Is axle breakage normal?
 

I have a Giant Boulder mountain bike that I only ride on smooth roads. A few years ago, the axle broke. Very surprising since I only ride on roads, only weigh 145 lbs, and don't carry cargo on my bike. Well, I got it fixed.

Now, my Specialized Hardrock, which I also ride only on roads, has a broken axle too! What's going on here?

I've never had broken axles at any other time in my life until a few years ago, and today. I'm 43 years old, so that's a long time to go to start having this problem repeat itself every few years at this point. If I can have 2 broken axles in just a few years on mountain bikes that are ridden on roads, they probably wouldn't last long at all if they were ridden off-road, as they supposedly were "meant" to be.

I have weighed between 300 and 350, and ride hybrids, and haven't broken an axle in 10 years (probably 4-5 thousand miles). I did used to break and bend axles sometimes back as a teen when I weighed about 150, but I rode in the woods a lot back then. Also, the old freewheel technology was more subject to axle issues than the current cassette technology.

The thing about random occurrences is that there will sometimes be clusters, but there is not necessarily a significant causative reason for the cluster.

Unless you jump off curbs or otherwise add a significant shock to the system, you should just write it off to being unlucky for the past few years.

But, out of curiosity, since back in the day all of my axle issues were the rear axle, is that what you have had?

I'm thinking these might be freewheel bikes also. I used to bend/break freewheel axles all the time. Pretty much never with freehubs.

Yes, just the rear.

That does seem most likely, since the axle is longer (more leverage) and also holds more weight.

I do think you just hit a bad streak.

Almost surely. The drive side bearing on a freewheel rear hub is quite close to the middle of the axle. That makes it prone to bending and eventually to breaking. The low cost but temporary solution is to replace the axle when necessary. The more costly but longer term solution is to replace the entire rear wheel with one that has a freehub. The design of a freehub places the drive side bearing much closer to the dropout.

Freewheel yes, Freehub no.

Both the Hardrock and Boulder have had over the years some very low spec part on them, and freewheel wheels is one where the spec can be very low.

For either of these bike being capable off road, that's subjective, yes both bike are capable of being ridden off road (as in what would be consider proper MTB'ing), but the spec of many of the part on them mean that they won't last long, for what most people buy them for, which will be non technical trails/MUP/riding on the road, they are more than adequate and will last many years doing the job.

the more cogs on the freewheel, the more likely it will break, it has nothing to do with the number of cogs, of course, but the length of the unsupported section of the axle, as has been mentioned. the last hurrah of freewheels had eight cogs and were quickly abandoned due to a large number of axle failures, IIRC. this was somewhere back in the mid-nineties. :50:

if so, that in itself does not explain the recent number of breakages, unless the freewheels recently employed have more unsupported axle length (i.e. more cogs) than previously, or possibly a different manufacturer.

yes, axle breaking is completely normal and expected given that both bikes are low end with weak freewheel style wheels
despite marketing the realistically were never meant to be used as real mtb

upgrading to freehub and cassette wheels will cost around 150$ each, but will eliminate the issue


sheldon has a nice photo showing the differences, makes the weakness obvious
Shimano Cassettes & Freehubs

alternatively you can unweight the wheels when going over potholes and curbs etc, becoming an active parts of the suspension system and not relaxing on the saddle, that might let the axles hold up longer

That's another thing--I avoid potholes and I don't jump curbs anymore. I used to do that with bikes in the past and had to get the rims retrued and decided I could save money by not jumping curbs. Now instead of bending rims, I break axles while staying on smooth pavement.

I'm not familiar with those two bike frames but I've seen a lot of low-end bikes with 130mm or even 135mm dropout spacing but with 7 speed freewheels. That's a lot of unsupported axle on the drive side. Think of the drive side cone as being the axis of a fulcrum and you'll understand why so many rear axles break. Oh, a lot of low-end axles aren't even Cro-moly.

Cheers from Miele Man

well'p if that's not it i guess that means its time to upgrade
on the plus side with a cassette wheel and double wall rims you're free to go back to the old habits
fun

Nah, it's just a matter of time with a 7s freewheel... unless you have a 14mm axle like the cargo bikes my boss bought.

Actually, I hadn't considered that some current bikes still use freewheels... I thought that any name brand was using cassettes, even for 7 speed... Now, I know better.

Freewheels and the hub they go on is still part of making a bike that sells for Less.

It's all about hitting lower price points .

Other posters have correctly noted the weakness of freewheel-style hubs. The long length of unsupported axle on the drive side. The axles break at the nose of the hub cone, the point of greatest stress.

Next time, install this cone on the drive side:

Wheels Manufacturing R100 Cone LX/XT10mm Front

I know it says 'front cone', but has a 10mm bore that fits standard rear axles. Note how it has a longer 'nose', so it will support the axle in this vulnerable area.

Understanding the cause of broken axles helps. Breakage is rarely related to the axle load or road bumps. A much greater force is the chain tension pulling the sprocket forward. This is especially true with strong riders, hilly terrain, or small chainrings which give the rider more leverage. Use of inner sprockets or hubs with inboard bearings also increase the deflection loads which is why freewheel hubs fare worse than many cassette hub designs.

Another contributing factor is the parallelism of the dropouts and the design of the axle face. Wide axle faces held flat with tight QR skewers support the axle the same way a wide base makes a floor fan less tippy. This reduces flex which is the enemy of axle life.

Lastly are various subtle considerations in the construction of the axle itself, including the material and specific details of how the axle and bearing parts are fitted together.

One reason we see more axle failure is that we've moved from European ateliers that built bike parts like the Egyptians built pyramids, to large factories building private brand parts with little regard for anything besides price and marketability. Bikes have joined the consumer age. They're not supposed to last forever. Instead you're supposed to replace them every few years with newer/better versions. Welcome to the new Millennium.

Hey, nice one.

It's not that much greater of a force but it is continuously, repeatedly applied, which leads to metal fatigue.

A 7 speed freewheel hub typically fatigues the axle rather than overwhelming it with too much force, although the last straw may come from some giant bump.

Freewheel rear wheels should be checked from time to time to see if the wheel feels loose on the axle because the axle probably bends before it completely breaks especially if it is solid. Riding around with a failing axle can ruin the bearing cups in the hub.

If you catch the problem when it first starts to develop it is possible to simply put in a new axle and cones to fix the hub. It should be good for about as much riding as the old one was if you buy a good one. Keeping an eye on it as it ages may prevent breakage. It's important to check or change as soon as a problem is noticed so you don't ruin your hub with misadjusted bearings. The bearings will become misadjusted as the axle weakens from fatigue and starts to bend.

Chrome moly replacements are available. Don't let anybody tell you a hollow axle is stronger than a solid one.

Bent dropouts may be involved but need not be involved.

Proper adjustment with absolutely no slack and a bit of preload will extend life considerably. The hub is able to reinforce the axle a bit if the bearings are properly adjusted.

Do you have a link to those? My MTB is 9sp but I wonder if they'd fit a 6sp rear wheel. Is it a custom hub or something you can retrofit onto a 6-7sp freewheel hub?

I Toured on Freewheel hubs, fairly expensive US Made ones in wheels I built.

https://www.philwood.com/products/hubspgs/touringhubs.php

your solution will be rebuilding the rear wheel , replacing the Hub not retrofitting yours, which is failing..

Dave, do you mind if I ask whether you've tried that cone?

I had the same idea and looked for cones that would give extra support to the axle just inside the bearing cup. However, an MH525 Deore front hub and a WH-R550 front hub may have a 10mm axle but the end of the axle is unthreaded and 9mm. The hole in the end of the cone is also 9mm and unthreaded. The 10mm threads don't go all the way through.

The cone you found may have the same design.

I rode into work this AM using this cone. The bike has a Campy C-Record freewheel hub at the back. I broke the original Campy axle a few months ago, and replaced the whole assembly with Shimano-threaded axle/cones/nuts.

I know what you are talking about. I have been digging around in my parts, and I've found several bagged "Dura-Ace front hub axle/cone replacement" kits. The axles are alu, and the cones have a standard 10mm threading. But as you write, the treading does not extend to the end, so they are useless in my rear axle kludge.

I have also done this fix on the older Campy "Record" freewheel hubs. Sorry for degrading Campy hubs with Shimano guts, but finding 136-140mm long Campy threaded axles is simply more of a hassle than the Shimano equivalents. At our local bike Co-op I can get pounds of these for nothing. Sometimes I have to hacksaw them to size. But with my fix, the new axles should be a lot more break-resistant.

OTOH, for my classic build..

I just bought a 'Wheels' substitute Campag pattern axle ..

I think Tullio & Company, tempered them a bit brittle-hard .
the Boulder CO company may have gotten the temper of the steel a bit more ductile..

I'm using it in a 130 frame now .. longer axle, added a 4mm spacer on the left from previous 126 Setup.