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There’s a fierce debate over whether the interface between a square taper spindle and crankarm should be lubricated or not. Adding to that, everyone seems to have their own take on the issue. Here’s some opinions I’ve heard thus far:

  1. Perfectly clean and dry. (Use solvent to clean the spindle.)
  2. Coated with a complete layer of grease.
  3. Extremely thin coating of grease. This entails putting some grease on, then wiping it all off again to leave just the thinnest layer of grease remaining.
  4. Oiled

Proponents of installing cranks dry say it’s to stop the spindles from excessively deforming the crankarm. Proponents of lubricated install say it’s to ensure the the crankarm gets smoothly and consistently pressed onto the spindle, and to prevent galling/corrosion. Everything else falls in between these two extremes.

Is there a definite best practice?

I honestly can’t believe this question hasn’t been asked already!

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    These things tend to become religious because at some theoretical level, maybe even born out in perfect lab conditions, it makes a measurable difference, but under field conditions, the difference is swamped by other things. Sometimes best practice from one activity (e.g. Aircraft engineering) is cited as best practice for another (cycling), but other differences are ignored (e.g aircraft engineers often discard used bolts in preference to new, factory greased bolt, so are always torquing a new, clean and correctly greased bolt, cyclists rarely replace bolts )
    – mattnz
    Aug 23 '20 at 2:54
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I started getting seriously into bike work circa 2002 and was lucky enough to come across Jobst Brandt's view of the topic around that time. Since then, most of which time I've spent working as a mechanic, I've observed that the Brandtian observations of the mechanical dynamics at hand are wholly correct, but I don't agree with him on what to do about it.

He posted a number of times on rec.bicycles.tech on this subject, material that can be found if you look, but there's an excerpt on sheldonbrown.com that I'll repost here:

My cranks get loose, quite quickly too; over about 10 miles or so from being solid to flopping about in the breeze. Any suggestions?

One or both of the cranks are ruined! Once ridden in the "floppy" mode, the tapered square bore of the crank has been deformed and can no longer be secured on a spindle. Install and properly tighten new cranks on the spindle after greasing the tapered square ends of the spindle. Proper tightness should be achieved with a torque wrench or by a skilled hand.

The admonition not to grease the spindle finds life mainly in the bicycle trade. When I discussed the "dry assembly" rule with crank manufacturers, I discovered that they had warranty claims from customers who split cranks. However, cranks cannot be split by overtightening them. This can be proven by attempting to do so. An M8x1 bolt is not strong enough to split a major-brand crank.

Failure from "over-tightening" is caused by repeated re-tightening of properly installed cranks. In use, an aluminum crank squirms on its taper, and because the retaining bolt prevents it from moving off the taper, it elbows itself away from the bolt and up the taper ever so slightly. The resulting loss of preload, after hard riding, can be detected by how easily the bolt can be turned.

Loss of crank bolt preload is greater on left than right cranks, because left cranks transmit torque and bending simultaneously while right cranks transmit these forces separately. The left crank transmits driving torque through the spindle to the right crank and chainwheel while the right crank drives the chainwheel directly. Besides that, the right crank transmits torque to the spindle only when standing on both pedals. Doing this with the right foot forward (goofy footed) is the only time the spindle transmits reverse torque.

Mechanics, unaware of why crank bolts lose preload (and commensurate crank tightening), have re-tightened bolts until cranks split. No warnings against re-tightening properly installed cranks are evident although it is here where the warning should be directed rather than at lubrication.


Because friction plays no role in torque transmission, preload in the press fit must be great enough to prevent elastic separation between the crank and spindle under torque and bending. This means that no gap should open between crank and spindle facets under forceful pedaling. Crank bore failure occurs when the press fit is loose enough that a gap opens between spindle and crank. Torque is transmitted by both the leading and the trailing half of each facet, contact pressure increasing and decreasing respectively. In the event of lift-off, the entire force bears only on the leading edge of facets and causes plastic deformation, causing the bore to take on a "pincushion" shape (loose crank syndrome). Subsequent tightening of the retaining screw cannot correct this because neither the retaining bolt nor crank is strong enough to re-establish the square bore.

The claim that a greased spindle will enlarge the bore of a crank and ultimately reduce chainwheel clearance is also specious, because the crank cannot operate in a plastic stress level that would soon split the crank in use. However, increased engagement depth (hole enlargement) may occur without lubricant, because installation friction could ream the hole.

With or without lubricant, in use, cranks will make metal-to-metal contact with the spindle, causing fretting erosion of the steel spindle for all but the lightest riders. Lubricating the spindle for assembly assures a predictable press fit for a given torque. Without lubrication, the press is unknown, and galling (aluminum transfer to the steel spindle) may occur during assembly. After substantial use, spindle facets may show rouge and erosion from aluminum oxide from the crank, showing that lubricant was displaced.

Crank "dust caps" have the additional duty to retain loose crank bolts. Because crank bolts lose preload in use, they can become loose enough to subsequently unscrew and fall out if there is no cap. If this occurs, loss of the screw will not be noticed until the crank comes off, after the screw is gone.

In other posts he put forward the theory that Campagnolo was the originator of the dry taper rule in cycling, because they were having issues with their cranks splitting at the taper bore with repeat tightening. Light vintage racing cranks such as old Record are in fact quite prone to this with lubricated spindles and repeat tightening. It is far harder to get such a failure out of any but the very fanciest contemporary square taper cranks. Most are pretty chunky.

In my experience, it is exactly right that square taper cranks squirm on the taper. It is also exactly right that if you grease the taper from the beginning, torque the crank bolts properly, and leave them alone, it will be fine. I've been doing this on my own bikes for about 17 years now with zero issues ever. I use 44 Nm as a generic square taper crank bolt value.

However, where the Brandtian line falls apart is that in practice, mechanics need to be able to rapidly torque check everything on a bike. We do it not necessarily because, as Brandt suggests, we don't understand that cranks squirm, but because poor initial assembly is rampant and we have to be able to correct it in an expedient fashion. That means crank bolts throughout their lives are going to have mechanics repeatedly putting a wrench on and tightening them until they hit full torque. A dry taper getting this treatment tends to reach a bottoming point where it's not going to squirm up the spindle any further, and where re-torquing the bolt won't drive it up the spindle any further either. If the interfaces were more commonly lubricated, splitting the taper would be a more widespread issue.

In some sense the ideal thing would be for mechanics to remove cranks all the time, grease the spindles to help ensure, as Brandt pointed out, the press fit is coming out as expected for a given torque input, and somehow compel the owner to make sure the crank bolts are never tightened again. In reality it's just not practical, and so we're left with the somewhat flawed de facto system of dry tapers as the norm. Brandt is correct that some galling of the mating surfaces can occur without lubrication, but it's rarely a meaningful problem.

Also, the nature of a press fit is that there's no room in there, so there's little if any difference in function between heavy and light lubrication. A thin coating leftover from the factory or applied as a rust inhibitor is pretty close functionally to slathering it with grease.

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    “somehow compel the owner to make sure the crank bolts are never tightened again” What if you used medium or high strength threadlocker? Would also prevent the bolt from falling out.
    – Michael
    Aug 23 '20 at 18:47
  • Is the pressure really that high on this interface that lubrication cannot be ensured? Naively, I should think that's a job for a dry lubricant like MoS_2. Would this help to prevent fretting?
    – gschenk
    Aug 25 '20 at 21:14
  • I don't quite understand why entire lack of lubrication would prevent the issues of splitting the cranks? Unless there is form of contact welding happening is there anything that keeps the crank from squirming, and moving further up the taper? (Sorry for naive questions, I have only a superficial idea of tribology.)
    – gschenk
    Aug 25 '20 at 21:17
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    @gschenk The nice thing about invoking Jobst Brandt is that he was an actual engineer who spoke critically about these sorts of issues in cycling, with no marketing or liability concerns acting as filter. I don't totally understand either the question you're asking, but I have seen evidence that Brandt's take on it was correct. Aug 25 '20 at 22:16
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Park Tool Repair says greasing the spindle is 'an option', but says it is to prevent corrosion, rather than having any effect on how the crank goes on the spindle.

Slathering grease on is seems like a waste as most is going to get pushed out of the joint.

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    I’ll edit the question to be more clear. By “slather it on” I meant a generous coating, while “thin coat” means “put some grease on then wipe it off again to leave just a tiny bit of residue”. “Perfectly clean” entails using alcohol to make the spindle spotlessly clean.
    – MaplePanda
    Aug 22 '20 at 23:31
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I've historically used a very light smear on new or good condition cranks/spindles, regardless of format.

If the interface is old and beaten up or a bit munched, I'll use a lot of grease and then wipe off most after fitting. I'll also add torque several times, after 10 minutes, an hour, and the next day.

My logic is that a new fitting should be pretty tight tolerance and there will be minimal creep. An old crank, especially one that is being redeployed to a new BB or vise versa, will be sloppier through wear. By greasing well and repeatedly applying more pressure, they will mate better.

Downside of this approach is a potential for the crank arm to be "too tight" and either hard to get off in the future, or any existing weak spots could be stressed harder risking future cracking. YMMV.


Oil seems an odd choice - it won't stay in place and will migrate out over time, leaving tiny voids. Oil is better for things that move fast like bearings but it washes out with water. Grease is for slower moving things where you want the greast to stay put, so also bearings.

For a non-moving part, grease, or water-resistant copper clay or a similar antiseize compound. The amount is what you can vary based on your skill/expertise level.

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    Regarding the use of copper anti-sieze compound, I notice that the MSDS for Shimano anti-sieze does not list graphite or any copper compounds in its composition. Apparently, graphite can cause galvanic corrosion in contact with aluminium in the presence of chloride ions (e.g. from road salting). Aluminium is also more electronegative than copper. So perhaps the choice of anti-sieze compound needs to be considered if it's going to be used. Aug 23 '20 at 13:51
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My opinion is lightly greased. I have had a least a dozen aluminum crank arms threads pull out before the taper loosened. Granted a lot of them are lower end Suntour cranks that have been in place for 10 or 20 years.

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