Trapezoidal vs triangular frame rear triangle?

[Scoox]

Has anyone had bad experiences frames that look like the red frame? The chain stay and the seat stay welds don't meet so in theory the black frame in the second pic would be stiffer and stronger.

[Ross McArthur]

22 hours ago, Scoox said:

Has anyone had bad experiences frames that look like the red frame? 

 

Yea, I barfed when I seen it.

[La Bourde]

23 hours ago, Scoox said:

Has anyone had bad experiences frames that look like the red frame? The chain stay and the seat stay welds don't meet so in theory the black frame in the second pic would be stiffer and stronger.

Why do you assume the rear end will be stiffer when the welds meet?

Around the welds, the mechanical properties are worst due to the heating. It depends also on the material, aluminium is more affected than steel or titanium for example.

Having longer welds shall be worst but it may also allow to dispatch the load on a larger section, thus reducing the punctual stress.

(This is done here on the chain- and seatstays: the welds are not orthogonal to the tube to increase the weld length)

So it really depends on the conception of the frame, the stiffness of each sections, etc. 

And increasing a section may not strengthen the frame: it can move the load or even concentrate it on a location that was less stressed before the change.

There are bad patterns in conception though.

I am more worried by the weld above the disc caliper, that will get repeatidly a lot of shear force...🤨

Finally, the only relevant fact we have is the difference in experience: Inspired produces street/trial frames with disc mount for many years with this specific design.

The design used by clean is present on a od comp trial bike only, where the forces transmitted by the wheel may be less (20" instead of 24")

But this is only an assumption, it may be well designed.

[craigjames]

1 hour ago, Ross McArthur said:

Yea, I barfed when I seen it.

Rough isn't it! It looks like the b*****d child of a 20" comp bike and 24" street bike, and it got all the bad attributes of both.

I don't think there is anything inherently wrong with design and i'm sure it's had some FEA to prove it's sound. Personally I wouldn't buy a street bike from a company that is known for comp bikes, especially when the alu comp bikes have had a reputation for cracking. Even more so when it appears to be a collection of parts from their other frames and not a ground up design like an Inspired.

[Scoox]

4 hours ago, La Bourde said:

Why do you assume the rear end will be stiffer when the welds meet?

A triangle is a truss, which is an inherently stable structure because all sides support each other in tension and compression. Any external force is distributed across all three members. As long as the lengths of the three members are fixed, the structure won't change shape, so it's inherently very stiff. In comparison, in a 4-member structure (like the Clean bike where you have the seat tube, chain stay, seat stay, dropout) both the angles and the lengths of all members must be fixed for it to retain its shape. The lengths of the members are inherently fixed, but the angles are not unless there is some kind of bracing. In this case the welds are what prevent the four-sided structure from deforming, so I'd assume the welds experience greater stresses in this configuration.

Edited 8 hours ago by Scoox

[Scoox]

4 hours ago, craigjames said:

Rough isn't it! It looks like the b*****d child of a 20" comp bike and 24" street bike, and it got all the bad attributes of both.

I don't think there is anything inherently wrong with design and i'm sure it's had some FEA to prove it's sound. Personally I wouldn't buy a street bike from a company that is known for comp bikes, especially when the alu comp bikes have had a reputation for cracking. Even more so when it appears to be a collection of parts from their other frames and not a ground up design like an Inspired.

The Inspired is a little heavier and several bits of it are objectively beefier, so that's what I'm leaning towards.

[Daan]

5 hours ago, La Bourde said:

Around the welds, the mechanical properties are worst due to the heating. It depends also on the material, aluminium is more affected than steel or titanium for example.

[...]

I am more worried by the weld above the disc caliper, that will get repeatidly a lot of shear force...🤨

Case in point 🤪 Anything can break, but better have something that at least looks good while breaking it.

Edited 7 hours ago by Daan

[Scoox]

1 hour ago, Daan said:

Case in point 🤪 Anything can break, but better have something that at least looks good while breaking it.

How did that happen? Is that an Inspired bike? to be honest the Clean street bike is their first foray into Street bikes and I couldn't find any reviews so for all I know it could snap on the first ride...

[La Bourde]

6 hours ago, Scoox said:

A triangle is a truss, which is an inherently stable structure because all sides support each other in tension and compression. Any external force is distributed across all three members. As long as the lengths of the three members are fixed, the structure won't change shape, so it's inherently very stiff. In comparison, in a 4-member structure (like the Clean bike where you have the seat tube, chain stay, seat stay, dropout) both the angles and the lengths of all members must be fixed for it to retain its shape. The lengths of the members are inherently fixed, but the angles are not unless there is some kind of bracing. In this case the welds are what prevent the four-sided structure from deforming, so I'd assume the welds experience greater stresses in this configuration.

Agree regarding the truss, it is inherently stiffer than a 4-member construction, if and only if the members are comparable. 

Not sure this is the case here, there are 3 tubes and a CNC part against a 3 tubes construction.

But I get your point and surely the inflection point at the weld on the top of the dropout is questionable at least. The difference in stiffness between a tube and a CNC/forged part could also be a concern (maybe also the reason of the damage on Daans picture)