[CR] Was: Woodrup frames. Now: BB height, etc.

(Example: Framebuilding:Paint)

Date: Sun, 31 Dec 2006 17:37:01 -0500
Subject: [CR] Was: Woodrup frames. Now: BB height, etc.
From: "Doug Fattic" <fatticbicycles@qtm.net>
To: "classicrendezvous@bikelist.org" <classicrendezvous@bikelist.org>
In-Reply-To: <C1BD56D6.5A23%dougfattic@qtm.net>


Happy New Year everyone:

There are several subject threads under one heading which I would like to comment on but first about bottom bracket height. I think a low bottom bracket height is a good thing. When on the framebuilder's list, this was described as making the frame more "stable", the meaning of what exactly that word meant was endlessly debated by the those that had engineering or physics backgrounds until I had no clue as to what the word actually meant. However in my vocabulary, one advantage of lowering the bb is that it allows a bigger frame (longer seat tube) to be made while still keeping the same standover height. This allows the stem to be higher so the handlebars don't have as much drop from the seat. As we age and our body fat is no longer at 5%, this makes riding more comfortable. I was admiring Freek Faro's collection of bicycles in Rotterdam with Toni Theilmeier. I noticed that all his bikes were set up with lots of handlebar/seat difference and I asked him about this. He said "it is most important to have a certain aesthetic which, if necessary, one must sacrifice to achieve". But for those that don't have Freek's middle aged fitness and willingness to suffer, a higher handlebar keeps cycling fun when other things change. In addition, the lower bottom bracket height also means the saddle is closer to the ground to put your foot down.

Bottom bracket height standards seemed to have been established when Campy quill pedals stuck out a lot more than today's styles and made hitting the pedals when racing crits a concern. In addition now days production frame designs have to be approved by lawyers concerned with liability so that doesn't bring it down much. A common standard road height then and now would be about 10 1/2" using 170mm cranks. 10 5/8" or 10 3/4" while on the high side would be what racing frames designed for pedaling through corner clearance would be. Above that was for longer cranks or just a mistake. Of course longer cranks are more than norm today then in on topic years. My Masi Gran Criterium that I got in 1972 had a bottom Bracket height of around 10 1/4" (when using Clement Criteriums). I loved the way this frame rode and early on that made me a fan of lowering the bb height. On the frames I made for myself that I ride today, I have the height set around 10" (I use 650C tubulars so mentioning what the drop is doesn't work for those unfamiliar with that size wheel's dimensions). My travel bike (which I use on our training rides) is 9 3/4".

Back in the 70's I made a number of frames for Tom Doughty when he was on the National team. Each time we would tweak the frame design a bit to increase it's fit and efficiency for him. Tom was a big guy and used 175 cranks but would have me lower the bottom bracket height each time even though a lot of his racing was criteriums. He felt he could get through a corner faster by not pedaling when leaned at the max point but liked the "stability" the lower he was. His Shimano DD pedals always had lots of scraps on the bottom (which lowered him even more).

Doug Fattic Niles, Michigan USA

From: oroboyz@aol.com: 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

From: freesound@comcast.net 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

Jerome Moos:

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