Does a Mixte have to have the split top tube, or is the name based on the "Style" of frame.

Raleigh




Schwinn

Depends on who you ask. Sheldon said that a "true" mixte has the two top tubes running from the head tube, past the seat tube, and run all the way to the drop outs.

https://www.sheldonbrown.com/gloss_m.html#mixte

That Schwinn is often called a "Faux Mixte". Doesn't make it a bad bike, just a different interpretation of the Mixte style.

This is an opinion and in my mind the Mixte must have the double top tube to be called a Mixte. Anything else isn't.

A quick hunt through old threads will show that the general concensus defines the mixte by having the third set of rear stays as both the above examples do. In addition to the two stated styles motobecane using a splitting top tube that in mid span went from a single large diameter tube two two smaller stay before adjoining the seattube.
I won't even try to explain the trevor flying gate.

Sheldon is saying that a mixte always has 3 stays and may or may not have a double top tube. That's the way I read it.

Always a popular discussion.

Do you really need to know? This will just come down again to argument over opinions.

I was just thinking back to the discussion a couple months back about compact geometry. People kept crowing about "smaller triangles" being orders of magnitude stiffer. So here's my question. When you have roadies constantly in search of ultimate stiffness and carbon construction bringing the weight of a bike down well under UCI regs - why are modern race bikes not all mixtes? Not only are the triangles WAY smaller than even a compact frame, there's an extra one......

Because standard mixtes, with the twin tubes are not stiffer, and really are not even as stiff as a diamond frame. The top tube on a diamond frame, together wth teh down tube, resists the bb twisting with pedal force. The stiffness is proportional to the fourth power of diameter. Each twin tube is about half the diameter of a top tube and hence 1/16 the stiffness. Two of them are 1/8 the stiffness. But you still don't get even that reduced contribution to stiffness because the twin tubes are not TIGged or lugged to the seat post, they're just located with some little links. The "modern" mixte like the Schwinn that was shown has a standard diameter tube attached to the seat tube with either TIG or lugs. That gives you back the stiffness relative to the diamond. And, that dropped down tube gives the front "triangle" a shape that is very similar to MBs and compact road frames. So teh "modern" mixte should be about as good as a compact frame, but the true mixte should not.

Sorry, I had to.

This same debate comes into play whenever a thread mentions the stiffness of the classic Mixte frame (twin top tubes). I’m intelligent enough to understand the theories of torsion load and stiffness of tubing in relation to thickness and diameter, but what I don’t like about comparing diamond frame and Mixte frames, is the theory applies best only if the two frames are constructed exactly alike; and they are not.

It doesn’t take into account that Mixte frames are not only braced between the top tubes, but also braced to the seat tube, but most importantly the top tubes go all the way to the drop outs, where they are tied together by the rear axle.

But to try and infer that Mixte frames are significantly weaker and inherently overly flexible is in my opinion a fallacy. My own riding experience tells me that the Mixte frame I’m riding is no more, or less flexible than the dozens of diamond frames I’ve ridden in my life. Actually the stiffest frame I’ve ridden in some time was a U-frame aluminum bike, with oblong tubing. There was no discernable flex in that frame at all. I wonder why all the new super bikes haven’t adopted that style frame?

Whoa...Haven't seen that one before. Very cool.

Well, for one thing, weight isn't the only UCI reg... My (very limited) knowledge of the rest of them doesn't provide a clear reason you couldn't do a mixte, but significant departures from what all the other bikes look like generally run afoul of something...

The extra triangle only provides more stiffness to the seat tube, which is irrelevant. And the two-continuous-tubes is really an advantage specific to steel, so moving carbon frame shapes nearer to mixte geometry is really just moving the top tube/seat tube/seat stay junction lower, which some frame builders both advocate and do.

Is there a reason not to go all the way down to a straight mixte-like line, and if so is that reason technical or regulatory? Beats me.

Thanks guys, I was not trying to start a debate or anything. I have just been buying every one of them I see for sale so I wanted to know a little more about them.

IMHO a Mixtie should have the twin "toptubes" that become stays

PDXaero just what is that?

Baines Flying Gate
https://sports.webshots.com/photo/208...55521085SDqfvf

Why are you buying every one of them you see for sale?

If you are looking for "sexy bikes" to resell, than regardless of definition the ones with twin lateral stays have the most caché at the moment.