When does an axle break?

[themadhatter106]

I went searching around but I couldn't find a topic about axle breakages in general. How can they happen? At what power levels do such breakages generally occur? How can they be avoided? Are some motors more prone to axle breakages then others?

I think this is a very important for hot rodders to be aware and informed of this because its one of the few ways that a DD hub motor can actually suddenly break without warning. This could be a dangerous situation if your in traffic.

I am running a 9c at 6kW so I am wondering if I were to increase the power at what point should I start to be worried about my axle breaking.

 

[tiny_n_terrible]

I have bent lots of axles. never broken one .

 

[Hillhater]

Axles do not break from too much power, they break from shock, jumping, hitting kerbs, pot holes etc.
I have broken and bent several axles....on a non motorised wheel !

 

[dogman dan]

They can twist off. But I always suspect other shocks starts the crack in the first place. Then a damaged axle twists off.

If you jump your bike and then put 6000w to it, it can happen to you.

 

[Eskimo]

I have been thinking this quite a lot. My rearwheel axel load is 105,6kg. When i hit holes at 25mph there is zero suspension because i sit low.
No damages luckily as far.

 

[Drunkskunk]

15,000w and no breakage here. I suspect these axles can take far more than that. Bending is the more likely problem. I think an axle is more likely to bend if the frame can flex.

 

[Merlin]

snap off an axle?
easy...just lift your wheel. full throttle, and press regen button. works for an HS4080

 

[wesnewell]

In the 5+ years I've been reading here, Clyte motors are the only ones I remember seeing here with sheared axles. And there's been a few. I've never had a problem with my cheap 1000W hub running 24s lipo and 40A controller with speeds up to 61.4 mph, and ~20K miles. I weigh 270 lbs and try to avoid pot holes, and jumping curbs or anything else.

 

[Chalo]

Axles do bend, and break, from both chain tension (which can be several times as much as rider weight) and dynamic riding loads.

The main culprits are freewheel hub axles set up for 7 or more speeds. Those have an overhang from the right side axle bearings to the locknut of 35mm or more, which is the lever that breaks the axle.

Cassette hubs generally don't break or bend axles, and that's why we have cassette hubs.

 

[ecycler]

Another common cause not listed yet is when someone has only a single torque arm and is running high power.

I hope more manufacturers go to the larger axles like the cro and MXUS 3k. I just ordered some extra long lug nuts that will hopefully work well as foot pegs!

 

[Merlin]

Axles do bend, and break, from both chain tension (which can be several times as much as rider weight) and dynamic riding loads.

The main culprits are freewheel hub axles set up for 7 or more speeds. Those have an overhang from the right side axle bearings to the locknut of 35mm or more, which is the lever that breaks the axle.

Cassette hubs generally don't break or bend axles, and that's why we have cassette hubs.

what are you talking about?
chain tension bend or break an axle? if we talk about shearforce, at least an doped armstrong pushes only 800w in peak.

i think you are talking about mainstream tiny 350w motors. Or did i missed the point there are above 5Kg Motors out there with a Cassette?

try this in Forum search; snapped axle
i bet you get hundreds of hits :wink:

 

[Chalo]

OK then, dig: a 200 pound dude stands up on his front pedal. He's climbing a hill in his granny ring of 24t. That's a radius of 1.91 inches. His crank is 175mm long, 6.89 inches. That's a ratio of 3.65:1, meaning his 200 pound of weight turns into 729 pounds of tension on the chain. That's a guy who isn't even working hard, just standing on the pedal.

Lots of us are waaaay over 200 pounds. And we can and do pull on the handlebars to add more force to the pedal than our own weight.

I am 6'8" tall and weigh almost 350 pounds. I can put more tension on a chain than Lance does, in my sleep. It's torque, not power. He uses a bigger ring than I do, which lessens chain tension. You see where I'm going with this? You don't have to be a jock to apply 1000 pounds or more to the axle. Apply that force to the big sprocket of a freewheel, and that's 1500 inch-pounds or more of bending force on the hollow, 10mm diameter axle. Before motor power.