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Thru axle loosening?

Old 08-12-19, 06:17 PM
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shelbyfv
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Thru axle loosening?

A friend told me that his front thru axle loosened on a ride this weekend. The wheel cocked enough that the disc brake grabbed. Fortunately he was going uphill and was able to get a foot down. He also related that another friend had a front axle come completely out. The wheel stayed in the fork and he was able to backtrack and find the axle in the road. One was the Allen key style, the other had the lever. I searched online and found a few discussions but no consensus as to what caused it. Precession and thread direction were mentioned but it was pointed out that nothing should actually be bearing and rotating on the axle. Is this becoming common? Something to be concerned about?
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Old 08-12-19, 06:32 PM
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hmm, 4 bikes for me so far with thru axles. no issues with loosening whatsoever over many years. Maybe someone else can shed more light on this.
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Old 08-12-19, 06:33 PM
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The bearing cones or cartridges bear on the thru axle, don't they? If not, were does the weight they are supporting go to get to the frame? If the bearing grease dries up or the cones are too tight so the bearing is no longer running freely, then the torque would be transmittted to the through axle, applying a torque in the opposite direction as would be transmitted by properly lubed bearings and in a direction the thru axle might not be designed to handle. (Pedals and English bottom brackets are designed to screw in tighter with the forces transmitted by the bearings. If your pedal bearings go bad, the pedal unscrews and falls out (unless you "honk
on that wrench at installation in which case your ankle unscrews and falls off).

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Old 08-12-19, 07:52 PM
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Originally Posted by 79pmooney
The bearing cones or cartridges bear on the thru axle, don't they? If not, were does the weight they are supporting go to get to the frame?
Don't know. I only have one bike with thru axle, so not an expert. It looks as if the ends of the hubs sit in shallow indents in the fork. The axle pulls everything tight. The axle shows no sign of anything moving on it, no wear marks.
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Old 08-12-19, 08:05 PM
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Thru-axles need adequate torque, as with any fastener. Generally 10-12Nm AFAIK. The bolt-head axles are better because you can put a torque wrench on them ofc.

Never seen one loosen-while-riding happen myself.
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Old 08-12-19, 10:56 PM
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I did have my front thru axle start working loose last year. I felt the play in the front wheel when it was slightly loose, there was still lots of thread in the fork so the wheel was not anywhere near falling out. Iíve taken care to torque it sufficiently ever since and have had no more issues.
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Old 08-13-19, 09:23 AM
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And there I was thinking one of the reasons bike manufacturers went to thru axles (at least on front wheels) was they wouldn't loosen when used with disk brakes (unlike with QR where wheel ejection was a well researched/documented occurrence). Maybe your friend is not following the proper procedures. Lots of you-tube videos saying how to setup thru axles (one being
). Also, if I am not mistaken one of the safety checks before each ride is checking your QRs/thru axles (if parked in public a passerby may have maliciously loosened them). Of course I don't follow this suggestion my self.
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Old 08-14-19, 05:05 AM
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Thanks all. It seems nothing is going on beyond user error
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Old 08-14-19, 03:26 PM
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Thru-axle assemblies are rather stupidly designed, since there is nothing providing an actual definite position of the parts. The axle has to be a loose fit in the hub to allow easy, hands-only installation. So the rider end up having to rely on the end caps of the hub being pinched between two parallel surfaces as the sole mechanism keeping the wheel positioned.
What happens is that applying the brake causes a downward force on the axle, and riding causes an upward force on the axle. In the absence of a definite centering feature, a TA that hasnít been closed with sufficient force will allow the wheel to move (ever so little) up & down, as dictated by how loosely the axle fits in the hub.
One trick that might help is to tighten the TA with the wheel off the ground. That way, the slack is taken out and the wheel is already resting against a definite reference.
Brake forces canít move it any further, and w/o jostling, thereís far less going on that can cause the axle to unscrew.
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Old 08-15-19, 08:08 AM
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Originally Posted by dabac
Thru-axle assemblies are rather stupidly designed, since there is nothing providing an actual definite position of the parts. The axle has to be a loose fit in the hub to allow easy, hands-only installation. So the rider end up having to rely on the end caps of the hub being pinched between two parallel surfaces as the sole mechanism keeping the wheel positioned.
What happens is that applying the brake causes a downward force on the axle, and riding causes an upward force on the axle. In the absence of a definite centering feature, a TA that hasnít been closed with sufficient force will allow the wheel to move (ever so little) up & down, as dictated by how loosely the axle fits in the hub.
One trick that might help is to tighten the TA with the wheel off the ground. That way, the slack is taken out and the wheel is already resting against a definite reference.
Brake forces canít move it any further, and w/o jostling, thereís far less going on that can cause the axle to unscrew.
Another trick is to just tighten the TA properly and not have any issues. It ainít rocket science.

I think it is a stretch to call the TA a stupid design due to what happens if it is not properly tightened. It is a whole heck of a lot better than what happens when you donít tighten a 9mm QR.

The reality out on the road and trail is that TAs do a perfectly good job of keeping the hub exactly where it needs to be, and are actually better than QR at getting disc calipers and rotors to consistently line up after wheel changes.
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Old 08-15-19, 08:34 AM
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Looks like there are some things you just can't idiot-proof.
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Old 08-15-19, 02:56 PM
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Originally Posted by Kapusta
The reality out on the road and trail is that TAs do a perfectly good job of keeping the hub exactly where it needs to be, and are actually better than QR at getting disc calipers and rotors to consistently line up after wheel changes.
+1 Years ago I had a bike with disc and a QR. Never again. The thru axle I have now requires that I loosen it slightly to close the lever. Seems iffy to me so I probably should replace it with the Allen key type.
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Old 08-15-19, 03:10 PM
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Originally Posted by shelbyfv
+1 Years ago I had a bike with disc and a QR. Never again. The thru axle I have now requires that I loosen it slightly to close the lever. Seems iffy to me so I probably should replace it with the Allen key type.
I don't know what kind of TA you have, but some designs you can adjust how much it tightens as you close the lever.
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Old 08-15-19, 03:14 PM
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Originally Posted by ThermionicScott
Looks like there are some things you just can't idiot-proof.
True. Idiocy is like a thin liquid that will find its way through the tiniest of cracks.
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Old 08-15-19, 06:56 PM
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My current bike came with DT Swiss RWS axles which I really like. Huge step up from my previous bike with disc/QR combo.

I do a decent almost daily of the most god awful chip sealed road you can imagine and they have never loosened one bit even though a bunch of other things on the bike have had to be Loc-Tited and re-torqued.

That being said, if I ever replace my current axles I'm going with these:

The Robert Axle Project

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Old 08-17-19, 07:14 PM
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Originally Posted by ThermionicScott
Looks like there are some things you just can't idiot-proof.
People tried. I have a Fox fork which has a QR clamp on each side, just to prevent the TA from loosening. Pretty much belt, suspenders, duct tape and super-glue at that point.
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Old 10-14-20, 02:26 AM
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My bolt type tru axle of my back wheel came loose 2 times in the last 3 months
(I often ride more then a thousand km a week on a gravel bike loaded up with everything I own riding lots off gravel and other intens train)

Last edited by rphvv@live.nl; 10-14-20 at 03:08 AM.
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Old 10-14-20, 02:53 AM
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A friend of mine had the bolt type rear thru axle come totally loose on a Stumpjumper while riding. I'm not sure if it was tightened properly though.

I've seen a few thru axle designs I don't like as they seem less secure: for example the rear one on my Canyon Grand Canyon. On the other hand, there are others that I feel are extremely safe, especially Suntour's Q-Loc seems to me like an outstanding solution: even if it gets fully loose, the axle can't go anywhere.
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Old 10-14-20, 07:31 AM
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As noted the tightening torque spec for bolt-type thru-axles is quite high. Surly's torque spec for the thru-axles on my new Midnight Special is 16 N-m which is a lot tighter than anyone would apply with a standard 5 mm allen key without a torque wrench as guidance. I expect the loosening stories are from inadequate torque since "snug" isn't nearly enough.
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Old 10-14-20, 09:24 AM
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Originally Posted by 79pmooney
The bearing cones or cartridges bear on the thru axle, don't they? If not, were does the weight they are supporting go to get to the frame? If the bearing grease dries up or the cones are too tight so the bearing is no longer running freely, then the torque would be transmittted to the through axle, applying a torque in the opposite direction as would be transmitted by properly lubed bearings and in a direction the thru axle might not be designed to handle. (Pedals and English bottom brackets are designed to screw in tighter with the forces transmitted by the bearings. If your pedal bearings go bad, the pedal unscrews and falls out (unless you "honk
on that wrench at installation in which case your ankle unscrews and falls off).

Ben
The bearings don't interact directly with the TA, which essentially plays the same role as a QR skewer. It provides the clamping force for the axle, which is stationary, as the axle ends are clamped against the inside faces of the fork ends/dropouts. The hub, supported by bearings, rotates around the axle. There should be no rotating force acting on the TA that would cause it to unscrew, as it's isolated from the only rotating component (the hub) by the bearings

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Old 10-14-20, 02:00 PM
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I haven't heard any more local loose axle stories. Maybe folks are learning that they do need to be properly tightened. I ordered one from Robert Axle Project. A nice product, could be cranked down w/o the fiddly QR type lever which would spin before the thing was fully threaded. I think my OEM axle was defective from the start. Sometime during the year since this thread was begun a guy came on BF with the theory that we were all torquing our axles too tight He had a half dozen threads about torque values with and w/o grease, grease vs anti-seize, on and on. He's disappeared but was running hard with this foolishness for several weeks.
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Old 10-15-20, 03:30 AM
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Maybe but my axle states 8 nm should be enough
(8-14 Nm)
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Old 07-01-21, 11:15 AM
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Hi all, I recently purchased a Trek Domane AL 2, have ridden for maybe ~150 miles so far. Anyway this morning this exact thing happened to me, my front thru axle came loose. Didn't fall out or anything but the wheel started to wobble. Luckily I was on a flat, calm section of road. But damn if I was flying down a hill when that happened...

All I can assume is that either the bike shop did not adequately tighten it (they seemed pretty professional tho), or somebody maliciously untightened it/attempted to steal wheel...? It's the bolt type, torque spec is 10 Nm. I hand retightened it and rode back slowly lol. Guess I should invest in a torque wrench
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Old 07-01-21, 11:26 AM
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I bet the spring is either broken, bound from losing its sprung ability, or both. Take apart the cam head & it should reveal the reasoning.
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Old 07-02-21, 06:32 AM
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A friend recently had his front thru axle come loose on a descent, and he narrowly avoided a crash. I didn't see the problem first hand, and am not familiar with his bike, but he blames user error.

Just as I see a lot of people using a QR lever as a wing nut of sorts, and see backward conical springs, I suppose there are just as many who don't understand their TA systems. I call it ignorance, not idiocy. People get it when you show them how to do it, and explain how important a secure front wheel is.
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