From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Fork Rake?
Date: 27 Mar 2000 22:46:49 GMT

Joshua Putnam writes:

>> Are you folks not getting your terms mixed up?  Rake is the angle
>> from perpendicular that the steering axis is set at.

> That is one of several meanings for the term.

However, the bicycle usage seems to arise from believing the curl in
the conventional fork is reminiscent of the bias in a garden rake,
unaware that a rakish angle is a steep one and that rake IS the term
for fork angle.  Bicycling is full of jargon that got mangled in the
care of mechanics who know that steel gets soft and that tires need to
age and develop cracks to be any good.  It's time to reverse some of
these notions.

> The majority of texts and consumer discussions of bicycle geometry
> use "rake" to mean fork offset, a meaning that dates at least to the
> era of high-wheeled ordinaries, whose blades were angled forward
> from the steerer to produce fork offset.

I don't know that to be fact.  Are you sure that rake was used to
denote offset for straight forks with angled crowns?  After all, the
bicycle industry is telling us that such forks are new today.

> I've seen "rake" used in this context both for the angle of the
> blades to the steerer and the amount of offset it produces.

That's strange, because it never got that notation with motorcycles
that are a derivative of early bicycles.

> This use of "rake" == "fork offset" continues in modern texts on
> bicycle frame design and is used by bicycle manufacturers in
> describing the offset of their forks.

I don't doubt that at all, but that doesn't make it correct.  Many of
these folks have no technical education other than high school.  Most
of them use the same jargon that others use.  I have heard explained
that it is derived from the fork, turned curl-down, resembling a leaf
rake.  That characterizes to me how this term got butchered, the people
in question not wont to read or refer to a dictionary.  Somewhat like
bike shops that sell "the Bicycle Wheel" because it sells well, but
whose mechanics have no idea what's in it.

> In motorcycles, "rake" is taken to mean the steering angle.

Not so.  It has always meant the inclination of the steering axis.
You must have been talking to bicyclists who motorcycle.

> I don't know the origins of that usage, whether it was invented
> independently or just changed meanings when it was borrowed from
> pre-motorized cycle design.

It remains that rake is an angle and is defined as "inclination from
the perpendicular" in dictionaries, another peculiarity of bicycles
where it is measured from the horizontal... not the plane about which
its dynamics operate.

> In any case, anyone who claims that it is incorrect to use "rake" to
> refer to the offset of a fork is arguing against more than a century
> of usage.  You can argue that it's ambiguous, but it's certainly an
> established meaning of the word.

Sure, and spokes break from overload as the hub gets pulled down from
the top spokes.  It's not like most bicycle mechanics understand
vehicle dynamics or English for that matter.  Most don't know what to
call the inclination of the steering axis.  Maybe you can clarify what
it is if, it isn't rake.  I know, "head tube angle" but what is the
word?  Rake, offset, trail are all taken.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Fork rake effect--debate?
Date: 13 Dec 2000 18:59:22 GMT

Michael A. Koenig writes:

> I have a question about the effect of fork rake. I always thought
> that the larger the rake the more stable the ride; the smaller the
> rake the quicker the handling.

From what you say I suspect you are confusing trail with rake and
offset.  Because bicycle mechanics are a breed apart, they have used
the term rake to mean offset and mix trail and rake freely.  In other
vehicles and English, rake: inclination (of the steering axis) from
the vertical.  In bicycles it is measured from the horizontal and is
called head tube angle.

This angle is chosen to approximate the shock angle of significant
road roughness, such as cobble stones.  On smooth road it could be
more vertical.  The idea is to take significant shocks axially into
the fork blades.  In spite of this, 73/75 degree (aka 17/15 degree
rake) head angle usually cause forks to fail forward, cracking at the
rear of the fork blades first.  Maybe our roads are too smooth for
this.

This angle causes trail, the distance between the intersection of the
steer tube axis and the road to the center of the tire contact patch.
Without fork offset trail at 73 deg is too large, so that pedaling
standing causes the bicycle to try to veer from side to side.  This is
also called lean steer.  Fork offset is achieved on road bicycle by
putting a slight forward curl in the fork ends.  On motorcycles this
is achieved by offsetting the fork tubes forward of the head tube and
on many bicycle suspension forks the wheel attachment is offset to the
front of the suspension plunger.

> While ordering my bike I was told something different, that it depends
> on the head tube angle: that up to a 73.5 head angle (anotherwords
> 72-73 degrees) the larger the rake the more stable the ride. But for
> 73.5 degrees and higher (73.5, 74, 75) the larger the rake the QUICKER
> the handling.

That's BS!  The offset is selected to reduce lean steer.  The terms
"quicker" and "responsive" are buzz words with no reasonable
definition.  They are moving targets that mean whatever the speaker
chooses.

> This is coming from the braintrust at Seven Cycles who I have respect
> for but it is new to me. Comments?

I don't think this bicycle shop is any different from most.  Dynamics
of two wheeled vehicles is a mystery to most folks.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: straight blade forks vs. raked fork
Newsgroups: rec.bicycles.tech
Message-ID: <X3O8a.69972$Ik.3055160@typhoon.sonic.net>
Date: Mon, 03 Mar 2003 19:31:03 GMT

Fork rake, trail and offset, are uniquely different in bicycling than
any other vehicle, the jargon being confused by people unclear on the
subject.

Check the 3rd listing for the word "rake" at:

http://www.m-w.com/

Rake in the normal vehicle world is the angle at which the steering
axis is inclined as in cars, motorcycles, and scooters... but not in
bicycles where people thought that the curl (offset) at the bottom
looked like a garden rake and assumed that's to what the term meant.
Rake is designed to prevent fork failure from bending, although that
is the mode in which forks normally fail anyway.  The angle is
intended to take the statistically greatest road shocks in
compression, making them act axially on the fork blade.

With the common 700c wheel the rock or bump in the road of about
15-20mm height puts an axial compression in the fork.  Smaller bumps
are less significant and larger ones rarer.  Bicycles before the day
of paved roads had a lower rake for the rougher roads.  Track bicycles
generally have steeper rake and could probably be even steeper, as we
see in special bicycles for motor pacing and TTT.

Steering is mainly affected by trail (also known as caster) that
should not be so great that is steers the bicycle laterally when
pedaling standing, where slide loads from leaning the bicycle act
laterally on trail.  For this reason, fork offset is used to adjust
trail, for any given rake, to a stable straight ahead ride while
reducing lean-steer.

Putting curl in the fork is a simple cold forming operation that is
done on a shaped fixture by hooking the dropout under a bolt and
bending the blade manually.  It is a trivial operation that requires
little time or skill.  As has been mentioned, this does not make the
fork springy and that is why straight forks, angled at the fork crown
for offset, perform identically to curled forks.

Maybe with the advent of suspension and straight blade forks, rake
will return to an angle instead of a garden rake.

Watch out for those rakish angles.

http://www.m-w.com/

See 2nd listing.

Jobst Brandt
jobst.brandt@stanfordalumni.org
Palo Alto CA

From: jobst.brandt@stanfordalumni.org
Subject: Re: Adjusting handling with horizontal dropouts
Newsgroups: rec.bicycles.tech
Message-ID: <PamXd.9883$m31.111988@typhoon.sonic.net>
Date: Tue, 08 Mar 2005 18:30:07 GMT

Mark Schecter writes:

> I know this subject must have been gone over many times, but I
> looked in the FAQ, and I found nothing about trail or offset.  I
> would like to understand more about what these are, and their
> relationship to handling.  Are they the same thing? How does one
> measure them?  Can you point me to a source?

Rake in cars and motorcycles is the angle of the steering axis from
the vertical although in bicycles it is measured from the horizontal
for some reason.

# Main Entry: 3 rake
# Function: noun
# Etymology: origin unknown
# 1: inclination from the perpendicular; especially : the overhang of
#    a ship's bow or stern
# 2: inclination from the horizontal : SLOPE
# 3: the angle between the top cutting surface of a tool and a plane
#    perpendicular to the surface of the work
# 4: the angle between a wing-tip edge that is sensibly straight in
#    planform and the plane of symmetry of an airplane

Offset is achieved by putting a curl on the end of the fork or by
angling the fork from the crown putting the axle an offset distance
ahead of the steering axis.

Trail is the distance from the intersection of the steering axis and
the road to the center of the tire contact (the located vertically
beneath the axle).

I don't know the dynamics of it other than pragmatically that too
little trail makes a bicycle difficult to ride no-hands and that too
much trail increases the tendency to shimmy.

Jobst Brandt
jobst.brandt@stanfordalumni.org