This discussion is quite fascinating as it is becoming abundantly clear how ways of taking measurements on a bike vary depending on which side of the Atlantic you live.
Over here we always..or at least the builders I have known and talked to.. talk about bottom-bracket height as being the vertical distance between the ground and the centre of the bracket axle. OK, this will vary with the siz es of wheels and the type and dimension of tyres or tubs used..and may in c ertain circumstances be only a compromise at best, but the measurement used is normally for the size of wheel and dimension of tyre that are to be use d predominantly. So here are some measurements, bearing in mind the followi ng very generalised info about the design of frames for a variety of purpos es. In the late 40s/early to mid 50s the majority of road-racing/mass ed start frames had 72// angles, time-trial and "club-run" frames 73/71, tr ack frames usually 74/72, touring frames 72// or 72/71.
The bracket heights for the massed-start /criterium/kermesse frames w ere often as low as 10.1/4", and often also 10.1/2", with the continental h eight of 265mms (10.7/16" being quite trendy. For time-trial and "club" fra mes 10.5/8" was not uncommon but 10.3/4" was far more popular..and 11 " was fairly standard for track racing, with 11.1/4" not being too uncommon . Light touring frames often used 10.1/2" while heavily loaded ones would t end to use 10.1/4" Cyclo-cross frames often had anything between 10.7/8 and 11.1/4".
It was always considered that a lower bracket improved stability, handling, road holding and cornering abilities...qualities needed in massed start an d crirerium racing. A higher bracket was considered desirable for time-tria l frames because the courses - sometimes as straight as drag strips, had fewer if any any severe corners except for the dead-turn at the out-and -back point. Track brackets had to be higher to prevent pedals from strikin g the surface of the steeply baked tracks..the steeper the banking, the hig her the bracket. Cyclo-cross frames had high brackets in order to avoid hit ting stones etc on uneven paths and country /off-road tracks. The lower bra cket heights on the touring bikes helped in bringing about a more sta ble and predictable ride.
As the years went by, the UK bottom-bracket height tended to standardise at the 10.3/4" height. This standardisation could have been in response to th e widespread use of longer cranks - 6.3/4 (170mm) instead of the 6.1/2" tha t were quite common a few decades earlier...or to the fact that there was n o longer a ready supply, off the shelf, of brackets made to provide for a w ider variety of BB heights...or, more probably to a combination of the two factors. In this respect jut recall all those numbers stamped u nderneath a Nervex Pro bracket shell...all corresponding to frame ang les..and hence bracket heights. This brand of shell and some other brands h ad been readily available in numerous combinations of angles and heights an d prepared for a wide variety of frame usages.
The relatively high brackets mentioned on the Woodrup(s) could have been in response to the customers' order for frames for use with longer cran ks than the standard 10.3/4"(170mm)..with 172.5 and 175 becoming increasing ly popular for time-trialling machines. Remember too, that it was not uncom mon for a cylcist to use the same machine for club cycling, training and ra cing. Additionally in the late 70s and through the 80s, some cycling magazi nes over here were advocating the use of longer cranks to make pedalling "e asier" (their word, not mine). Also in the later 70s and early 80s many cus tomers were still in a quandary about which wheel size to use ie. 27" or 70 0mm.,.and sometimes opted for a frame that could accommodate both, leading to frames that had a bracket height ideal for one set of wheels and not ful ly appropriate for the other. Somewhere in the UK there are three "flying g ate" type frames that I built for a customer who suffered from this indecis iveness. He was an engineering draughtsman..hence his frame drawings were i mpeccable..but building the frames for his variety of wheel sizes, tyre dim ensions and idiosyncratic choice of brake stirrups tested my patience on ea ch occasion.
I think that in recent years, on occasion, higher bracket heights have resu lted from the use of investment cast shells..in inappropriate applications. these brackets do not ,generally speaking, and without risk of being disto rted.. lend themselves to having their angles manipulated and modified...an d should not therefore be used in applications where the angles between the ports do not correspond exactly with those required by the design of the f rame, unless you have the tools, the machinery, and the expertise to alter them accurately.
Because such cast brackets are not always available (..not in the UK anyway ) ..unlike the formerly ubiquitous Nervex Pro..in a wide variety of angles for a multitude of purposes, there is always a possibility of an inappropri ate bracket being used. I remember once asking a well-known frame-builder h ow he managed 2to work.." these brackets and to adjust the angles..to which he answered .." I don't..I'm a frame-builder, not a ****** engineer!"
The meaning of the word "stability" has been raised.. The French vocabulary , known for its smaller range of words than the English one, even though th e Frnch gave us the word "nuance" has the word "rendement" to describ e how a bike rides..and probably how a motor car drives. At one and the sam e time it translates as road-holding in the widest possible sense ie grip, adhesion, cornering ability, tracking, ability to a hold a line, pred icatability..in short all those qualities that lead to sure- footedness.
Norris Lockley, Settle UK (2007)
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