Fatti con le moni

[vaxn8r]

What's the deal with these humongous chain stays? I distinctly recall the Jerk telling us many times that larger chain stays offered no increase in lateral stiffness and that they were a misguided attempt to cover up bad frame design. Yet he and DBRK are all gaga over this big legged monster. Can someone explain this conundrum? Jerk, help me understand, oh wise one.

Here's the quote from Competitive Cyclist website:

What's the story behind the name Big Leg Emma? Someone told us once that it's a reference to a Frank Zappa song. Someone else told me that it was a loving reference to Dario's mother. While I can't guarantee that information, I can assure you that "legs" are a reference to the unimaginably oversized chainstays you'll find on a Big Leg Emma. No matter how prepared you are to see them, you are guaranteed to say "omigod" at first glance. They are full suspension mountain bike big, and that's another reason why the bike should ride with such phenomenal stiffness.

BTW, I like DBRK's BLE with orange paint and black components, especially the flat black Reynolds fork. Seasonal motif too. Boo!

[jerk]

you can't mask a lack of torsional rigidity by simply installing honking stays on a road bike. like wise, that red herring "bottom bracket rigidity" means nothing when taken out of context. the front and back end of the bike and the top tube determine bb stiffness more than anything else.....dario's monster stays work because of his dropout design, his top and down tube design and his head tube design. the thing is stiff at the ends so it doesn't flex torsionally.....what the jerk means when he calls monster stays a crutch for a bad frame design, he's simply stating the obvious.....a frame design must work from head tube to drop out.
jerk

[vaxn8r]

Jerk, thanks for replying. Can you give an example of a poorly designed frame with beefy stays you referred to in earlier posts, just to give me some context.

I'm not impuning the Pegoretti. Just trying to understand how this design is an improvement in bike frame technology.

[Climb01742]

also, sir jerk, could you talk about how much the downtube impacts BB stiffness? i ask because most of the frames i've found too stiff have pretty OS downtubes, and those i've found to have a nice amount of flex in the lower half of the frame have more modest DTs. thanks.

[jerk]

the jerk doesn't really want to point fingers but a lot of foco tubed bicycles made by builders without access to custom drawn tubing fall into this category as do many chinese ( of both the red and r.o.c. persuasion) carbon jobs. a frame should have a certain amount of spring to it and the back end should complement the front end....anyway sorry for not really answering the question.....o.k. cannondale six thirteen. super stiff stays and bb area....strange torsional issues in the big guy size the jerk tried. obviously works for cuenego though so take this with the normal grain of salt applied to the mutterings of your favorite secretive bike jerk.

climb-o-

the down tube complements the top tube in terms of adding torsional rigidity yet also has a strong effect on stiffness on the vertical plane....a big fat downtube doesn't seem to do much a big fat tob tube wouldn't be able to do on its own, but as many stupid attempts at aero downtubes have proven, they can make a bicycle ride something awful. all this being said, the jerk stands behind the notion that all this talk of tubes and tubing diameters and materials have aslightly more important role in determing the ride charachteristics of the bicycle than the color of the paint and a less important role than tire choice. the thing that makes a bike ride well is geometry and whether or not the damn thing is straight. so don't worry about it. for most of us a palosanto is a far better choice than an emma. if you're overpowering a palosanto you are either too fat to be riding bicycles or the jerk has some people in professional bicycle team managment who really need to talk to you.
jerk

[zap]

I would think that this is something the boys and girls at Serotta would know quite well, what with all the cad analysis software available today.

My understanding is that the downtube has a greater influence on bb stiffness than the top tube. Basiclly, run the shortest line from the front hub (fork-headtube-downtube) through the bb to the rear hub.

To improve frame stiffness, the down tube needs to resist more torsional loads. I think one way to achieve this is what Pegoretti has done by inserting metal plates in the downtube to counter these forces. Placed properly, this shouldn't have much affect on the ride. Another way is of course increasing the diameter of the tubing. I've also seen honeycomb structures (good app. for ti ;) ) inserted into tubing to add stiffness without adding much weight.

But anyways, I think that designers would fine tune the torsional stiffness of the front triangle with the top tube. Here the top tube needs to counter deflection from the headtube.

This discussion brings up an interesting point. How many small builders (and not so small) with all these tubing choices really understand the cause and effect of selecting one tube over another for all frame sizes offered?

[Climb01742]

zap, it was actually ben himself that clued me into the DT's impact on BB stiffness. he talked about "tuning" the stiffness of the top and bottom halves of a frame by tweaking the TT to stiffen the top half and tweaking the DT to tune the lower half.