Originally I replied directly to Dale, because I think my reply has a lot of OT content and possibly no relevant CR content. But since there has been on-list response to Dale's query, I'll post this to the list and see how the judgement goes. This is really more bicycle science than vintage race bike content. I would not normally try to have this discussion on CR.
Ken Freeman Ann Arbor, MI USA
Ken replied to Dale:
_____
From: Ken Freeman [mailto:freesound@comcast.net] Sent: Sunday, December 31, 2006 3:09 PM To: 'oroboyz@aol.com' Subject: RE: Woodrup frames. Now: BB height, etc.
Well, this point about stability v. BBheight has been hashed over ad nauseum on Ibob, since theory and bicycle science do not seem to be well accepted on CR, v. bold assertion of common prejudices. Well since this is about vintage racing bikes, I won't argue that point.
But back to stability. If you read the MIT press book Bicycling Science, 3rd edition, page 266, the authors discuss the broomstick analogy. This simple experiment shows that it is easier to balance a long broom on the palm of one hand than a short broomstick. They quote a mathematical result that states that the time it takes such an object to topple to a predetermined degree is proportional to square root of the height of its center of mass. Longer broomsticks have the center of mass higher off the support plane (the palm) than short broomsticks. So much for principles.
Similarly, the BB height affects the height of the center of mass of the rider/bike combination. All other things being equal, a bike with a higher BB will take more time to lean due to an exterior disturbance (say a crosswind) than a bike with a lower BB. By " all other things equal," I mean same wheel radius, same seat tube length, same seat tube angle, same saddle height, same rider, and the same rider response to the disturbance. It's an idealized situation, but it does IMHO influence real world observed behavior of bikes and riders.
I choose to call this slower response time stability, keeping in mind that I think there are many aspects to stability. As an experienced design engineer I know that the term has many definitions, and is in general meaningless unless one specifies what is meant.
Other types of stability include resistance to oscillation or shimmy, maintaining mechanical integrity for a long time, ability to keep rolling in a straight line without rider input, and the ability to respond precisely, predictably, and quickly to rider inputs in the presence of other forces. I suspect this last one is the type of stability that is improved in a Sachs frame due to a lower BB. I don't have one so I don't really know how it feels.
There are general mathematical defintions of stability as well, from which engineers often derive contextual definitions of stability to enable design work. With bikes, I don't have any suitable math models to appeal to.
So IMHO, stability is as clear as mud. I've elaborated on what I meant. I would like to hear your definition of stability, as you meant it.
I completely agree with you about the value of alignment. I've had two frames aligned by experts (my Masi GC by Schwab Cycles in Colorado and my Trek 610 by Ron Boi in Illinois), and the improvement in riding was dramatic in both cases.
My GC btw seems to be custom, and has very small clearance front wheel to downtube, about 19 mm. My Woodrup in contrast has about 43 mm. It's harder to see because I have a fender on. The 43 mm is of no concern in itself, but I wouldn't want to have a smaller clearance than the GC has, at least if the fork has some flexibility.
I hope this has been interesting to you!
Ken Freeman
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From: oroboyz@aol.com [mailto:oroboyz@aol.com] Sent: Sunday, December 31, 2006 9:42 AM To: freesound@comcast.net Cc: Classicrendezvous@bikelist.org Subject: Was: Woodrup frames. Now: BB height, etc.
Hey Ken:
I can't help but wonder about a couple of things you wrote here:
<< Mine (1980, pre-TSD) also has a high BB, the drop is about 6.4 cm. Compares
to about a cm more for my Trek and others. I think this contributes to the
Woodrup's sense of stability. >>
"In Theory" the lower the BB, the more stable and of course the opposite for
higher BBs.
In fact, if I remember correctly, that is one of Richard Sach's unique
characteristics in his frames... He has used quite a bit lower bb height
and while you may not be able to pedal through the curves quite as much,
that is a well considered trade-off that results in a more secure control
(stability)while cornering.
I think that much of the sought after stability and steering accuracy is part
of accurate frame alignment and dishined wheels... So many frames, of all quality
levels, are not straight.. Just a 1/2 CM in misalignment can make a huge
difference and we tend to blame other factors (frame angles, dimensions)
when in fact, if the frame were carefully aligned, would make the bikes
ride ever so much better....
<< My theory is that both of my frames are small frames, and subject to
compromises inherent in minimizing toe overlap and gettign adequate front
tire to downtube clearance, without extremely long top tubes. One design
feature to address this is to raise the BB, and another is to lay back the
head tube to perhaps 72 degrees. >>
In my (limited) experience, the reason many builders/manufacturers make
a higher BB in smaller frame is to solve the problem/save a lot of work
in joinery at the compacted head tube /head lugs area...
By raising the BB, that allows raising the upper head lug, allowing quick and unmodified use of the stock lugs. I.e., no cutting or fitting, etc. Another solution to this was a one-piece head lug that allowed the top tube & down tube to intersect...
On road bikes of any size, I don't think the clearance of the down tube vs tire is much concern...
'Course I could be wrong. It is fun the theorize about all this mysterious stuff!
Happy New Year!
Dale
Dale Brown Greensboro, NC USA
-----Original Message----- From: freesound@comcast.net To: jerrymoos@sbcglobal.net; hydelake@verizon.net; Classicrendezvous@bikelist.org Sent: Sat, 30 Dec 2006 7:43 PM Subject: RE: [CR] WOODRUP frames
Jerry,
Mine (1980, pre-TSD) also has a high BB, the drop is about 6.4 cm. Compares
to about a cm more for my Trek and others. I think this contributes to the
Woodrup's sense of stability. The SOH on mine is 77.6 cm, seat tube is 53.5
c-t, 52 cm c-c.
My '84 or so Mondonico (sure looks on-topic, but I can't be sure!) has a BB
drop of 7.2, 52 cm c-c seat tube, and 78.3 cm SOH. Both bikes seem to have
high BBs, so I don't think national style is necessarily being illustrated
here. My theory is that both of my frames are small frames, and subject to
compromises inherent in minimizing toe overlap and gettign adequate front
tire to downtube clearance, without extremely long top tubes. One design
feature to address this is to raise the BB, and another is to lay back the
head tube to perhaps 72 degrees. My Woodrup and Mondonico respectively have
head tube angles of 72.0 degrees and 72.4 degrees (I have less confidence in
this latter number).
Both bikes are sort of a French fit for me.
Ken Freeman
Ann Arbor, MI USA
-----Original Message-----
From: classicrendezvous-bounces@bikelist.org <mailto:classicrendezvous-bounces%40bikelist.org>
[mailto:classicrendezvous-bounces@bikelist.org <mailto:classicrendezvous-bounces%40bikelist.org> ] On Behalf Of Jerome &
Elizabeth Moos
Sent: Saturday, December 30, 2006 11:56 AM
To: Barb & Dan Artley; Classic Rendezvous
Subject: RE: [CR] WOODRUP frames
I have an early/mid 80's Woodrup. Nice bike, but does have a very high
bottom bracket. Haven't measured the actual BB height, but the standover
height is what I'd expect on a bike with a seat tube about 2 cm longer. No
one else has mentioned this, but were high BB's typical of Woodrup? On the
other hand I also have a 52 cm ctc 1988 Mercian KOM with a standover height
about the same as a 55 cm French of Italian frame, so maybe the high BB's
were a British thing in the 80's.
Regards,
Jerry Moos
Big Spring, TX
Barb & Dan Artley <hydelake@verizon.net <mailto:hydelake%40verizon.net> > wrote:
I can't say how pleased I am hearing so much of Woodrup Cycles. A Woodrup
was my first really nice race bike replacing what I considered more of a
tourer, my PX-10 (Sorry Peter K.). It was unfortunately crashed, badly
repaired and sold, but recently repurchased. I'm hoping that someday it will
get the restoration it deserves for the fond memories of my only race season
back in 1973. Thanks to all who've provided this information. Does anyone
know if they are still building keepers of the flame in lugged steel? ...
More?
Dan Artley in Parkton, Maryland
Archive-URL:
http://search.bikelist.org/
1653.eml
Date: Fri, 29 Dec 2006 21:57:24 -0500
Subject: RE: [CR] WOODRUP frames
From: Doug Fattic
The subject of Woodrup frames reminds me of my own experiences visiting
their framebuilding shop when I was learning to build at Ellis Briggs.
I
wanted to learn how to do a fluted seat stay top like what was on my Masi
and Jack Briggs rang up Woodrup to see if one of them would be willing to
show me how. What I vaguely remember Jack Briggs telling me was that somehow
Jack's father helped Woodrup get started. The date around 1953 or 4 sticks
in my mind from our conversation about it. Leeds is about 15 miles to the
east from the much smaller town of Shipley where Ellis Briggs is located.
The good size city of Bradford is about 3 miles to the south.
In
other words, these places are one big megalopolis. 15 British miles is not
15 American miles. The roads are not laid out on a square because of the
shape of the land and going to Leeds seemed like a big trip. It was lots of
stop and go city driving on winding roads in my old Morris Minor. This
generosity (to help others when it wasn't to his own advantage) was part of
Jack's character too and something I've been deeply grateful for (since he
did the same for me).
I was a little shy going in the door and was glad Jack had asked permission
for me. One of the sons (I don't remember which one) spent several hours of
the afternoon showing me what to do. That day he was the only one there. I
had some seat stays with me and he demonstrated how to miter the end and
braze another piece of tubing in that place and then file off the excess. I
looked around a bit and realized they did things a bit differently than
Briggs. I also remember him suggesting to me that there wasn't much need now
days (as in 1975) to pin frames together before brazing since hearth brazing
was replaced with oxyacetylene brazing. As he explained, a spot isn't likely
to break or move. All in all a valuable and pleasant afternoon. As a newbie,
I was respectful of his advice and didn't try to argue how we did things a
bit differently at Briggs. My impression was that Woodrup was a bit more
production oriented - meaning that they concentrated on getting a certain
number of frames made in a decent way in a week.
It
was the primary thing that brought in money for them. The frame shop at
Briggs when I was there was a bit more of an extension of the bigger
business. There was the regular retail sales on the ground floor with
several sales people. There were the regular Raleigh and other bikes and
another area had pro stuff. In the back was the repair shop with 2 workers.
Upstairs in one room was Bill and Rodney the painters and in another, Andrew
mostly made the frames one at a time to a particular person. The result of
not having framebuilding be the center of the business was that it allowed a
bit more individual attention to be paid to each frame being made. Jack
never pressured Andrew to be more productive, he just wanted him to make
them right. Jack himself also helped out in there but mostly he and his wife
kept an eye on the entire business. When he was in the frame shop, it was
primarily to teach me and share his considerable knowledge or finalize
instructions about another frame for Andrew to build. Those circumstances
really were a benefit to me which I have always deeply appreciated.
Another
advantage was the ability to wander into the paint room next door and
observe all the steps in painting. Bill and Rodney always enjoyed company
and Andrew and I also ate our lunch in there.
There are lots more memories of that time but not more time to write about
them now. About the other framebuilders in West Yorkshire and the area
itself.
Doug Fattic
Niles, Michigan USA
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