosen corroded lug nuts off a wheel during a breakdown on the side of the road with no hope of changing a flat tire? While your girlfriend screams at you for being an idiot? Then, having to pay a tow truck & garage $200 to do a simple repair? Grease can help that.

I always put anti seize on those (never grease, just like most other bolts). Never had any problems. They get easily removed when wheels need to be taken off, but never loosen during use. For cars at least - didn't do any heavy machinery (trucks etc.) so take it with a grain of salt.