Freakin scary dropout design

Discuss light weight issues concerning road bikes & parts.
stormur
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Location: FIN

by stormur

Got a frame in my hands .... interesting DS dropout design :shock: None from relatively "common" hubs axle goes over derailleur hanger to be supported by frame dropout. ALL weight goes to hub axle ONLY thru hanger. Overlap is less than 0.05mm with fully tightened skewer . Arrow shows vertical force in bicycle natural position ( when ridden ).

I contacted manufacturer yesterday and asked about it, still silence :mrgreen:

https://photos.app.goo.gl/B5XOkY84H3ZYP0Tt2

https://photos.app.goo.gl/WFIldDXeM3qBeQNH3

Hanger is inside dropout, not outside (as usually) . Some frames have clamp hanger ( like Cannondale ) holding dropout from both sides... This one is inside.
So technically, on DS all the weight is on hanger mounted to dropout by 2 tiny screws...

I've been asked "is it safe to ride this thing"... :roll:
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

by Weenie


964Cup
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Joined: Tue Dec 18, 2012 1:31 am

by 964Cup

Well, not quite. It might be an issue if you didn't bother with a skewer. Or left the skewer undone. But otherwise quite a lot of the weight is borne by the clamping force of the skewer. And if the hanger fails somehow in some extraordinary way, and the clamping force doesn't provide enough friction between the inside skewer faces and the outside of the dropouts to hold the wheel in place, it will just drop down onto the axle of the skewer. It doesn't look like a brilliant design, but I'd be surprised if there was a real safety issue assuming the rider has some clue how skewers work.

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prendrefeu
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by prendrefeu

Technically speaking you don't even need the screws on the a derailleur hanger, the clamping force of the skewer keeps everything in place.
You can even save some weight by gluing the derailleur hanger onto the frame (and carefully removing it from the frame if on the rare case you need a new one... which is rare)
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stormur
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by stormur

Apparently not.

Dropout is designed to lie on hub axle and take all the forces coming from the rider weight/ force. Skewer tightened ( as example DT Swiss to 15Nm ) is far from keep all vertical forces. Skewer clamping force prevent only moving axle from dropout ( accurately shaped to axle ), but is not able nor designed to survive such vertical forces as dropout.

Look at "frction area" of the skewer... If that solution would be sufficient ( and you're right ) , there's basically no need for dropout, which sounds wrong , doesn't it ?

If I'm wrong ( and I am not, thing is already consulted with engineer / quote: "I wouldn't ride it. No way." / ) why I can't find any ( except this particular model ) frame with similar "innovation" ? Even across same brand !

All hangers are designed this way, that dropout is covering hub axle, not JUST hanger, assembled on 2 M2 bolts.

Some frames designes ( cannondale as example ) went even further: dropout and hanger are somewhat "integral" part, which is much better than side mounted hanger ( same for thru axle ).

Theory saying that skewer clamping force is able to hold hub in place is- to name it very kindly - at least ridiculous.

@prendrefeu : image of your bike :) : hub axle reach dropout first, then ( in this situation irrelevant ) hanger, isn't it ?

Image

In "my" frame hub axle DOESN'T REACH DROPOUT at all ! All weight is on hanger ONLY !



To make thing clear : hub in frame . Axle ( cup, but same ) to short to even reach dropout, all weight applied to hanger.

https://photos.app.goo.gl/mPCHg7T4tdRIwO7H3


More, dropout is not "build into" a frame, is just side mounted ( 2x M2 bolts ), so those bolts are only supporters of the force.
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

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prendrefeu
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by prendrefeu

Yes that is pretty weird :(
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stormur
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by stormur

I thought your comment came from misunderstanding... it's hard to imagine such crap solution....

I went all frames at home plus 20-30 different in net. NONE of them had same set ( side inward hanger mount ) . Inward happened just with trhu axle, so no issues here.

And imagine this frameset price is above 3k$ :shock:
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

blamester
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Joined: Tue Feb 19, 2013 10:33 pm

by blamester

Manufacturer decided to do it differently for what ever reason. Edge distance looks close. Common practice would be 1.5 times the diameter of the bolt or rivet which may increase to two times for a countersunk bolt or rrivet. This is also dependent on materials used and usage.
They may also be using the clamping force of the skewer to make up the difference.
Use it, keep an eye on it. Check the torque on the bolts and if they require regular retorqueing i would imagine that would lead to problems. If not then it will be fine.

stormur
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by stormur

it's not my thing, just given for inspection. I wouldn't ride it. Oh no. From Engineering point of view "clamping" is irrelevant. Such clamp cannot hold such weight as rider longer than half second. All is supported by der hanger bolts, and looking how one of them is close to dropout cut out... it won't last long. it's half mm from the composite border (!). If you look at 1st image hanger with its 2 tiny bolts is holding all weight. Unacceptable. My "engineer friend" just laugh... He couldn't believe anyone accept such thing to give to the people riding it.

I'm waiting just for manufacturer reaction. If frame owner won't like it, I will share what brand/ model is it :mrgreen:
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

blamester
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Joined: Tue Feb 19, 2013 10:33 pm

by blamester

How can clamping be irelevant. Your handle bar are clamped to the stem , seatpost to the seat tube , cranks to the bb spindle , brake cables to the brakes etc etc.
But if you don't have confidence in the part everything else is irelevant. I would not ride a bike if i wasn't confident of it's reliability.
Send it back.

stormur
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by stormur

Ask engineer, will explain you relation of bolt torque to clamping force in function of clamped (friction) area. Ask for sheer of two parallel objects in contact with each other on less than 0.5 square cm and being dynamically loaded ( explain him also loads : weight and dynamic ). He will explain you why such connections are glued, rivetted ONLY if cannot be avoided, because are weak from its design. And definitely any bolt/pin/ rivet won't be at the border of any connected surface.

Clamping "pipes" is completely different thing ( and clamped area to -many times bigger ) . And as people experience tells, not free of troubles ;) specially with seatposts.

Again ( last time ) : IT'S NOT MY FRAME. Owner will decide.
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

eric01
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Joined: Mon Feb 06, 2006 1:06 am

by eric01

Ah it wasn’t until the third picture that I understood the problem you are referring to. When you see the hub axle not extending beyond the width of the hangar, it’s clear. Yes I agree this is dodgy.


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prendrefeu
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by prendrefeu

Yes, that third picture definitely convinced me, sorry if my first post was mis-understood in context.
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stormur
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by stormur

No worries :)

I was extremely surprised that such thing leave designer room with approval... Really. Right dropout in this situation seems to be ... not necessary :shock: just small hole for skewer shaft would be enough :mrgreen:
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

DamonRinard
in the industry
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Location: Connecticut, USA

by DamonRinard

Very clear pictures and your analysis of the load path seems correct.
But...
How did the wear marks get on that dropout? Did someone already ride it without failure (so far)?
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

by Weenie


stormur
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by stormur

Frame was ridden around 150km according to owner statement. Didn't fail apparently, however rider is rather light ( 65kg ish ) . He came to me with inconsistent shifting.
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

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