Health knowledge made personal
Join this community!
› Share page:
Search posts:

The Evolution of Frame Design. Part I: The Wheelbarrow Effect

Posted Oct 05 2009 10:00pm

The picture above is Italian cyclist Giuseppe Martano, seen here on his ride to 2nd place in the 1934 Tour de France.

Probably the first thing most will notice is that the bike has a single fixed sprocket. Gears were available at that time; however, Tour de France riders were restricted to a single speed at the whim of Tour organizer Henri Desgrange.

Desgrange felt that multiple gears were for bicycle tourists, and they took away from the purity of the sport of cycle racing. So riders had to struggle over the same mountain climbs the Tour currently goes over, with a single gear, on roads in far worse condition than today.

The other thing you will notice about the bike is the long wheelbase, some 4 or 5 inches (10 to 13cm.) longer than a modern race bike, the shallow frame angles, and the long curved front fork blades.

One of the reasons for the long fork rake or offset, was always thought to be because roads were so bad back then; in most European countries little more than dirt roads.

The long curve of the fork would allow the fork to flex acting somewhat as a form of suspension.

However, there was another reason; a long held theory that trail made the steering sluggish on a bicycle.

If you look at the drawing (Above left.) an imaginary line through the center of the head tube, (Steering Axis.) reaches the ground at the point of contact. On a bike from this era, there was zero trail.

On a modern bike (Drawing right.) the point where the wheel contacts the road will be some 2 to 2.5 inches (5 to 6.3cm.) behind the steering axis.

Hence the term “Trail,” because the wheel trails along behind the steering axis.

Bicycle geometry did not change much from the 1930s until the 1950s when I started racing.

Standard road frame angles were 71 degree seat angle, and 73 degree head angle. This was true for any size frame.

Frame lugs were heavy steel castings, machined on the inside to accept the tubes at these standard angles. It was not cost affective to make lugs in different varying angles. It was established probably around the 1930s that 73 degrees was the ideal head angle for a road bicycle; this is still true today.

The reason for the seat angle being 2 degrees shallower was because when a framebuilder made a larger frame, the top tube became longer because the head and seat tubes were diverging away from each other.

These standard angles were not for the benefit of the rider, but for ease of construction for the framebuilder.

For a shorter rider like myself, the top tube was always too long and I was sitting back too far.

When I made maximum effort I always found myself sliding forward and sitting on the nose of the saddle. As well as being uncomfortable, it had the effect of the saddle being too low.

Because of the long top tube, I always had to use a short handlebar stem, and this lead to another problem when sprinting or climbing out of the saddle.

The rider’s weight was behind the front wheel’s contact point with the road; due to the short stem and the forward sweeping forks. Out of the saddle, the bike swung from side to side in an arc causing the front wheel to steer first one way then the other; not holding a straight line.

At the same time the gyroscopic action of the spinning wheel was trying to keep on a straight line. So the two actions were fighting each other; hence the bike felt sluggish and unstable.

To demonstrate this effect to yourself; hold a pen or ruler on a table top at 90 degrees to the surface, and move from side to side keeping the point of the pen in one spot; you are moving in one plane. Now hold the pen at an angle of 45 degrees and move from side to side and you will see that you swing in an arc.

This was something I later called the “Wheelbarrow Effect.” In the next article later this week, I will talk about how frame design evolved through the 1960s and 1970s to arrive closer to what we see today.


Post a comment
Write a comment:

Related Searches