Quote:
Originally Posted by Michael Moore
One of the things that Tony Foale wrote about is that with a FFE (funny front end) with steep rake (around 13-16 degrees) you don't need any offset between the steering axis and the wheel axle to have sufficient trail. That lack of offset means that the side wind blast against the wheel is balanced to either side of the steering axis. With a normal rake and fork clamps that are offset 50-75mm moving the axle in front of the steering axis the wind blast will push the wheel around the steering axis and perturb the steering.
cheers,
Michael
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Hi Michael,
Please don't think I'm picking on you.
Is the "offset" you referred to an imaginary line (as viewed from the side, otherwise known as
elevation view) from the rotation axis of the steering axis (about the bearings in the head tube) and the wheel bearings?
<rant on>
Maybe it's me but I get awfully confused whenever bicycle and motorcycle people speak of front fork geometry. To me, it is
SIMPLE GEOMETRY and nothing more, confounded by terminology concocted by the respective groups (bicycle or motorcycle).
From simple geometry, a steep rake will inherently put the center of rotation of the steering axis far ahead of the contact point of the tire unless there is a huge offset of the fork clamps or a non-parallel clamping of the forks. Most of the fork clamps I've seen appear to be interchangable (maybe not). That difference is the trail.
As an aside, a steep rake will cause what (to my knowledge) is known as "flop" which causes the front of the bike to raise and lower as the forks are rotated about the steering axis. This is a separate effect on the handling.
Bicycle people argue a lot about forks that have bent lower ends toward the front and straight bladed forks as to whether which has less or more trail. A straight bladed fork can have exactly the same trail as the bent ones if the attachment angle at the head tube is adjusted accordingly. To this engineer, it's just elementary geometry and no magical fairy dust. It's my opinion that most bicycle people are simply "geometry challenged".
<rant off>
-- Teri