Broken 20 mm thru hollow axle

macribs

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I've got a broken front axle. 20 mm thru hollow axle. It is the same axle that came with the fox 40. Anyone experienced anything like that before? I thought the 20 mm axle was the tits. Seems more like shits now. Worst part is my weekend ride went down the drain with the axle. And this is the first weekend with great weather this year. Damn I should have an extra bike fir situations like this. New axle on express order, but I am wondering should I get a custom axle made just to be sure I don't have this happen again?

I run a 19" moto wheel with mc tire up front. Before I swapped braked I used to have hope mono 6Ti 6 piston caliper with that large diameter rotor. Could that heavy break setup and heavy wheel be the cause of the damaged axle? I guess the heavy bike and husky rider does not help either. Either freak accident or material fatigue or to heavy load from heavy front end, heavy bike and heavy rider.

What you reckon was the reason this happen? And should I just as well have a custom axle made? Like a 20mm Ti axle?
 
That's interesting and a bit scary. I take it you didn't end up flipping or anything to bad when it failed ?

Last night I was working on my raptor build and putting the 203 disc on my front wheel which involved removing the 20mm hollow axle from my fork.

It's a Suntour RUX and the 2nd I have purchased. Never had any issues , but I was looking at the axle thinking it seems pretty light for all the forces probably on it.

If these types of forks are made for jumps id hope they could handle what you were throwing at it. Esp since IMO the fox 40 costs a premium so should be made from quality stuff.
 
Possibly it was bending slightly during use and the metal fatigued.

How thick is the wall? Maybe a 20mm solid axle might be better.
 
Fox axles don't last forever. They are very light weight, and need to be inspected regularly. That is especially true when you lace a motorcycle wheel on the hub. Don't forget that most modern motorcycle front hubs are made for 15mm solid steel axle, and when they use Alu hollow axles they are 25 mm dia and much thicker tubing than bicycle axles.

I would trust the axle of a Marz Monster T to use a motorcycle wheel for a long time. The Boxxer or The recent Marz axles would be good if replaced each year I guess. The Fox, I would inspect every week. Heavy wheels do require heavy hardware to match, and that is not only axle, but also headset, and steertube especially. A cheap bicycle fork steertube is dangerous when beaten by the weight of a motorcycle wheel.
 
Could you post a close-up pic of the break? That might help identify some of the characteristics of the cause. Not all steels are the same. It may look beefy, but they used cheese-grade steel?
 
No, it is 7000 grade Alu. All DH axles are hollow 20mm Alu for a very long time. Normally, it is broken about 1" from the locking screw, that is where I have seen them crack just about every time.
 
A common reason for braking axles are the bearings of the hub.
I prefer hubs that has a sleeve between axle and bearings because if there isn't this condition a bearing that doesn't works well can literally cut the axle.
I hope that I have explain my self well. Sorry for my bad English
 
With a 19 inch motor wheel ( heavy ) and MC tire ( heavy ) up front,
Then

Yes, head off to your local Machinist and have him make a custom made front Axle , thicker , and if he can do it with thick walled / solid CroMoly then even better.


macribs said:
I run a 19" moto wheel with mc tire up front. Before I swapped braked I used to have hope mono 6Ti 6 piston caliper with that large diameter rotor. Could that heavy break setup and heavy wheel be the cause of the damaged axle? I guess the heavy bike and husky rider does not help either. Either freak accident or material fatigue or to heavy load from heavy front end, heavy bike and heavy rider.

What you reckon was the reason this happen? And should I just as well have a custom axle made? Like a 20mm Ti axle?
 
Damn Macribs, hope no real harm came to you or your bike. How hard do you ride? Thx for the info though, because now I'm so glad I stuck with the heavier solid steel moto axle and just made bushings to fit it to my Titanium 888's. There are certain things where failures are unacceptable with my street riding at highway speeds, and a broken front axle is one of them. Similarly, I never bother with a chain (who wants to hear all that freewheel clicking anyway?). The only way I'd ever put a pedal line on a high power ebike is with 2 freewheels between the pedals and wheel...Imagine a freewheel failure and seize-up at 100kph or more, a low % risk of happening, but too high a risk in the event of failure.
 
That is the right way to do it if you are using a motorcycle wheel. Yet, I would inspect the steertube once in a while for signs of fatigue. Downhill racing components are made without an ounce of extra weight, and tested with much lighter wheels. On Trial motorcycles they are using bicycle DH forks to save weight, but they fit them with the motorcycle axle and steertube.

I find best to build a light weight wheel, but if I would use a motorcycle wheel I would do just that.
 
MadRhino said:
That is the right way to do it if you are using a motorcycle wheel. Yet, I would inspect the steertube once in a while for signs of fatigue. Downhill racing components are made without an ounce of extra weight, and tested with much lighter wheels. On Trial motorcycles they are using bicycle DH forks to save weight, but they fit them with the motorcycle axle and steertube.

I find best to build a light weight wheel, but if I would use a motorcycle wheel I would do just that.

When I used bicycle tires (with bike rims, spokes, and hub) I was always thinking about a front tire blowout. Since I had a downhill front wheel wheel go flat in just a few seconds while in the center lane at 80kph or so, in traffic, but despite my low experience and skill level I managed to coast to a 1m wide shoulder without incident. Unfortunately down here there just aren't any tweener tires like for mopeds, so it's a matter of getting the lightest moto tire I can find.

Since I'm running a triple clamp fork, how much do I need to worry about the steel steer tube? I don't do any drops, avoid potholes, and the only significant forces on the steer tube is during braking, which is generally gentle on the front thanks to regen doing most of the work.
 
Luckily I was at the start of the ride. I was just going down the driveway, giving it a little front end lift. Not high of the ground at all.
And when front wheel came down I could feel something was off. If this would have happen in 60 mph down a fire lane or on a backroad things could have gone ugly.

I got the bike over to a shop friday evening. Custom axle is coming along, don't know what material as he will use what he had in shop.

This will work for short term. I once was thinking of going mx fork with mc hub and wheel. Then I got persuade the weight was too much. Well I think it is time to loose a little in the tight single tracks and gain some more safety margins. After all, heavy rider on a heavy bike with an appetite for WOT, max acceleration, stop and go, big brakes etc. I am not sure DH forks will take this kind of beating long term.

I might chop the head tube of the frame and have one custom made to fit a standard mx fork. But that will throw my rear setup off. So I would probably need to rework the swing arm to have longer stroke for rear shock as well to keep some sort of harmony.

I will check the steerer tube and all bearings before I mount it together. If things are ok I will try out the new steel axle. Carefully inspecting front end before every ride.
 
A blow out is not a problem if you are not nervous, but impossible to fix on the spot and THAT is a problem. This is rare though, and when you ride tires in good condition with proper PSI, it is not more likely to happen with bicycle tires than motorcycle tires. Both times I have had blow outs in my life, were on motorcycles.

It is the insert of the steer tube in the lower crown that need to be inspected, once in a while. I do this even with lightweight wheels of my street bikes, because the streets here are a minefield. Younger, I have had a few bad crashes caused by mechanical failures, and I am now meticulous with inspection and maintenance. Almost any failure can be prevented with good inspection and maintenance habits.

@macribs
With a motorcycle fork, it is the neck of your frame that will be at risk of a failure. That is the problem with mixing bicycle and motorcycle components: One is making for the need of another, and the other for yet another... Your Fox 40 is a good racing fork, but it is just that, with the busy inspection and maintenance schedule that is coming with light weight racing forks. Check the user manual, how often you are supposed to do what. It will freak you out. :wink: Buy a good old Monster T, that is much more robust and can go years without maintenance.
 
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