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Machining axles - steel grade?

Old 09-23-22, 05:21 PM
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Machining axles - steel grade?

All,

I am looking in to machining some custom axles for a bike trailer. The long and short of it is I robbed the wheels/axles off an old kid trailer and they are 16". I can't easily find tires for that wheel size that will take high pressure (50+ psi). There are some odd-ball tires out there, but the other issue becomes the strength of the rim. So to alleviate all the nuances - I am going to upgrade to a 20" wheel set with traditional cone and race hubs (specifically front wheel hubs with disk brake mounts).

Therein lies the project. I need to make a stub axle that will allow a cone and race hub to mount to it.

The machining isn't an issue. I have access to every conventional type of machine under the sun.

The question is what to machine the axles out of.

There are likely 2 parts - the "axles" themselves and the "cones". I quote those because I don't think I want to use traditional off-the-shelf cones. There only needs to be threads on the outside. The inside can have a press-on cone that bottoms out. The cones need to withstand the pressure and abrasion of the bearing balls and the axle needs to be strong.

Why I don't think I can use off-the-shelf cones is I want to maximize the axle diameter. The limiting factor is the cone races - that there is enough material to engage the balls. What that allowable diameter ends up being I am not sure - maybe 13-14mm? I'll figure it out. I just don't think I can find a cone for over a 12mm axle. The other conundrum is there aren't press-on cones - they are threaded for conventional threaded axles.

Thoughts?
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Old 09-23-22, 05:50 PM
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Is there really any need for axles larger than the standard 10mm used for most rear hubs? They support a lot of very heavy riders with no strength problems. You could machine out the threads of an inner cone and make it a press fit on the inner race and use conventional M10x1.0 threaded cones for the outer race. Unless your trailer is going to be tremendously heavily loaded I don't see the need for an oversize axle.
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Old 09-23-22, 06:28 PM
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A few comments-

Stub axles see far higher bending forces than axles supported at both ends, way higher.
Do make sure the increased trailer height (with the 4" larger diameter tires changing the hitch geometry) won't change how the handling works.
Consider sourcing wheel chair hubs, hubs from already made trailers or jogging strollers.
Consider making your own hubs with cartridge bearings.
How much load does the trailer carry? You mention the strength of the rims as being a problem? What width tires are you using?

Traditional bike parts have only so much strength/capacity/application ease all driven by the profit wanted nature of business. When one uses them in different ways than intended, all kinds of issues can develop. Andy
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Old 09-23-22, 06:30 PM
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4140 PHT (pre heat treated) is a good choice for axles.
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Old 09-23-22, 06:38 PM
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Originally Posted by Charles Lathe View Post
4140 PHT (pre heat treated) is a good choice for axles.
And with a last name like you have we should heed your machining advise Andy
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Old 09-23-22, 06:39 PM
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I have a design in mind for a custom trailer. I was on tour the fall of '20 and ran in to a fellow cycle traveler that was pulling a custom trailer. He made his with an external frame rail that allowed him to use conventional bike hubs where they are supported on each end (thru axle). That is one major design upgrade I am going to incorporate in to my new design. However, that is a larger project down the road.

Until then, one of the big challenges I have is rolling resistance. In order to overcome that I need higher pressure tires. to go to higher pressure tires I need to upgrade to 20" wheels. In order to get a 20" wheel set to fit the trailer frame I have now and be an improvement over what I am running, with the possibility of using them on the new trailer - I need to mount a conventional cone + race hub to the trailer frame.

no matter how I get there - the issue I run in to is there isn't an axle out there that I would trust in the application.

I am not concerned with the weight of the axle/hardware. That is a very small price to pay.

So to answer the question of making an over-size axle and needing one for weight - if I am making a custom axle for the application a few more ounces weight for an over-size axle won't matter so I might as well make a burly axle.

I could get a 20" rim and re-use the current hubs and axles. But they are cheap and I want something stronger that will hold up over some harder miles. Around town is one thing, but I have some tour ideas down the road I want to have something I can trust on a trip away from home also. If I break spokes or split a hub I can likely still get home here. If I'm 3-4 days out that is a tour end'er. Plus if I have some more conventional bike parts I can have a better chance at getting a replacement at a bike shop on a trip (another major reason for going to a 20" wheel set).
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Old 09-23-22, 06:42 PM
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Originally Posted by Charles Lathe View Post
4140 PHT (pre heat treated) is a good choice for axles.
We were talking chromoly at the shop today, so this is in-line with that. I'll check it out more.
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Old 09-23-22, 06:53 PM
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Originally Posted by KC8QVO View Post
I have a design in mind for a custom trailer. I was on tour the fall of '20 and ran in to a fellow cycle traveler that was pulling a custom trailer. He made his with an external frame rail that allowed him to use conventional bike hubs where they are supported on each end (thru axle). That is one major design upgrade I am going to incorporate in to my new design. However, that is a larger project down the road.

Until then, one of the big challenges I have is rolling resistance. In order to overcome that I need higher pressure tires. to go to higher pressure tires I need to upgrade to 20" wheels. In order to get a 20" wheel set to fit the trailer frame I have now and be an improvement over what I am running, with the possibility of using them on the new trailer - I need to mount a conventional cone + race hub to the trailer frame.

no matter how I get there - the issue I run in to is there isn't an axle out there that I would trust in the application.

I am not concerned with the weight of the axle/hardware. That is a very small price to pay.

So to answer the question of making an over-size axle and needing one for weight - if I am making a custom axle for the application a few more ounces weight for an over-size axle won't matter so I might as well make a burly axle.

I could get a 20" rim and re-use the current hubs and axles. But they are cheap and I want something stronger that will hold up over some harder miles. Around town is one thing, but I have some tour ideas down the road I want to have something I can trust on a trip away from home also. If I break spokes or split a hub I can likely still get home here. If I'm 3-4 days out that is a tour end'er. Plus if I have some more conventional bike parts I can have a better chance at getting a replacement at a bike shop on a trip (another major reason for going to a 20" wheel set).
I was going to ramble on in a prior post about hub and trailer frame design. Specifically on the Burley D'Lite enwrapping frame around the hub aspect. Besides being able to use conventional bike ft hubs the added frame members add an amount of strength/stiffness to the overall design. Do know there are drawbacks to this design like weight and added overall width. I sold a lot of these trailers (when they were still USA made) and many others with stub axle designs. The D"Lite design made for a more solid trailer that had less wheel slop. Andy
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Old 09-23-22, 06:57 PM
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Have you looked at drilling out the inside cone of a conventional axle to press onto your oversize cantilever axle? If that can be cone and leave enough material under the races, that would be a fairly simple approach. And the dust caps would fit. Do you have the machining equipment and skill to drill a tapered hole and matching machining on the axle to maximize the diameter inboard?.
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Old 09-23-22, 07:03 PM
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Originally Posted by Andrew R Stewart View Post
I was going to ramble on in a prior post about hub and trailer frame design. Specifically on the Burley D'Lite enwrapping frame around the hub aspect. Besides being able to use conventional bike ft hubs the added frame members add an amount of strength/stiffness to the overall design. Do know there are drawbacks to this design like weight and added overall width. I sold a lot of these trailers (when they were still USA made) and many others with stub axle designs. The D"Lite design made for a more solid trailer that had less wheel slop. Andy
Cantilever axles are used in many non-bicycle applications and come out plenty stiff. Cars, trucks, airplanes, and as mentioned before, wheel chairs ... Certainly can be done.
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Old 09-23-22, 07:15 PM
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If you use 4130 or 4140, both commonly available as machining bar stock, you'll have more than you need. You can heat treat these at home to RC45-50 or so (no not go harder than 50) or so and be good to go. (plenty of info for DIY heat treating both these alloys).

For maximum strength, machining below nominal and rolling threads is preferable, but cut threads are fine in this application. Depending on the specific design, odds are you can get by with a boron or manganese grade, or if you want to go RollsRoyce you can use a triple alloy like 8620 to build a super tough axle.

If you can find a non threaded cone, or grind one open, you can build a stronger part by modelling in more like a pedal spindle to eliminate the stress riser at the point of maximum moment.
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Old 09-23-22, 08:11 PM
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Originally Posted by 79pmooney View Post
Have you looked at drilling out the inside cone of a conventional axle to press onto your oversize cantilever axle? If that can be cone and leave enough material under the races, that would be a fairly simple approach. And the dust caps would fit. Do you have the machining equipment and skill to drill a tapered hole and matching machining on the axle to maximize the diameter inboard?.
I didn't really think about drilling out/machining out the threads on a conventional cone. That is an idea.

However, it might be a moot point - if I go with a larger diameter axle that a conventional cone would be too small for I would have to machine one for the outside anyway. I suppose there is a chance I could machine the inside of conventional cones then re-thread the turned inside face.

I'll have to think through the threading - the two manual (one is CNC but can be run manually also) lathes won't cut metric threads. We have an enclosed CNC lathe also that will do anything, but the set up time on it is a giant turn off. Unless we were running production where the set up is spread out over a week or two run it doesn't make much sense. I may just settle for standard threads so it can run on the other lathes. We can thread on mills also - with a mill cutting the threads, not a die or tap. I am not sure if we can get a small enough mill to do internal threads, though. If we can that would be the way to do it with what we have for a few custom (non-production) parts.

I realize forming threads (as opposed to cutting threads), in formable material, are stronger. But I don't think its worth trying to do that. That process would require forming taps and dies. I don't believe we have any metric, and not many even in the 1/2"/13mm range or larger. I will check...

As for tapered holes - that's easy. No problem. I had already had that as a design idea for the interior cone - so it self-tightens without the need for a jam nut etc.
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Old 09-23-22, 08:57 PM
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Originally Posted by KC8QVO View Post
I didn't really think about drilling out/machining out the threads on a conventional cone. That is an idea.

However, it might be a moot point - if I go with a larger diameter axle that a conventional cone would be too small for I would have to machine one for the outside anyway. I suppose there is a chance I could machine the inside of conventional cones then re-thread the turned inside face.

I'll have to think through the threading - the two manual (one is CNC but can be run manually also) lathes won't cut metric threads. We have an enclosed CNC lathe also that will do anything, but the set up time on it is a giant turn off. Unless we were running production where the set up is spread out over a week or two run it doesn't make much sense. I may just settle for standard threads so it can run on the other lathes. We can thread on mills also - with a mill cutting the threads, not a die or tap. I am not sure if we can get a small enough mill to do internal threads, though. If we can that would be the way to do it with what we have for a few custom (non-production) parts.

I realize forming threads (as opposed to cutting threads), in formable material, are stronger. But I don't think its worth trying to do that. That process would require forming taps and dies. I don't believe we have any metric, and not many even in the 1/2"/13mm range or larger. I will check...

As for tapered holes - that's easy. No problem. I had already had that as a design idea for the interior cone - so it self-tightens without the need for a jam nut etc.
I was thinking the outer cone would be left as is and you would taper the axle down to it's diameter and threading. That the inner cone would be pressed on or perhaps slip fit with epoxy. With no threads on the inside cone a) you can machine out a larger hole without stress risers and b) leave the axle larger diameter and also without stress risers, never mind both being far easier to make.

Edit: and yes, like FB I was envisioning a pedal spindle-like axle. (Spindles spin withing fixed enclosures. Axles hold spinning parts. So pedal spindles are axles.)

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Old 09-23-22, 09:52 PM
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If you want to go oversized, then go with something like a 3/4" or 19mm through axle.

There are also "Lefty" hubs designed for just about what you're doing.

Chromoly (4130 or 4140) would be fine. But, at 3/4" you'd probably also be OK using a Grade 8 or grade 10.9 bolt.

There are a number of different axle materials you can work with. A while ago I encountered Stress Proof Steel being used for drive shafts.
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Old 09-24-22, 02:09 AM
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Just throwing this out there,
If you are going to use 20" wheels and you want durability, look for a set of front 20" Mag rims (5 spoke type) with sealed bearings.
Should take a good load and virtually no spoke breakage problems, should be pretty easy to find an spindle axle to fit the sealed bearing
https://www.bikepartsusa.com/Product-...in-Z-Mags-prk/
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Old 09-24-22, 08:01 AM
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Originally Posted by 79pmooney View Post
Cantilever axles are used in many non-bicycle applications and come out plenty stiff. Cars, trucks, airplanes, and as mentioned before, wheel chairs ... Certainly can be done.
The point I was thinking of, but didn't yet fully describe, is that the stub axle's diameter at the inner bearing will be quite limited by the ID size that bearing can have. By converting a conventional dual sided hub (typical ft) the inner bearing still has a pretty small ID. I think you will find that pretty much all stub axle hubs, when designed as such from the start, use a tapering axle diameter. Big next to the frame/fork and smaller at the outer bearing, as has been said like better pedal axles are. How much bigger is enough and will that fit the conventional dual sided hub, without modding the hub shell, are the real questions IMO. While the OP says he has access to a fully capable shop to mod an existing hub a little bit is not too far less than just making a hub that has optimal design and not a cobbled up result. Andy
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Old 09-24-22, 08:09 AM
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Originally Posted by JoeTBM View Post
Just throwing this out there,
If you are going to use 20" wheels and you want durability, look for a set of front 20" Mag rims (5 spoke type) with sealed bearings.
Should take a good load and virtually no spoke breakage problems, should be pretty easy to find an spindle axle to fit the sealed bearing
Thanks for the thought. However, I prefer traditional laced wheels.

My comment about spokes breaking earlier was in respect to the original wheels. They are cheap construction. I already replaced the bearings in them. They are sealed cartridge style. The new bearings have been holding up fantastic. I really didn't trust the originals - they had too much slop and the first few times I ran the trailer after assembling I lost trust in them pretty quick. I was convinced the bearings were loosening up every time I ran the trailer. The new bearings aren't that way - they were still pretty cheap bearings, but have proven to be much better to where I don't worry about them at all - though I have the old ones still as spares if I need a quick fix. That gets back to the spokes - as well as the rim and hubs - they are cheap and I can see them failing down the road, more so than the new bearings.

With a cone and race hub I can tension the bearing and completely disassemble and inspect. With cartridge bearings all you can do is replace the cartridges.

I don't get to lace wheels often, either, so I am looking forward to building these.
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Old 09-24-22, 08:23 AM
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Originally Posted by Andrew R Stewart View Post
The point I was thinking of, but didn't yet fully describe, is that the stub axle's diameter at the inner bearing will be quite limited by the ID size that bearing can have. By converting a conventional dual sided hub (typical ft) the inner bearing still has a pretty small ID. I think you will find that pretty much all stub axle hubs, when designed as such from the start, use a tapering axle diameter. Big next to the frame/fork and smaller at the outer bearing, as has been said like better pedal axles are. How much bigger is enough and will that fit the conventional dual sided hub, without modding the hub shell, are the real questions IMO. While the OP says he has access to a fully capable shop to mod an existing hub a little bit is not too far less than just making a hub that has optimal design and not a cobbled up result. Andy
I understand the point. One of the guys at the shop is building a 3 wheel kit car and was using axles on it as a discussion point yesterday for how the bearings on it work - they are tapered roller bearings.

That brought up the hub design on what I am trying to go after, also.

What I am trying to do is use as many standard components as I can for the sake of ability to replace down the road, if necessary.

With respect to the axles - in my design here - the axles can't be off-the-shelf axles. So the only option I have is to make more than I need so I have spares on-hand already. If I work through those in a couple years its possible to make more, but if I am tooling up to make a couple why not make 4?

However, with the trailer design changing in the future - the likelihood of needing the spare axles or making more beyond that is not very high.

That gets to the hub design. Down the road the trailer design I have is to have a hub supported on both sides with an outer rail. That will allow the use of a conventional axle and cone set.

All of this gets right back to the idea of using as many "standard" components as I can. If I machine a custom hub set that allows for a tapered shaft (larger race diameter for the inside facing part of the hub) then when I go to the new trailer design I would have to go to a standard hub anyway. I don't think the effort to machine a new custom hub set is worth the work and expense just for a temporary solution while I am still using the trailer I am using when that is going to change.

That gets right back to the axle question - the limiting factor on the axle diameter is how far I can go in to the cone internal hole diameter while still giving enough race face for the balls to roll on. That hasn't been determined yet. I think the answer to that lies in how thin of the race material I can have that will support the load of the bearing balls. Then I can bring up the shaft diameter to meet the thickness of the cone.

Another idea with the cone diameter question is the bearing ball size. If I scale down the size of the balls that allows the diameter of the parts inside to expand. That might be the trick.

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Old 09-25-22, 09:50 PM
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Originally Posted by KC8QVO View Post
All of this gets right back to the idea of using as many "standard" components as I can. If I machine a custom hub set that allows for a tapered shaft (larger race diameter for the inside facing part of the hub) then when I go to the new trailer design I would have to go to a standard hub anyway. I don't think the effort to machine a new custom hub set is worth the work and expense just for a temporary solution while I am still using the trailer I am using when that is going to change.
I wonder why no one has pointed you at the hubs used on recumbent trikes. These are cantilever design with axle diameters and bearing sizes appropriate for single-sided support. As a bonus you can get them with drum brakes or fittings for disk brakes. You can buy prebuilt wheels, too: Utah Trikes Catalog - Front Wheels - Trikes, Upgrades & Accessories
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Old 09-27-22, 05:06 AM
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Originally Posted by Jeff Wills View Post
I wonder why no one has pointed you at the hubs used on recumbent trikes. These are cantilever design with axle diameters and bearing sizes appropriate for single-sided support. As a bonus you can get them with drum brakes or fittings for disk brakes. You can buy prebuilt wheels, too: Utah Trikes Catalog - Front Wheels - Trikes, Upgrades & Accessories
Interesting thought.

The ones I see there appear to be sealed cartridge style bearings, not cone and race.

The advantage to cone and race is those parts are ubiquitous in the cycling world - you can find parts easy just about anywhere. The catch is the custom axle + cones etc, though. If I had a couple spares then that wouldn't be much of an issue - but that goes right back to what I said earlier about going to a trailer design that has the external rail to support a conventional axle - by going that route then all the components could be standard cycling parts including the cones, jam nuts, and axles.
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Old 09-27-22, 06:43 AM
  #21  
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Originally Posted by Andrew R Stewart View Post
I was going to ramble on in a prior post about hub and trailer frame design. Specifically on the Burley D'Lite enwrapping frame around the hub aspect. Besides being able to use conventional bike ft hubs the added frame members add an amount of strength/stiffness to the overall design. Do know there are drawbacks to this design like weight and added overall width. I sold a lot of these trailers (when they were still USA made) and many others with stub axle designs. The D"Lite design made for a more solid trailer that had less wheel slop. Andy
Yep, I like the Burley trailers, and other trailers with wrap around frames. I feel they are more stable and can take heavier loads. And if I manage to run into something, I'd rather the frame hit rather than a marginally supported wheel.

Note, by default, Burley tended to dish their wheels to give wider support for the trailer.

This thread is jumping around a bit. The concept that ball and cone bearings are more readily available than sealed bearings is only true if one is using off the shelf components.

If you have custom made components in a small fab shop, then any replacement parts would have to also be custom made.

Some sealed bearings may be off the shelf items and relatively easy to acquire. They should be fairly long life, but one could also pack spares.

Thinking of unique hub shells, you might look at the ubiquitous coaster brakes commonly found with 16" and 20" rear wheels. It has been a while since I've taken one apart, but I think they have fairly large outer races that you could make custom cones and axles to match. Or build in a method to insert sealed bearings.
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Old 09-27-22, 06:52 AM
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One thing you might consider for trailer tires might be the Tannus airless tires.

https://tannusamerica.com/pages/tannus-airless-tires

At least I've thought about trying them out on a trailer. One less thing to worry about, trailer flats.

For some tires they have different pressure equivalent ratings, but not necessarily on the smaller tires.

They may increase weight slightly and rolling resistance slightly. But it may give you peace of mind.
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Old 09-27-22, 04:18 PM
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The Op mentions having a "split hub" while on a tour, breaking spokes and seems to be concerned about a bearing failure that will stop function and finding replacements. I've commented on design a bit but here's my opinions on the 'while on a tour' stuff.

Very few hubs fail compared to other wheel aspects. Very few. Flange life is generally really a long time as long as radial spoking is avoided. Hub splits or cracks in AL shells are way down the list of likely issues. Axle break or bending far more common, generally only found on rear hubs with significant bearing location off sets (dishing, from a rim's view). Bearing degradation is usually a slow process, lack of periodic maintenance helps speed up this process as does extreme exposure (water, grit). I have found that most all claims of bearing failure being sudden are because the rider didn't pay attention and take care of the gradual wear and tear with maintenance (cleaning, relubing the bearings if not replaced and good preload adjustments). The rider only notices the bearing when it is so bad that the performance is affected to a significant degree. I often describe this to getting a cancer diagnosis. The cancer has been there for a while and only after growing big enough will the rider notice.

Now when we talk about on the road repairs of bearings (independent of why) we need to look at availability of parts and ability to do the work. Cup and cone bearings are not widely available in many areas, pretty much the only stores that deal with them are bike shops. Premanufactured cartridge bearings , on the other hand, are widely distributed via a large number of different industries and can be found in car/motorcycle repair joints as an example. These bearings are generally made to many industry wide dimensional standards and have a huge supply chain presence. The math favors being able to source a cartridge bearing over a cup and cone. Installing cartridge bearings is a job that way many people do in a variety of jobs. Cup and cone replacement and readjusting of preload wants the proper cone wrenches. With so few bike shops dotting the roadsides in most countries this means the rider is now also carrying cone wrenches along with the bearing spares. The big reason why the bike world still uses cup and cone bearings is because of manufacturing tolerances being able to worse. So a hub will work well on a frame that wasn't well built, cup and cone tolerate misalignments better than cartridge units do.

Spoke breakage has nothing to do with hub bearing design although is a problem for those who don't stay on top of their equipment. I've carried spare spokes on all my tours, of any real distance, yet I have never needed one after 10,000+ miles of loaded tours over 40+ years. Not to say that one won't need spokes or that carrying spares in not a good idea,, just that well taken care of bikes generally don't suffer fatigue spoke breakage until after a lot of miles.

I don't think any of this will change what the OP does though. We tend to have tunnel vision as we do stuff. Andy
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Old 09-27-22, 06:25 PM
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Generally "puncture-proof" tyres pay a heavy price in terms of weight, poor suspension, poor grip and rapid wear. Puncture-resistant tyres like the Schwalbe Marathon series are a lot better, but I'd rather deal with an occasional depressurisation event and use lighter more free-rolling tyres.
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Old 09-29-22, 09:41 PM
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FWIW, I used 12mm off the shelf engine studs for cantilever axles in my homemade trailer (wheelchair hubs with cartridge bearings and self-locking nuts) and they never bent, even loaded with 60+kg.
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