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I've just bought my first carbon frame roadbike and realised that it has thru axle (previously I had quick release). Before I would do anything stupid, could someone give me advice if I should apply bicycle grease or carbon paste on it when I take it out/in? I'm afraid of breaking the frame. By the way is it easy to break it here, or I need to be really stupid to do that?

Thanks

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  • Is there a torque value written anywhere on it? Ideally you'd use a torque wrench to tighten it, but without that you want to somehow "learn" and calibrate your elbow to how tight it needs to be.
    – Criggie ♦
    Commented Oct 28, 2021 at 10:55
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    @Criggie We do not know what type of thru axle is being used. Maybe it’s a handle type, or one with a cam, or it’s a bolt-on, or it’s a cervelo with that crazy RAT system.
    – MaplePanda
    Commented Oct 28, 2021 at 14:48

4 Answers 4

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I usually put a very small amount of grease on the threads at the end so that it will be easier to remove when you need to take it out again. As with all threaded connections these tend to seize-up over time especially when exposed to water.

This is similar to what you do when installing your pedals.

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  • Should I use grease or carbon paste if the frame is carbon?
    – Mat
    Commented Oct 28, 2021 at 16:38
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    @Mat Grease is fine. The axle is going through your hubs for the most part. Carbon paste adds friction for clamped parts, which is not what you need here.
    – MaplePanda
    Commented Oct 28, 2021 at 17:27
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I have a different question for you.

What happens if the thru-axle threads and shaft are not greased (or the grease has washed out)?

Answers:

On a Cube eMTB with a 12mm rear thru axle and a Shimano XT hub, left undisturbed for 3 years between services but ridden quite hard at trail centres: It took nearly an hour (including thinking time) to gently persuade the thru axle out of the hub with a hammer and extension without damaging anything, hampered by the frame, which obviosly wants to stay closed to 142 (or 148 or whatever it was).

On an older Specialized FSR with an older DT 9mm thru axle on the front wheel (svc history unknown): I ended up cutting the hub axle apart, destroying the hub, as there was no way of getting the axle out without damaging the suspension fork. Fortunately the wheel was badly buckled so a replacement was justified!

Both of these were due to corrosion expanding the size of the thru axle (if the coating was scratched) or corrosion on the inside surfaces of the hub expanding to fill the gap, or galvanic welding. All of those problems are preventable with a little care.

Keep those axles greased!

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  • +1. Some of the more truly awful repair situations I've seen in recent years have involved dry thru axles stuck in hubs. There is no easy way of doing that kind of surgery.
    – Nathan Knutson
    Commented Oct 28, 2021 at 22:53
  • That implies greasing the whole length, not just the threads, which is a very good point and not one the OP appears to have considered
    – Chris H
    Commented Oct 29, 2021 at 10:06
  • I'm guessing the forks have a threaded steel insert or I wouldn't think the conditions would be right for galvanic corrosion between an aluminum alloy thru-axle and fork lowers.
    – DWGKNZ
    Commented Oct 29, 2021 at 15:16
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    @DWGKNZ it's the inside of the hub, not the fork, that presents the problem. The threads usually will turn fine but the thru axle is stuck inside the hub so pushes the frame apart by the length of the threads if you keep winding.
    – Noise
    Commented Oct 29, 2021 at 17:26
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    @JoeK thanks, I never would have expected that as a failure mode. I guess even if the inner race seized to the axle, if there was no shape distortion, the wheel would still turn so you may not catch it until you wanted to remove the wheel.
    – DWGKNZ
    Commented Oct 29, 2021 at 17:41
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Information about what to grease on a through-axle can be contradicting even for the same model of an axle. An example below.

Santa Cruz uses DT Swiss axles for their frames. The instructions on their website state that you should grease both the shaft and and the threaded part:

SC instructions

However, DT Swiss' instructions for the same axle state that the threads "must be free of grease":

DT Swiss

I wrote to both manufactures regarding the conflicting information. SC replied that one should grease the threads. DT Swiss gave no reply.

In my understanding, not greasing the threads may allow it to seize. Greasing it, however, may cause it to loosen under vibration more easily (it did happen to me).

In the end, I decided to use anti-seize compound instead of plain lithium grease on threads. I still check the axle to be tight before each ride.

For the axle shaft, regular grease should be sufficient and safe.

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  • My front TA has a similar handle and also becomes looser with time. It was greased by the bike vendor. The rear one has a hex nut and If torqued properly stays closed all the time. However, perhaps I just don't press the handle enough? It is harde to judge the torque.
    – Vladimir F Героям слава
    Commented Oct 28, 2021 at 16:30
  • I find it very odd that Santa Cruz's website instructed people not to grease the threads for the thru-axle mounts. That diagram has to be in error. I can't think of any situation where you would not grease threads. Also, if 15-20Nm of torque is a lot, and if you applied that much torque it should be difficult for the TA to loosen itself. I suspect most of us, myself included, don't put 15Nm of torque on our thru axles.
    – Weiwen Ng
    Commented Oct 28, 2021 at 17:50
  • @WeiwenNg you might have misread the answer. Santa Cruz's position is to grease threads, both on the website and via their support. Interestingly, they do not specify any torque guidelines. Not many reasonable people would assume that no torque specification means "as tight as heck" in this case.
    – Grigory Rechistov
    Commented Oct 29, 2021 at 6:31
  • @VladimirF judging torque by hand is really hard. I reckon it's better to pull up rather than pushing down, because then you're comparing to lifting a weight. Assume the force acts where your middle finger is (that's the strongest finger so a reasonable assumption, though surprisingly the ring finger exerts more pressure than the index finger) to estimate the lever arm, and you can work out the torque. Here, guessing about a 5cm lever arm 15Nm is equivalent to lifting 30kg in one hand, pretty close to "tight as heck"
    – Chris H
    Commented Oct 29, 2021 at 10:15
  • In general checking safety-critical threads are tight is a good idea, especially with ones that are routinely undone, so you've got into a good habit.
    – Chris H
    Commented Oct 29, 2021 at 10:18
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One issue not addressed in answers (but MaplePanda did say in a comment) is that carbon paste is not necessary. Carbon paste is grease with friction compounds. Sometimes, items like carbon seatposts and stems may slide at the specified torque, especially if they're lightly built. Carbon paste can eliminate that issue. These are not threaded interfaces, however.

Carbon doesn't hold threads well. The threads in the dropouts are aluminum inserts that are bonded into the carbon. Basically, carbon paste should not actually hurt you, since it is grease, but it's also completely unnecessary.

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    So if its aluminum insert, that means I can't break the frame that easily, right? Tighten it well (not too hard) would be enough (don't need torque wrench). 10Nm is written there. I'm just a bit afraid, because I've heard that it is easy to break carbon frames if you don't respect those numbers written at the screws.
    – Mat
    Commented Oct 28, 2021 at 18:31
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    You won't break the frame if you overtorque it - you'll dislodge the insert from the surrounding material which is just as bad.
    – max
    Commented Oct 28, 2021 at 19:28
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    I suspect you would need a lot of torque to actually break the insert out of the frame. Hopefully this doesn't happen, but this may be repairable at a skilled carbon fiber repairer if it does.
    – Weiwen Ng
    Commented Oct 28, 2021 at 23:24
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    @max that's a rather fine distinction given that the insert is bonded into the frame; the damage can be expected to include the frame
    – Chris H
    Commented Oct 29, 2021 at 10:07
  • Get a torque wrench and/or develop muscle memory for appropriate torque of a levered thru axle. If you're into the carbon level of frames and parts, you're spending an egregious amount of money*so why risk damaging the carbon fiber by foolishly wrenching a fastener into it? Peace of mind is a valuable commodity.
    – Jeff
    Commented Nov 1, 2021 at 20:16

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