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Are universal pedal axles weaker than standard axles? If so, should they be avoided?

These are inexpensive pedals so let's focus on inexpensive normal, solid axles vs these universal pedals.

enter image description here

Each pedal comes with a 1/2 inch and a 9/16 inch adapter that must be screwed into the pedal body.

The left pedal adapter threads in with a left hand thread, the right pedal adapter threads in with a right hand thread.

Edit 4/10/2020

Would they be strong enough for any of the following applications?

Could these pedals be strong enough for some applications not displayed below?

The following bikes were chosen because they come from bike shops with roughly comparable inexpensive plastic pedals.

All the bikes are Trek because it was easy to find a wide variety of Trek bicycles. This is not meant as an endorsement of Trek.

Option 1: Trek Tag Along enter image description here

Option 2: Trek cruiser
enter image description here

Option 3: Trek children's bike
enter image description here

Option 4: Trek 24 inch wheel bike
enter image description here

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    A good quality pedal axle goes through the pedal from side to side The ones shown here carry the rider's weight on half a dozen threads. They may be good for an emergency replacement in a poorly furnished workshop when nothing better is at hand but certainly not for day to day riding. – Carel Apr 9 at 19:10
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    @Carel Technically the pedal is attached to the crank arm with a half dozen threads, so I'm not sure I see that as a big downside assuming the threads are sufficiently tight and the metal is of good quality. – Kibbee Apr 9 at 20:06
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    Definitely not a strong as solid axles. Why use these if you can get normal pedals with the correct thread? – Argenti Apparatus Apr 9 at 21:14
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    Fascinating that this maker has decided providing four extra parts, and performing 8 threading operations is overall cheaper than making two separate axle threads and carrying two different SKUs through their inventory/supply chain. – Criggie♦ Apr 10 at 0:28
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    I can't understand what problem they solve. If one needs 9/16 pedals, get those, if its 1/2" then get those. Who's swapping pedals between adult bikes and kids' bikes? – Swifty Apr 10 at 9:33
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In context of the low cost pedals, you need to look at the user and how they ride. Would I trust them on a trials bike or downhill MTB?, no, but then I would not trust a cheap pedals with a one piece axle. Would I trust them in a situation I would trust a similar pair of cheap one piece axles, absolutely.

In theory the two piece axle will be less reliable as it has another failure mode that does not exist on a one piece axle. However, the failure of the extra threaded join is probably much less likely than the pedal to crank join, due the thread locker. Therefore, the increased risk is marginal.

So the question is not 'should they be avoided because they have a two piece axle", its "Should cheap pedals be avoided"

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  • Exactly. Especially since all but the last image in the question show bikes where the cheapest possible pedal will work like a charm. Absolutely no point in using high-end pedals on a child's bike! – cmaster - reinstate monica Apr 10 at 18:20
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It is an interesting concept I haven't seen before. In theory they should be as strong as a solid axle. I have never seen a pedal axle break. In any type of collision, the crank arm usually breaks before the pedal shaft. The thread-lock on the adapters is a good sign that some thought went into the design. However using two fasteners instead of one doubles the odds of something coming loose. I imagine they would be more expensive than a single size pedal as they require extra machining, but could be useful if you were unsure what size to order.

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    re: 'In theory they should be as strong as a solid axle'. I respectfully disagree with that – Argenti Apparatus Apr 9 at 21:12
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    "In theory they should be as strong as a solid axle" yeah not even close, not in theory nor in practice. – whatsisname Apr 9 at 22:23
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    The neck of the small threading in the adapter piece will be the weak point. It is submitted to shearing forces and to stretching from being tightened. – Carel Apr 10 at 6:53
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    @Carel The pedal will also distort under load around the smaller threads making those forces even worse, something that doesn't happen for a solid-axle pedal. So that's another weak spot and failure mode that doesn't exist on a solid-axle pedal. It's a kid's BSO pedal, or maybe a stationary exercise bike pedal. – Andrew Henle Apr 10 at 13:37
  • I remember that you could get axle extenders that would screw in a similar fashion between the pedal and the crank for people with extra wide feet. They must have disappeared for a similar reason. Also people with wide feet often having 'wide' weight, worsening the mechanical problems. – Carel Apr 11 at 13:42

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