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Frame Geometry

Old 12-14-17, 04:24 PM
  #126  
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Originally Posted by Timmi View Post
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.
I think your comments are correct, but they are based on the assumption that stiffer drivetrains are faster, and there really isn't much evidence of this. And there is some evidence that the opposite is true - elastic drivetrains transmit power more efficiently by translating vertical pedaling into rotation more smoothly.





The Slingshot's were pretty cool - they stored cornering and braking energy by inch worming forward, behaving much like the Teledyne Titans were said to. Another example of how elastic materials can transform energy efficiently.

Anyone doubting how energy can be efficiently stored and re-transmitted needs to watch some pole vaulting. Same fiberglass as used in the Slingshot.
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Old 12-15-17, 12:20 AM
  #127  
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Originally Posted by Kontact View Post
I think your comments are correct, but they are based on the assumption that stiffer drivetrains are faster, and there really isn't much evidence of this. And there is some evidence that the opposite is true - elastic drivetrains transmit power more efficiently by translating vertical pedaling into rotation more smoothly.





The Slingshot's were pretty cool - they stored cornering and braking energy by inch worming forward, behaving much like the Teledyne Titans were said to. Another example of how elastic materials can transform energy efficiently.

Anyone doubting how energy can be efficiently stored and re-transmitted needs to watch some pole vaulting. Same fiberglass as used in the Slingshot.



This reminds me of driving a 1962 Ma Bell van. The steering was so sloppy... you'd be constantly swinging the wheel about to stay on line.


Sorry but this isn't what I look forward to n a bike. Andy
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Old 12-15-17, 12:58 AM
  #128  
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Originally Posted by Andrew R Stewart View Post
This reminds me of driving a 1962 Ma Bell van. The steering was so sloppy... you'd be constantly swinging the wheel about to stay on line.


Sorry but this isn't what I look forward to n a bike. Andy
Who said the steering is sloppy on either? Have you ridden a Slingshot? The fiberglass leaf is wide to prevent the frame twisting. The bikes were able to compress in length, which isn't much different than saying a bike can compress vertically.
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Old 12-15-17, 08:18 AM
  #129  
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Originally Posted by Kontact View Post
Who said the steering is sloppy on either? Have you ridden a Slingshot? The fiberglass leaf is wide to prevent the frame twisting. The bikes were able to compress in length, which isn't much different than saying a bike can compress vertically.

Yes, I have ridden a number of Slingshots. Otherwise I would not honestly be able to say what I did. Andy
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Old 01-15-18, 05:01 PM
  #130  
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Originally Posted by Timmi View Post
.

I can't find my Framebuilder's book by Talbot in all of my boxes... HELP!
I haven't followed this thread. Did it get to recommending this manual:

http://www.timpaterek.com/paterek.pdf
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Old 01-19-18, 02:45 AM
  #131  
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Originally Posted by MassiveD View Post
I haven't followed this thread. Did it get to recommending this manual:

http://www.timpaterek.com/paterek.pdf
Dear Massive (if that's your real name),
Paterek did not come up however, we seem to have established 3 things:
  1. First an individual had a bike that he remembers going very fast on and the bike handled very well; said handling attributed to 'Crit Geometry'.
  2. Second, several people agree there is something called 'Crit Geometry' as proven by a website quoting same
  3. Third, several people agree that 'Crit Geometry' is marketing speak and loosely translates to 'slightly steeper HTA and STA combined with more or less fork rake and slightly higher BB and shorter stays but well within the realm of what is generally agreed to be a Classic Road Bicycle'.

Happy Friday Everyone,
Duane
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Old 01-19-18, 10:49 AM
  #132  
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Originally Posted by duanedr View Post
Dear Massive (if that's your real name),
Paterek did not come up however, we seem to have established 3 things:
  1. First an individual had a bike that he remembers going very fast on and the bike handled very well; said handling attributed to 'Crit Geometry'.
  2. Second, several people agree there is something called 'Crit Geometry' as proven by a website quoting same
  3. Third, several people agree that 'Crit Geometry' is marketing speak and loosely translates to 'slightly steeper HTA and STA combined with more or less fork rake and slightly higher BB and shorter stays but well within the realm of what is generally agreed to be a Classic Road Bicycle'.
Happy Friday Everyone,
Duane
Community Smartass (Am I the only one laughing again?)
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Old 01-19-18, 01:33 PM
  #133  
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back when "crit geometry" was a thing, I was a lot faster than I am now. But I don't think I ever had a bike that met that description.
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Old 01-19-18, 07:27 PM
  #134  
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Certainly some of my early self built frames shared Crit Geo themes. But as I got older I began to more fully understand what Davis Phinny said, after his first year in Europe as a road pro, about the then current "American Crit" frame design standard. It sucked for general road racing and day in and day out riding. The longer the race the worse the rider felt riding a Crit fashioned frame. Andy
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Old 01-20-18, 10:56 AM
  #135  
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Originally Posted by Andrew R Stewart View Post
Certainly some of my early self built frames shared Crit Geo themes. But as I got older I began to more fully understand what Davis Phinny said, after his first year in Europe as a road pro, about the then current "American Crit" frame design standard. It sucked for general road racing and day in and day out riding. The longer the race the worse the rider felt riding a Crit fashioned frame. Andy

I think that's where Richard was coming from. Experienced pro's don't want extreme geometry - they know they have to get up in the morning and do it again.
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