bike_galpal

so, i've been told that 8 speed freewheels are likely to cause bent and broken axles. is this true? how likely/often is this in reality? is it possible to reduce the risk with say, a stainless steel solid axle?

thanks

Bill Kapaun

I've bent several, but never broken an axle.
Stainless isn't the strongest steel and also can risk galling on the threads.
I don't know if these are "fool proof""
Wheels Manufacturing Hub Axles

I just installed one a couple months back, but haven't had reason to pull the wheel and inspect.
I've also installed a fatter tire to help absorb some of the shocks the entire wheel assembly gets, including the axle.
This is on my "grocery getter" Rockhopper that carries 310 lbs. when I have a heavy grocery load. (solid axle)

JohnDThompson 

The problem with freewheels is that the axle attaches to the frame at some distance from the drive-side hub bearing. This creates a lever arm that flexes the axle with use and can eventually fatigue it and fail. The more cogs you pile onto the freewheel, the greater that distance becomes, and the more leverage is exerted on the axle. That's why you don't find modern hubs with nine or more cogs using freewheels. Instead, they use a "freehub" design with the ratchet mechanism built into the hub. This allows the drove side bearing to be moved outboard and provide better support for the axle.

And BTW, a solid axle doesn't make much difference. I've seen as many solid axles fail as hollow ones. The good news is that bent or broken axles are not catastrophic. I've known people to ride around for weeks or months with broken or bent axles and only realize it when they have to remove the wheel to e.g. fix a flat and the broken axle falls right out of the hub.

CliffordK

I think I'm running 8s on my cargo bike. I may have bent the axle slightly, but restraightened it.

I think there is a bit of a divergence. Campy and other companies worked on making strong hardened hollow axles for years.

Many of the bolt on axles seem to be a lot weaker. Are they even chromoly, or some other hardened alloy? Simple carbon steel?

Anyway, while I occasionally hit a harsh unexpected bump, I'm pretty nimble on my road bike, so I'm considering experimenting with 8s.

Cargo, touring, groceries, etc, would all add maybe 20% or 30% to my weight... or 20% more potential force on that axle.

Bill Kapaun

Not anymore. 10 speed exists.
https://www.jensonusa.com/Sunrace-Multi-Speed-Freewheel
I guess since the width (and same problems) is basically the same as 8 & 9, why not?
Do I hear bids for 11?

gsa103

Cargo is significantly harder on a bike than it's weight indicates, so 20% more cargo, might be twice the impact loads on the wheels.

The rider typically uses his legs to absorb and isolate impacts, while cargo is typically relatively rigidly attached to bike, so it dramatically increases the effective impact forces.

CliffordK

Depending, of course, if the cargo is in a backpack or in panniers. But even so, I exclusively rear-load my bike, so say 20 to 50 pounds (or more) gets directly transferred to the rear wheel.

My heavy hauler (which has the 8s DNP Epoch) does have quite a spongy tire, depending on the pressure I put in it, but can also carry up to 100 lbs on the rear (plus me).

But, lately, I've been more likely to tow than heavily load the bike, except touring. The heavy hauler is still a heavy bike

Andrew R Stewart 

Drive side axle offset to allow wider freewheels isn't the sole consideration for axle durability (with common threaded axle diameters). It's also the difference of dive and non drive side loading. So if the non drive side had the same axle offset then both sides would share the loading equally. It is possible to design a bike around said axle/hub dimensions. But this isn't done almost all the time. Some will approach this by setting up their bike with a 140/145 rear hub spacing (as tandems have used for decades) to help reduce the axle loading differences. Before freehubs were the game serious touring bikes used this method. Andy.

nfmisso

A slight tangent: hollow vs solid: there is very little difference in strength of a tube (hollow) vs a solid. The bending strength of a solid axle is proportional to the diameter raised to the fourth power and inversely proportional to the length. For a hollow axle it is the outer diameter raised to the fourth power minus the inner diameter raise to the fourth power.

Lets look at some numbers:

10mm solid axle, the strength is proportional to 10^4 = 10,000

10mm axle with a 5mm hole through it: 10^4 - 5^4 = 9375

less than 7% difference, which is easily made up be a slight alloy or heat treat change.

Jeff Wills

Woohoo! Numbers!

And for what it's worth: back when I was a bike mechanic (Jurassic period? Cretaceous? So long ago...) I saw many, many broken solid axles. Those were on Schwinn Varsities, so they weren't great material and the bikes were usually abused, so it wasn't uncommon to replace a couple every week. Bikes with QR axles were not as common and treated better, so we didn't replace as many.

dabac

Also, with hollow axles you have the q/r skewer as a back-up, further reducing the consequences of an axle breaking. I'd happily trade those few percent of lost strength for something that'd keep the assembly under compression even if the axle should fail.

79pmooney

Another consideration: the dropouts. If the faces of the right and left dropouts aren't parallel and the slots inline with each other, they will apply a bend to the axle. This bend will cause real levels of stress that will add to the stresses that your (and your bike plus your cargo) weight(s) cause. This is the first place to look if the bike regularly breaks axles.

The good thing is that correcting the dropouts is easy on any steel bike (as long as those dropouts were reasonably correctly located in the first place). Take the bike to any bike shop. They will have a fancy pair of tools that clamp on to each dropout and are used to a) see how close the dropouts are to being parallel and in line and b) serve as levers to bend the dropouts to the best possible compromise. (Usually to perfect as far as hubs are concerned.)

Any bike should have its dropouts checked at least once, if only so you know. (On non steel bikes, correcting may involve other measures. Talk to someone who knows the materials.)

Ben

davidad

The only problem is finding that some of the cassette hubs are nothing more than fancy freewheels. Cassette or Freewheel Hubs by Jobst Brandt

trainman999

Can you simply insert a bearing in place of a spacer at the outside of the freewheel for more support ? Google says you can get one that fits over the axle and inside the freewheel.

Bill Kapaun

Google says WHAT?
Apparently that's 2 of you that have never serviced a FW hub.

fietsbob

and how is the Current Production of Malliard Helicomatic hubs and sprocket clusters, that meet that description
doing these days?.


That last cog # 8 requires the right end of the axle to be even longer than 6/7 speed which was lengthened from 5 speed

show a Picture of the Machine shop you have to make weird custom Parts..



as said... the introduction of the freehub made the freewheel old technology..

the gain made is precisely moving the drive side axle support bearing outboard, very close to the dropout.


You can Buy a Phil Wood freewheel Hub https://www.philwood.com (now relegated to special order ?)

why the lust for that 8th sprocket?








./.

FBinNY 

To put your mind at ease, there is no Danger.

It is true that broken axles are more common with 8s freewheels, but broken axles don't lead to any consequences, and in most cases are not noticed at all by the rider, and only discovered when removing the wheel to change a flat, or diagnosing a strange click or noise coming from it.

When the axle breaks the wheel stays put and turns because the axle is supported either by the nuts at the ends or the QR running though it's center.

Lastly, since the vast majority of axles don't break, this isn't something to fret over, unless this bike is intended for long distance touring in remote areas. Then the remedy isn't to replace the axle, but to carry a spare.

dabac

I've seen that too, in a post years ago on cyclingforums.com.
Someone had found a roller bearing that was a nice fit between axle and f/w. Can't imagine it'd work on f/ws needing a splined puller, but other designs perhaps.

Bill Kapaun

Since the axles bend at the edge of the inside cone, I don't see how additional support on the outside of the lock nut will have any meaningful result.

trainman999

Dabac
Did it work and were there any problems mentioned?
I would think it would work on a splined freewheel you would just need to remove the bearing to remove the freewheel
Bill Kapaun
I am asking about removing the right side axle locknut, removing a spacer that sets inside the freewheel body, and replacing it with a bearing the correct size to take up all the clearance between the axle and the freewheel body then replacing the locknut. The axle will no longer have the clearance to bend at the inside edge of the cone.

dabac

Seems my memory was off a bit, but here's a link to where I saw it:Broken rear axle | Cycling Forums


There used to be thread there with a pic, but the text is clear enough

Retro Grouch 

Where can you buy an 8-speed freewheel today?

andr0id

While bent axles were annoying back in the day, I never knew one to break or cause any danger.

Cassette bodies with bearings near the dropout are an under-appreciated evolution of the freewheel and rear hub.

ThermionicScott 

The same place you buy your 9- and 10-speed freewheels. For reasons I'm still trying to understand, freewheels are the main choice for e-bikes and conversions...

Retro Grouch 

Now see, that's why I don't bet on this kind of stuff. Who ever would have thought?

I test rode an e-boosted fat tire bike yesterday while I was at the bike shop buying shoes. If I had known, I would have checked to see if it had a freewheel or cassette.