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Lately I have been looking on new bikes, and I have seen some design on an aluminum frame which left me quite dubious:

bent frame

That bend seems to scream "I am gonna buckle at the first hard hit!".

Are my worries just the fruit of a "conservative mind", or indeed such design value coolness over safety/durability?

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    Remember the low top tubes that you supposedly didn't hit with your crotch? This is designed to work the other way. – ojs Apr 29 at 19:27
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    Looks like a "compliance" feature to help smooth the ride. – Criggie Apr 29 at 19:55
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    Does not look like the style of bike designed with handling "big hits" as a priority. Seriously thgouh, if you ride the bike as intended, there are a thousand other things more likely to give problems than the frame. – mattnz Apr 29 at 20:06
  • Not unusual for an AL frame bike. – Daniel R Hicks Apr 29 at 22:49
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Frame Feature of a Canyon Inflite Cyclo-Cross Bike

A cyclo-cross bike that had been quite successful in world cup and UCI championship races has a similar feature, IE a top tube bent up. Cyclo-cross is very stressful for the materiel. In this specific carbon frame this bend is apparently not a significant weakness.

The same manufacturer also offers an aluminium version of the bike. Of course that's isn't race tested to such a degree.

The main reason for this bend is to bring the top tube up, about level to the ground, while exposing as much of the seat post as possible. For a cyclo-cross bike a high top tube is necessary as it makes shouldering easier.

The bend also allows the seat stays to attach at a shallower angle to the seat tube while joining at a nexus with the top tube. This in turn is supposed to improve rear end compliance.

The manufacturer also claims the bend would be beneficial to general handling, stiffness, and compliance characteristics in the typical vague way all manufacturers talk about their stuff.

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    Nevertheless, a frame with such a bend cannot have the same stiffness and stability as a frame with the same materials and a classic diamond shape. The double triangle shape of the classic diamond is near perfect in that regard, and the only thing that would improve its stability would be to add a third tube between seat tube and headset to divide the front quadrilateral into two triangles. – cmaster Apr 30 at 6:26
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    To be noted that in world cup and UCI championship racers change bikes with the same frequency I change socks. So I am not 100% sure they would notice the same issues I fear by riding 8000 km/year. – L.Dutch May 1 at 7:28
  • @cmaster that might very well be the case. However, I should be reluctant to assume that. The lower limit of bike tube wall thickness is typically not determined by the frame stability. (Resistance to damage, material for welding joints, handling in production). The tubes might be too strong the first place and a hypothetical frame design that optimises other weak points like joints could become stronger than a diamond frame. Point. Unless I've seen experiments with enough samples I don't believe anything. (Not even a finite element sim because of welds.) – gschenk May 1 at 7:55
  • @L.Dutch Not the same bike, not the same material, not the same use. What you can take away though I'd that it is not a necessarily a complete frame building blunder. I thought you were not asking for 8 Gm but "the first hard hit". Does the mfg provide a warranty for the time it takes you to ride 8000 km? – gschenk May 1 at 7:59

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