The Evolution of Frame Design, Part III: Clinging to Traditions
Mon, October 12, 2009 
The final article in a 3 part series; Part I and Part II precede it.
After more than a decade of hard times from the late 1950s through the early 1970s the lightweight bicycle business finally came out of the slump, helped to a large extent by a bike boom in America.
By the end of the 1960s the 73 degree parallel frame was now the standard road geometry. Although it had been born out of necessity to build something that was easier to construct, it was still far better than the 71 degree seat angle, 73 degree head of the 1950s and before.
However, tradition dies hard, especially when those who had survived the hard times were the old established framebuilders that were around in the 1940s and 1950s, or new ones schooled in the belief systems of the old builders.
If you remember from the first article I wrote in this series, how the 2 degree difference between the head and seat angles suited the framebuilder, because the head and seat tubes diverged away from each other, and as the frame got taller the top tube got longer.
No one wanted to go back to 71 degree seat angles, so by the early 1970s the standard racing frame geometry became 73 seat angle and 75 degree head. Both Italian and British framebuilders followed this trend.
Typical are the head and seat angles on the 1973 Italian DeRosa shown at the top of this article. Picture from The Racing Bicycle Collection.
It was necessary to shorten the fork rake, otherwise, with the steeper head angle the point of the wheel’s contact with the road would actually be in front of the steering axis, making the bike just about impossible to ride.
Many of these traditionalists still held the firm belief that a bike should have zero trail; so by steepening the head and shortening the fork rake, (Offset.) they maintained the status quo.
See the picture (Left.) from the same DeRosa with the steering axis superimposed in green. Note there is little or no trail.
Now the head angle was steeper, steering was much more sensitive; less forgiving towards rider error.
Over the years road surfaces had greatly improved in Europe, bicycle tires had become narrower; as a result rear chainstays could be made shorter, therefore stiffer. Couple this with the steeper head and less fork rake, and bike wheelbases became a lot shorter.
Riders noticed with the new steeper head and short wheelbase, the bikes felt much more lively and faster when sprinting or climbing out of the saddle. Both riders and framebuilders attributed these ride qualities to the shorter steeper frame.
However, if you remember from the first article, “The Wheelbarrow Effect,” the livelier feel came from the fact that the rider’s weight was now directly over the front wheel, not behind the front wheel’s point of contact as it had been in the pre 1950s.
During the period from the late 1950s and through the 1960s, I had been building frames mostly for my own use; trying to find something that suited me. Because I never had any real notion to build frames as a business, I was not restricted to what was fashionable or what everyone else was doing.
In the early 1950s I found the shallow seat angle and long top tube totally unsuitable, I would always end up sitting on the nose of the saddle. Because of this I experimented with a frame that had a steeper seat angle and shorter top tube; my reasoning was, if this is where my body wants to be, I will build a frame to accommodate it.
I was also aware of the wheelbarrow effect. I experimented a little with different head angles but accepted early on that 73 degrees was the ideal head angle for a road bike, although a degree either way is okay. (72 to 74.) However, I did shorten the fork rake considerably to get the front wheel under the handlebars.
The resulting trail made the bike handle better, and go round corners faster, especially on fast descents. By the early 1970s I had established my design. The top tube was even shorter, seat angle steeper, and by using a longer handlebar stem, the handlebars were directly over the front wheel’s point of contact.
I was now building frames for other people and by 1974 had a full time business. The formula I used was simple; as the frame got taller, (Larger.) the handle bar stem had to become gradually longer to keep the handlebars directly over the front wheel.
This set up had the same desired feel when sprinting of climbing, but without the over sensitiveness of the steep head angle and less trail. Trail was a good thing; it helped keep the bike on a straight line, and gave certain self-steering qualities when cornering at speed.
The top tube became longer as the frame got taller, but at a lesser amount than the seat tube, because the handlebar stem was also lengthening.
With other people riding the bikes, some of them International class riders, my reputation grew as a framebuilder; the reason was the way the bike handled.
As a young rider in the 1950s if I mentioned that my bike felt sluggish on the climb, I was told, “Good climbers, climb sitting down.” In the 1970s if an inexperienced rider crashed because the steering was over sensitive, he was told he didn’t know how to handle the bike.
My thinking was, put a novice on a good handling bike and he is an adequate bike handler; put an expert bike rider on the same bike and he becomes a brilliant bike handler.
Several readers of these articles have mentioned that they find this history interesting. What the reader sees as history is just a memory to me. However, I have found it interesting to reflect on the way the racing bicycle has evolved over the years, in many ways accidentally.
By the 1980s most of the world’s framebuilders had dropped the steep head angle thinking and gone back the old standard 73 degree head angle. They kept the shorter fork rake and found the resulting increase in trail was a good thing.
This was something I had discovered ten or fifteen years before. Did I influence anyone? I very much doubt it; I imagine most of the world’s framebuilders had never even heard of me in the early 1980s.
The saying, “Thinking outside the box” wasn’t even around when I was playing with different frame design ideas back in the 1960s.
Tradition is one thing that will always keep you firmly inside the box
Reader Comments (7)
Dave,
great overview!
Could you write also something about frame geometry suitable for commuters with fatter tyres, longer chain stays and longer wheel base ?
Cheers, Gregor
Great series, Dave. I never realised how big a part the expediency of mass production played in the changes in geometry over the years.
What is rake ... and trail?
This has been an education!
Rider,
Rake and Trail. Read part 1 in the series (Link at the top of this one.) in particular look at the drawing.
Dave
Extraordinary series. Can you comment - at some point perhaps - on your feelings about contemporary geometries? Best.
A few years back I bought an old Dawes frame and forks from ebay, I rebuilt it using 700C wheels when it was intended for 26 x 1 1/4. It was very hard to ride, super twitchy. I used to get pains in my shoulders from keeping it straight. I rode it in various configurations, fixed among them. I deduced that there was insufficient (maybe negative trail). Does this theory make sense? My solution (not yet implemented) is to put mountain bike wheels with road tyres in there in order to give it some trail. The reasons I don't use the proper size wheels or even 650B are expense and availability. Rivendell sell 650B kit but I'm in the UK and not very well off. I'm a tourist rather than a racer but I think this bike would feel twitchy even in the hands of a racer.
Very informative, I've never have guessed that stem length has such an impact on handling, and always thought that it should be kept short. Thanks for broadening my horizonts :)