The Sam Braxton bike recently for sale on Ebay and discussed in some depth on the List really did generate some interesting data and theories both about Sam's frame in particular and frames in general..
I think that it was generally agreed that Sam preferred shallow head-angles, particularly for touring bikes, while there was some opinion expressed about such angles causing steering shimmy and wobble. Evidently Sam often sued head angles of between 70 and 71 degrees..
Fotunately I have only ever once experienced bad shimmying..and that was on a mid-range Bernard Dangre - Starnord ( Paris Sport ) bike that could have been categorised as 10sp sports/type Course. The fault was put down to a pretty steep head angle and a long abrupt rake, on a 22" frame. Some how I started to associate such frame design with bad steering until I read that some of Eddy Merckx's top road frames of a similar size had head angles of 74 and sometimes 75 with rakes of about 50 to 55mm ; I had never heard of a Merckx frame suffering from bad steering, but have never ridden one of his frames, so I cannot comment.
Recently I have been trying to buy several more ex-Pro rider frames, including one that is reckoned to be one of Lucien Van Impe's Tour-de-France machines, from his days at Lejeune in 1977 More likely than not it is one built by Bernard Carre.
Van Impe is quite short, around my size.-one reason why I am particularly interested in obtaining this frame - and rode a 51 cm frame measured centre-to-centre, with a 52.5 cms top-tube, 41cms rear triangle and 59cms front end clearance. These measurements were manipulated by altering accepted angles to provide a frame that had the same measurements front to back as Luis Ocana's 57.4cms. Gazelle . and only 1.5 cms shorter than Gimondi's 57.7cms BIanchi whicj=h boasted a 58.5 cms !!! top-tube...No mean feat..
The seat angles on these frames were 74.10 for Van Impe, 74.33 for Ocana and 73.40 for Gimondi...whereas the head angles were respectively *68.4,* 73.24 and 75.5..
As I read these measurements, particularly the head angle on Van Impe's frame, I had in my mind's eye, the shallow head angle on the Sam Braxton..which was presumably over 70 degrees.
I then remembered attempting to copy a Vitus 979 frame for a customer when building a winter frame, and rememberd that these frames had interesting angles. However for a 51 cms VITUS the seat tube angle would be 75 degrees, the head angle a respectable 72 degrees, and the top-tube at 53cms just half a centimetre longer than Van Impe's I cannot remember ever building a frame with a head angle less than 71 degrees and that was on a touring machine, and consequently I am really puzzled about the claims made for Van Impe's Lejeune. Would there have been much shimmy on the front fork which had a rake of 35mm and a trail of 9.68 cms.?
Has anyone got any good photos of Van Impe riding his late 70s LEJEUNE that they could post please?
Norris Lockley
Settle UK