Bicycle Mechanics - bent axle

I had taken my ever-so high quality Mongoose MGX into a bike repair shop becuase the rear end of the bicycle was a little out of whack. They looked at it and found that the rear axle was bent. Very bent. Now I just said, 'Ok, just replace it,' which they did. On my way home from school one day, I noticed that the breaks were rubbing up on the rims and I couldn't tweek them to get rid of the rubbing. I took it into the bike store on the way home and they asked if I had done any jumping on it. I said no, of course not. Well, they ended up calling me a liar, because the rear axle was bent, once again. I swear I never did anything strange to that bicycle, other than ride it. Well, it turns out that I took it into another bike shop a little further away, and they just straightened things out a bit here and there, and it rides better than new now. So now that you have the story on my bike, here is my actual question:

Can a rear axle for a mountain bike bend like that? Can it be a problem with the way it is mounted? I swear I never gave it a bump more than a speedbump or over a cuve (I didn't even do any off-roading, for pete's sake). Maybe I should just not ride my bike to school anymore, cause my only other guess would be that someone was jumping up and down on it while it was innocently sitting in the bike rack. Any ideas?

When the bike is a $79 department store special, yes, it can. Those Mongese may look like an ATB, but internally, they are essentially a granny bike. They even put a sticker on the bike, telling you that you should never jump it, or ride it off-road.
Sorry, but that's the risk when you buy junk. Those axles are made of mild steel, and are about as strong as silly-putty. When an axle breaks on such a bike, it's usually cheaper to just throw it away.

If you can strip the rear bearings, you can roll the axle on a flat surface (eg mirror) to see if its bent.
It may also be that the rear dropouts(slots for the axle) are missaligned, which can stress the axle.
If you think someone is messing with the bike, leave it with the wheel rotated so you know where the axle is. Put a chalk mark on the top of the tyre or whatever. Yo can usually see if someone has tried to abuse it .

Junk bikes are junk, but should survive a short regular road journey for a year or 2.

....let's see...
2 bent axles, one broken pedal...gee, toy bikes can be expensive, can't they?
I remember reading once about the "40 lb rule" on commuter bikes (a 40 lb bike doesn't need to be locked, but you need a 20 lb lock to keep a 20 lb bike from being stolen...), and I now have a corollary for basic bikes:

A basic bike will never cost you less than $300

If you spend only $100 for a toy bike, you will spend at least $200 on fixing all the things that break in the first few months.

Although I have always owned mid-grade or better "bike shop quality" bicycles, I have broken two rear axles (one QR, one solid), two left cranks (one cottered steel, one aluminum), two frames, an aluminum pedal cage (SunTour platform), and a front hub flange (Shimano aluminum HF) while cycling. I hate to think what my record would have been with *-Mart bikes.

Originally posted by D*Alex
When the bike is a $79 department store special, yes, it can. Those Mongese may look like an ATB, but internally, they are essentially a granny bike.

Hey, D*Alex, that's not a very scientific answer.

Are you saying that the axle from a lower cost bike is more prone to bending than an axle of an expensive bike? Are you sure?...

We have to be careful about poo pooing other dude's bikes by brand name.

Remember the old rule about bicycle parts; Light, strong, cheap; pick two.

Expensive does not necessarily mean strong and cheap does not necessarily mean weak.

I think there is something more involved here than the price or name of the bike. Let's at least guess that the LBS that did the first repair replaced the axle with a good quality part. That one bent too.

I should have been more specific.

The first time the axel bent, it was the one that came with it (quick release). They replaced it with a solid, bolted (what are those called?) axle and it, too, bent about 3 weeks or so later. I was beginning to wonder if a bad connection between the axle and frame could cause that.

Also, Everyone is saying that it costed $79. It costed a little more than $300 at a place known to be cheap, but very good quality (Costco, if anyone has heard of it). They also sell Schwinns (sp?) there, if that means anything.

at a place known to be cheap, but very good quality (Costco, if anyone has heard of it). They also sell Schwinns (sp?) there, if that means anything.
COSTCO?? Selling good bikes???
BWAHAHAHAHAHAHAHA!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Costco buys overstock, and shoves it out the door as quickly as possible. Last year, they were selling a bunch of Cannondale road bike, bought dirt-cheap from a russian wholesaler, unable to pay for his order. Back on the boat they went, and they ended up in Costco stores, all banged-up, most haphazardly assembled by minimum-wage workers inside the store. Cannondale will not honor warrantees on thes bikes.

Originally posted by D*Alex
. They even put a sticker on the bike, telling you that you should never jump it, or ride it off-road.


Where?:confused:

Originally posted by D*Alex

COSTCO?? Selling good bikes???
BWAHAHAHAHAHAHAHA!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Costco buys overstock, and shoves it out the door as quickly as possible. Last year, they were selling a bunch of Cannondale road bike, bought dirt-cheap from a russian wholesaler, unable to pay for his order. Back on the boat they went, and they ended up in Costco stores, all banged-up, most haphazardly assembled by minimum-wage workers inside the store. Cannondale will not honor warrantees on thes bikes.

This is exactly why Badger did not want to be associated with this forum. Alex, please re-read the community guidelines and general principles. Im not going to let these type of posts on this forum.

Originally posted by ledhead69
I should have been more specific.

They replaced it with a solid, bolted (what are those called?) axle and it, too, bent about 3 weeks or so later.

Man! You bent a solid axle. I guess it happens, but if you are doing it on the flatlands... Zowie.

I am surprised something else isn't happening like bending your rims or wrinkling the frame at the joints.

here is my take on the issue, ok maybe it is a cheap bike... but that means about nothing. cheap bikes do not = crap. My Gt cost me $400 8-9 years ago, and it has not had a problem since I bought it. yes it was cheap but it was not crap. Now if your LBS accuses you of lying I would go somewhere else and get a second opinion. I mean they don't seem to be that nice if they don't believe you. :rolleyes:

also if this keeps happening, maybe you need to get a better wheel set on that bike. one with better quality hubs? but if you're on a limited budget I don't know..... :confused:

good luck getting your ride fixed :D

This is exactly why Badger did not want to be associated with this forum. Alex, please re-read the community guidelines and general principles. Im not going to let these type of posts on this forum.

If I have a say about it, let 'im go. All of the other stuff I buy there is a good quality. Now I know differently (could have said it a bit nicer, though ;-))


Man! You bent a solid axle. I guess it happens, but if you...

That is what is so strange! I did no trail riding on it; a speed bump or a curb at the most. Oh well...When all else fails, blame it on the bike.

The problem might be in the design. The older, freewheel style rear hubs are far more prone to having axles bend and break.

http://www.sheldonbrown.com/freewheels.html

Also, the dropouts on the frame could be misaligned which puts a lot of additional stress on the axle. They could even be cracked.

It's possible that the bike shop gave you a bent axle. This happened once to me. And let me pre-empt Veloslob, er I mean SNOB, that it came from a very reputable bike shop.

It sounds to me like the (stays ?, swingarms ?), are not lining up properly and this is making the wheel out of alignment.

This is possible on an aluminium bike.

Bend a soild axle ? Drivel !
Cheap axles are made from cast steel, not as strong as forged, no, but plenty strong nevertheless !

The crankshafts on car engines are made from cast steel (special type, true) for crying out loud !

Originally posted by john999
It sounds to me like the (stays ?, swingarms ?), are not lining up properly and this is making the wheel out of alignment.

This is possible on an aluminium bike.

Bend a soild axle ? Drivel !
Cheap axles are made from cast steel, not as strong as forged, no, but plenty strong nevertheless !

The crankshafts on car engines are made from cast steel (special type, true) for crying out loud !

but wouldn't the LBS put it on a trueing stand to double check the hub? or are you saying the stays are maybe doing the bending?

First of all...i'm with alex on this one.. most likely its a bent frame that is causing your axle to bend. your bike is worth about 3-400 bucks. i would buy your next bike from a reputable bike shop instead of costco so that you can then take it back in and say 'hey, my frame is bent". try that at costco and you'll get squat. Bikes are somewhat like cars in that if you buy a **** box for $2000...you might think.."I just spent $2000 bucks....its gotta be a good car" while in reality the cheaper car will cost more in parts and tune-ups (not to mention headaches). If you go out and spend $1000 ona bike, you can expect it to work for a while without problems. I understand that not everyone has the money to buy a solid bike, but if you're serious about riding I would consider saving up for something a little more stand-up. In the meantime you should take that frame to a different bike shop and try to find out whats not grooving.

Originally posted by trialsin
If you go out and spend $1000 ona bike, you can expect it to work for a while without problems


With all due respects, you don't have to spend $1,000 for a rideable, reliable bicycle.

Sorry, guys but the bike snobbery that is trumpeted lately is just simply unfounded.

There are a lot of people putting on a lot of miles on bikes that cost several hundred dollars or less. I'm willing to bet a lot of those people are getting a lot more miles and a lot more fun out of their bikes than the snobs with expensive machines and costly frills.

I have worked on cheap bikes and I have worked on expensive bikes. Expensive bikes and expensive parts fail too.

i'm not suggesting that $1000 equals a good bike, or that you have to spend that much. I just think if you go to a reputable bike shop and buy a good quality bike....you might not be having problems like the one being discussed. Buying a bike from costco or some other wholesale store is risky. And I'm sure there are lots of deals out there for under $500....but its been my experience that its really easy to get ripped off, or get a rig that has catastrophic failiers. I don't think its snobby to recomend that someone buy a higher quality bike from a higher quality shop. And i think its fair to say that high-end pats are for the most part, more reliable. Instead of attacking me, why don't you make a suggestion for what this guy(girl) should do about his(her) bent axle....It looks like all you've said is ...."whoa....you bent an axle!"

I have no answer for bent axle so I
won't even try. However (you knew there
had to be one, right?), for alot less than $1k you
could find an excellent USED bike.
I agree in principle that you get what you pay for.
Marty

agreed.....$1000 is a really nice bike. lets just be friends.:beer:

Originally posted by trialsin
agreed.....$1000 is a really nice bike. lets just be friends.:beer:

Ya, after re-reading my post about snobbiness it seems to have more bite than I had intended. Sorry about that - especially to trialsin.

Sure, $1,000 bike should be a nice bike. Some will say it is hardly enough for a truly nice bike. Many will say that less than $1,000 won't get you anything at all.

I just like to see people bicycling and enjoying bicycling - no matter what they ride. Sometimes, people get discouraged by negative comments about their machines. That's not good.

That was my main point, I guess.

Also don't forget, the person already owns the said bike, if it truely has a bent axle, then a new one can be purchased maybe of better quality. As for quality issues, most products whether it be automotive or Bicycles now days need an ISO 9000 rating or better for quality. Putting out bad products is a quick way of having that rating pulled out of the company. Which usually means that the company ends up shutting down.

:mad: :rolleyes: :irritated

No harm done. We all get a little carried away sometimes...and its true, whatever your bike costs isn't as important as how much enjoyment it brings you.:D

I'm saying one or both of the stays was bent.
This happens when you do jumping on an aluminium bike.

The stays that I'm talking about are the bars running from the bottom bracket (where the crankshaft is) to the axle.
They sometimes bend out with impacts (or this may have occurred in transit, or at the factory).
If this happens most weight goes to one side of the axle, on the stay that is lower, and the wheel runs at an angle, instead of vertical.

This might bend the axle, theoretically, but not really.
A cheap solid axle is forged (I was wrong, ok). It is a piece of rod that has been threaded by running it through two pinch discs.
It is very, very strong. The weight of a person could not bend it.
That's my opinion.

The second shop just bent the stays straight - a 10 second job.

Hi there
Having snapped and bent axles in the past on many a bike low range bike (and having done so again recently) I thought I would look into this a little further.
This site suggests that freewheel hubs (the ones with screw on freewheels aka sprockets) are prone to axle bending because the hub isn't central on the axle.
Check it out
It was a revelation for me. Its under the section titled "How much quality do I need"

Peace out
Adie

Damn forgot the site
http://www.bikebits.ie/bike_info.asp

John999 - how much do you weigh? If you are over 200 lb and you have a freewheel hub, you need to change the rear wheel to a freehub. You will then have a problem matching a 7 speed cassette to a 6 speed shifter but this can be done with alternate cable attachment as described by sheldon brown.

You don't even have to do jumping to bend a rear-axle on a freewheel hub. Just hit a couple of potholes or speed-bumps medium hard with your weight on the saddle and the thing's toast!

Bend a soild axle ? Drivel !
Cheap axles are made from cast steel, not as strong as forged, no, but plenty strong nevertheless !

The crankshafts on car engines are made from cast steel (special type, true) for crying out loud !

That's a terrible analogy. Parts of certain spacecraft are as thick as aluminum foil, it's all about how it's used and loaded. That is the sort of analogy that makes people think steel brake rotors work better on cars than cast iron ones, which is not at all true.


John999 - how much do you weigh? If you are over 200 lb and you have a freewheel hub, you need to change the rear wheel to a freehub. You will then have a problem matching a 7 speed cassette to a 6 speed shifter but this can be done with alternate cable attachment as described by sheldon brown.

You can probably get a cheap 7sp shifter. If not, you can probably get it close enough to just not use one of the gears.

That said, with the exception of track axles, most of the solid axles I have seen are weaker and more flexible (not the same thing) than their hollow counterparts. This is because the solid axles tend to go on cheaper bikes (and look like the same material as hardware store threaded rod) where hollow axles tend to go on nicer bikes. I have bent and broken several hollow axles, and a couple solid ones doing nothing but hitting potholes on old freewheel hubs. They are a poor design, and are far inferior to modern freebody type hubs which I have never destroyed an axle on despite crunching a couple rims and other things.

As for Costco, sure, they sell reasonably good stuff at a reasonably good price. Kmart also sells reasonably durable jeans and sweatpants at a good price (opposed to WalMart who sells sweatpants and jeans made of much thinner fabric, at the same price as Kmart). However, none of these stores sell good bicycles. A lot of what makes a bicycle good is what the shop does to clean them up upon assembly before they sell them to you. While a box store will sell you a crap bike and blame you for the problems, a bike shop cannot survive doing this and thus will usually sell a better product. A $300 Giant from a bike shop will likely do well. A $300 bike from WalMart will likely have far more bells and whistles, but will weigh more, not work as well despite the "improvements", and will fall apart.
A friend of mine last year bought (and then returned) a $300 bike from Walmart. It had disc brakes, a front and rear suspension, a gel seat, and an aluminum frame. After returning that I took her to the local bike shop where she bought a nice Giant model left over from the previous year. It did not have disc brakes, it only had a front suspension, the seat wasn't as soft, and the frame was steel. All in all this bike with less bells and whistles actually stopped faster, rode more comfortably, had what turned out to be a better seat, weighed less, and has stood up just fine to several years of regular use and poor maintenance. In addition the shop owner threw a $15 helmet in with the new bike to get her going.