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Frames and Framebuilding (1986) Frame Flex Testing and The Tarantula

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Frames and Framebuilding (1986) Frame Flex Testing and The Tarantula

Old 01-20-21, 10:49 AM
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Frames and Framebuilding (1986) Frame Flex Testing and The Tarantula



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Old 01-20-21, 11:59 AM
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Good to remember that there has long been a recognition that some flex can be a good thing, or at least a benign thing.

I can't help but wonder what became of the Tarantula. They certainly spent a fair bit of money on it! I don't remember how long they published stiffness numbers in their bike reviews, but it doesn't seem like it was very long. A few years, maybe?? Anyone still have any of these reviews?

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Old 01-20-21, 12:16 PM
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I'd like to suggest that you begin a thread in the Bloggers section. Each time you want to post a copy of an old article you can add to the thread. Folks could find them more easily and it could serve as a resource going forward.
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Old 01-20-21, 01:44 PM
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Interesting read but what struck me most was the bad math! The author suggests that the difference between 1.8 % and 3% is just 1.2%
Say what? 3% is almost DOUBLE 1.8%
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Old 01-20-21, 02:17 PM
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Originally Posted by Biketiger View Post
Interesting read but what struck me most was the bad math! The author suggests that the difference between 1.8 % and 3% is just 1.2%
Say what? 3% is almost DOUBLE 1.8%
I'm curious now, how do engineers usually express it? Did Redcay have an engineering background?
Biological scientists typically talk about absolute vs relative difference. In this case, an absolute difference being 1.2% as the author wrote, and a relative difference (as you point out) being 66.7%.
Finance types use basis points, at least in part, to eliminate confusion. They might say the difference was 120 basis points when talking about a disparity between two figures expressed as percentages.
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Old 01-20-21, 02:24 PM
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Originally Posted by Biketiger View Post
Interesting read but what struck me most was the bad math! The author suggests that the difference between 1.8 % and 3% is just 1.2%
Say what? 3% is almost DOUBLE 1.8%
very true.
to say "just 1.2%" suggests that frame stiffness might have values over the whole range from 0% to 100%. If they were made out of actual wet spaghetti, this might be true.
To express the stiffness in context of the range of what they had measured would have been more meaningful.

Steve in Peoria
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Old 01-20-21, 03:19 PM
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My modern BMC road machine flexes noticeably on the trainer. It is enough to sometimes lightly kiss a chain link to the front derailleur and on a couple occasions with high wattage sprint efforts - a ghost half shift.

I'd prefer a stiff bike if it were to stay put but then there is the whole comfort factor to contend with.
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Old 01-20-21, 04:36 PM
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One curiosity that I remember from that period of testing was that the Centurion Carbon and the Specialized Epic Carbon road frames were the most- and least- (respectively) flexible frames that they had yet tested, at that relatively late point of their testing period.

The Centurion Carbon frame had carbon-wrapped, standard-diameter aluminum main tubes, while the Epic had oversized carbon main tubes that were fitted into lugs with both internal and external lug support.
And I've owned and ridden both extensively, both ride well but I prefer the Centurion for rides having rougher surfaces.
My Centurion Carbon also has a Look fork on it, which is likely stiffer than the aluminum original.

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Old 01-20-21, 06:33 PM
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Originally Posted by SpeedofLite View Post
I'm curious now, how do engineers usually express it? Did Redcay have an engineering background?
Biological scientists typically talk about absolute vs relative difference. In this case, an absolute difference being 1.2% as the author wrote, and a relative difference (as you point out) being 66.7%.
Finance types use basis points, at least in part, to eliminate confusion. They might say the difference was 120 basis points when talking about a disparity between two figures expressed as percentages.
I always laugh when a bike or car brand states, the new frame (chassis) is xx% stiffer than the previous...
I don't care for Hype.
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Old 01-20-21, 11:03 PM
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Old 01-20-21, 11:06 PM
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I am curious. For frames below say, 58CM, does frame flex out on the road ever even get noticed outside of maybe, loaded touring and bike-packing bikes?

Because, maybe on a trainer, I can tell there is flex, on the road, I can almost never, ever tell there is flex, unless on my SS touring bike with a heavy, heavy case of Coor's Banquet on it after a long ride beforehand.
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Old 01-20-21, 11:57 PM
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Thanks for sharing this! The article references a table of deflections based on bikes they've tested in the Tarantula - any chance you could post that as well?
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Old 01-21-21, 12:25 AM
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Originally Posted by Biketiger View Post
Interesting read but what struck me most was the bad math! The author suggests that the difference between 1.8 % and 3% is just 1.2%
Say what? 3% is almost DOUBLE 1.8%
Excellent point. At the risk of an unnecessary tangent, I notice you list a '78 Speedwell Ti track bike in your profile. (We must be a rare pair to own both a Speedwell Ti and an '85 De Rosa.) My '73 Speedwell Titalite is fun to look at, and soaks up the road, but it's an overcooked noodle. It doesn't instill confidence, especially on rough, twisting descents--not like the stiff, SL-tubed De Rosa. How does your Speedwell manage on the track? Sprinter or more of a pursuit bike?

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Old 01-21-21, 12:44 AM
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Originally Posted by delicious View Post
Thanks for sharing this! The article references a table of deflections based on bikes they've tested in the Tarantula - any chance you could post that as well?
The author really didn't make it clear, but I believe he was referring to the tables at the end of another article in the same issue that I also posted:
Road Test/Bike Review (1986) Non-Ferrous Showdown --14 Aluminum and Composite Bikes
This Road Test article shows columns of Tarantula data for all of the featured bikes as well as for two "generic" steel bikes, one made of Tange No.2 and one made of Reynolds 753.
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Old 01-21-21, 01:03 AM
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Thanks for sharing these resources.

Cross-posting the table here for reference:

Originally Posted by SpeedofLite View Post


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Old 01-21-21, 10:32 AM
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Originally Posted by gaucho777 View Post
Excellent point. At the risk of an unnecessary tangent, I notice you list a '78 Speedwell Ti track bike in your profile. (We must be a rare pair to own both a Speedwell Ti and an '85 De Rosa.) My '73 Speedwell Titalite is fun to look at, and soaks up the road, but it's an overcooked noodle. It doesn't instill confidence, especially on rough, twisting descents--not like the stiff, SL-tubed De Rosa. How does your Speedwell manage on the track? Sprinter or more of a pursuit bike?
Hi Gaucho - thanks for asking - there aren't too many Speedwells around. Mine is from the last year they were made - 1978. Frame flex was a concern the designers were trying to improve in working with titanium and apparently they found ways to stiffen the frames over time. While I would not describe my frame as stiff it is an amazing ride - it feels more organic than machine. It is incredibly responsive and resilient. It will handle a sprint and a hard climb while still keeping the line. The part that is whippy is the fork. I can see it flex when I take my hand off the bars - especially so in a crosswind! It's strange to see a titanium bike with traditional shaped tubing today. What you almost never see is a titanium fork on a roadbike. Even with all the innovations in titanium construction, most modern ti frames will have a carbon fork.
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