Bicycle geometry question

[Annirak]

What is the advantage of seat stays that join the seat tube below the top tube?
E.g.

[Paulatic]

I suspect it makes a smaller and stiffer triangle

[Mick F]

I suspect it makes no difference at all other than an aesthetic design choice.

[Annirak]

Funny, it looks to me like it uses the seat tube as a leaf spring.

[Mick F]

Frames aren't springy.
They have side-to-side flexibility, but up-and-down springiness doesn't exist.

[Dave W]

How about the Trek Domane?

[Dave W]

Some bikes have the top tube lower than the seat stays too.

[Brucey]

Frames aren't springy.
They have side-to-side flexibility, but up-and-down springiness doesn't exist.

Not so; the front of a diamond frame is a quadrilateral with a significant bending load in it from the forks. In a typical light steel frame (with standard gauge tubes) a good portion of the springiness that you might attribute to the fork is actually in the frame. That is why the frame often bends in a frontal collision, and frames break at the lower head lug etc; these parts of the frame are highly loaded and do contribute significantly to vertical compliance.

cheers

[Mick F]

Yeah ok, but not "springy" at all.
I'm sure a frame flexes up-an-down to a tiny degree, but not anything a rider would REALY notice.
Having the seat stays below the top tube wouldn't give any benefit to REAR suspension.
Front forks and steering angles OTOH are a totally different kettle of fish.

What do I know?
I may be talking a complete load of twaddle.

[Brucey]

I agree the frame in question may not be significantly more compliant vertically but that is not to say that frames can't be made appreciably vertically compliant by changes in design. I know that I very much prefer some frames to others and the vertical compliance is part of that. Apparently small changes can add up to about double the vertical compliance in the front end of the bike, and yes you will notice that supposing that you are not dead from the neck down or something.

Now, the back end is a different matter; I've not (say) tried a frame with bendy seat stays back to back with an otherwise identical one with straight stays but those who have done tell me the ride is different, and I see no reason to disbelieve them. Many riders report that they can feel a difference of (say) 5psi in tyre pressure; I'd expect the effects could be comparable with that, perhaps...?

cheers

[bensonboo]

I'm told it is more aerodynamically efficient.

[cycleruk]

I'm told it is more aerodynamically efficient.

I would assume, as the stays become more acute, that the frontal drag area must reduce.
I could see that some "springiness" must come into play compared with more vertical stays plus, I would imagine, that they would be more likely to twist at the wheel hub.
Obviously this will depend on the material, the design and diameter of the stays.

[bikes4two]

What is the advantage of seat stays that join the seat tube below the top tube?

You get someone to buy one who hasn't already got one like that in their 'N+1' collection?

[Mick F]

What is the advantage of seat stays that join the seat tube below the top tube?

You get someone to buy one who hasn't already got one like that in their 'N+1' collection?

+1

That can be the only reason.

[1942alexander]

I would imagine that the strongest rear triangle is an equilateral one which that first picture seems to be, (somewhere near). The problem as I see it is that the top tube should be attached at the same point on the seat tube as the seat stays, thereby eliminating the bending moment on the seat tube. Of course, by the same argument, this would then weaken the front triangle but the force brucey mentioned would then be transmitted, just like a flying buttress, straight down to the rear hub.