bcubed

I recently moved the rear dropouts back ~4cm by use of 3/16" steel stock. everything has worked fine (850 mi so far), but the recurring problem I've had with this (and all freewheel bikes) is that I always wind up having to replace a bent rear axle.

Considering this, and that the rear wheel is no longer "quick-release," regardless of skewer, I wanted to rebuild the hub w/ a STRONG axle. To my knowledge, metric 10.9 grade steel is the best commercially available, and similar to SAE grade 8.

Does anyone make such an axle, in MTB lengths? If no, would a competent machine shop be able to fabricate me one if I specified length, dia, and thread pitch?

AndrewP

Get a new wheel with a freehub, or go on a diet till you have lost 50 pounds. If you have an axle built, make sure it has rolled threads.

operator

Get a cassette wheel.

There's nothing you can do to change a weak design.

DannoXYZ 

Without increasing the diameter of the rear-axle, there's not much you can do to increase strength. Using different materials in the same diameter would work. Try boron or beryllium.

joejack951

Slightly off topic, but a comment on the original post, metric grade 14.9 is the strongest commercially available fastener. 12.9 is much easier to find though. But M10 x 1, which is the axle size you'd need, is not a common fastener size.

I agree with those who have suggested a freehub wheel.

TallRider

It's also worth noting that to my knowledge, solid axles are not meaningfully stronger against bending than hollow (quick-release) axles. This is because the stiffness from a rod comes mainly from the material toward the outer edges of that rod.
Also, solid axles tend to be made for lower-quality bikes, and the average solid axle is probably more prone to bending than the average quick-release axle.
That said, a solid axle should be very slightly less prone to bending than a hollow axle made of the exact same quality material.

But as mentioned above, the main issue is the design. Diameter of the axle is one factor, as DannoXYZ mentioned, and the fact that there's exposed axle hanging out between the drive-side bearings and the drive-side dropout is a big problem that cassette hubs don't have, as operator pointed out.

I used to have a 5-speed freewheel on my commuting bike and still had to replace the axle periodically, so I ended up building a wheel with a 7-speed cassette hub specifically for that bike, and put the 5-speed freewheel rear wheel on a bike I built up for a friend who ways a lot less than I do. For the record, I weigh 185#.

Jeff Wills

A couple comments: if you're consistently bending rear axles, you should check to see if the dropouts are aligned correctly. Park Tool shows how: https://parktool.com/repair/readhowto.asp?id=40 . If they're OK, Phil Wood hubs have very large axles: https://www.philwood.com/, and they're probably cheaper than having an axle machined for you.

jgedwa

Not an answer to your question, but I am not sure what you are describing here. Just curious, but how and why did you modify your bike this way?

jim

TallRider

Yeah, but for the price of a Phil Wood hub, not to mention the effort of building a wheel around one even if it were free, you may as well just update to a cassette hub which will never bend axles.

Similarly, it's probably not worth the cost of having a special axle machined from Boron or whatever, either.

DannoXYZ 

You're right, the rigidity of a tube is related to the 4th power of diameter. Increasing the diameter by just 10% will increase its rigidity by 46%.

Well, some people just want to do things a "certain way". So here's what it would be to custom-make a solid beryllium axle:

$250-300 AMS7906 beryllium bar-stock 20x150mm
$250/hr prototyping time, estimated 1.5-2.0
$250/hr machining time, minimum 2.0 including set-up
$300 diamond-tipped tools and non-sulfur/non-chlorinated coolant
----------------
$1050-1300 TOTAL

In the end, you'll end up with large-diameter axle that's 8x more rigid in cantilever bending and 4x higher yield-strength at about the same weight as a normal steel axle. I've got a design in my head with a 20mm section to the right of the cone to be as strong as possible. My machine's ready to go. Just need 80% deposit to order materials & tools and we're off and running:



BTW - $200 discount if you've got SolidworksPlus file of the design.

LarDasse74

+1.

I read some time ago that axles only bend when the dropouts are misaligned.

I think that is BS, or else every freewheel equipped bike I have ever ridden had misaligned dropouts (they probably did after I was through riding them). However, if you bend your axle then your dropouts have become misaligned - although the dropouts are most likely twisted by the axle, not the other way around. But if you follow the smartass advice and 'lose 50 lbs' and put in a new axle and your dropouts are still tweaked, I'll bet you $1 that the replacement axle will bend faster than the original.

The solution: Build a freehub hub wheel for your bike and your problem is solved.

LarDasse74

+1

Modifying your frame to suit the way you want to use it is cool!

bcubed

TY for asking! Basically, I'd had a '96 Trek 1100 that I'd bought as a "sport-tourer," then modded a bit for one season of noob racing, that I recently elected to modify into a commuter. The 700X32, flat-resistant Michelin Citys I spec'd were too wide to clear the rear chainstays, so I took a piece of 3/16" steel stock, a little drilling and an angle grinder, and voila! the new dropouts were back far enough to let the tire clear the 'stays.

Currently I'm running w/o paint until the bolts corrode securely into place on the steel...safety first, after all!

I just figured solid would be better from my experience with rivets vs. pop rivets...plus, I figure having wheels that don't remove w/o tools would be beneficial for an "urban assault bicycle" (remember Stripes, anyone?)

LarDasse74

Hollow axles are plenty strong.

If I am locking my bike up regularily I use steel hose clamps to keep my wheels from getting took.

Some theives might be equipped with an adjustable wrench when they approach your bike, but I bet almost nobody wants to fiddle with a rusty hose clamp to steal a wheel. Imagine a theif approaches your bike and the rear and is all frankensteined out with rusty steel plates and hose clamps? Theft proof!

bcubed

C'mon, now...you gotta realize a few cm of bailing wire'll get the job done at a weight savings of at LEAST 5-10gm...GEEZ

J/K, sounds like a really good setup.