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Thru Axle for Heavy Cargo Rear Rack?

Old 01-20-18, 11:31 PM
  #1  
raywood
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Thru Axle for Heavy Cargo Rear Rack?

I have a Trek 7.3. I want to carry heavy loads on back. At present, I have an old aluminum rack that attaches to eyelets. There are stories of heavy weight breaking eyelets (e.g., in a crash, or if the bike falls over, or with enough potholes).

It seemed that I would want a rack that would rest on the axle. This seemed to require a thru axle. At present, I have the stock skewer type axle (see photo).

I'm handy, but I am not a bike mechanic. I guess I would need a thru axle that would extend out past the frame, so that the rack support could rest on it, but not so far as to prevent the clamp from holding the axle in place? Is it easy to replace the axle?
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Old 01-21-18, 02:01 AM
  #2  
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You mean something like this?

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Old 01-21-18, 02:28 AM
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Exactly! But about $200 less expensive.
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Old 01-21-18, 02:33 AM
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Originally Posted by raywood View Post
I have a Trek 7.3. I want to carry heavy loads on back. At present, I have an old aluminum rack that attaches to eyelets. There are stories of heavy weight breaking eyelets (e.g., in a crash, or if the bike falls over, or with enough potholes)......
1. define "heavy" - 20 pounds? 40 pounds? 100 pounds?

2. your bike frame was made with rack and fender eyelets, so
manufacturer would have envisioned carrying a load.

per trek:

This bike has a maximum total weight limit (combined weight of bicycle, rider and cargo) of 136 kg (300 lb).

3. your rack prolly has a weight rating on it. most likely 25kg.
you planning to carry more'n fitty pounds on the rear?

4. unless your rack is total carp (photo please), you should be fine.

5. can you tell us some of these "stories"?

6. instead consider a small front rack to carry part of the load.
better handling and takes some strain off the rear wheel.

Last edited by saddlesores; 01-21-18 at 02:37 AM.
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Old 01-21-18, 02:58 AM
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I appreciate your feedback. I've spent a substantial amount of time researching related matters. I have considered the various possibilities you raise. For my purposes, the questions I've asked are the ones I need information on.
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Old 01-21-18, 03:26 AM
  #6  
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Threaded fasteners should not be loaded in shear, which is what you’re intending to do.
Ignoring everything else, it’ll chew up the threads and/or the eyelets.
In the majority of normally designed and dimensioned fasteners it’s the friction between the flat surfaces being pinched together that carry the load.
A properly designed internal cam q/r will do that just fine.
Replacing the axle is a so-so thing.
Assuming a cup&cone hub, You will need some special tools called cone wrenches. And know how to use them.
And manage to source a replacement axle with the right thread.

Last edited by dabac; 01-21-18 at 03:31 AM.
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Old 01-21-18, 06:21 AM
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raywood, You maybe able to use a tandem length rear quick release and fabricate something similar to the pictured rack. Another option would be to drill and tap into the rear dropout. The rack will need either a modification itself or fabrication of an "adapter".

Brad
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Old 01-21-18, 06:36 AM
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If your particular frame has weak eyelets and you want to continue to use that frame, gerryl proposed the best solution.
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Old 01-21-18, 08:02 AM
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Originally Posted by raywood View Post
Exactly! But about $200 less expensive.
I wouldn't buy it either, way too expensive.
Have a look at Axiom, they have racks that can be skewer mounted.
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Old 01-21-18, 10:55 AM
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(Note: this reply lacks links. I don't have enough reputation to post links here yet.)

Gerryl -- good call re Axiom: e.g., Streamliner Road DLX. But there's still a need for the DIY approach in this case.

Dabac -- I hear you re loading weight on threads. But that's the way the bike already is (see photo): the frame rests on the axle threads. Granted, the threads on a longer thru-axle may be burred beyond redieing, if I remove the rack. But if the weight is largely borne by friction, as you say (and I think you're right), it shouldn't be that bad. In any case, I'll deal with that when/if that day comes.

Re: wrenches: this may be a job for the bike shop. Dreaded words, for a man on a budget, but it doesn't hurt to ask them. I'll report back if I get anything noteworthy there.

Dabac and BradTX -- I was concerned that skewers don't seem to be designed to bear weight. I see, for instance, that BOB trailer skewers bend sometimes (frequently?) from trailer weight/pulling. Some seem to feel that a little skewer bending never hurt anybody. But I think the bending is being arrested by the wheel's aluminum hub. OK if it works, I suppose, but possibly not a great situation from an engineering perspective.

BradTX -- I hadn't thought of drilling and, optionally, tapping my own. It's a possibility. I'd still rather transfer the weight directly from the rack to the axle if possible.

It occurs to me to wonder how they deal with such things on cargo bikes. A search on that leads me back to Old Man Mountain: $70 for a thru axle! At that price, I'll just use Uber.
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Old 01-21-18, 02:27 PM
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Swap the rear axle out for a solid version, they're tandem rated:
https://www.universalcycles.com/shop...ls.php?id=7255

This way you can keep your bike. Thru-axles take a specific style of rear dropout and hub that isn't available for your bike. As for what rack to use, BTFOM, the dropouts you have are good for 70lbs easy, why bother?

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Old 01-21-18, 04:15 PM
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Originally Posted by raywood View Post
...
It occurs to me to wonder how they deal with such things on cargo bikes. A search on that leads me back to Old Man Mountain: $70 for a thru axle! At that price, I'll just use Uber.
My expedition bike uses M6 rack bolts, virtually all other bikes use M5 rack bolts. The manufacturer of that bike frame rates their heavy duty rack at 60kg with M6 bolts or 40kg with M5 bolts.

In other words, for most bikes that carry heavy loads, the limiting factor is the rack bolts, not the axle. My expedition bike uses a Rohloff with the standard 135mm rear hub spacing and hollow axle for skewer.

You mentioned that you were concerned about weak eyelets, but I think you will find that most bikes designed for heavy duty use have really good rack mounting points.

I know a guy that is worried about his rack bolts shearing on one of his bikes. For that reason, he has installed his rear rack bolts from the inside side of each dropout, then attaches his rack to the bike with nuts on those bolts. He does it that way so if a bolt shears off, he can extract the part of the bolt in his dropout with his multi-tool and easily install a new bolt.
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Old 01-21-18, 09:26 PM
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Originally Posted by Tourist in MSN View Post
I know a guy that is worried about his rack bolts shearing on one of his bikes. For that reason, he has installed his rear rack bolts from the inside side of each dropout, then attaches his rack to the bike with nuts on those bolts. He does it that way so if a bolt shears off, he can extract the part of the bolt in his dropout with his multi-tool and easily install a new bolt.
That is a very good idea!
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Old 01-22-18, 01:46 PM
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Mr IGH -- that Universal Cycles link is a good one. I found they also carry the hub on my wheel. It's not the stock Trek -- it's a Shimano Deore FH-T610.

Tourist in MSN -- yeah, that is a clever solution. If I can't make the axle-mounting work, I may do that too.

All -- thanks for your responses. I've started another thread (Wide Load to Establish Road Presence?) that explains the reason for my interest in axle-mounting. Sheer weight is part of it. The other part is leverage. I'm contemplating a wide load, supported by angle iron, for reasons of safety.

In response to a structure-oriented comment in that other thread, here are some design considerations for the ideal porteur rack, sufficient to accommodate the crates: (1) Bolt the two plastic crates together, so that they can be detached and carried as a single unit. They could be too heavy if filled with e.g., liquids, but that’s what the hiking backpack (strapped on top) is for: move contents from crates to the backpack, and then carry the empty crates onto the bus, so that the bike can now fit into the rack on front of the bus for crossing big cities. (2) Arrange the rack so that it can accommodate the crates aligned either crossways or downstream -- the latter being useful for circumstances where the wide crates would not allow passage into e.g., a bike trail, where they have those posts or gates that prevent motorcycles and other vehicles from entering. (3) Design supports so that nothing protrudes from the bike or the underside of the crates, so as to interfere with loading onto the bus (see (1), above).

Last edited by raywood; 02-17-18 at 08:27 PM.
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Old 01-22-18, 02:08 PM
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Old man mountain makes racks to be used with through axles, I'm sure they would have something for you.
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Old 01-22-18, 07:22 PM
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Originally Posted by raywood View Post
... my interest in axle-mounting. Sheer weight is part of it.....
How much weight are you talking about?
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Old 01-22-18, 11:07 PM
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You have a bike not designed for thru-axles and mounting to QR skewers isn't a great idea. The bike in question might be cheap but it is still designed to hold a rack and so long as you aren't overloading things you will be fine. If you are truly worried you might look at Tout Terrain who make touring and commuting bikes some of which have integrated racks (welded or brazed to the bike) there are also plenty of custom builders who could do the same.

Relax and go ride your bike, mount the rack as it was intended and you shall be ok. Don't carry gallons of lead paint with you and you will be fine : )
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Old 03-18-18, 02:13 PM
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I worked up the rack I was thinking about, without a through axle. It appeared that a through axle might have helped, but was not necessarily the best solution by itself. (Details)
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Old 03-20-18, 10:34 AM
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If that top picture is yours, You don't have a through axle bike, are you thinking of buying one?
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Old 03-20-18, 12:31 PM
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Thought about a trailer or cargo bike for your weight needs?
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Old 03-21-18, 07:47 AM
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I have indeed thought about that.
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Old 03-22-18, 07:21 AM
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Originally Posted by fietsbob View Post
If that top picture is yours, You don't have a through axle bike, are you thinking of buying one?
After having a look at his blog, it seems the OP is using different 'through axle' terminology.
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Old 03-22-18, 12:20 PM
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Am I? I thought a through axle was a solid rod in place of a skewer.
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Old 03-22-18, 01:03 PM
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Originally Posted by raywood View Post
Am I? I thought a through axle was a solid rod in place of a skewer.
I'm not totally clear on all the terminology, but I believe 'through axles' came over from mountain biking. They are thicker and stronger, and screw directly into threads in the dropout.

I think you're referring to what's known as a solid or bolt on axle.
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Old 03-22-18, 01:52 PM
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This StackExchange discussion says there's just solid through axles and slender skewers. Through (or "thru") axles have threads, but that's for the nuts on each end. I think I've seen screw-on quick releases in lieu of the usual wrench-tightened nuts, but I haven't figured out where to buy them.

I found out I can get a through axle that will fit in my skewer hub, but it's $20-25 and then there's another $20 for the bike shop to replace it.
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