Teri, most every section of a sport, technology, field of study, what have you, will have a specialized vocabulary. When you became an engineer you had to learn that a moment was not just a short period of time.
From what you said at the beginning of this thread you are a newcomer to motorcycles, so you shouldn't get upset when you have to learn the new terminology.
It is my impression that bicycle and motorcycle terminology does not always match up so you can't always apply something about bicycles to motorcycles without adjusting the terms being used.
"Offset" is the amount a parallel line to the steering axis through the axle differs from the steering axis when viewed from the side. Zero offset means the steering axis goes through the axle. With common ranges of rake angle most bikes will have some amount of offset.
I think you'll also find that most motorcyclists (for at least the last half century) are going to view a "steep" rake angle as one that is closer to vertical, not one closer to horizontal. The "flop" you mention is a problem with shallow (not much rise) angles, not steep angles (closer to vertical). Road racers have steep rake angles, choppers have shallow rake angles. Choppers will have problems with "flop".
I'll agree that there are a lot of motorcyclists (and probably bicyclists but I'm not a bicyclist so I don't keep up with what is going on in that field) who don't understand the difference between rake and trail.
cheers,
Michael
Quote:
Originally Posted by Teri_TX
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
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