Originally Posted by
Andrew R Stewart
I well remember the Tarantula test rig and the Finite Stress Analysis effort done by Bicycling. Bike Tech was an interesting read until it became more of a marketing rag for it's sponsors. IIRC the Tarantula had some bike holding issues, as in not allowing complete freedom of motion due from the pedal pressure. There was a review of it some years later in one of the mags describing in better detail the short comings.
But all this focus of stiffness is, IMO, misguided and not really wanted by the sporting rider masses. Just look at the very fast acceptance of the road bikes with some sort of shock damping designs (Specialized Roubaix and the Trek Domane come to mind), the call for deeper padding on (now) oversized and stiff bars and the search for lower pressure tires.
So I never gave the stiffness tests much importance in how I looked at how to design my frames. Instead I look at how a bike's design can benefit the rider over the long term, not in the imaginary sprint we dream of winning.
Timmi- I suspect we are closer in mind as to design and fit then it looks like in this thread. I do raise my comments because I saw some overly broad claims and a bit of word play that IME isn't what is really going on. I do find it interesting that you're aiming toward the goal of frame building. I hope you both make it happen and keep us in that loop. I also will find it interesting to see how your views evolve over time and hands on experience in building for clients as well as now having to be part of the greater market place.
While this forum is interesting I find that over on Velocipede Salon the business and personal motivation info is better. Also there are more real builders who chime in, including more then a few carbon builders. Have you checked it out? Andy
Many people, including builders, have gotten the term "stiffness" completely confused.
You want to increase stiffness in the direction where your pedaling flexes the frame, which results in small efficiency losses (for the mechanics of which I have explained). But not increase it in the vertical plane: there, you want to exploit/allow any possibility of more "compliance" as they like to call it.
The Trek design you mention, with the split in the seat tube, maintains the lateral stiffness thereof, while allowing flex on the vertical plane, so as to absorb some of those road shocks. I haven't tried it, but in theory, if they have twist under control, that design would have no to very little effect on efficiency, and may even enhance it because the rider is getting less beaten up. Smart folks over at Trek.
As for Specialized, it's not a company I will ever buy products from again. For their morals (aggressively flexing their monetary muscle to litigate smaller competitors into the poorhouse), and for too many failed products of theirs that I have had over the years, to (most likely intentional because no one is that stupid) integrated designed flaws/obsolescence (limiting the lifespan of the product before you have to buy replacement parts/product from them). I just don't trust the company: I see the image they project just as well as anyone else does, but their actions and products have contradicted that in my experiences.
Cases in point, here are some examples of builders completely confused with "stiffness" and other design decisions:
Daccordi (and others) On some of their fancier models (Griffe), vertical plates behind the head tube lugs (inside the lug elbows), to stiffen it there... on the vertical plane.
That is NOT what riders mean, when they say they want stiffer! All that does, is make life more miserable for the rider, while adding zero performance/efficiency benefits. I even saw a model with a larger, full plate brazed in behind there, to make the torture even more complete.
Colnago with dual downtubes: You need added lateral stiffness on the seat tube. The downtube needs torsional rigidity. An obvious fail there.
Moser (and others) How about those time-trial bikes, with a seat tube curved back and over the rear wheel, to shorten the wheelbase. That only makes the bike twitchier and follow a more erratic course, actually increasing the distance you are traveled, versus a standard racing bike. Use that idea on a criterium bike if you must, not for time-trials.
Aero tubing: well, wasn't that just one of the dumbest ideas ever. Poor lateral rigidity in the seat tube, poor torsional rigidity in the downtube, more transmission of those vertical road vibrations. Dumbest idea ever.
Ferari (Colnago) crimped tubing: Like aero tubing, the torsional rigidity of the downtube is compromised, while the shape transmits vibrations very well, riders report. And the aerodynamics, well, they head in the opposite direction of where the aero tubing is supposed to take you. Gilco tubing might be good inside a car chassis where everything is joined together in pyramidal structures, but it doesn't transpose itself well into a 2D structure.
Colnago: or how about the bikes that eliminate the seat tube altogether? I suspect the Tarantula is at fault here, because it was affixed at the dropouts and head tube. It did not take into account the essential lever that the seat tube is, on a bike.
In fact, most bikes today, are designed with oversized downtubes, because that is the way the Tarantula tested frame stiffness, and this stuck in the minds of many, becoming the newly accepted "truth" : using the wheels and handlebars as anchors, and not the rider (where the seatpost, with the saddle, is anchored against the rider, between the legs, and forms the perfect anchoring point for the lever that the seat tube is, when pedaling.
And let's not forget a final piece of torture equipment for the cyclist, which adds no performance benefit: the straight fork blades. While these are less costly to mass-produce (because you are eliminating the curvature, and need to have them all evenly curved), they somehow made it onto mainstream bikes as a modern "upgrade". No more shock dampening by the curve at the bottom. Now all vibrations are transmitted to the bottom headset bearing, where it's life may be shortened, vibrating the frame, and then, following along the steerer's path, into your palms.
Yet, racers have won races on such bikes! This prives only one thing: that despite the design, it's the rider who makes the win, not the bike. They won despite the insane design flaws their sponsorship made them ride on.
To the general readership here: Never be afraid to question what is being done. Try to understand the why, and then ask yourself: does it work? Sometimes there is a "why", but it fails in execution.
Here are some pictures of the nonsense I was referring to:
No, I am not experienced with Velocipede Forum. Most forums activities have been gradually migrating to facebook groups over the past decade. I try to keep my memberships per topic/task to a minimum (attempting to have a life - failing at that already), and just chose the largest or what seemed the most pertinent one. Maybe I should check it out, as I'd like to be in touch with more builders.